Solid Improvement on 1296MHz.

A little while ago I found a power amplifier for my 1296MHz setup.

This is essentially a W6PQL design with improvements and control/safety circuits by OZ2ELA.

A group had built this as a project, and one of the participants lost interest and sold the unit.

A test showed a solid output of 80 - 90W, enough for my purpose.

Controlling the mast preamplifier through the coax was not available, so I got myself 2 high power bias-tees for 1296MHz, capable of handling 600W.

Now I can bypass the DC control voltage from the radio to the preamplifier, and still use the PA as TX amplifier. This works well, and I am now running 50W on 1296 most of the time, with a drive of 3W from the transceiver.

I do have some cable loss, so often I could hear people who did not use mast preamplifiers at the antenna, but they could not hear me. With the amplifier, now there is a better balance between the local (FM) stations and my station.

There is still a lot to optimize here, mostly with respect to antennas and cable loss, and now the spring is coming, I can get started with that.

At the moment I am using a vertical monoband 1296MHz antenna. 

Some yagi or other directional antenna is in the planning for use with DX (SSB/CW/DIGI modes, or even FM), and I do have some decent cable available for this purpose.

2400MHz Amplifier Test.

Finally, after the winter solstice, I had a bit more energy.

I purchased the 2400MHz amplifier from SG Lab in Bulgaria. This has a good reputation for reliability, and I wanted a bit more output than the 2.5W I already had.

This is the v3, needing less than 40mW to deliver a typical output of 20W @28V power supply and 17W @24V.

I did have a signal generator using a computer control Windows program, but no usable Windows machine with a CD-ROM drive. Oops! What do we do now?

Well, well. I do have my IC-905 with variable power output up to 2W nominal.

The RF unit is in my "shack" on the ground floor, and the lab with all my test equipment is in the attic, so I picked up the controller unit and a piece of cat8 network cable, so I could control the thing from the upstairs lab. Now to get the RF power upstairs. As I only needed maximum 40mW, I could use some cheap SMA cables, RG174, two lengths of about 5m. 

This makes for a neat cheap attenuator. With the 2W output from the TRX I could measure about 30mW, using the peak indicator of the spectrum analyzer. That is good, as I can't overload the amplifier.

Because the output of the PA is 10-20W max, I needed to bring that down the level. I used a directional coupler (800-2500MHz), with 40 dB coupling. Bingo! 10W becomes 1mW. Of course a dummy load capable of dissipating the output power was connected to the "through" output.

Connecting the system I could measure about 10W out with a drive from the TRX of about 33% (650mW minus the cable attenuation) Result: 0dBm out of the directional coupler 10W from the amplifier.

Increasing the drive gave about one more dB.

This looks like to low output, but I would consider it within the tolerances of the test equipment. There is some extra loss in the connectors, adapters and cables after the output of the amplifier, and the spectrum analyzer, as well as tolerance of the input power measurement of the spectrum analyzer. so measuring 12W maximum output is within the tolerances of the minimum 15W specified from the amplifier, by about 1.5dB. That is good enough for me.

The amplifier test setup was the module attached to a cooling fin, with Kapton tape, and using some good thermal compound. 

It did not get hot to the touch by normal operation, even using full carrier FM.

I intend to use it for a while indoors, and if it looks stable, I will likely mount it outdoors. this will require a better mechanical construction, but also provide more power available to the antenna.

This setup is intended for QO-100 uplink use.

If this works well, the next step is some more power for 1297MHz FM.

What a Mess. Projects.

 Yes, a literal mess.

The whole house has gradually become so messy that I have trouble finding space for a guest. Yes, that kind of mess.

So now the huge project is getting it pushed out. This may take some time, but in between there are a few radio related projects I want to get started, so I started making space in the electronics' lab.

While everything else in that small room is a total (well, not total, but still..., the workbench surface is now mainly visible, and I can access some test equipment and tools. It's still a long way to order, but slightly less chaos.

Now for some projects:

Antennas.

In freezing temperatures and snow outside? No, not for me. When the weather gets warmer and better again, there is still several antenna projects, as my antenna system has been deteriorating for a while.

I am glad I got my 23cm vertical up and running in a decent way, with a preamp at the antenna. It's working well in most directions, there are still some poor directions. 

A rotatable horizontal directional antenna is in the plan for better weather conditions. Some preparations are needed, so I will get there, probably in the spring.

23cm.

I can hear more stations than can hear me. I think this is due to my use of the preamp near the antenna, almost no one else around here does that with their verticals, just using an existing cable and possibly a triplexer. A quite lossy system to work with. So what do I do? Build a PA.

23cm Power Amplifier.

I got a linear amplifier built with 4 power modules. It is supposed to deliver about 50W, although I would not try that with a mode like FT8 (or other digital modes). I will need to build a coax relay system and more importantly, a sequencer, so I can avoid blowing up the preamp.

When that system is up and running, I will focus on another amplifier, running 40-50W, but for FM only.

I found a module in China, that has been used for sweeper jammers, a power amplifier covering 1200-1300MHz, with a nominal 50W output with about 10mW drive, quite some gain there. The module has no cooling, so some external cooling is mandatory.

This module requires a more elaborate sequencing procedure, as the output needs to be connected to a correct load before even applying supply voltage (28V). Initially all this will be indoors, but it could be mast mounted at a later stage. Ughh! Weather proofing needed, so maybe not ;)

QO-100 Uplink Power Amplifier.

My uplink system for the QO-100 satellite broke a while ago, the power amplifier blew at some experiments, so I need two things:

- repair the amplifier I had, if I can find the IC or transistor.

Before that I will be testing a 13cm PA module from SG Lab in Bulgaria.

This is my test setup. The mechanical part will come later.

This PA should deliver 15-20W (enough for the narrow band uplink) with a max drive of 40mW.

I intend to use my IC-905 directly on 2400MHz As this transceiver has a 2W output maximum, I will mount a 10dB attenuator, followed by a 6db attenuator at the inout of the PA, and then run the TRX at 80% output power. I don't want a power spike from the TRX to ruin the PA.

No relays are needed, as the PA has a built-in RF-VOX circuit with delay, not for the test. There is a PTT output from the IC-905, so that can be used in a permanent setup.

PA Transistors Found at the Rally.

 There was one more thing I found at the rally.

1.9GHz PA transistors capable of about 60W linear output, apparently LDMOS. 

I found a set of 14 pieces packed in an antistatic container.

The transistors come from CREE Microwaves and are marked LGA19060-171. Does this relate to 1.9GHz and 60W output? 

I do not know if they are internally matched. If they are not they could be interesting for a number of PA constructions for different frequency ranges.

My main interest will be to see if I can get those running on 1296MHz. Two of those should be capable of generating 100W. If they have internal matching an external impedance matching circuit should be made.

Since they came at a low price I can do some experimentation without being afraid of destroying a transistor, and with 14 of them I should be able to make a workable amplifier with them.

I was recommended contacting a local amateur, as he may have some tips for overcoming the possible internal matching, so I can use the transistors well outside the design frequency.

As there most likely will be a lot of experimentation, this will be a future project, as there are already so many ones already to be made.

If anyone knows more about these transistors, please let me know.