Icom IC-705 PA500 Setup Guide

Hello Operators. A new Icom IC-705 DIY599 PA500 setup guide video is live on YouTube (and Rumble soon after).

In this video we go through setting up and troubleshooting the Icom IC-705, with the DIY599 PA500 amplifier. The video also has settings useful in troubleshooting the IC-705 while running data modes wirelessly, over the 705s WLAN. Perhaps this Wireless 705 troubleshooting section can be extracted and shared as a separate video. Let me know if you think that’s useful.

Even if you don’t have the PA500 amp, the video has settings useful to a variety of different portable amplifiers.

I’ll do a similar video for the Lab599 TX500 if y’all are interested.
Julian oh8stn
Video url: https://youtu.be/VRGDak9vn9k

ICOM IC-705 Portable QRP Ham Radio:

DIY599 PA500

Spread the love


  1. Dear Julian,

    I think I could do with a similar guide for the TX-500! As of now, I have a TX-500 connected to the PC with a digirig, and also with a PTT splitter cable (also from digirig) to the PA500, so I don’t rely on RF-VOX. I just tested it with VARA HF, trying to achieve faster TX transfer rates than just the TX-500 alone could give me. My test object was an email with a 75kB attachment in the Pat-Winlink outbox.

    The results are interesting: the best rates I got were from the TX-500 alone running at 100% power (about 10W with the digirig at full bore) — VARA topped out at mode 12 (briefly even 13). Adding the PA500, I got almost the same results at 10% power going into the PA, which isn’t surprising as that should give approx. 10W output overall. From this point, however little I tried to increase power, every percent more on the TX-500 made VARA switch to lower rates. At 16%, I got of the order of VARA mode 3! And the PA500 was miles away from its power limits.

    Is there something I’m missing here? Oh, this was on 40m, the output going through a 1kW common-mode choke into a 250W balun and into a 40m EFHW antenna. Thus, power ratings should be more than sufficient.

    After all, you said a while ago that the PA500 is nice to have in the field because it gives you better link reliability in case of EmComm. Well, my results don’t show that, I’m afraid.

    Hope you have some answers here, because I really haven’t got a clue what’s going on.



    • VaraHF with PAT Winlink? Show me!
      Second and most likely problem, ALC. Full bore means you’re probably over driving the radio and the amplifier. This is why you should monitor the ALC on the rig. Never run the tx500 at more than 2-3w into the PA500! In the Raspberry Pi or whatever you’re using for Pat winlink, make sure you disable auto gain control for the Digirig in volume control. Also make sure to adjust the volume level for the Digirig, so that you have very little or almost no ALC. Even at the lowest volume setting, AGC will put your radio into overdrive sending out a dirty signal through the amplifier. This would account for the poor performance.
      I can assure you 100%, if you are not monitoring ALC, the problem is between the radio and the chair. Not trying to be a smart-ass here, it’s just a common mistake.

  2. Hi Julian,

    That’s exactly why I’m looking forward to your guide on the TX-500 plus PA500.

    Just a few notes on what you wrote:

    1. VARA-HF runs as a pure TNC in 32-bit Wine on an otherwise 64-bit-Linux-only computer. Pat Winlink connects to it via local network ports. No raspberry pi.

    2. ALC, as displayed by the TX-500, is 0 throughout all my testing. Thus, the amp stage of the TX-500 can cope with continuously outputting 10W of VARA-HF. “Full bore digirig” simply means that the soundcard mixer of the digirig is at 100% for playback, just to make comparison easier.

    3. For all tests with the PA500, TX-500 output is turned way down. I wrote 10% to 16%, which is less than 2W throughout my testing. At no point was the PA500 driven hotter than 2-3W!

    4. You mentioned AGC. In my book, that’s an RX-only thing, it doesn’t influence TX power/gain/whatever in any way.

    5. So the question remains: if I turn power up slightly (starting at about 10W out of the PA500, not even reaching 20W), VARA rates go down, not up (as they should when S/N improves). Why is this?



Comments are closed.