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Saturday, April 9, 2022

Summer QRP => Portable Antennas

Summertime is QRPxpedition time here at W0VLZ. After a winter of playing with boat anchors in the basement I'm ready to get out to a park with my KX3. With any rig I always have to think about an antenna. Looking back on my blog and website I see that I've gone through this before.

Here are some links: Construction details and experiences using a 20 meter endfed halfwave wire "tuned" by 14' of TV twinlead. A portable 20 meter vertical Building and using a C-Pole Vertical My quest for a stand-alone 20 mtr portable antenna A 30-10 meter "clothes line" dipole

See you next time from a convenient park.

73, Niel - W0VLZ



Thursday, March 31, 2022

A Shack Tour

This past winter I finished setting up my new ham shack. It has 10 operating positions but (reflecting my ham radio interest in vintage technology) only one antenna.

See it on YouTube at

Friday, March 25, 2022

Building and Using a Push-Pull TNT Transmitter

My first '29 transmitter was a push-pull TNT. I built this transmitter in 1989 based on an article in the Nov 1930 issue of QST. I have pages on my original website about this transmitter but those pre-date this blog. Here are links to those pages: 

- A 1930 TNT transmitter:

- Operating a late 20s/early 30s ham station:

Friday, March 18, 2022

Winter 2022 Vintage Radio

As of last Sunday my winter 2022 vintage radio season is history. Along the way I was on the air in five different events using 5 receivers and 5 transmitters. Three of these events are sponsored by the Antique Wireless Association ( ). One other, Straight Key Night, is sponsored by the ARRL ( ). The fifth was the Novice Rig Roundup ( ). These events allowed me to get comfortable with my new QTH and were low key enough that I could identify any hidden station quirks without feeling rushed or having to worry about keeping QSOs as short as possible. Each of these events was more like a saunter through the bands rather than a sprint.

The Novice Rig Roundup was my favorite. Its nine day operating window let me work around stormy weather, other contests, family obligations and propagation while still having fun.

I did find that I really like my Drake 2NT/R4B station. The 2NT operates break-in well with the R4B and its delay/timing circuit allows the crystal oscillator to run between code character elements. This minimizes chirp, even for the laziest of crystals. The R4B has KHz frequency readout and great filtering options. This pair is a keeper.

With almost 40 years of radio technology between my '29 transmitters and the 2NT it is not surprising that my '29 station is the more unique (and challenging) to use. Challenging, though, does not mean unusable. While unique and challenging my '29 station is still usable. Depending on conditions I can switch between an SW3, an early 30s National regenerative receiver, and my early 80s Drake SPR4. Once and a while it is good to go back and experience ham radio roots.

We've already had temperatures in the 60s this year. With spring arriving the snow has melted here in southeastern Minnesota. Now I'll start thinking about my QRP in the Park plans.

Saturday, September 18, 2021

On The Air Again!

 After almost a year off the air I'm finally back with a working antenna system.

Before my move I started thinking in terms of a trap vertical at the new QTH but I had safety concerns. My backyard butts up to a public golf course. For many reasons this is a great location but how can I keep a golfer from straying through the yard and, possibly, leaning against my ground mounted vertical as he is searching for a ball? A vertical would not work. I needed something up in the air.

The layout of the yard, safety and the need to keep my installation as unobtrusive as possible led me to an inverted L using insulated wire. I have almost always used some sort of end fed antenna, both for portable/QRP operation and for the main station. An inverted L would be no exception and a 66' wire would easily fit.

I installed my 66' inverted L over a south facing half circle field of 22 40' radials, all terminated at a DX Engineering Radial Plate. This easily loads up on 80 and 30 but presents a very high impedance on 40, 20, 15 and 10 where it is a half wave (or voltage fed) antenna. The solution on these bands is a 49:1 wideband EFHW matching transformer. This allows the high impedance (2.5K-3K) inverted L to be transformed down to 25-100 ohms, a load my transmitter and/or antenna tuner can easily handle.

My shack is just behind the radial plate/hub. I mounted the 49:1 transformer on the inside wall here. I can easily bypass this transformer for operation on 80 and 30. In addition, everything is out of the weather.

Does it work? The Reverse Beacon Network says that my KX3 at 10 watts is covering the US on 40, 30 and 20. On 80 it appears to be working as a NVIS (Near Vertical Incidence Skywave) antenna as expected . I'll find out for certain starting in November as we move into the winter vintage radio contest season.

Wednesday, November 4, 2020

A tour of W0VLZ

 Last Sunday Phil, WE0K, stopped by. I'm lightening my load in preparation for a move and Phil was acquiring a heavy load.

While Phil was here he did a video tour of my shack including many of my vintage operating positions. You can view it at

Wednesday, July 22, 2020

A 1929 Transmitter on 14MHz

This year the Bruce Kelley Memorial 1929 CW QSO Party will include 20 meters. I decided to see how my Push-Pull Colpitts does on 14MHz. It has a fairly good note and is very usable in the BK.

