Wednesday, January 22, 2020

Zuni WFD Get-Together Venue Change!

Mike, N6MST, just saved our bacon. All the way up in Bakersfield, he spied that Mile Square Park -- where we were originally to meet - was going to be occupied the entire wekend by the Vietnamese New Year -- Tet - celebration so, consequently, we are moving the venue a little down from there.

My so-called Plan "B" has become Plan "A" and it involves our commandeering a part of the green belt in my community. There are trees and a vast open space and, with our bringing two or three portable tables and chairs, we can set up there. See the pictures below. The Green Valley Park offers these advantages:

(1) Some trees.
(2) Open spaces where verticals and poles for antennas can be erected.
(3) Abundance of free parking that is walking-close to where we would set up.
(4) No crowds to speak of.
(5) Restaurants/7Elevens close by. CostCo also close. ($1.50 dog and a coke special ant their "food court".)
(6) Close to my QTH so we can grab some stuff from my shack/bench if we need to.

Some downside: we are going to need for folks to bring chairs and another table. I have a table and two chairs but it's not conducive to operating or outgassing if everyone does not have a chair.

So, we will still coordinate on the PAPA System so give us a call there if you are lost.

Sorry for the change but this should still be tons of fun and we're still doing the pizza debrief afterwards.

To get here, head South on the 405  to the Brookhurst Street and go under the freeway and loop around so you're heading North on Brookhurst. turn right on Warner and proceed past Ward (the next light) to Los Jardines wher you take a right. we'll be listening on PAPA or 146.52 MHz to talk you in.

Monday, January 13, 2020

Get a grip..

In an attempt to scrape some rust off my CW fist, I am currently matriculating through the CW OPs CW Academy and it is a marvelous experience. Sure it's the beginner class and sure I can solid copy around 15 WPM but I am doing this for the discipline -- and getting myself into a routine of practicing my CW daily.

But more on that later. The purpose of this post is to bring CW operators attention to a discovery I made -- thanks to my wife. She found this stuff called Grip Liner Magic Cover which is billed as a non-adhesive and non-slip cupboard liner for dishes and glassware. It is by Kittrich Corp in Pomona, California and can be found in many homewares stores, super markets, and it and variants are available on Amazon. (You do your own search.)

A small square of this stuff anchors my paddles to the desktop and essentially squelches any side-to-side slipping. So far, the squares I have been using for my Bencher (below) and Kent (out on the shack) are well over six months old. So, a roll of this stuff should last a lifetime -- and more.

Wednesday, January 8, 2020

It Begins! Prepping for Zuni Loop MEF Field Day 2020!

Rust Never Sleeps!
The Zuni Loop Mountain Expeditionary Force is an ad hoc association of some of the best and brightest QRP ops who came together each year for ARRL Field Day. One of the groups consistent mainstays and organizer for the past 35 years was Cam Hartford, N6GA, who ensured that QRP and antenna and operation experimentation resulted in good contest results, an enhancement of participant knowledge, operating skills, and -- mainly -- fun!

Sadly, Cam left us last year before Field Day and we carried on as best we could. But, armed with that rebuilding experience and a determination to regain past glory, we are resolved to not let the tradition of Zuni Loop fade away. What we have going for us is this tradition and one heck of a great location. But we will peak of that later on. For now, the planning begins.

Where We Sit Now
We need more ops. So far we have a commitment from three veterans and four promising new-comers: John, n6vcw (trustee of Cam's N6GA callsign - now officially assigned to the Zuni Loop MEF), Ed, KM6TNT, Matt, KM6TOA, and Mike, N6MST. The returning regulars include Dick, WB6JDH, myself, K6WHP, and long-time Zuni veteran, Keith Clark, W6SIY. Ed has done a great job in recruiting and has secured three new hams to join us for 2020. We welcome them and others with a profound interest in QRP and pushing the envelope. If you are intrigued and proximate to Southern California, let us know. My email is good in QRZ under my call sign or click on this link and blast away!

Preparation and Related Logisics
Our first step in preparing for Field Day will be participation in the Winter Field Day on 25-26 January. We will be setting up in Orange County at Mile Square Park in Fountain Valley.

