Batboard

Has anyone been able to successfully interface a Ham 1 kW amp (such as an Icom PW-1, Yaesu Quadra, or perhaps a THP) to a Micom 2 or 3 HF radio?

It looks to be very problematic, as the Micom 2/3 needs a positive going ALC, and virtually all Ham linear HF HPA’s use a negative going ALC. I suppose I could design and build an inverter circuit, but now things start getting more complicated. I was looking at bagging the ALC altogether (I guess I must like to live dangerously!), and use something like an Alpha 9500 (expensive amp, but darn nice) that uses an Eimac 8877 tube, and therefore the nature of its design does not even require an ALC protection circuit. I got stopped in my tracks, as the Micom 2/3 will not even supply the necessary PTT for the linear amp keying circuit if there are is not an ALC connection present between the amp and the Micom. You get the infamous "PW_LATCH" error code.

The error code I mentioned (due to no ALC connection) occurs when you activate the 1 kW AMP option in the Micom's menu. The Micom’s external PTT indeed works, but now the power output from the Micom is forced to zero. Useless! On the other hand, if you try to get around this dilemma by not turning ON the AMP option, the external PTT (Pin 19 PTT signal to Pin 18 Ground on the Micom's rear apron 24 pin Accessory connector) will not even activate. Dang! Motorola has got me nailed at every turn on this project.

Yes, the Micom 1 kW amp (RM-1200) would definitely work very nicely, but it costs a cool $45,000, so something like an Icom PW-1 would be a tad bit more palatable economic choice (e.g., an order of magnitude less costly). I don't want to revert to using a typical Ham HF Icom transceiver that would easily plug-and-play with various Ham HPA’s, as I am running ALE, and the Micom is absolutely the bomb for operating in the ALE mode. A lot of times, 125 watts is perfectly fine for ALE, but sometimes having a 1 kW linear is very handy.

I'm all but ready to give up on this little project, so I'm hoping perhaps someone else here may have already invented this wheel?

Thanks!

If you really want to have ALC you’ll need to build a unity gain opamp based inverter as you said.

But you don't need ALC if you can properly adjust the maximum output of the exciter to suit the HPA. Why not try using a small 9V battery and 10k pot to feed a 0 to 9V adjustable supple to the Micom’s ALC input and use that to set the maximum drive to your HPA? I know it’s kind of open loop but you don’t really need the HPA running full power so if you set up the fixed ALC for say 75% of the HPA full power then there is a bit of safety margin as the gain of the amp is going to vary with frequency.

If this works as a long term solution you can extend the battery life by using a spare set of contracts on an external PTT relay in series with the battery supply. You need to you a battery rather than a PSU to avoid unintended AM on the exciter output from PSU hum or other noise.

I think the ALC connection needs to also have the REV and FWD closed loop ALC function , in addtion to the positive going variable ALC voltage. The more I look at it, the "PW-LATCH" error may also be thrown because the band selection function is missing (KW CC - Channel Change). I may neeed to have the entire suite set up (involves 9 discrete lines) to make the Micom happy with a Ham HPA. I emailed Microham as they build custom interface boxes for linears, but they have no such animal for the Micom. That's why I took a shot in the dark here to see if anyone has undertaken such a project. I'm still hoping...