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Problem: Low Transverter Output
Several of you hv asked me to post the solution I find pertaining to interfacing the FT-1000MP with it's low xvtr output (-20dBm at 28MHz in my unit) to vhf or uhf xvtrs (SSB LT-2S & LT-70S in my case). Bob, K6PF

Solution: Previously, I posted a message that Down East Microwave made a board kit (MMICK-6) which sell for $10 US or a complete little amp in a nice enclosure with BNC connectors, wired & tested for $35 US. Both circuits use a MAR6 MMIC. A link to DEM's webpage showing the circuit & R & C values for the various
devices is below. I recently rcv'd my wired & tested amp & when looking at it, noticed a couple of changes from the circuit shown in the attached link. In mine, R is 300 ohms & they inserted a 22 ohm resistor between the output pin on the MMIC & the junction of the 300 ohm resistor & output coupling cap. Vcc is 10 to 15 VDC. The chart that came with the unit showed a bias voltage of 3.5 VDC & current of 16 ma which I didn't know how those values could be obtained with the components used. I also wondered if the 22 ohm resistor was being used to tame the devise down for use at 28MHz. I called Steve today at DEM & he said:

1. The 22 ohm R is to set the gain at 28MHz to abt 19-20dB
2. The spec sheet bias voltage & current is for Rx operation. For use in a Tx situation, they bias them at 35-40 ma which makes sense with the component values used.
3. Also, as before, he suggested turning off the Vcc supply to the amp when not in Tx mode.

I'm passing this info on to those of you who may hv an interest in this application & decide to order the kit & not the wired & tested unit in the enclosure. You might want to consider implementing these changes to what is shown in the schematic on the attached link.

http://www.downeastmicrowave.com/pre-cat.htm





 

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This site was last updated 08/21/07