Tuesday, December 31, 2013

Determining the internal resistance of a meter..

This from a .pdf document on meter shunts posted on the internet.

Clearly, though, you need to know the resistance of the meter itself in order to work out the value of the shunt you're going to need. Luckily the internal resistance of most meters is specified when you buy them new.

For example the resistance of the MU-45 type 0-1mA meter movement sold by Electus (QP-5010) is specified as 200 ohms, while the more sensitive 0-50uA model (QP-5012) has a specified resistance of 3500 ohms. So it's not hard to work out the value of shunts needed to adapt either of these meters to read higher currents. But what if you have a meter movement salvaged from a piece of equipment, and you don't know its resistance? Or even its current sensitivity? (It might already have an internal shunt, for example.) The simplest way is to measure it -- but don't just slap a multimeter across it, because that could damage the meter by passing too much current through it. The best way is to use the simple test circuit shown below.


Here the meter is connected to a 12V battery via a DMM (set to a suitable current range) and adjustable resistor RV1, which is carefully adjusted until the meter is just giving its full-scale reading. The DMM will then be showing the current needed to produce this current FSD -- in other words, the meter's sensitivity.

Now switch SW1 is closed, to connect the second adjustable resistor RV2 directly across the meter, as a shunt. RV2 is then adjusted until the meter reading is reduced to exactly half scale, while monitoring the total current via the DMM and, if necessary, adjusting RV1 to maintain it at the original FSD figure.

When the meter reading is exactly 50%, the value of RV2 will be equal to the meter's own resistance, because the current is being split equally through the two paths. So you can then disconnect the battery and use the DMM to measure the value of RV2 (by itself), to learn the meter's resistance.

Note that even if the meter should have a current shunt built inside it already, this test will still give you its effective sensitivity and resistance including any internal shunt. So the figures you get will allow you to work out the value of any new shunt you need to adapt it for measuring higher currents, regardless of what may be inside the meter case.

Sunday, November 17, 2013

Algo mejor..

After a monumental tussle of some 6-7 months  --  actually, work, CAP, intervening projects, and the like -- I finally finished the New England NEScaf[e] filter. I will be writing some of my thoughts and comments on the building and debugging process but any negative remarks I make  should not be construed as a deprecation of the fine folks over at NE QRP. Rather, this little project lingered on because of stupidity and inattention. Here are some interior pictures of the completed project with appropriate commentary.






 Bottom line is that this is a very decent and reasonably priced product (about $35 to get to your door) and NE QRP has offered this for around 10 years. This is not their day job and I must imagine you would blow someone off if they came back after almost a decade. To NE QRP's credit, they did not. While their web site and forum links may be decaying a tad, they nonetheless did respond and even shipped me a replacement SCAF chip free gratis.

Compared to the dreadful inattention I experienced at the hands of the Idiot Press folks, this was all sweetness and light. Would I  order and build another one? To quote Leon Spinks, "Abba-lutely!"

"Abba-lutely!"
Maybe I could get Leon to come out of retirement and punch the lights out of Idiom Press.

Friday, November 1, 2013

Slice of Schlumberger..

NOTE FROM THE FUTURE: With the greatest respect to the Swedish gentleman who firsty proposed and did this to his Schlumberger, this mod sucks. I restored this beautiful instrument to its original condition and moved on. Everything is so-o-o-o much happier in my world now. Also, I am over the VTVM jones at this point, retraining two of the four or five that I had. I believe it to be this and a fully-restored, pristine V-7A that adorns my bench.

Not all of the VTVMs I stumbled onto were dogs or fraught with problems. In fact, I should have quit winners. My friend Lloyd said he had a Heath-Schlumberger SM-20 he wanted to part with and I picked it up from him for $15. it was a little dinged on the outside (what sixties vintage meter isn't) but a little TLC and a nick of paint brought it back to its former glory.(Heath-Schlumberger was the commercial side of Heathkit and these were usually the pre- or commercially-built kits that you found at trade schools, etc. This one had those stenciled markings on the case before it was repainted.

Turned out to be reasonably accurate also -- after I exorcised the demons with some contact cleaner and a few joint re-melts.

Like a lot of Heathkits and VTVMs of that era, it had that single stereo phone jack for its test leads. In this case, the probe served a dual purpose (see schematic snippet below) and was switchable between AC Volts+Ohms to DC Volts. Of course, the probes and leads have gone by the boards and it will require some art to reconstruct them. Heath buried a 1-megohm resistor in the probe to isolate it from DC pickup. (I am still trying to get my head around that one.)


In any event, since there were no probes, I regrettably did some cosmetic surgery on the box and made it usable with standard banana jack leads. I got the idea from a very nice Swedish ham, Hans Gatu, who has quite a collection of Heathkits and tends to make this mod on all of his older VTVMs.


Hans wrote me and explained that he found not a lot of problems putting the extra 1-megohm resistor inside the unit and it was a decent trade-off for being able to use conventional cables and test leads. As my pictures show, I mimicked Hans quite closely.


Here is the SM-20 before the surgery and below it is the unit afterwards.



Below -- before the operation -- I was doing a little checkout.

At 25 VDC

..at 1,030 ohms..

..at 2,030 ohms..

..at 3,030 ohms..

..at 4,030 ohms..

..and at 5,030 ohms..

There seems to be a little difficulty with the AC voltage measurements so I think the DC blocking capacitor is needing replacement.

-30-

Thursday, October 31, 2013

Vitamin "V"..

..get it? Thought not.

