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ICOM IC-735 Transmit Mod [message #3071] Sat, 07 March 2015 22:37
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Registered: December 2004
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I don't have either one of my 735's open and I can't seem to find the precise location or information but roughly...

There are two diodes, D30 &D31 (or maybe it's D32&D33 D34&D35 I can't remember) located toward the front center of the board containing the CPU. The diodes were end mounted with yellow insulation over the end of the leads away from the board. Cutting these diodes out of the circuit enables broadband transmit. My radios were purchased new in spring of 1989 so I don't know if they acurately reflect current production units. This is a particularly nice feature since it allows wide coverage when used with transverters. I use my 735's with my 144MHZ - 10.368 GHz transverters with the radios operating in the 20-30 MHz region. It allows 10 MHz of all-mode coverage on every vhf-uhf-uwave amateur band.
Glenn Elmore n6gn
From: Glenn Elmore
Date: Mon, 4 Feb 91 9:28:24 PST

> Do you have any documentation and/or suggestions on how to build or > design the 50 MHz through 902 MHz units ? >
> Chris

I don't have anything explicitly written but it is very much along the lines of the microwave stuff I showed.

The LOs are partly there already:

Band       LO           circuit
50M     30M             3 X 10 (2n5179 tripler from 10M) 
144     120M            I'm presently using the 100 MHz Xtal circuit
                        with a 120 M xtal but 6X20M with filtering
                        would work too.
220     200M            2X 100M  (single stage of 2n5179)
420     410/420         Just like 260M LO shown
900     620M            Like 1010M  6th harm of 100M and 20M PLL reference

Only 420 and 900 even need to use another of the PLL boards. The others just take a single stage. I have 50,144 and 220 done. 400 is sitting 90% completed. I have PA bricks for 50 and 400 waiting to be used.
As I said, 144 and 1296 have been running for years.

I build the RF decks in metal "shoeboxes". I pipe the LO and IF(with tx switching as DC on the line) to each deck which lets me remote them if I want to. The only thing I really need to add that I haven't is an ALC line coming back from each PA to control the 735 so that I keep things linear. Linearity hasn't been a problem but like any of the current commercially available transverters it is possible to overdrive things.

Glenn n6gn

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