I wanted to stay with a high capacity tank circuit. This minimizes RF current through the tubes and should improve tone and performance. In addition, I wanted a number of turns in the tank coil so that I would have reasonable transformer coupling between the tank coil and the antenna link. I ended up with two 4 turn, 3" long coils wound on a 1.25" form. This 1.25" form resulted in more tank coil turns on 20 compared to the 2.5" form used for the tank coils on 40 and 80 and the antenna link coils. Tank capacitance is about 100 pF on 14 MHz. My Colpitts now runs at about 20% efficiency giving 2-3 watts output on 20 meters.

My 14 MHz CW Signal as recorded on July 22, 2020 using the Northern Utah WebSDR:

For comparison listen to this same transmitter on 80 meters:

Sunday, May 17, 2020

What Do I Sound Like?

Have you ever gotten a 597 signal report after putting a lot of time and effort into building that new rig copied from an old (or really old) issue of QST? What is the other station hearing? More than likely they aren't familiar with the definition of a T7 signal (which to many of us sounds fine). Maybe it just sounds different or maybe it has chirp or maybe it sounds like a buzz saw the morning after a big party.

The first thing I do is check my signal in the shack receiver, but lots of times I'm overloading my receiver and I sound like that buzz saw. Is this really what others are hearing? Maybe being so close makes a minor problem sound worse than it is.

The next step is to have a friend a few miles away listen to you and, possibly, hold a phone up to the speaker so that you can hear your self. This can be real helpful but lots of times I need a more complete listen.

As a final check I recommend taking advantage of one of the many web based radios available all over the world. Link into one of these, turn on your own computer speaker, set the frequency/mode you wish to test and then transmit. Given needed propagation you can listen to yourself and the waterfall display helps you see what your signal is actually doing.

Friday, May 1, 2020

Push-Pull Colpitts Tips

(As questions/answers/tips concerning my Push-Pull Colpitts come up I'll post my thoughts here.)

How do you get this transmitter on frequency? Typically I'm tuning my transmitter to a frequency I'm listening to on the station receiver. If so, I simply tune the transmitter until it is heard in the receiver. Now, a couple of things to keep in mind. First, the load on this sort of directly coupled oscillator transmitter will effect the frequency. You will have to have the transmitter connected to your antenna when setting the frequency. Try to keep this short as everyone can hear you swishing the band. Second, be careful that you are listening to your actual signal and not an image. A superhet receiver will receive two signals at the same dial setting. The second, unwanted and weaker signal, is called the image. Filtering within the receiver rejects this image signal but filtering can only do so much. The strong local signal from your transmitter may get through the receiver filtering as a weak station. If you use that as your transmit frequency, you will be far off your intended frequency and, possibly, out of band. 

Where's the key? Many early transmitter construction articles left the keying method up to the builder. Everyone had their favorite. In this case I used cathode keying by placing the key between the filament center tap and ground. Lacking a filament transformer with a center tap I could have simulated the center tap by using two 40-75 ohm resistors. Keep in mind that cathode keying results in some amount of voltage on the ungrounded key terminal. See my blog entry at  for how to deal with this. Also, be sure to provide a separate path for B- to ground. Otherwise you will be doing B- keying and have the entire power supply voltage across your key terminals.

Why are your coils different from what the article says? Studying the original January 1934 QST article I decided that the 80 mtr coils were just too tightly wound for my comfort. The author allowed only 1/16" between each turn. Shorts were bound to happen. I added 1/2" to each tank coil, spacing the tank coil supports 3" apart rather than 2 1/2" apart. I had enough spare capacity in my tank capacitor to compensate for the decreased inductance. For the same reason I allowed 2 1/4" between the inner to tank coil supports rather than the specified 2". My antenna link coil has only 5 turns rather than 7 like the article recommended. I found that 5 turns gave me more output at 12-15 watts input.

What are the coil sizes and turn counts? Here's what I came up with for coils for 80, 40 and 20:

Band Coil Material Diameter # Turns
80 Tank 3/16" Cu 2 1/2" 10
80 Ant Link 3/16" Cu 2 1/2" 5
40 Tank 1/4" Cu 2 1/2" 5
40 Ant Link 1/4" Cu 2 1/2" 3
20 Tank 3/16" Cu 1 1/2" 4
20 Ant Link 3/16" Cu 1 1/2" 2

Keep in mind that there are two tank coils per band with the antenna link coil swinging in a 2 1/4" gap between them. Each tank coil is 3" long and each antenna link coil is 1 1/2" long. Wind all of the coils in the same direction. I found 3/16" copper tubing on Amazon.