Anyway, wanted to also start up a thread on my recent VTVM jag (see my previous signal generator post) so I can lay down a placeholder and get set for the Ugly Weekender project I and Alan are going to embark upon.

As with the other stuff I do, I pick up one thing at a swap meet (or somewhere) and then determine I need something else to help me with the original item so I run off on that tangent. In this case, it was the need to correctly measure high DC voltages accurately to help me align a Hammarlund receiver I am going to restore and the fact that ordinary 20 KOhm-per-volt VOMs would load down the circuit. Actually, I don't know why I couldn't use a DMM..oh wait! Yes, I do. DMMs only have that bullshit series of tick marks on the bottom of the LCD display and that just would not do, would it?

The real reason, of course, is that it was a perfect opportunity to acquire more neat-looking electronic junk that I mostly will never use. But it's my money, my time, and my pleasure.

So there!

Well, of course, the W6DQ syndrome (Remember? "Never buy one thing when you can get two at twice the price") set in and I managed to score THREE of these gadgets in various states of repair. Here they are in various states of undress:

Left-to-right is a Knight KG-620, picked up at the TRW Swap Meet in Los Angeles towards the end of September 2013, a Heath-Schlumberger picked up at the Chino Hills Swap Meet in the middle of september, and a Heathkit V-7A I got off of eBay from a lady in San Burning Doo-doo.

Funny thing about all the VTVMs you will find on eBay and at swap meets: they have pretty similar circuits. It is basically a pair of triodes -- one with a "standard voltage" and the other with a voltage derived from a voltage divider and slammed into the grid. With a constant, identical plate voltage on the two triodes, the differing grid voltages will cause differing currents and, hence, an imbalance in a meter circuit thus causing a deflection in the meter. But that's as far into the weeds as I want to go for VTVM theory. The internet abounds with pages devoted to the theory of these instruments from Ryder's tour de force on the subject to a marvelous compendium on Heathkit VTVMs -- principally the V-7A -- by Bob Eckweiler, AF6C, of the Orange County (California) Amateur Radio Club. Bob has a regular series he runs over on the OCARC site on Heathkits that are superbly written and beautifully laid out. They are must-visit treasures from a ham who clearly knows and loves his subject.

Various VTVMs with Heaths among them
If you read Bob's piece or do a little research, you will find that is surprisingly standard among kits of the mid-fifties on. The V-series meters (from V-1 through V-7) settled on a circuit using a 12AU7 dual triode and a 6AL5 dual diode for the AC measurements with a pair of voltage dividers for volts and ohms. (The ohms divider used a 1.5-volt D cell battery for power.) After the V-7A, Heathkit went into the IM series with the IM-10, IM-11, IM17, IM-18 and thence to the IM-52xx series with the newer paint jobs. But they all had pretty much the very same circuit.

I kinda fell for the V-7A because that was extant when I was a kid in the late fifties and, although my dad bought and built the venerable Eico 232, I remember my grade school buddy, Jeff Smith, had a V-7A and I always lusted after the gray box and gray wrinkle paint finish on the case. I especially loved the knobs being used for the zero controls -- as opposed to the cheesy pots with the plastic slotted shafts on the IM-11s, IM-18s and other later models. Oh sure, you could turn then, but for any zeroing accuracy, you had to use a screwdriver and even then it was difficult.

Another thing I liked about the V-7A was fact that it had a printed circuit board inside and far less point-to-point wiring than the previous models. Never mind that the PCB was absolute shit (hey, it was the fifties) and the traces lift off when heated up above anything more than room temperature.

That said, when I started my VTVM Jones, I was dead set on getting a working, pristine unit for the bench. So, I was thrilled when I nailed the eBay auction for the unit pictured above -- but crestfallen when it arrived. It was in so-so shape inside. Nothing too grungy but nothing to write home about either.

Anyway, it did not work 100% and the symptoms were variously an inability to zero, the wandering meter needle and a frustrating problem with adjusting the "AC BAL" control. So I joined the Heathkit Yahoo group (a heartfelt recommendation), took it apart, waited to hook up with wise gentlemen like Bob Eckweiler, and went stem to stern on the thing, poking and prodding.

About the best piece of advice I got was from Bob. He told me to plan on scouring the switches and controls with contact cleaner and re-heating every solder connection on the PCB as well as any suspicious looking ones on the switches. He also advised checking out the precision resistors on the voltage divider as well as the other resistors on the ohms divider.

Also consider cleaning any corrosion from the battery cup, checking the resistors on the PCB (most will ohm up to their marked value despite being in circuit), and replacing the power supply cap with a 22 uF electrolytic and the rectifier with a 1N4007 would not be amiss if you suspect ripple.

After I got the meter apart -- I was able to remove the front panel from the PCB and rest of the guts -- I could work more freely and accomplish these tasks. And, what do you know, the little beauty waked right up!


That was the good news. The bad news was that the meter needle seems to have been sprung and prying off the plastic cover and inspecting the innards revealed that the movement was irretrievably bonked. Someone had measured about 500 VDC with the switch on -DC Volts. So, while the unit innards may be copacetic, the problem with the "AC BAL" control and problems consistently zeroing seemed to be because of the sprung meter.

Which brings me to my first rule of thumb: run like the wind from ANY meter that has a droopy or non-zeroed meter. If it is on eBay or you cannot physically lay your hands on it to verify otherwise, if the meter is not zeroed where you cannot lay hands on to verify the condition consider it trashed and move on.