While Winter Field Day is a contest and we will set up to operate -- patterned after the Summer Field Day but with a few rule changes -- our emphasis will be a little different. Our main goals will be to get to know one another, check out some equipment and antennas, orient folks not familiar to in-the-field QRP operation, and generally observe the newly coined variant of the Zuni Loop motto:

We're deadly serious about having fun!

Although Winter Field Day goes overnight (like Field Day) for two days, we will only set up and operate for a short time, from about 0900L PST until about 1500L PST. Note that the actual contesting starts -- like FD -- at 1100L but we want to get a head start with prep and such. Also, I live adjacent to the park and will be heading over early to stake out tables and trees at an appropriate site. (Probably will be "spot #2" per the map below.) If you wish to coordinate the entry and "carpool" into the park, there is parking in the adjacent strip mall next to my QTH. I would recommend coordinating with Ed, KM6TNT, on this noting that we both can be found on the PAPA system. It is one of those sprawling, linked "closed but welcoming" repeater system whose info can be found at this link here. Suggest PAPA 03 or PAPA 04 as you penetrate Orange County.

Mile Square Park park charges $5 admission on Saturdays and does not allow re-entry (unless you pony up again), so I recommend picking up something -- sammiches, sodas, etc. -- for lunch around noon time if only to stave off hunger. We will probably have donuts and/or bagels available at first but if you you are a coffee drinker, you are on notice that I am not and your daily caffeine hit is your responsibility. 

We plan on folding our tents and heading over to a pizza joint close by where we can eat, "hydrate ourselves", and debrief. This socializing will be an invaluable opportunity to gather our thoughts and ideas in preparation for the real thing.

Prerequisites and Skills Required
Again, if it looks like you want to participate in the Zuni Loop MEF effort this is a great way to get to know the folks. If your CW is rusty or non-existent, don't worry! we do phone too and you will be surprised how -- with a little coaching -- you can pick up CW contesting by logging and using a CW reader. Also, don't let low power throw you. Up at 7,000 feet, a five watt signal carries pretty far. Several of us have done WAS (Worked All States) during a field day. (I have done it three times and once I came within four states of doing a "double WAS".) Also, foreign countries now participate in Field Day so there's a chance for DX as well.

Send me an email and I'll answer any questions you might have.

Park Environment
For reference and orientation, here's some pictures of the Mile Square Park surrounds.

K6WHP QTH, External Parking, and Mile Square Park Spots

Map of Mile Square Park

Friday, December 20, 2019

Simply Half-Wave Trapped Antennas Addendum 1 - Nice to Have Stuff

Paul Carlson in a small part of his lab
This is a short rant about [electronic] tools and what you should anticipate arming yourself with.

If you are new to ham radio and foresee getting into serious tinkering, First get yourself a DMM (Digital Multimeter).


These range from literally free (with a coupon from Harbor Freight Tools) to a Fluke (or higher grade instrument) that will cost you almost a thousand buckos. Scout YouTube for some reviews but cease once your eyes begin to glass over. Guys like Dave, the histrionic Aussie host of the EEVBLOG series, will have you believing you cannot survive without owning a Fluke meter that can withstand being thrown off a skyscraper. M. J. Lortin, the laconic Englishman, will have you sound asleep five minutes into part one of an hour long video of which there are two additional parts.

Other guys will show you anywhere from three to ten DMMs they bought just so they can do a review of the infinitesimally subtle differences between each. Trust me, if you get a decent one for about $15-50 with auto-ranging and a few other features you might want, you will be fine. Also, trust me: it will not be the last one you own.

O.K., that covers DMMs and we'll leave oscilloscopes for later. But, when you get one, you will be surprised how you did without it.

I would only add -- for the moment -- that you make a modest investment into three items that will save you a lot of headaches, guesswork, and make this corner of antenna and radio building a lot of fun. These are a component checker, an LC meter, and an antenna analyzer. Examples of these are shown below but are not exact product recommendations. They are part of the bounty of cheap Chinese stuff exported and sold on eBay for a reasonable price. Recommendations can be sought amongst friends and on VHF/UHF technical nets and round tables. Wise shopping will set you back from $20-100 tops.

