[NLRS] IF radio power consumption

[John P. Toscano]

Hello, all.

My 10 GHz setup is currently powered by a pair of 31 amp-hour gel cell 
batteries in parallel, which can be charged either by plugging into a 
home power supply or by using the cigarette lighter socket in the back 
of my SUV though a "PowerGate" device which isolates the batteries from 
the vehicle electrical system and limits the charging current to prevent 
damage to the batteries or the car's electrical system.

This weekend, unfortunately, I had to run the engine of my car much more 
than I'd have liked in order to keep the battery voltage from sagging 
too low. In fact, on a couple of occasions, when I was sending CW 
beaconing or in a CW QSO, my signal was FM'ing because the battery 
voltage had dropped too low. This is in spite of using a "battery 
booster" device, which normally boosts my voltage to 14v or so to keep 
everything happy, but even it can't cope when the battery voltage falls 
to 9 volts or so. Donn quipped that I probably used more gas as a fixed 
station than as a rover. Well, it wasn't quite that bad, but it was 
definitely not optimal.

I opted for the pair of 31 amp-hour batteries because their weight (one 
at a time) is manageable for situations where the rig has to be carried 
to a setup location that is too far from the vehicle to simply run a 
power cable from the car. (Hey, I'm an old guy with bad knees. With any 
luck, you'll get there someday too.)  I guess I could go with a bigger 
battery that would stay more-or-less permanently in the car. But brute 
force is not necessarily the best answer -- efficiency might be better.

My setup uses an Icom IC-706 MkIIg as the IF radio. I am very happy with 
the performance of this radio in this application, with one big 
exception. My whole station draws a peak of 30 amps during transmit, and 
most of that is going to the IC-706.  Yikes, 400 watts of DC power drain 
to generate a 1.5 watt signal on 10368 MHz! There's got to be a better way.

I thought about the FT-817, which is designed to run in QRP, and I'm 
sure that my battery problems would go away if I used this for the IF. 
But several people told me that they liked the FT-857 a lot better than 
the FT-817 in this application. That sounded good to me, so I went to 
Yaesu's web site and downloaded the Operator's Manuals for the FT-857 
and for the FT-857D. Much to my surprise, the tech specs for the radio 
state that it draws 22 amps on transmit, which is not much lower than my 
IC-706.

Of course, as an IF rig, I only need low power at 144 MHz. My 10 GHz 
transverter is set up for 1 to 10 watts of drive. The IC-706 seems to 
draw full DC current even though the 2M output is turned down to this 
level. Does the FT-857 do better in this regard? I'm hoping that the 22 
amp figure quoted in the specs is really the maximum current draw at 
maximum output power, but when the output power is reduced, the current 
draw actually goes down to something reasonable.

Can anyone tell me?

Thanks in advance.
John (WØJT)