Here is my second rule of thumb: grow a severe case of patience and DO NOT buy a VTVM on eBay. You will eventually find one at a swap meet and you can verify its condition up close and personal. Chances are it is trashed and the guy either knows what he is doing and wants to bend you over or he does not know jack squat and you will get bent over.

Now, if you look closely on eBay over the next two weeks, you will see an auction from me for a Heathkit IM-11 "for parts or not working". That's the meter in this unit swapped out and with really clean parts and switches and controls. IT IS FOR PARTS ONLY. Did you get that? JUST FOR PARTS. The meter does sit at zero now because went inside and moved it to zero. But the little mechanical needle will not do that externally with screwdriver adjustment.

We clear on that?

Good.

O.K. That's all for this evening. Gotta grab some rack time. Will be back with more stories on the revitalized V-7A and my spiffy SM-20 and the Knight Kit KG-620 -- the really neat swap meet find

-30-

Tuesday, October 29, 2013

Signals, Set, 1..2..3..

I am skipping over the Ugly Weekender to post an effort last weekend that yielded some interesting results. Be advised that I am not abandoning it -- far from that -- I am only time-slicing while I gather parts. Also, I have a couple of other irons in the fire like putting the VTVMs to bed (a post will be up on that adventure shortly) and doing some fix-up on the NesCafe CW filter kit from NEQRP. (Ditto.)

When family, work, and the USAF Auxiliary allows it, I frivolously waste time on ham radio and electronics projects and, when doing so, I am in one of two modes: gathering projects at swap meets or building, fixing, or operating the treasures I haul in.

But, alas, my hunter-gatherer skills far outstrip my builder-operator skills and I have built up quite a backlog of these projects. To shame myself, I order my "acquisitions" into a FIFO list so that there is some throughput at least and the scenery in the workshop garage changes over time. Anyway, somewhere back in the past six months, I went on a jag and started accumulating Heathkit IG-102 signal generators. You know, these beasts on the left there. (For that matter, I always go on these jags. As Dennis Kidder, W6DQ famously says, "Why buy one of something when you can have two at twice the price?" The VTVMs were the result of such a bender.) I amassed three of these generators, two in good shape and one having no power cord and generally requiring more attention. Well, last weekend, as they were gathering dust on the shelf, I decided it was time to act and started in on refurbishing them.

Now, for those looking for a low-end signal generator at a reasonable cost, the IG-102 is a good one. It's about $35-75 (or more) on EvilBay or $20-50 (or more) at a local electronics swap meet. (I prefer the latter venue because of the cheaper prices and the fact that you can eyeball the product INSIDE and OUT.) Also, the fact that the entire manual can be found as a .pdf (think mods.dk) is a definite plus as the build "how-to" is definitely more informative than the troubleshooting chart in the back of the manual.


As for refurbishing the units, I rescued the two and breathed life into 'em in a far shorter time than I thought it would take. Initially, both did not produce any RF out whatsoever. So, after poring over the schematic for a while, I poked and prodded from where I thought the RF should originate and was delighted to find a signal. I proceeded to follow it to the RF out connector but I lost a little bit somewhere between the plate of the pentode side of the 6AN8 and the wiper of the fine attenuator pot. The rest of the RF fled on the input side of the course attenuator switch.

Judicious application of contact cleaner at various points on that path materialized the RF at the output connector and we were in business. One of the signal generators had a "lumpy" fine attenuator pot so I replaced it with a 10 KOhm one I had lying around. (The original was a 3 KOhm audio taper jobbie.) The 10K worked fine; it was a little tight but, with practice, I was able to set my signal level right enough.

The only problem was that I only had one set of tubes so I ordered another 12AT7 and 6AN8 off of eBay. Just to let you know, they ain't cheap and, surprisingly, the 6AN8 is a little more dear than it's cohort. If you want to rebuild one of these machines, budget another $20 for the tubes if yours are shot or missing. Also, here's a re-cap of the recommended debug steps:

(1) Don't hesitate to clean the switch contacts on the attenuator pot and the band switch (where the coils are).

(2) Trace the obvious signal path from the grid of the pentode half of the 6AN8 through the fine attenuator pot through the coarse attenuator switch. If you are using a scope, mind the DC on the plates of the tubes and such. There are convenient DC blocking caps where you can pick up the RF if it is available. One prime spot would be at pin 8 of the 6AN8 as I recall.

(3) You might find the fine attenuator pot "lumpy" -- it can be replaced by a 3 KOhm pot or a 5 KOhm one or even 10 KOhm pot -- which I used on my "keeper" unit.

(4) Replace those useless mic connector plugs on the chassis with BNCs. It's very easy to do and makes your unit more compatible with coax links you might have laying around.

The remaining unit of the trio lacks an AC power cord and will probably end up becoming "transistorized". I actually was going to do this with all three, except the first two work so great when refurbished, I did not want to go to the extra effort. (If it ain't broken, don't fix it.)

In any event, to convert this unit, I'll have to strip out the AC power supply and the tubes and replace the latter with a pair of MPF-102s each. When done, it will be powered by a 9V (or 12V) battery. Notes on the project (it came from the May 1978 73 Magazine) advise soldering the MPF-102s to the actual tube socket lugs underneath the chassis. But, I am thinking about getting some tube-pin-diameter copper wire and stick those into the appropriate tube socket pins and then wire the JFETs to the copper wire. That way, if I blow up a JFET, I can pull it and insert another.