Component checkers are surprisingly good at telling you a lot about each little doodad you hoover up at swap meets from transistors to inductors and including resistors, capacitors, diodes, and other stuff. They might even be good enough to tell you about the inductors and capacitors you are using for your traps. They are around $15-25 on eBay.
LC meters are higher quality gadgets that give you a more accurate reading of the inductors and capacitors. If your component checker is crappy, then consider one of these. They are a little more than $20 on eBay.
Antenna analyzers range from cheap to literally a kilobuck (or more). If you pick up one for HF only (1-60 MHz), expect to pay around $50-80 for a low end one. I have a couple I picked up in that price range and am perfectly content with what they show me and don't need curves of graphs drawn.
But, trust me, you start tinkering and you will always see "something better" and end up having about three or four items that essentially do the same thing. Of late, there is a "NanoVNA" on eBay that sells for about $60 and will actually draw curves of your "network" (the trap). If it is sexy enough to compel you to open your wallet, knock yourself out.

If you want to go old school, you might consider picking up something called a Grid Dip Meter or "GDO" (Grid Dip Oscillator). Back in the day (the 1950s onward), these were considered the "Swiss Army Knife" of test instruments as they could be used to test LC tank circuits, antenna resonance, and even serve as a signal generator. Here, Alan Wolke, W2AEW, does a nice video on how these can be used.

When my dad passed away back in 1992, I inherited his Millen 90651A which, at the time, was considered the Cadillac of GDOs. I developed a "jones" for these and over the course of time owned a number. The collection dwindled but I kept my dad's and the cream of the crop and still use them quite a bit, to wit:

The Heathkit transistorized version of this -- like the one in Alan's video -- is worthwhile and is as near as good as the Millen. The Millens and the Heathkits are not worth owning if they are in questionable condition or do not have the coils with them. Most of the time, the ones offered on eBay are dog meat and way overpriced at that. Occasionally, one will come along and is worth nabbing. Even better is picking up one at a swap meet or ham fest.

Alan produces some outstanding technical videos and they are well worth watching. His work is thorough, explanations are straightforward, and he publishes those magnificent notes he makes for download from a link on each video.

Another simple "old-school" tool is the noise bridge. These are simple circuits that generate white noise. As explained by an Australian, Ralph Klimek in a 1995 article on his website:
A noise bridge is an impedance measuring device that can measure real and imaginary components of complex impedance at RF frequencies. It uses a radio receiver as a detection device and a broadband noise source as the excitation source for the bridge. This eliminates the need for a precision signal generator notwithstanding the fact that the average signal generator does not have sufficient output amplitude to excite and bridge and simple detector. A radio receiver is an excellent detector being sensitive down to microvolt signals and low bandwidth. The noise bridge is an excellent antenna tuning instrument because it gives a rapid and precision measurement and also the noise power induced into the antenna is very small and will not cause interference to others.

Basically, is is an even cheaper version of an antenna analyzer and, if mastered, can be quite useful.
There are "commercial" products available like the venerable Palomar Engineers version or an old Heathkit, and an MFJ unit that turn up from time to time on eBay priced from around $20 on up. I would not, however, pay more than $40 for one. These are shown below:

There is a kit available from QRPGuys for about $20 plus shipping. It works identically to the units above but the advantage is that you get the experience of building it and there is a comprehensive assembly manual here and an "operations manual" here.

Like the GDO above, if you see a noise bridge at a swap meet or ham fest for a reasonable price, pick it up and learn to use it. Anyone can drive one of those idiot-proof antenna analyzers but it takes going old-school to really understand the underlying electronics and antenna theory.

By the way, Paul Carlson is one of the more impressive techs on YouTube. His lab (a smidge of which is shown in the picture above) is truly expansive and, given that he is prone to radios and equipment built in the 50s and 60s, borders on the Gothic. Don't let this put you off. The man is a genius -- both in the literal sense and as a statement of my admiration for him. His YouTube channel is a treasure trove. Here is the intro.

Simply Half-Wave Trapped Antennas Part 4 - Putting the Antenna Together

A small contingent of the The Zuni MEF will be doing Winter FD but not as a contest, rather a one day antenna and rig "burn in".

As part of that, I will be assembling both a 40m/20m trap dipole as well as a 40m/20m trap vertical and will have pictures and notes on that in this space.

..see you at the end of January 2020.

