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[KA9J]

I want to connect a SDR to my current rig in order to have a 2nd receiver.      I know that I have to protect the SDR from the Rf from the transmitter.   The MFJ-1708B-SDR is a device that is supposed to do this.   Has anybody used the MFJ-1708B-SDR?    Does anybody else make a similar device that you've used?

Thank You, 
Frank  KA9J

[VE3TMT]

What radio is it?

Normally tapping into the first receive IF works.

[K7LZR]

The MFJ 1708 works simply by shorting to ground the input to the receiver. Such is adequate to protect the SDR from excess RF voltage. My concern would be redundancy i.e. what if the relay fails and doesn't ground the RX input?. I'd feel more comfortable with (2) such relays in parallel just in case.....

[G8FXC]

What radio is it?

Normally tapping into the first receive IF works.

We certainly need to know what kind of radio is already in the shack before we can give any reasoned advice. Tapping into the first receive IF may be easy, but unless the radio includes support for that, it can be intrusive and not something that everyone would want to do. It's also worth noting that tapping into the IF anywhere will restrict the frequencies visible on the SDR to the band selected on the radio and possibly narrower than that depending on the exact design of it. I have my external SDR connected to the RF output of the main receiver and it will do a reasonable job of receiving on an adjacent band to that selected on the main RX. If you use the MFJ-1708, then the SDR will be able to see the full HF spectrum at all times...

Martin G8FXC

[KA9J]

The radio is an old Kenwood TS-930.      I was thinking that I want to see the full spectrum display so I can see band activity and places that it might be better to transmit on to get through pile-ups created by dxpeditions or look at activity on one band while the main rig is on another band.

Frank  KA9J

[G8FXC]

The radio is an old Kenwood TS-930.      I was thinking that I want to see the full spectrum display so I can see band activity and places that it might be better to transmit on to get through pile-ups created by dxpeditions or look at activity on one band while the main rig is on another band.

Frank  KA9J

It's an old radio, but I think it does have suitable antenna switching to drive an external SDR without any modifications or an external switch. Do you have the manual for it?

Martin (G8FXC)

[K6BRN]

FYI- The site below discusses TS-930S modifications needed in order to attach an SDR for use as a panadapter, which usually means it will work as a 2nd receiver for the current band as well (and depending on the rigs BP filters, sometimes good for the band above and below the current one as well).

As always, these mods are an "adventure" and may have some unwanted side effects.

https://www.tspelettronica.com/en/2020/10/30/panadapter-sdr-per-ts-930s/

Its a pity the existing TS-930S IF output (for the SM-220 panadapter) is limited to 100KHz.

Good luck!

Brian - K6BRN

[N4MJG]

My friend tells me there is a 3 verion of sdr going have a look and find when can i read them.

73
Jackie
N4MJG
SKCC 7305 SINCE SINCE
NAQCC 5233
OMISS 11548
General LIC SINCE 2007
PREFER EQSL

[KA9J]

It's an old radio, but I think it does have suitable antenna switching to drive an external SDR without any modifications or an external switch. Do you have the manual for it?

Martin (G8FXC)

Yes.   I have the shop (repair) manual.   That's how I've kept in working well for so long.--Frank