Looking at the pin-outs and how one wires the drain, gate, and source, I surmise that the two JFETs will face each other and the pin-outs will be:

12AT7
FET #1 - 1=Drain, 2=Gate, 3=Source
FET #2 - 6=Drain, 7=Gate, 8=Source

6AN8
FET #1 - 1=Drain, 2=Gate, 3=Source
FET #2 - 6=Drain, 8=Gate, 9=Source

..but DOUBLE CHECK; I could be wrong!


I'll get back on this last project and post some pictures.

Thursday, October 17, 2013

Whooped with a ugly stick..


Jeff Tranter, VE3ICH, produces some of the best You Tube ham radio videos going. I absolutely love his style: polished, matter of fact, and everything is neat ~~ as in tidy, cleaned up, organized. Anyway, Jeff built Roger and Wes Hayward's "Ugly Weekender" transceiver as he shows you above. Of course, nothing Jeff does is ugly but you get the idea.

So I was doing a little research and found that there were PCBs -- by Far Circuits, of course -- and they were reasonable at about $13 for the set plus $5.50 shipping. So I tumbled for them and will see how this turns out.

Perusing the two Hayward articles reveals that the components required are surprisingly commonplace: a handful of 2N3904s, an MPF 102, and SBL-1, and an LM-386 audio amp. The rest are resistors and capacitors and easily-wound toroid coils and transformers. The circuits themselves are fairly prosaic (said the electronics whiz kid) with the MPF 102 VFO and a direct conversion receiver. However, there are some interesting features like semi-break-in, a frequency spotting mechanism, and sidetone.

Anyway, so there it is. Probably my next project, the first phase of which will be to roam through my "well-stacked" junk box (as Jeff Tranter describes it) and stuffing the parts into the boards -- or hoarding them and building it up in stages.

"Hmmmmmm, that broad sure has a well-stacked junk box!"
So there it is, too many notes!

-73-


Thursday, August 15, 2013

After the Gold Rush and the mid-seventies..

The confusion of a private high school in the San Francisco Bay area (football,girls, soccer, track and field, girls, Summers in Massachusetts, and yet more girls) served to relegate my amateur radio endeavors to the back burner. This state of affairs continued on into college at UCLA (and now surfing and yet more girls) and thence to the U. S. Air Force and a grim four years at Strategic Air Command in Bellevue, Nebraska.

Ironically, one of my good friends while in the Air Force was Captain Don McMinds who held WA0LGS at the time, I believe. (He is now K7DM and lives in Ocean Shores, Washington) But even Don's ardor for amateur radio could rouse me from the dreariness that was Nebraska so I spent four years in a location where I could have had an awesome antenna and a robust ham station and the wherewithal and time to operate some righteous DX.

It was pretty much the theme for me around that time: I eschewed opportunities to develop my running (I was to become a marathoner in the late Seventies), my cycling (a bicycle racer in the Nineties), and various other things, ham radio among them. Pretty much spent those years feeling sorry for myself.

That said, I returned to Southern California and began the desultory prospect of wresting my daily crust maintaining civilian software systems. Let's face it, deriving war plans and telling B-52s where they should deliver their megaton gift packages relegates accounts receivable and payroll programs a distant second.
Largely by dint of an argumentative conversation with some young German double-E asshole at a cocktail party, I got this chip on my shoulder. I was bragging about a Nordmende short wave radio I had just acquired and tried to one-up the kraut prick by telling him I was once a ham radio operator and wanted to show him up so, the next day, I set out to revive my amateur radio adventures. Discovering that the local JC offered a course, I enrolled at Orange Coast College and and acquired WN6EPZ -- a two-year, non-renewable Novice ticket.

My dad then presented me with a nice, shiny Kenwood R-599. It was actually one of two he bought at the old Henry Radio store in Anaheim. Seems he got a discount deal on the pair. When the ticket came (we waited for them in the mail in those days), I went up to the other Henry store (in Santa Monica) and, with the help of a very nice salesman, I scored the receiver's mate and thus ended up with my twins. Somewhere, I managed to scare up an S-599 speaker as well. The picture at the left is NOT my station, but it's close. 

These along with a Hustler 4BTV served my purposes during the two years as a Novice and I worked a lot of CW on 40 and 80 meters. My memories stray to one early rainy morning session where I worked Virginia, Washington state, Hawaii, and Antarctica consecutively! Talk about a demonstration of how omnidirectional verticals are!

Sadly my license expired and, owing to a move to another nearby residence to accommodate my second son's birth and my upwardly mobile income, I did not devote time and effort to move on to a General class ticket. However, in 1978, when asked by a client to babysit a software system I had just installed in their factory, I took advantage of the opportunity. They said they didn't care what I did -- I could even bring in Playboy and read it all week if I wanted to -- as long as I was immediately available. So, doing the next best thing, I brought in the ARRL license manual, studied all week and, when they gave the Friday morning off, I went down to the FCC office and sat for the Novice/General combination (75 questions) and scraped by the 13-WPM code test by the skin of my teeth.

Remembering the advice of my JC course ham instructor, I also sat for the Advanced license: same code test (already passed) and 50% more HF spectrum. When the FCC examiner said I missed thirteen questions (out of fifty) I was crestfallen -- until he reminded me that was a passing grade. Walked out of the office on a cloud and resolved to come back a year later and take the Extra. (It was actually almost two decades later that I did so.)

The really cool thing about an Advanced Class license in those days was that it earned one of those sexy 2x2 call signs. So, three weeks later, when my ticket arrived pronouncing me as KB6HK, I jumped on 20 meters CW with the twins and worked a few Qs. It was amazing to have a wall of folks come back to you thinking that you were on Baker or Howland Island. When I gave out my QTH as Huntington Beach, California, the traffic faded away like dew in the morning sun.