Tuesday, December 17, 2019

Simply Half-Wave Trapped Antennas Part 3 - Constructing Traps

Constructing Traps
It goes without saying that almost anything can be used as a coil form for the inductor in a trap from air to iron. Classic traps in the days of yore was one made out of the Air Dux™ coil stock (shown below) where one sawed off a hunk for the correct inductance.

Of course, wood dowels, PVC, pill or other plastic bottles -- even card board tubes -- can be used. Take, for instance, this trap made out of a toilet paper tube, a hunk of wire, and a couple of 27 pF silver mica capacitors in series. Obviously, it will not stand up to a cat 5 hurricane -- or even a moderate drizzle -- but it can be "hardened" and weather-proofed and/or hidden in an attic where it will serve duty. (I Would not run more than 100 watts through it unless you have your track shoes on and your homeowner's insurance paid up.)

Also, there's no law that says you have to have a round coil either. A piece of wood with a square profile would work just fine. The take-away here is to use your imagination and see what you have on hand. My preferred material is PVC and generally in 1-inch to 2-inch diameters. The material is rugged, weather-proof, and easy to work with.

Here are a pair of traps I fashioned with some PVC, a 27 pF silver mica cap, some screws, and solder lugs:
The bottom line on constructing traps is the more perusal and experimentation you do, the better your antenna building kills will become. I did a post before this series with a bunch of pictures of traps I built for a vertical antenna. You are invited to peruse those -- as the rest of the blog if you like.

Testing Traps
Once you build your traps you will need to test them; measure their resonant frequencies. I like to measure each component before I assemble the trap and then measure the resonant frequency of the resulting trap. As you will find out, components are not always dead on with respect to their marked value nor are the coils you wind going to exhibit the calculated inductance. Consequently, the resulting resonant frequency will not be what you calculate either. But not to worry. All you need to do is get things "close enough for government work".

First, let me digress and recommend you take a quick gander at this as a hint on tools you should be considering if you would like to progress further away from being an appliance operator.

All of that said about the "nice-to-own" tools, here's some notes and comments on ways to measure the resonant frequencies of your traps. First up is a video by yet another ham who does a great series on how-to projects, Peter Parker, VK3YE. It pretty much describes a way to use your radio and a broadband antenna (i.e., a long length of wire) to roughly determine the traps. It is fairly self-explanatory, illustrates a "cheap method" of doing this since you already have your HF radio, and it follows through with how Peter calculated the values necessary to achieve resonance at the desired frequency. Finally, he shows the resulting traps which -- along with my pictures and pictures of other traps on the internet -- should give you soem good ideas how to fabricate yours.

Unfortunately, he flashes by a piece of information from W8KI's website on traps that speaks to the desirability of component traps versus coaxial traps:

- Trap loss greatly exaggerated by advertising hype
- Traps should not be resonant at the actual planned operating frequency
- Coaxial traps are more lossy than articles conclude
- Coaxial stubs used as capacitors cannot be calculated using pF/foot unless the stub is a very small - fraction of a wavelength long
- Coaxial stubs have a low Q (are relatively lossy) compared to normal lumped components

The actual website is here and it is definitely worth a glance as he develops this theme with calculations. The bottom line is that you don't sacrifice anything by building traps with discreet components versus pieces of coax, the busy-body naggers notwithstanding.

In the link above where I made the recommendations as to the inexpensive test equipment you should avail yourselves of, I mentioned an RX noise bridge. These can be used in conjunction with the receiver on your HF rig to measure the resonant frequency and a good explanation on how to build one as well as use it can be found here. Note that the noise bridge will substitute for Peter's broadband antenna and provide you the antenna radiation resistance as well as the inductive or capacitive reactance.

There is a great article on an antenna noise bridge detector here.

..and another one here.

By this time you should have a couple of traps resonant just below the highest band of your dual-band antenna. (That is, around 13.5 MHz for a 20m/40m antenna.) Next we'll take up building the antenna itself. But rest assured, the toughest part of the job is done.

Simply Half-Wave Trapped Antennas Part 2 - Calculating Trap Values

Antenna "traps" are nothing more than parallel LC (inductor/capacitor) circuits -- also called "tank" circuits. The derivation of "tank" and "trap" is intuitive once one understands how a parallel resonant circuit works or, more specifically, the nature of LC circuits.