What sort of tank tuning cap is that? This Push-Pull Colpitts calls for 250pf across the tank coil with the capacitor rotor grounded and the tank coil connected to the two stators. This requires each section to be 500pf. What I found is a dual 550pf per section Cardwell capacitor. It is physically laid out with the two sections, both rotor and stator, turned opposite each other. It looks like a differential capacitor but it is really just an mechanically unusual two gang variable capacitor. This design helps balance the two section rotor. Any 500-700pf per section two gang variable capacitor would work here.

While we are on the topic of the tank tuning capacitor...notice that many variable capacitors have stator connections on both sides. This allows a convenient path for routing from the plate of one tube through a feedback capacitor to the grid of the other.

What is the order of the connections along the back? See the photo below. Facing the transmitter from the outside/back, left to right: B+, B-/Gnd, Key+, Key-/Gnd, Fil CT, Fil, Fil.

Will this design work with other tubes like 45s or 27s? I've never tried a 27 or 45 in this circuit but others have run Push-Pull Hartley and TNT transmitters with 27s and 45s so they will probably work here. R, the bias resistor, will need to change if a different tube type is used with different characteristics. The Push-Pull TNT article in the November 1930 QST recommends a 10K bias resistor for type 10s and a 50K bias resistor for type 45s. 50K is a good starting point if planning to use 45s.

What's that insulator in the center of the tank coils? This insulator is there as a safety precaution. B+ is on the copper strip just below the antenna swinging link. I worried that the antenna link, if not tightly secured, might sag down and short B+ to my antenna system. This insulator limits the movement of the antenna link.

If I'm using 2.5V tubes like 45s or 27s do I need a 2.5 VAC filament transformer? The 27 has an indirectly heated cathode. The two 27 filaments can be connected in series and lit from the 5V winding common on many tube era transformers. 45 tube filaments, while 2.5VAV, are directly heated. I don't know if they can be operated the same way. Try it and let me know.

What sort of B+ supply do I use? I use a regulated 200-325VDC supply. 10s can handle higher B+ but why stress them and risk an expensive tube failure? 15 watts input is fine with me. The regulated supply also results in a more stable signal.

The bare wiring underneath looks like it might short together. Shouldn't that all be insulated? There is more room underneath the "deck" then you might guess looking at the photos. That space is 1.5" high by almost 12" x 12". There is plenty of room for three layers of wiring given stiff wire. In a few places where I needed extra stability I used brass screws as standoffs/supports.

This looks pretty dangerous. Shouldn't you have a cover so you don't get electrocuted? There are lots of places where B+ is exposed on this transmitter. This is not unusual for these early designs. Always shut down the power, checking it twice before doing anything behind the non-existent front panel or underneath the chassis. I also recommend leaving a metal screw driver (with insulated handle) levered between the B+ and B- power terminals while changing coils.

Saturday, February 29, 2020

A Dingey size Boat Anchor

I first started on this project over 15 years ago. I wanted a 6L6 based transmitter with a spotting function. Over the years it has gone through several iterations to the "Dingey Size Boat Anchor" I use today. Along the way I added a loading control, regulated the oscillator plate voltage to 108 volts, shifted the output circuit to a pi network and repackaged it in a metal cabinet to better match my HRO Sr. Like many projects it has been a journey. Here are a few more details about this transmitter as it stands today.

The circuit itself is fairly standard using a separate 300 B+ power supply. About the only thing I don't see in most designs is SW, the spotting switch. It allows me to check my crystal frequency against any station I might want to work or against QRM. As an important serendipity it also allows me to run the oscillator continuously while keying only the 6L6 output stage. This cuts down on chirp caused by the crystal restarting at the beginning of each code element. C10, the loading capacitor, is really two capacitors in parallel. One is a typical 300pf variable. The second is a 300pf high voltage "door knob" capacitor that can be switched it/out with a toggle switch.
Coils are what I could find. The 80 and 40 meter coils are commercial Bud coils that I had. I'm using only the tank portion, not the link. For 30 I found an old plug-in coil that looked about right and tried it. It works. In general look for coils that  dip and load to around 60% efficiency (ie. 6 to 7 watts output for 10 to 12 watts input).

Inside I arranged everything so that it made sense.  Across the back, left to right, is the 6J5 oscillator, the 6L6 final and then the plug-in output coil. Just to the right of the coil is the toggle switch that switches in/out the additional 300pf  loading capacity. The crystal socket is near the 6J5 and the 0C3 108 V voltage regulator is just to the right of that.

When changing crystals or, especially, coils it is important to recognize where high voltage is exposed. In this case the unprotected meter  terminals have 300 VDC, a lethal voltage, on them. Power this transmitter down when under the covers. This is even more important when working under the chassis. Don't take chances. Power down before working on it. As a safety modification consider placing the crystal socket on the front panel.

Are you looking for something more modern looking? Try  W1TS's 6C4-5763 MOPA in the October 1968 issue QST. Just add a resistor and 0B2 to regulate the oscillator B+ to 108V and include a switch to run the oscillator stage while keying the final.