[NLRS] Setup of DEM TIB/222-28 + IC-706MkIIg

[John P. Toscano]

Brent Casavant wrote:

> For my first attempt I started with the ALC set to -4.5 volts.  I keyed
> up, and the VHF wattmeter on the output of the 222-28 and read about 15
> watts for CW, FM, and SSB.  That didn't seem quite right (particularly
> for SSB), as I'd expect the power output to be zero.  The 222-28 manual
> said that at full output power I should expect to see about 6W of draw

I'm guessing you mean 6 AMPS, not 6 WATTS. . .

> on the power supply, but even counting the 706's power in the mix, I'm
> seeing about 5W.  Neither the VHF wattmeter nor the power supply
> current reading fluctuate at all on SSB.

I'm worried about the RF power meter showing 15 watts on SSB with no 
audio into the microphone.  I wonder if you have an oscillation that is 
driving the transmitter fully even when you aren't talking into the mic. 
  And if you have an excess of ALC voltage, even in FM mode, the RF 
output should be much less than 15 watts.  Maybe your VHF wattmeter is 
not working properly at all?????

> Given the symptoms, I suspect that the 706's RF output is still fully
> supressed at -3.5V but I don't dare go above -3.5 right now because
> I fear blowing out the transmit end of the 222-28.

Your caution is admirable.  Now I don't recommend doing the following on 
purpose, but. . .  while setting up my system (IC-706MkII, not IIg; TIB; 
222-28) at one point I accidentally disconnected the ALC completely, so 
the radio pumped full power into the transverter.  Fortunately, there is 
a little resistor (1/4 or 1/2 watt) at the input of the transverter, and 
it let out its magic smoke, but no other components were harmed.  The 
resistor acted like a fuse and saved my bacon.  I dug a replacement out 
of my parts bin and had it repaired in a jiffy.  So, caution is still 
highly recommended, but you can be at least a little bit more agressive.

My meter's most sensitive scale is 4 watts full scale.  I played with 
the ALC adjustment with the 706 transmitting into a 50 ohm dummy load, 
and got an idea of what ALC voltages gave me power output around the 
first tick mark on the 4 watt scale.  The watts are divided into 5 tick 
marks, so each tick mark on that scale is (VERY CRUDELY) 200 mW.  I 
watched how much I could vary the voltage before the power level was 
indicated to be 400 mW, 600 mW, etc., not that these were presumed to be 
accurate, but I knew that I didn't want to send anything even close to 1 
watt into the transverter, and I couldn't even estimate anything smaller 
than 200 mW.  I found that there is VERY LITTLE DIFFERENCE in ALC 
voltage that you have to play with.  In fact, I wish they had two 
cascaded 10-turn pots for the ALC voltage, one for "coarse" and one for 
"fine" adjustment.

Anyway, once I had the radio throttled down to something that looked 
like it was at least in the neighborhood of 200 mW, I hooked up the 
transverter, moved the dummy load to its output, and tested.  I could 
feed more (negative) voltage into the ALC line and drop the 222 MHz 
output from full drive (close to 25 watts) down to 1 watt (or less!). 
In other words, once I got the ALC in the proper ballpark, I adjusted it 
with the 222 MHz output level instead of the 28 MHz output level.  Since 
you probably want maximum power out, you could provide enough negative 
ALC voltage to see a clear drop in 222 MHz RF power below 25 watts, and 
then very gently reduce the ALC drive (bring it closer to zero volts) 
until the 222 MHz RF output stops climbing, which should be at about 25 
watts.

(In my case, I actually re-designed part of the TIB so I could easily 
use a single 7-position rotary switch to (a) disable the transverter, 
(b) drive it to 5 watts, (c) drive it to 10 watts, (d) drive it to 25 
watts, (e) drive it to 1 watt and enable the external brick to give me 
50 watts, (f) drive it to 2 watts and enable the external brick to give 
me 100 watts, or (g) disable the transverter again.  This helps keep me 
from pumping 25 watts of 222 MHz RF into my brick which only wants 2 
watts max.  But it is way overkill -- I should have done at most: off, 5 
watts, 25 watts, 2 watts plus enable brick for 100 watts.  But I like to 
tinker.

And all these tests were done with the 706 in FM mode so I would get a 
full-power 100% carrier whenever the PTT was activated.  After getting 
it set up on FM, I switched to the other modes and verified that 
everything was still being driven to the proper levels in CW or SSB.

I hope that helps somewhat.
73 de W0JT