Somewhere along the line, I wanted to have everything "in one box" and dealt away the twins for a brand new Kenwood TS-520S and started working a lot of 80 and 20 meter phone. All in all, I loved the 520 from the day I bought it. It was one of the first times that I actually took my (then) younger son, Erich, along with me. He was about three years old and heretofore had only ridden with either his mom or the both of us. But this time it was just dad and son and the only downside to that was that he was a little young to understand the thrill of picking shopping for ham radio equipment. When we got to the store, however, I made sure Erich had a lot of time to press the buttons and play with the toys. (Strictly supervised, of course.) To hear him tell it today, he liked the adventure.  

Also, the neatest thing about the 520 was that I could port it downstairs, set it up on the patio, drive a post into the grass and use a piece of 11-foot EMT conduit as a 15 meter vertical. I managed to work all over the Pacific those lazy Sunday afternoons -- Australia, New Zealand, and Japan.

Life was great!

(It was about this time that I also got into VHF FM -- brand new to us back in the late 70s -- and will chronicle the great VHF and UHF rigs I owned/built in a separate post.)

-72-

Wednesday, August 14, 2013

Memorable (or not so memorable) Radios..1961..

I remarked to a friend on a Yahoo Group the other day that, in reality, two of my fondest wishes would be to have (1) sufficient wealth to purchase and keep all of the radios I bought over the course of my amateur radio years and (2) to have a shack big enough to stable them all.

Let's face it, we may not be geniuses but we ain't that stupid either. Like me, certain sure you have hauled in some real dogs from a swap meet and, after twiddling the dials and putting out a few calls, you realize that, while your little treasure works just fine, it ain't making it into your rig hall of fame.

Nossir!

I thought I'd make an entry here and post some of the goodies I have owned and some of the dogs as well. Consider it a work in progress and a labor of love. Here we go.

Where to start? Well, some radios in my past put an emotional tug on the heart strings. The melancholy is intertwined with the richness and promise of my (relative) youth, my two sons, and the circumstances in which I was forced to part with them. (The radios, not my sons.)

I was first licensed in 1961 as a Novice (one-year, not renewable) and received the call sign WV6KJK. (Wholly unmemorable; definitely not a keeper.) I still have that shred of paper -- hand signed by C. B. Plummer -- along with other fragments of that pre-high-school period including my Vibroplex bug and some no-so-fond memories of my Heathkit DX-40 and Hallicrafters S-38E receiver. I also built up a Heath VF-1 but never used it because we were required to be crystal controlled. I remember my crystal crystal
frequencies: 3,720 Mc, 3,730 Mc, and 3,740 Mc for 80 meters and 7,196 Mc and 7,198 Mc for 40 meters. (I think I still have a couple of the 80 meter crystals.)


But nothing in that setup tugged at my heartstrings and I worked no memorable DX (unless you consider Castro Valley from Woodside, California. And, I want to go on record as saying that the Hallicrafters was THE WORST receiver a young, aspiring ham could have.


About the only thing that can be said about that era was my dad's generosity: he bought
me the receiver and the DX-40 which came as a kit, so I built my own. In fact, dad (at that time a former ham) also sprung for the VF-1 kit, a Heath O-Scope and signal generator kits.

As desultory as my ham radio efforts int those days were, my father's kindness planted the hook firmly. After high school, college, and the U. S. Air Force, I was destined to return with a vengeance.

-72-


Monday, May 13, 2013

For my personal reference..

I inherited (for a pile of greenbacks) a really mint Tek 485 and wanted to check it out so I came up with these videos courtesy of this really nice guy (who sounds eerily like Gomer Pyle).


He does a pretty job of explaining and demoing this feature. I post it here as a convenience for myself. There's also this video on how to check one of these beasts:


..and some more:




Enjoy; I shall.

-73-

Wednesday, May 1, 2013

Idiom Press SCAF-1 Wars: My own fresh hell continues..


Well folks, I was forced to capitulate. The guy at Idiom Press still yet again continues to ignore my pleas for information. I was lucky to have scooped up one from my good friend and mentor, Dick, WB6JDH, and "opportunities abound". (See below.)

But to close off this little chapter of my own fresh hell, I cancelled my order with Idiom Press and told them that I was not going to be joining their fan club anytime soon. Closing the loop, I published the following review on eHam.net:
I am compelled to weigh in with a less-than-sunny evaluation of this product. I had written a previous review (removed by eham.net) based upon my experiences with the Idiom Press people and their failure to not only not deliver their product BUT TO REFUSE TO ACKNOWLEDGE MY ORDER AND RESPOND TO E-MAILS AND PHONE CALLS OVER A SIX-WEEK PERIOD. (I was not alone in travails like these; another ham had similar contemporaneous problems and likewise cancelled his order.) I can understand the previous review being removed because it was not about the product per se.

Anyway, aside from the fact that I did not have my order honored and ultimately cancelled with them, I bore the actual product no malice. In fact, because I was able to pick up one at a swap meet -- one requiring repair work, by the way -- I want to now write of my experiences and offer caveats to anyone contemplating purchasing the product or the kit. Here goes:

Firstly, the unit I got at the swap did not work. Attempts to find a manual were fruitless until a fellow ham graciously sent me a copy of his. Upon commencing the repair work I noted that there were radical differences between the manual and the actual unit I had on hand. While the board may have been accurate per the manual, the front switch was not. My unit had a DPDT with six tabs and the manual had nine tabs. The wiring on the unit I had bore only the remotest resemblance to the wiring in the documentation.

