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Re: Converter TX protection-- MMIC "fuses"



I packaged up a DEMI TCK (Transverter Control Kit) which has the option of a 
MAR-6 as my means of feeding a transverter/converter ftom my FT-847. I've 
reversed the logic of the board by adding an additional transistor (RTL) 
logic inverter and hooking a choke and a cap to "feedline" power the logic.  
(But not the rest of the unit)

If there is no preamp voltage on the line to the TCK, the relays in the TCK 
are stuck in transmit-- meaning if I transmit on 2m, the relays go to TX-- 
and if I forget to turn on the "preamp" or otherwise lose the preamp power 
up the 2m coax from the rig, the TCK switches to TX.  And since I've 
installed the MAR-6 in the TCK, I have the MMIC fuse.  This is another valid 
option for rigs like the FT-847 that can power preamps.  I have the thing 
set for correct transverter drive (not used obviously at S w/144 IF but for 
other transverters, like Mode-L) with about 12W into the TCK, with the large 
heatsink I provided it seems fine- and short periods of 100W result in no 
more damage than overdriving the transverters and producing a low quality 
signal.  It works well.  With no internal mods to the FT-847...

The TCK kit I think is $40, and a die cast box to put it in is $10-- 
connectors and heatsinks can be scrounged, or add another $10 to the damage.

Fred W0FMS



>From: "Edward R. Cole" <al7eb@ptialaska.net>
>To: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Weak Signal Banquet NF numbers..
>Date: Fri, 25 May 2001 10:53:06 -0800
>
> >From: "Frederick M. Spinner" <fspinner@hotmail.com>
> >Also one other argument I've heard is that it's simple to replace the 
>ERA-3
> >in the SSB converter as a 2M transmit fuse.  I think a mmic could be 
>fitted
> >in the IF of the 3033's easily if the IF amp is toasted.
>
>Here is an alternative to placing the mmic into the unit:
>
>I have built two broadband VHF mmic amps using the MAR-6 to produce 20 dB
>IF gain [per stage] for boosting the IF level of my radio telescope's 144
>MHz IF [output of the DEM 1420/144 Rx converter] to drive a hot-carrier
>detector diode for wideband [about 35 MHz bw} astronomy observations.
>There is no reason that you couldn't build these to augment the VHF or UHF
>output of your 2.4G conv.  10 vdc produces 20 dB gain.
>
>Everything was ordered from DEM:  A small diecast box with sma connectors,
>pcb for the mmic, mmic, feedthru cap for power, chip caps and resistor for
>biasing.  It has been a few months since I ordered this, but I believe it
>cost about $35 per stage.  It takes about half hour to build and they work
>[no tune up].  If wanted as a kind of RF fuse,  just order a few extra
>mmics.  Ten minutes max to change out [four lead device].
>
>DEM:  http://www.downeastmicrowave.com
>
>Look under catalog/accessories:
>
>MMICK (mmic kit)...$10
>MAR 6 (17 dB min)...$2.20/ea
>ROSE-S (2x2x1.25 inch case)...$15
>SMAPANEL...$2.50/ea
>
>Tell Steve what you are doing and he'll make sure you have everything 
>needed.
>
>Ed
>
>
>----
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