More Panadapter help - from N4PY

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More Panadapter help - from N4PY

Postby jon » Sat Oct 15, 2016 8:32 am

Carl Moreschi N4PY kindly provided these useful suggestions for those of you looking at options for configuring the RSP as a full bandwidth panadapter and wanting to share antennas for TX and RX.

Subject: Re: FW: can I do this without damaging the sdrplay unit

Hi Jon,

I offer two solutions here with external boxes form either MFJ or DXE.

The one from DXE is a little safer but more expensive.

Solution to share antennas with an SDR panadapter receiver

The DXE-RTR-1A can be used to share antennas between the transceiver

and the SDR receiver. This is a $170 unit that will provide a safe

way to share antennas between the SDR receiver and transceiver.


1) Place the "Main On" switch in the middle "RX ANT" position.

2) Connect the amp key line of the transceiver to the "Transmit Ground" connection.

3) Connect a radio shack Y cable (part #42-2535) between the "Main ANT OUT"

and "RX ANT IN" connections.

4) Connect the third leg of the Y cable to the antenna input

of the SDR receiver.

Here's the MFJ solution. It requires a small mod.

The solution to share antennas is to add an MFJ-1708 T/R switch. This

unit will automatically sense RF from the transmitter and then remove

the panadapter radio from the receive antenna connection. But the MFJ

switch will also remove the transceiver from the transmit connection

while in receive. So the MFJ switch needs two very simple mods. You

must solder a 14 gauge wire between the transmit and antenna SO-239

connections. This will then make the switch operate properly for this

use. Additionally, you should wire the relay to energize from your

radio's amp key line for faster and safer switching.

Also for safety in case something fails I recommend adding two back

to back diodes between the receive SO-239 and ground. These diodes

will act as limiter and further protect the panadapter receiver in

the event of a timing problem. Radio Shack 276-1661 diodes should

be fine.


Carl Moreschi N4PY

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