Please note that the instructions were published in 2006 and there was an addendum of corrections outlining a means of modifying the LM386 circuitry so it would perform better. (I think circa 2008) It was a very complex series of "four instructions up from the bottom change x to y" steps and occurred to me that perhaps the owner should have REWRITTEN the original to reflect the changes and tied them more tightly to board/kit revisions.

When I finally got my unit working, I was pleased -- BUT ONLY MILDLY IMPRESSED -- with its performance. The circuit is merely a low pass filter comprised of the two SCAF chips driven by a 555 timer. It ain't rocket science. Frankly, the NEScaf kit by the New England QRP club (http://newenglandqrp.org/nescaf) and the HI-PER-MITE (http://www.4sqrp.com/HiPerMite.php) offer products with as much promise, are very well supported, and are much more reasonably priced than the Idiom Press SCAF-1 unit.

Finally, previous "I bought mine several years ago, built it, and love it" reviews might be nice and fuzzy and heartwarming but you will be spending anywhere from $95 to $130 for one of these things and, if so, you had better be prepared for

(1) At least six weeks of being ignored after your order is taken.
(2) The prospect of a kit whose instructions are ambiguous and possibly out-of-date.
(3) A pathetic record when it comes to support and service.

The 2 is for the performance of the unit. Were I to rate the overall experience with Idiom Press with respect to the SCAF-1, it would be zero.

Color me unimpressed.

The Adventure Continues
That said, Dick's unit -- that he graciously sold to me and that was working when he did so -- went South when I began to operate it around the shack. It performed (as I said in the review) adequately but I was not screaming and the Earth did not move for me. I would rate it a so-so and look more eagerly to buttoning up my Hi-Per-Mite and NeSCAFe filters since they are documented better and seem to perform AS WELL AS the SCAF-1. Actually, truth be told, I am casting about for a really, really sexy container for the Ramsey AF-1 -- it performs very well but cries out for a better looking home.

Though my "Filter Days" are coming to an end (I have learned a lot and have several units that will make the various receivers sound good), I will get Dick's SCAF-1 working (with Dick's help of course) since there are the following unexplainable anomalies:
(1) The two Zener diodes to derive the +5V and -5V display run hot (very hot!) when a phone jack is plugged in the back and 12.5 VDC is applied.

(2) The unit does not work (i.e., complete silence) when powered by 12.5 VDC and switched on. See above regarding hot Zeners.

(3) The unit will not work with the right rear PCB mounting screw put in place and tightened down. It's intermittent. Again, see #1 and #2 above. This also happens when the box lid is mounted.
Now, I have no Earthly idea why all of this happens (which is why I am going to WB6JDH's QTH Saturday) but, when I find WB6JDH finds out, I will write it down here.

Breaking News!
I have discovered why the Zeners heat up and it'll surprise you. It is a fundamentally BAD DESIGN. I write the following to Joe, K3JLS, and let it serve as a warning to you if you are contemplating the purchase of one of these units:

Joe:

Just a word to let you know that there is a potentially serious bug (thank you for the schematic and manual) on the SCAF-1. It will not affect 99% of the people who use it, but it bit me in the fanny.

As you know there are two grounds in the unit. One is the power supply common ground and the other is the "artificial ground" in the circuit to derive the +5 VDC and -5VDC voltages for the chips. Turns out, if you have a common power supply for your SCAF-1 and your HF rig, then the two grounds on the SCAF-1 touch pee-pees and cause the voltages to get all hosed up and the Zeners to get hotter than blazes.

It affects my station because I use an Astron RS-20M to drive my IC-745 *and* the SCAF-1.

First noticed it when I was researching why the board seemed to have "microphonics" when I buttoned up the board and put on the cover. At the risk of boring you to distraction, I kept the cover off when I was testing it in the station and noticed every time I plugged in the station PS,that the unit stopped working and the Zeners began to sizzle. I then powered it with a separate gel cell and everything worked fine.

Also, my unit was one built by one of my SK friends and it had 4-40 screws from the chassis to the board which -- after a little abrasion -- shorted the two grounds together. So I replaced them with nylon screws to avoid any problems.

Probably obsessing over this, but would not feel right if I did not inform you. Oh, and I am NOT a EE but I got a friend who is [one and is the smartest ham I know when it comes to fixing things: WB6JDH] and he confirms [my analysis].
So, the bottom line is that common ground problem exists for anyone who buys the SCAF-1. Also, here's a tidbit: the SCAF-1 circuit was ripped off a 1995 QST article (reference upon request) that has a Far circuit board made for it. I was gonna get that but, now that I know the dual-ground problem, I think I'll live with my other swap meet treasure -- the Ramsey AF-1 -- and that should be fine. Besides, can you imagine a company propagating a circuit error like that? (But it does beg the question as to why this problem has not been discovered before.)

Besides, I have to build the upscale version of Lou's noise bridge.

..so many kits/projects, so little time.

-72-

Monday, April 22, 2013

The wonderful thing about amateur radio..


I spent the last post gassing about what was wrong with my order from the Idiom Press people. Turns out, I was a decade late and $95 short. Seems this is part of the Idiom Press culture; those folks have been doing that since at least 2004 so far as I can determine. There are a number of threads abroad on the internet -- some dating from as long ago as 2004 -- complaining about their lackadaisical, cavalier business mien.

Most threads start with the interrogatory, "Is Idiom Press still in business; I just placed an order and.." followed by several respondents relating similar anecdotes and subsequent replies strangely savaging the original messages for not having enough patience or relating how the son has taken over the business and "needs time to catch up".

