AN/GRC-109 at it again: Bush Ops 2025

[PTF Guy]

Hi 18E's. We ran an emergency communications readiness FTX as part of "Winter Field Day" 2025 from the field. The 60 year-old GRC-109 was along and still worked great on CW as usual but I left the hand cranked generator home this time.
A quick AAR: https://www.n6cc.com/winter-field-day-2025-n6cc/
Cheers T
BT
NNNN

[Badger52]

First-class report, thanks for sharing! Leg key is best key for enjoying coffee.
Always thought that key (and the standalone J-37) had a smoother action than the J-38 due to the 'leaf' spring vs. coil spring setup.
N6CC DE KC9TNH . .

[mojaveman]

Neat.

Hard to find components and repair parts for that vintage equipment?

How long can you operate with car batteries?

[glebo]

Is it 1, 2, 3, 4,3, 4, 3, 4, 2 ?? Been awhile, or am I all jacked up?..lol (tuning sequence)

[PTF Guy]

Hi - Well the GRC-109 is simple, rugged and repairable to extent downrange if necessary, the operators Spares kit is good. My set had considerable service wear when I got it in 1985 shortly after the Army excessed them. My units have the original 1965 tubes in them and I put another 40 years on them. Replacement tubes are readily available online, most for around $5 if needed. Other internal components could be replaced easily with modern equivalents (eg: silicon diodes in the power supply).
More 109 history and Ops if interested: www.n6cc.com/angrc-109-special-forces-radio-set/
Modern gear is fantastic but generally unrepairable beyond the manufacturers DEPOT level with their custom microprocessors, LCD displays, memory chips and exotic test fixturing. Downrange they would become wheel chocks. (The 109 would make a great wheel chock!)
As to power consumption, the PRC-174's we used would receive 24/7 for over 2 weeks, a bit less depending upon transmit time but a long time on a deep cycle marine battery without recharging. The GRC-109 with the hand cranked generator would be on the air indefinitely unless the Power Supply staged a rebellion - as many of you could attest to! ;o)

[doctom54]

Very cool. We used those on my team when I was in. Along with the PRC-174, which if I remember correctly could do voice also. It could have been a PRC-74. (50 years dims my memory)

[PTF Guy]

Hi Doc - Yes, you likely had the PRC-74. The PRC-174 came later but with the same capabilities as the 74. The 174 was being evaluated as a replacement for the 74 but with newer technology. However the PRC-104 won that competition and is still in use today but being phased out. The PRC-174 was offered to the IDF and then built by Tadiran under license. Both are very capable CW, SSB and Data sets. Good to know that there are still some actual GRC-109 ops around!

[PTF Guy]

Hi Glebo - You remembered! Step 5 is to extinguish thumb fire....

[glebo]

Originally Posted by PTF Guy

Hi Glebo - You remembered! Step 5 is to extinguish thumb fire....

Haa, I also remember getting RF'd tuning the 74, damn fat thumbs..lol

Hmm, peak noise, zero beat, tune, load, tune, load. tune..
I was taught to use an RF meter near the transmission line on that ol twin lead going up to the feedpoint. It worked, but I always thought that it meant you were tuning the xnsmission line not the antenna??

Any gurus want to set me straight?? Or was that ok to do that. You'd tune it to max field strength. I always wondered if I was tuning the antenna....or xnsmission line..

ETA: Now that those memories have emerged, maybe I'll ask the facebook SF commo page if they know. However, I'm not sure there'll be anyone old enough to know...lol

[PTF Guy]

I think you were doing it right with the field strength meter. The transmitter doesn't know if it is connected to a transmission line or a good or bad antenna directly. Resulting field strength is the best indicator - tune for maximum smoke.

[glebo]

True, but I always had the feeling I was loading the xns line and not the ANT. The big thing that concerned me was if I was tuning/loading the xns line, I had an omni-directional ant instead of a directional ant for tactical purposes as intended..
Oh well, I'll put it to bed, it's been over 45 yrs since I've dealt with a 74 anyway..

[Hartley]

I always used a (set to length) dipole with the -74, including coax feed and an SWR meter in-line a foot or so from the R/T unit. Once in a blue moon, I used the whip antenna with a ground wire (worked best in an RB-15 out in salt water).

BTW, the "zero beat" adjustment would allow you to tune to a freq off of the nominal 1 kHz increments

I got out in December '78 - it was all PRC-74s then (though the -109s were still in the team boxes in BT)

Hartley