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Re: Re: Converter TX protection-- MMIC "fuses"

HMM.. well.. It's a stock Down East Microwave TCK kit with an additional 
transistor and two resistors to form an inverter-- I mounted it in a hammond 
Die Cast Box with a heatsink and connectors I had.

The box has RF input/output and a TX IF output/RX IF output and a PTT input 
-- the PTT "high" circuit is used with an additional transistor inverter 
stage on it that forces the unit into TX when not connected to anything or 
at 0V DC on the 2m RF cable from the radio.  The +13V DC on the preamp line 
on the 2m cable provides a logic high to the extra transistor inverter 
stage, which pulls the PTT "high" circuit low, dropping the TCK into 

Otherwise on TX its a simple attenuator- on RX a MAR-6 MMIC amp.

The heatsink is necessary for the non-inductive TO-220 cased 50 ohm load to 
burn off most of the energy on TX.

I'd put a schematic of it up, but I think Steve Kostro at DEM is a bit 
sensitive (or should be!) to these sort of things. So here is the mods 
instead:  Literally build the kit as intended and add a molded choke 
(provided in the kit) to the center conductor of the rig RF line, and shunt 
the other end of that inductor to a 0.1 uF cap to ground.  Run this point 
(cap and inductor junction) through a 10K resistor to the base of a 
2N2222/2N4401/etc.. have a 1K resistor in the collector, and the collector 
tied to 12V.  Emitter to ground.  The collector should be tied to the "PTT 
high" circuit on the TCK.

With the preamp on, and the "External VHF preamp ON" menu item enabled, the 
radio will RX via the MAR-6 in the TCK (and the RX in jack on the TCK) and 
TX out through the attenuator and the TX out.

If you lose DC to the modified TCK, it'll go into TX mode (deafining the RX 
so it'd be obvious) making the RF from the rig burn up mostly in the 
attenuator in the TCK.  This is normal on key down (TX) on the 847, and 
abnormal if you accidently turn off the "preamp" voltage or something bad 
happens.  It should protect the converter in any case.

After building it, if it works, it should go into TX with +13.8V applied to 
power it, but disconnected from the radio.  Once connected, turning on and 
off the "preamp" should key it on and off.

Fred W0FMS

>From: "hasan schiers" <schiers@netins.net>
>To: "Frederick M. Spinner" <fspinner@hotmail.com>
>Subject: Re: [amsat-bb] Re: Converter TX protection-- MMIC "fuses"
>Date: Fri, 25 May 2001 21:37:10 -0500
>I'd love to hear more about this...I have an FT-847 and you KNOW I wanna
>protect that UEK 3000 <grin>
>hasan schiers, NĜAN
>----- Original Message -----
>From: "Frederick M. Spinner" <fspinner@hotmail.com>
>To: <amsat-bb@AMSAT.Org>
>Sent: Friday, May 25, 2001 7:40 PM
>Subject: [amsat-bb] Re: Converter TX protection-- MMIC "fuses"
> > I packaged up a DEMI TCK (Transverter Control Kit) which has the option 
> > MAR-6 as my means of feeding a transverter/converter ftom my FT-847. 
> > 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
> > (But not the rest of the unit)
> >
> > If there is no preamp voltage on the line to the TCK, the relays in the
> > are stuck in transmit-- meaning if I transmit on 2m, the relays go to 
> > and if I forget to turn on the "preamp" or otherwise lose the preamp 
> > 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
> > option for rigs like the FT-847 that can power preamps.  I have the 
> > set for correct transverter drive (not used obviously at S w/144 IF but
> > other transverters, like Mode-L) with about 12W into the TCK, with the
> > heatsink I provided it seems fine- and short periods of 100W result in 
> > more damage than overdriving the transverters and producing a low 
> > 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
> >
> > 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 
> > >IF gain [per stage] for boosting the IF level of my radio telescope's 
> > >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
> > >output of your 2.4G conv.  10 vdc produces 20 dB gain.
> > >
> > >Everything was ordered from DEM:  A small diecast box with sma
> > >pcb for the mmic, mmic, feedthru cap for power, chip caps and resistor
> > >biasing.  It has been a few months since I ordered this, but I believe 
> > >cost about $35 per stage.  It takes about half hour to build and they
> > >[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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> >
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