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SDR Isolation from Xmitter (or Transciever )

 

All;
Sorry for crossposting this.. but I thought it may be of interest here
I asked this question on the SDRPLAY users group.
------------------------
Hi all;
I have an RSPlayduo. I am using it mainly as a test instrument, spectrum Analyzer.
I would like to try to use the receiver(s) as part of a receiver/transmitter configuration where the transmitter has its own DDS front end to a simple transmitter. Completely separate receive/transmit controls with the possible exception of a pin diode mute to the duo.. (something like the MFJ-1708, but homebrewed).

Have any of you done this?

For the transmitter, I am NOT talking about simply using an exsiting transciever as the transmitter. But it would work that way..

If you look at QRZ for W6JL and look at his rig.. he is using a completely separate receiver/transmitter config... heck... I just answered my own question.. take a look.
Instead of his homebrew Tayloe receiver I substitute the sdrplay.. heh heh...

I ramble. If you have set up something like this I would be curious.

Thanks!
N1GMM
---------------------------------

I got a response pointing me to a video here:
it is in Italian.. but you will get the idea.

The specs for the ELAD isolation switch is here:


$102..

MUCH better specs than the MFJ unit. and even costs less and better constructed...

Have Fun, Stay Safe and keep on the Sunny Side!

Guy
 

Hi Guy,

Ignore the fact that your receiver is an SDR. Ignore the fact that your station is solid state. Look for information about how amateurs have configured their gear for a century to accommodate separate transmitters and receivers.

That PIN diode is for the antenna changeover and covers the functions of removing the antenna from the receiver during transmit. It has nothing whatsoever to do with muting.

You can just as easily use mechanical relays for the antenna T-R function or any of several electronic means. There has to be a means to reduce or the amplification in the receiver or completely turn it off. For phone operation just turn it off. Short the RX antenna terminal to ground in any case. The PIN diode circuit probably does that for you already. Turn off the amplifiers and mixers. If you completely silence the receiver during transmit on CW you will have to introduce your keyer sidetone into the receive audio or just not use a sidetone. If you allow the mixers and the audio channel to operate you can use your own transmitted signal as the sidetone. That may not be practical with your SDR. Mixers? OY!

Some amateurs use all mechanical relays or hand operated switches to accomplish all of those functions. Try operating that way just to get a feel for what has to happen and an appreciation of the automation.

Look at how this is done in other transceivers and separates. You will be able to apply what has been written up in the old handbooks for those legacy tube rigs. The same principles apply. Best to you with your project.

73,

Bill KU8H

bark less - wag more

On 10/2/20 8:59 AM, Guy Mengel wrote:
All;
Sorry for crossposting this.. but I thought it may be of interest here
I asked this question on the SDRPLAY users group.
------------------------
Hi all;
I have an RSPlayduo. I am using it mainly as a test instrument, spectrum Analyzer.
I would like to try to use the receiver(s) as part of a receiver/transmitter configuration where the transmitter has its own DDS front end to a simple transmitter. Completely separate receive/transmit controls with the possible exception of a pin diode mute to the duo.. (something like the MFJ-1708, but homebrewed).
Have any of you done this?
For the transmitter, I am NOT talking about simply using an exsiting transciever as the transmitter. But it would work that way..
If you look at QRZ for W6JL and look at his rig.. he is using a completely separate receiver/transmitter config... heck... I just answered my own question.. take a look.
Instead of his homebrew Tayloe receiver I substitute the sdrplay.. heh heh...
I ramble. If you have set up something like this I would be curious.
Thanks!
N1GMM
 

Hi Bill,
I read your note somewhat puzzled... I am 64 and have been around a bit..I said to myself "did I say mute?" Sure enough that is what I said.
I should have been much more accurate. Muting is not the right term... perhaps blowing out the front end is better especially when the input limit is 0dbm.
I was looking to PROTECT the SDR from transmitting directly into it. Heh heh ... I could have used a manual knife switch like Mickey Rooney's friend in
this video.. heh heh..

Pin diodes work too just as w6JL does.. in his separate receiver/xmitter.

Anyway.. thanks for the note and i am very interested in doing things in an old fashioned way... knife switches or not!

Best to you and yours Bill!

Keep on the sunny side!

Guy
 

Hi Guy,

yeah...dumping watts into a receiver front end isn't good:) Ask me how I know.

I rigged up a set of switches a couple of times. It really does keep us in touch with what is happening by magic in more modern gear. I appreciate not having to throw more than *one* switch (the CW key or PTT) and everything goes in order like a military drill team with no further effort.

I have not been too annoyed to flip just one switch besides the key or PTT. I have watched some hams flip several switches - including the antenna knife switch - and turn the gain up or down to go from receive to transmit and back again :) No thank you.

73,

Bill KU8H

bark less - wag more

On 10/2/20 12:13 PM, Guy Mengel wrote:
Hi Bill,
I read your note somewhat puzzled... I am 64 and have been around a bit..I said to myself "did I say mute?" Sure enough that is what I said.
I should have been much more accurate. Muting is not the right term... perhaps blowing out the front end is better especially when the input limit is 0dbm.
I was looking to PROTECT the SDR from transmitting directly into it. Heh heh ... I could have used a manual knife switch like Mickey Rooney's friend in
this video.. heh heh..
Pin diodes work too just as w6JL does.. in his separate receiver/xmitter.
Anyway.. thanks for the note and i am very interested in doing things in an old fashioned way... knife switches or not!
Best to you and yours Bill!
Keep on the sunny side!
Guy

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