Final Notes on the U.RAT

I installed the URAT out back at the base of the “Mod Bob” antenna. I experimented for a few hours and I was able to get a decent SWR on 160, 80, 40 and 30 by doing this:

  1. 160M – bypass the capacitors and use a shunt coil at the antenna feed
  2. 80M – use the capacitors with that same shunt coil
  3. 40M – same as 80M
  4. 30M – same as 160M

There is one wire left in the control cable, this means with a clever use of a relay or two, you could bypass the capacitors for 160 and 30M. Here is a relay board that could be controlled with that last signal wire coming from the Raspberry Pi GPIO:

I’m pretty sure a simple DPDT relay does the trick – its NO or NC which means it will normally be set for 80 and 40M or 160 and 30M – and by using a button on the KPOD – or a simple switch in the control box – you could send that signal to the URAT relay and bingo!

This means for about 1/2 the price of the Palstar BT1500A, you can have an remote controlled balanced feed tuner. If you have the junk box parts – it would be less of course.

HOWEVER, I’m very spoiled by the Palstar BT1500A. It was $720 and worth every penny, by far. It’s design and high powered components give me the confidence that my antenna is coupled to my solid state amplifier, which is less forgiving SWR wise than the tube amplifiers, and every detail as far as matching the Mod Bob fits like a glove.

This has been the most interesting ham radio project I have ever worked on. I have learned so much – its really quite amazing. The project was rich in facets – antenna, matching circuits, Raspberry Pi, stepper motor control, a fun use of the Elecraft KPOD, and much more.

Its way too hot to go out and replace the URAT and put the BT1500A back out – so I will do it first thing in the morning.

U.RAT Version 2.0 and Experiments

The u.RAT that I will set up tomorrow will replace the Palstar BT1500A, but only as a test – to see if two Palstar C600 variable capacitors plus one inductor will work on 160M. I expect it will work on 160 and 30M, but not sure about 80M.

I split the control box and the drivers so that the Raspberry Pi Zero is in the control box:

Which realizes my original design, and it takes 7 wires in the rotator control cable, which is great:

The back has all of the connections that add power and signal out to the remote URAT:

And the on light and 12v to 5v converter is inside:

I have just the wires to and from the capacitors to wire up, then it’s a big finger crossing time early tomorrow morning before it gets too hot. I’ll need to experiment a bit using my fabulous Rig Expert AA-30, which I have gotten my money’s worth 100 times over.

If I need a coil or two, I’m hoping to wind them using refrigerator tubing and making them fixed. Here are some experiments I can try:

  1. Test with just the two variable C600 capacitors – they are rated at – 5.5 kV and 23-550 pF
  2. Add a shunt inductor at the input of the two capacitors and then at the output
  3. Add a shunt capacitor at the input and output of the two capacitors
  4. Add series inductors at the input and then output of the capacitors
  5. Some combination of 2 +3

If I do pull this off with these two variable capacitors and a coil or two – then I guess I wouldn’t have needed the Palstar BT-1500A, but since all of this was funded by selling my car – its all good. But if it does work – then the BT1500A either goes on the shelf or goes up for sale. Not sure – I really, really love this tuner.

SO – I have (and am still) learning so much – how much is that worth?

The S and Z Match for the URAT

I was going to disassemble the u.RAT and re-use the components, but I have just come into a second variable capacitor – which is the Palstar C600, a true work of art. I am trying to get rid of having a roller inductor in the circuit, but would much rather have a switched inductor. Yesterday I posted this circuit:

And the Palstar BT1500A has this circuit:

Pas, PE4BAS, alerted me to PA0FRI’s wonderful web site (thanks Bas!):

And his S Match circuit:

I also found Phil, AD5X’s Z Match project:

What is really fantastic is how I will be able to use the URAT, and either use a switched tapped inductor, or maybe just have two variable capacitors under URAT control. I don’t have the heart to mangle the Palstar BT1500A and make heavy modifications by adding relays to its switching circuit.

The URAT spins the variable capacitors at the right speed with the Elecraft KPOD, and while the NEMA-23 steppers are more than adequate for the variable inductor, its too slow to tune with the KPOD.

If I can get one of these circuits to tune on 160, 80 and 30M with only two variable capacitors and an “auto transformer” or single tapped inductor, I will be “in like Flynn” . . .

Stay tuned, we have a three day weekend, and I will be experimenting when its not too hot out (we have predictions for 43 C / 110 F heat wave today and tomorrow). I might get lucky and have Sunday and Monday in the morning to play with this.


Collins 32-V3 Antenna Tuner Circuit

I stumbled on a suggestion for a balanced tuner circuit that is suggested in an old Collins 32-V3 transmitter manual. The top circuit is one that I am most interested in. I’d love to try it and compare it to the Palstar BT1500A – which works perfectly, but it would be super if I could use the URAT with two variable capacitors and a fixed tapped inductor.

This “series tuning” circuit I just have to try.

TX5K is the QSO’s Per Hour and QSO’s Per Day Champ!

I worked on the TX5K Clipperton DX-pedition a few years back, and it was the “warm up” for working on the VK0EK Heard Island DX-pedition. TX5K did receive a very nice award – the “Best Communication” award for our work in communicating “near real time” with DX-ers, Sponsors and Dx-peditioner family members during the DX-pedition. But if you go to the GDXF “Mega DX-pedition Honor Roll” page:

You will see that TX5K – which was mainly the Bavarian Contest Clubs doing, deserves an award in this class. Its nice to see them mentioned and listed on this site – because its quite the accomplishment!

VK0EK also just won this award as well. VK0EK also went on to win the DX-pedition of the Year Award:

There are many different ways to slice and dice the statistics, and like my friends – who are really into baseball and especially pitcher stats – its fun to see why they like one pitcher over another. The same thing can be done with DX-peditions, but for me – it was just a joy and a lifelong great memory to have been very involved with VK0EK and involved with TX5K in a meaningful way.

Hats off to the teams who activated these entities, and to all DX-peditions and DX-peditioners – its a lot of work and a huge commitment in time and money.

Balanced Vs. Unbalanced Antenna Matching

I’m going to add the URAT to a 70′ tall wire vertical with 96 buried radials, and this is a classic 80M quarter wavelength vertical. Its an unbalanced feed with an unbalanced antenna. It will require an L matching circuit:

I like VE7BPO’s diagram, and I am guessing that I will need to wire the variable capacitor and roller inductor using circuit B, but I will report back this weekend.

This is the BT1500A circuit, which is a balanced tuner where you can switch the capacitor to be at the input or output of the dual roller inductors. This is perfect for the “Mod Bob” antenna, and is quite different than a simple vertical feed.

Its funny, but I’m becoming exclusively a low band only DXer, and I do believe this is where I will stay. The low band antennas will still let me work the higher bands, but not as well as with a high yagi. In fact, I will take down my 2 element 20M home brewed yagi after I make Top of the Honor Roll, and that will be it for the high bands. I also am not interested in climbing roofs or towers any more, and am happy that I don’t have anything big and heavy hanging over my roof. If anything happens to my low band antennas, they are very easy to maintain and require no climbing.

New 70′ Wire Vertical

Simple LC circuit for matching a vertical

I’m going to put up a 70′ vertical wire into a tree and feed it against 96 buried radials. This can be done alongside the Mod Bob, and I can use the URAT to remotely tune it.

This will be my Labor Day Weekend project just because its fun. It will be dedicated to 80M. It might tune fine on 30M since its close to the 3rd harmonic.

This should be fun while I watch the DX Grass Grow.