[MRCA] T-195 Auto-NoTune

[aj1g at comcast.net]

WU2D's infamous distant uncle struck hard at AJ1G during the MRHS Night of Nights operations Sunday night here. I fired up the T-195 on 40 CW just fine with full output and worked W4WLO, then went to shift it up to 20 meters to try for K6KPH. The set was last used a few months ago on 40 CW and I assume that it did not need to go through an auto-tune cycle, which is why I got full output there. When I tried to auto=tune to 20, I got a much lower than normal output, and the tuning cycle went very long (it usually tunes up very quickly on all bands but 80, which has always been extremely slow). I didn't get through to KPH on 20 and tried to shift back down to get them on 40. Set would not auto-tune at all, would only give me about 10 watts output, no matter how long I held the tune switch. Gave up trying for KPH and tried tuning up into my dummy load, with no success on any bands, the set seems to have lost its auto-tune function. 

I am aware of the sensitivity of the auto-tune response to low DC supply voltage to the set (mine has the original dynos and is run from my 28V DC bus that is powered by a PP-7333 floated across a pair of nearly new Johnson Controls (sounds better than saying Wal-Mart) series-ed up deep cycle marine batteries. I checked the DC bus output under tune cycle load and got 26.7 volts, with nearly equal 13.4/13.3 volts across each battery. I read Jeep's comment from a previous post on this topic on how the auto-tune system is unhappy with anything less than 28.5 to 30 volts. I don't think I have ever had my DC bus voltage up that high with the present batteries and PP7333, and the system would always auto-tune, even if 80 meters was a long process. I checked the individual batteries' charge with a 12V 10/6/2 amp charger and they came up as being fully charged to the 13.4 volt level within a few minutes, so i don't think the batteries are down on any cells. 

I did not ever have the set connected to anything other than a nominal 50 ohm load with low SWR for any band I tried to tune up on, so I'm not sure as to why the tune has stopped working, except for the Murphy factor. 

Any other GRC-19 ops out there have any advice as to what to look at next? 

If the auto-tune is so sensitive to needing a high DC supply voltage from 28.5 to 30 volts to work, how did they work in their iintended vehicular application? Wouldn't the typical military vehicle electrical system be putting out voltage with the vehicle generator running something more like the 26.7 volts like I'm seeing across my batteries? 

If a low DC input voltage is indeed the culprit, has anyone thought of a way to goose up the DC voltage applied to the auto-tune system, say by powering it with a small nominal 30 volt supply independent from the main set supply? 

How about being able to temporarily boost up the PP7333 output voltage while tuning, is there an adjustment for the regulation of the output voltage of the supply that I could crank a pot up on temporarily, and if that works, then add a relay to change the settings with a second pot that could be switched in for a temporary voltage boost? 


By the way, I never did get to work K6KPH, too many stations calling and eventually the propagation went out. I would have tried on 80 meters, but I never heard them there. How many hours did they stay on into the night, I gave up at about 0500Z/0100 EDT. I did work W4WLO from the Tacoma 4X4 on 20 with my K1 QRP mobile set up, got a S9 plus 5 from them, not bad for about 3 watts to a Hamstick! I tried hard for KPH with that set up but I must have been crushed by all of the other stations calling them, many of whom appeared to be W6's very close to them. I did copy almostyall of the commercial frequency KPH/KSM/KFS and the NCM tranmissions. Was great fun to hear that type of traffic again, it was great code practice back in the day. 
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