Give them a break? Give me a break!

A very representative thread of this discourse can be found on, strangely enough, an Elecraft e-mail forum -- it includes a verbose lecture from W7AQK that just screams of "no, I have not done business with Idiom Press":
What a lot of folks don't realize is that a great many of the amateur radio suppliers, and especially the QRP type suppliers, are "one man operations"! As such, they don't have a particularly organized and sophisticated ordering and shipping process. Accordingly, if you are in a particular hurry, or need something quickly from one of these very small companies, you should talk to them personally and make sure you are going to receive your order in the timeframe you are expecting. There are a thousand reasons why it might take longer than you expect to fill your order. Most of these little companies are operating out of their garages, or similarly small space, and parts coming in versus things going out can be an issue. I'm not making excuses for bad service, but so many of these operations are reliant on their receiving the necessary parts, which they really can't control. They can't afford to maintain large inventories of parts, so a sudden rush of orders probably means a lag time that would normally be considered unacceptable.
...
Bottom line, if you are in a big hurry, call them and talk to them personally to find out what delay might be in the offing! I know, some of  these operations promise more than they can handle, but most of them, I think, try to be reasonably forthright in their advertising. In any event, If time is of the essence, I'd be verifying things with them personally.
You go in business, advertise a product and you either deliver or you respond to e-mail inquiries as to timeliness of the order-filling process or an explanation re parts shortages, etc. I would just salivate to see W7AQK order something from those folks and then try to phone them up for a status. That's the point, dummy! They do not respond.

Well, I was able to get a SCAF-1 from my very good friend, Dick, WB6JDH, last weekend. I took it home and hooked it up and heard..

..Zero..zip..nada!

Turns out somewhere in the handling of the unit, the two 5.1V zeners that comprise the -5VDC supply took a dirt nap. And for the sake of honesty, it probably wasn't Dick who did the dirty but rather yours truly, Mr Heavy Hands. So I still have a ways to go to test this unit and give a competent review. Although I will say this: it's a low-pass filter and I am prepared to not be as impressed with it's performance as I was. (But, I am prepared to be surprised.)

Enough sucking lemons. I want to hand a out a mighty kudos to folks like Dick and to those hams you seem to bump into all over. Another soldier in the Idiom Press Wars is Joe, K3JLS, who has come to be a very fine acquaintance. Seems he scored a manual for the SCAF-1 and is generously sending me a copy in the mail. I will be scheming and plotting how I can get even with such a fine gentleman. But, to me, guys like Joe and Lou (the progenitor of the two noise bridges I wrote so much about earlier) and Dick are what make this hobby worthwhile.

Also, here's a little tidbit to look for if you are traipsing around a swap meet or see it pop up on eBay: The Ramsey AF-1 CW filter kit. It is out of production, I believe, but is a rare exception to the old saw about Ramsey kits being trash. If you can score one, then my advice is to pounce! The manual for the kit is here.

More on this and gentlemen like Joe and Dick and how really great ham radio is.

-72-

Wednesday, April 10, 2013

I would love to review the Idiom Press SCAF-1 but..

..I placed an order a little over two weeks ago and have not received it nor have I heard a peep out of this guy. Moreover, three e-mails and a phone call have gone unreturned. All I am looking for, fer crissakes, is some acknowledgement that the tool has received my money and will be shipping the kit -- whenever.

I mean, Midway, U.S.A. back ordered my turret-press reloader but at least have the courtesy to inform me of the status, etc.

The Idiom Press K-3 keyer is the best around but I don't remember there being any such delay with that. Oh yeah, that's because I bought it off-the-shelf at Ham Radio Outlet in Orange County, California.

You'd do well to heed this and read the eHam Net reviews on this product, particularly ones like this:

 
Caveat emptor, as they like to say.

UPDATE: Still nothing on this front. However, I put up a "me too" review on eHam.net echoing that K3JLS's experiences were my own. Basically one month after K3JLS came up dry, I was too.

I went over to eHam.net today (04-17-2013) and found that both our reviews had been scrubbed. Another review was leading the list by some guy who bought the kit several years ago and experienced a delay in receiving his order but got an e-mail from Idiom Press saying that he was getting the built product for the kit price.


With respect to eHam.net pulling K3JLS's and my reviews and, at the risk of sounding like I do not have a life, I cry BULLSHIT! Firstly, the eHam review editor may be on firm ground in redacting our reviews because, technically, neither of us had the product delivered and -- by some tortured logic -- relating our experiences to POTENTIAL CUSTOMERS of Idiom Press might be misleading.

Whatevs.

But, were I a potential customer (who else reads reviews?), I would want to know if there was problems with the supply and availability of a product. Since -- at latest inspection -- there are no caveats on the Idiom Press site about delays or "we're running behind" then the guy is setting up customers for a big disappointment and certainly not creating any good will.

All this said, I want to be clear on one point: I am not one of those piss-and-moan types who gets mad and demands legal recourse because a kit maker has my precious $80-100. Some time ago, Steve, K1EL, was producing a follow-on edition to his K-40 CW keyboard device -- the K-42 -- and my order was not filled for a longish time. I e-mailed Steve and he said he was running behind because he had been in a terrible car crash and was recovering but I could have my money back if I wanted.

