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Re: Inhibit Xmit on 736

In a message dated 11/5/01 7:59:33 PM Pacific Standard Time, 
r.sturgis@worldnet.att.net writes:

> Sometime back I saw a post explaining how to inhibit the 2M xmit function on
>  the FT736r.

Is this what you were looking for?  Hope it helps.  From my personal SIG 
archives on the 736.


Date: Fri, 14 May 1999 09:12:51 EDT
From: Mike73@aol.com
Subject: [amsat-bb] Yaesu 736R RF power up delay

Howdy all,

>From time to time messages surface here about RF output foldback problems 
with Yaesu's 736R. This can sometimes be caused by external devices 
(bricks/preamps) not being fully switched inline before your 736R starts to 
transmit. This causes the 736R to sense a higher than normal SWR and foldback 
the RF output. Here's are a couple of solutions.
- ------------------------------------
Thanks to Richard, K4RTS for this one......

1.  Remove the top cover from the 736.

2.  Locate the Transmit Unit board - it will be the be one of three
horizontal circuit boards on top. . . the Transmit Unit is the one on the
far left hand side.

3.  Locate jack J10 (has 6 leads on it) which is in the back right hand
corner of the board.  Pin 3 of J10 has an orange lead attached.

4.  Grounding this lead will inhibit the unit from transmitting any RF.

5.  Nick the insulation of the orange lead and solder on a small wire.

6.  Carefully remove the Receive Unit located on the far left hand side of
the radio.  This board mounts vertically (stands on it's side).

7.  Solder the other end of the lead the goes to the orange wire on the
Transmit Unit (from step 5) to the unused pin 5 of the CAT DIN plug.

I then tie pin 5 of the CAT DIN plug to one of the relay contacts in my DEM
sequencer.  I tie the 736 PTT in/out to the PTT input on the DEM sequencer.
I also use pin 6 of the CAT DIN jack to provide 13.8 vdc supply voltage to
the sequencer.

Remember, a ground on CAT DIN pin 5 (once the 736 is modified) inhibits the
736 from transmitting RF.  I have the DEM sequencer set up so that it keeps
a ground on this lead at all times until I begin the transmission sequence.
The relay in the sequencer pulls up about 500 ms after I initiate PTT (and
releasing the ground), thus allowing the 736 to transmit after everything 
else has had a chance to switch.  500 ms is more delay than I really need, 
but it doesn't hurt anything.
- --------------------------------

Another solution to look at is the OH5IY TX-Delay circuit. This one doesn't 
require an external sequncer. (This is what I currently use) Ilkka has just 
released a mod to the original circuit that I'm currently testing. This 
appears to solve a minor issue with the drive level control setting.

As with any mod, proceed with caution. Your mileage may vary. etc.

Mike, N1JEZ
AMSAT #29649
AMSAT Local Area Coordinator
"A closed mouth gathers no feet."
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