There is a great discussion of these on Wikipedia and other renditions abound all over the internet.

But, basically, the take away on these is that -- at a circuit's resonant frequency -- the impedance of the series LC circuit is zero and the parallel LC circuit is [almost] infinite. Leaving the series LC circuit, the parallel resonant circuit's high impedance is due to the interaction between the capacitor[s] and inductor[s] in the circuit. I stole this image from the Wikipedia article but it shows this graphically:

Again, borrowing from the article, this animated diagram showing the operation of a tuned circuit (LC circuit). The capacitor C stores energy in its electric field E and the inductor L stores energy in its magnetic field B (green). The animation shows the circuit at progressive points in the oscillation. The oscillations are slowed down; in an actual tuned circuit the charge may oscillate back and forth thousands to billions of times per second.

Gradually without replenishment, this activity will dissipate. However, with an oscillating power source like energy from your transmitter or received at your antenna, the activity will continue uninterrupted by accepting the energy into the "tank" and or "trapping" it and not letting it pass further - hence the high impedance. (I am beginning to skate on thin ice here and suggest you seek hard tech info elsewhere before this erupts into a fount of formulas.)

The steps to build a trap are as follows:

(1) Determine the resonant frequency of your trap.
(2) Calculate the capacitance and inductance values.
(3) Calculate the number of turns for your inductor.
(4) Construct the trap.
(5) Measure the resulting resonant frequency.

We'll cover steps #1 through #3 here and take up #4 and #5 in the subsequent post on building and measuring the traps.

For the moment, let's assume we're building a 40m/20m trap dipole. (For the sake of this whole series, we are talking about a two-band antenna. I will comment on constructing three or more band trap antennas in the building segment.)

Determine Resonant Frequency of the Trap
The resonant frequency of the trap should be a shade under the starting frequency of the higher frequency band you are designing, in this case 20m. So we are looking for a trap that is resonant in the range of slightly less than 14 MHz (around 13.5 MHz will be fine) so that it will cut off all frequencies above that frequency and acting like the automatic switch described in the first segment.

Calculate Capacitance and Inductance Values
This is almost arbitrary; you can obtain the same resonant frequency by selecting one LC combination and achieve the same resonant frequency with another difference set of values. Avoiding formulas, there's a nice parallel LC calculator to be found here -- and below, I have used it to demonstrate different values achieving almost the same resonant frequencies.
Note that with the selection of two pairs of components -- 27 pF cap and 5 uH inductor or 14 pF cap and 10 uH inductor -- we have achieved traps with approximately the same resonant frequencies and either one would be suitable. Of course, there are other design niceties to be observed in selecting values of components but that is left for your further study.

Further restrictions are, of course, the availability of the values selected. We can wind inductors (which will be covered below), but capacitors come in discreet values. You can kluge a desired capacitance value by either connecting two or more in series where, like resistors, you are adding the reciprocal of the values) or parallel where you are just adding the values.

The voltage handling capacity of inductors and capacitors need to be considered as well. Since traps are at "the end" of the 20m antenna, they will be at a voltage node and that has to be accounted for. If you are working QRP any decent working voltage or gauge of wire should be fine; you can even construct the inductance (coils) from toroids. However, the kilowatt level is another matter so be very careful. (I will probably do a fourth segment on these considerations.)

Also, I need to pause here and enunciate a prejudice. Research into this subject will show you that hunks of coax can be used to build traps. As you can imagine, coaxial cable has, in effect, capacitance between the shield and center conductor and, as such, can serve both as an inductor or capacitor when wound around a form. The advantage to this that you only need to cut off the appropriate length and build the trap. I chose to keep the components separate so you got a better notion of the LC principles.

Calculate Number of Inductor Turns
Inductors take many forms: single-winding layer, multiple-winding layers, toroidal, etc. For our traps, we are constructing a single layer inductor; I pilfered these formulas from the 1981 ARRL Handbook:

Of course, you can enter this into your calculator laboriously, build a spreadsheet, or just use one of the internet sites to do this:

This covers the first the first three of our five above steps and, since this is somewhat long, we'll leave the rest for the third segment on actually building the traps, measuring the resonant frequency, and building the antenna.