AN/GRC-109

T-784 (RT-3)	R-1004	PP-2684	PP-2685	CN-690

		G-43 Set eBay photo
	H-65/U	MX-6793	G-43 Generator

		BG-175 or BG-402?	G-43 to PP-2684 Cable Belden 8424 HAS 4 ea 20 awg maybe 6 feet long

This is a radio set where each major component is built into a waterproof cast metal housing. This would allow the set to be stored under ground, under water and retrived when needed. Came into being after W.W.II and prior to 1969. The GRA-71 Code Burst Keyer can be used with this set after the T-784 has been modified to handle the high speed Morse code.

Used in Vietnam by forward observers with the GRA-71 burst transmission device. In this application the radio opertor would only take with him the parts of the system to be used , not the metal storage boxes and not all the parts. Would like to know when? before or after 1969. In 1969 U.S. forces discovered a NVA/VC communications listening post that proved the NVA/VC could and were using COMINT against us on a scale that no one imagined.

Note that this radio was not desinged to be used while moving. It's for use in a fixed position.

The PRC-64 (aka CIA Delco 5300) may also have been one of the rdios that repalced the GRC-109.

I've read that the GRC-109 is based on the GRC-9. There is a resemblance, but not exact match.

Adding AM Tx to the GRC-109

Components of Radio Set AN/GRC-109

Power Supply

Internal T/R Switch Problem

Date: Wed, 15 Feb 2006 10:16:51 -0800
From: "Kenneth G. Gordon" 
Subject: Re: [Milsurplus] GRC-109, RS-1 transmitter - keying

On 15 Feb 2006 at 11:54, B. Smith wrote:

> Has anyone modified the Transmit Receive (TR) circuit for the T-784(GRC-109 or RT-3 (RS-1) to improve receiver sensitivity when using the internal automatic antenna switch between transmit and receive?

I have.

> is keyed. The problem is that there are extreme loses in the receive side of the TR circuit due to the receiver coupling capacitor C14 which is only 18 pf but is in the output circuit of the transmitter.

No. That isn't the problem: the problem is called "suck-out" and is caused by the transmitter's final tank circuit being tuned to the same frequency as the receiver's input circuitry. One of the list members on the Glowbugs list calculated the losses due to the final tank circuit being connected effectively in parallel or series (I have forgotten which) with the receiver's input circuitry, and it amounts to -30DB LOSS!!! in the case of the GRC-109.

Suck-out was a common problem for hams who used TR switches which were connected directly to the final amp's tank circuitry.

> The receiver sensitivity loss is paraphrased in TM-11-5820-474-14, Chapter two, 14e, under "Preliminary Connections, Separate Transmitting and Receiving Antennas."

Yes, but it doesn't tell you why: it is "suck-out", period. The receiver coupling cap is plenty big enough to do the job.

> In Vietnam at base camps the sets were used with separate antennas.

Yes, and that method was suggested in the manual too. The internal TR switch was only to be used in an emergency.

> I have been using an external antenna change over switch for the set to prevent the receive loses but I am preparing to modify the set
> using either pin diodes (ugh) or a small relay. :-)

There are several ways you can do it: what I did was non-destructive. I mounted one of those small 5 VDC Radio Shack relays internally on a bit of double-sided tape, and used a single diode to rectify the filament voltage as a 1/2 wave rectifier. I oriented the diode in such a way that if you used 6 VDC on the filaments, the diode would pass that voltage on to the relay so the circuit works the same way whether you are using AC or DC.

I use the relay to both key the rig and change the antenna so that QSK is preserved. It easily follows my bug at 20 WPM or more.

It works very well.

Or you could build an external TR box that does all that. Electric Radio mag recently had an article on just that subject.

BTW, I REALLY like the AN/GRC-109. It even runs off my PE-162C generator, although I have not yet gotten my DY-88 to work with it. My GN-58 does a superb job with it, especially since I mounted the GN-58 to an old exercise bicycle. I can even send while pedaling. :-)

Ken W7EKB

40 mm Grenade Antenna

Is anyone familiar with a 40 mm grenade launcher cartridge intended for use with the GRC-109 radio? (let me know) It was intended to be fired in an M79 grenade launcher. The projectile is a black anodized aluminum cylinder filled with green plastic insulated antenna wire that pays out in flight. One end of the wire was attached to the heavy steel cartridge case and the other in the projectile. When the cartridge is fired, the projectile was supposed to penetrate through the jungle canopy and leave the wire hanging in the treetops. The other end remained attached to the fired case, and when unloaded from the M79, could be cut off and attached to the radio.

I've seen three of these over the years and the one in my collection is marked (in felt pen) for SEAL and SF use with GRC-103 radio. I believe this is incorrect and was actually intended for the GRC-109. One example I've examined was a cutaway that came from the manufacturer, AAI Corp., via a retired engineer. The other was at the EOD unit at Camp Pendelton about 20 years ago.

So I know they existed but don't know how extensively they were used or if they are documented anywhere in the literature for the radios themselves. Are any of you spy radio enthusiasts familiar with this device?

I'll take a couple photos and post them if anyone would like to see it. Thanks. Rick

Links

RS-6 Spy Radio

This is the 07287 hits since time this page has been accessed since since 27 July 2001

	GRC-9	GRC-109
Tx Modes	CW-AM-MCW	CW, HSCW
Rx Modes	CW-AM-MCW	CW
Tx tubes	3A4 3A4 2E22 0C3 3A4	6AC7 2E26
Rx tubes	1L4 1R5 1L4 1R5 1S5 3Q4 1R5	1T4 1L4 1T4 1T4 1T4 1U5

AN/GRC-109

Adding AM Tx to the GRC-109

Components of Radio Set AN/GRC-109

T-784/GRC-109 Transmitter (RT-3)

R-1004/GRC-109 Receiver

PP-2684/GRC-109 Power Supply

PP-2685/GRC-109 Power Suply

CN-690 Voltage Regulator

Power Supply

G-43/G Generator

Manual

Operation Accesssories

Internal T/R Switch Problem

40 mm Grenade Antenna

Links

RS-6 Spy Radio