I would hear nothing of the sort! I told him not to sweat the small stuff, get better, and when the K-42 was ready to ship, it was ready to ship. PERIOD. I even offered to help him test/debug some of the firmware and/or a prototype device. Point here was that the man was honest and responsive and was in a real bind. Having the unit on the market was far more important to me that having my grubby loot returned. It is even the case with Idiom Press. I am looking forward -- someday -- to receiving and building the kit.

And, as for Idiom Press, I have spoken with the gentleman before several years ago when I was contemplating the purchase of a new version of his K-3 keyer. He was pleasant and accommodating and, I believe, he is still so.

It's just that we -- K3JLS and I -- would appreciate hearing something -- anything -- about our orders.

As for eHam.net, well, I am buying a built SCAF-1 from my good bud, Dick, WB6JDH. (He has two of everything.) After I get it, I will post a review of it on eHam.net and relate that the reason I bought a unit because I got bupkis out of Idiom Press.

Let's see if that review sticks. 


-72-

Friday, February 22, 2013

Revisiting N6TWW's Calculations..


In a preceding post, Mike, N6TWW, discussed the calculations he made in order to develop a phasing harness for a couple of VHF antennas. I borrowed on his numbers to further ingrain this poor boy's TDR technique.
(1) Speed of light = 186,000 miles per second.

(2) 186,000 x 5,280 = 982,080,000 feet per second.

(3) 982,080,000 / 1,000,000,00 = 0.98208 feet per nanosecond.

(4) 0.98208 feet = 11.78 inches.

(5) Light travels 100% in free space but travels only as fast as the velocity factor along a cable.

(6) The velocity factors of popular cables are:

      CABLE    -  VF
      RG-8     - .66
      LMR-400  - .85
      RG-8X    - .84
      RG-11    - .75
      RG-58    - .66
      LMR-195  - .83
      RG-59    - .82
      RG-62    - .84
      RG-174   - .66
      RG-213   - .66
      RG-214   - .66
      RG-217   - .66
      RG-218   - .66
      RG-316   - .79
      RG-400   - .695
      LMR-500  - .85
      LMR-600  - .86
      1/2 HARD - .81
      7/8 HARD - .81

(7) I got 2 hunks of cable I want to determine the length of. One is a long piece of RG-8X and the other is a shorter piece of RG-58. I have another hunk of coax that I want to verify the velocity factor of.

(8) For the longer hunk of RG-8X, I assume that the velocity factor in 84% so that means that when an electron travels through it it's only going 84% as fast as its cousin in free space. Consequently, it is traveling 84% of 11.78 is 9.98952 inches. So let's say 10 inches for grins.

(9) I lashed up the scope and the function generator like these two lads did and found that the RG-8X cable's out-and-back trip was 2.4 divisions at 100 nanoseconds per division. So 100 x 2.4 = 240 and half of that (only want one-way) is 120 nanoseconds. Thus, the cable is 120 x 10 inches or 1,200 inches long. Obviously, 1,200 inches is 100 feet. (Do I really have to?) And, guess what, that's what the guy at the swap meet sold to me: 100 feet of RG-8X.

(10) The shorter hunk was 1.6 divisions at 100 nanoseconds which works out to 160 nanoseconds. The one-way time, of course, is 80 nanoseconds and, since it's RG-58, the distance traveled in a nanosecond is 11.78 x 0.66 or 7.78 inches. So electrons traveling 80 x 7.78 inches or 51.8 feet. Let me get a tape measure and check that number.

(11) Now for the third hunk of coax, I know it's 22.75 inches long and I know that it "scopes out" to 0.7 divisions and 100 nanoseconds. Half of this (one-way trip) is 0.35 x 100 or 35 nanoseconds and 35 x 11.78 or 412.3 inches or 34.36 feet.

But that's the distance in free space, and I know that the coax is 22.75 feet long. So the velocity factor would be 34.36 / 22.75 or 0.662107 or 66% -- which is what they say RG-58 should be.

Funny thing, that!
-72-

Probing the mysteries of 'scopes..

Here's the deal-e-o on scope probes:


..remember, this blog is for me and not for heavy duty PhD EE types. Sorry for my pedestrian pace.

-72-

Wednesday, February 20, 2013

Time Domain Reflectometry for the poverty stricken..

Munching my tuna fish sammich today at work and came across this:


..thought I'd store it away here for reference. Here's a practical application of this method:


Let's face it, I'm like a kid in a candy store. I am smitten with this application. Here's a variation on the same theme:


..graphic explanation for characteristic impedance and possible entre into the phenomenon of SWR? Lord, is this fun or what? I feel like one of those freaking apes at the monolith in 2001.


Ain't life grand?

-73-

Tuesday, February 19, 2013

RX2 Wrap-up..

Here's some pics just as I am buttoning it up after calibrating the unit. Lou's checkout procedures seem very cryptic at first but, after you become familiar with the operation it makes perfect sense. I plan on going back in and re-doing the unit just because I am an inveterate tinkerer. And, let's face it. I need something to do until the RX1 arrives.

"Rex, the Wonderbridge" (the RX2) along with my FT-817  ~~ affectionately, "Tex".
(I actually used to own a Sangean receiver, by the way.)
Close up internal view.
Buttoned up, next to Tex, ready for business.
Close up of the cabinet and dial.
Rex and Tex, mates for life!
The dynamic duo about to elicit some dark secrets from Mr Coax.
The pair attracts the attention of Mr Palomar, who is contemplating retirement.
Left side of the bench and the Ten Tec I am trying to breathe life into.
..and we fade out with a view of the clubhouse, our hero shutting down operations for the day and contemplating the blissful prospect of a cool one and the pleasant company of Mrs K6WHP.
-72-