Tuesday 28 September 2021


When my shack gets into a bit of a mess (which is often), I start to lose interest in spending time in there. This was happening recently because I'd removed the big MB1 base station and it left everything looking untidy. The answer was to devote some time to getting my house in order.

The new FT-891 needed to be permanently setup and it was important to do a proper installation complete with the SignaLink USB to give me FT8 capability  and the RSP1A to give me a Panadapter and Waterfall.

The SignaLink was straightforward but fitting an RSP1A meant introducing another piece of hardware to isolate the RSP1A from the FT-891's transmissions. I achieved this isolation by placing a clever little device called an MFJ 1708B-SDR in the loop.

The unit works in two ways - one is by sensing RF and the other is by detecting a control signal from the FT891's PTT circuitry. The latter is the preferred method and it is achieved by purchasing a CAT cable which has an RCA Phono lead that is connected directly to the MFJ-1708B. Such a lead is available from Techtronics here in the UK.

The “B” series offers better isolation, achieved by additional relay isolation, and is specified up to 450MHz. An internal hybrid splitter reduces the antenna loading effect and provides isolation between the rig’s input and the SDR input. A TX LED on the front panel provides visual confirmation of correct operation when the transmitter is keyed. The MFJ-1708B-SDR features 3 SO-239 connectors, the MFJ-1708B-SDR-S substitutes an SMA female connector for the SDR connection.

It was quite a bit of messing around reorganising the shack because there's no way to access the back of the radio equipment (it's all mounted on shelves in a tiny alcove), but it's all sorted now and it's good to have the flexibility of SDR UNO software.

I'd forgotten how good this software is. It integrates perfectly with the 891 and it obviously permits one to listen through the radio or through the computer speakers. A friend recommended installing OmniRig but I'd already got it running in the background from a previous installation - I just had to switch ini file to suit the 891.

I also took the opportunity of bringing the DVMEGA CAST into the shack. I now have LW, MW, HF, VHF, UHF, C4FM, DSTAR and DMR (plus everything the RSP1A receiver provides (which includes Airband and Marine, etc)). 

73, Tom, M7MCQ.


VE9KK said...

You removed the MB1.....did I miss something is that rig sold?

MadDogMcQ said...

Oops! You missed a post then Mike. I had a failure with it, so I sent it back and put the money toward the 7610 :-)

Regards, Tom.

Matthew Foutch said...

What cable did you use for this (CAT cable which has an RCA Phono lead) and what did you connect it to on the back of the FT-891?

MadDogMcQ said...

Hey Matthew, thanks for the visit. The link to the cable has now been put in the Post. Please re-read it.

73, Tom, M7MCQ