Pages: [1]   Go Down

Author Topic: Anyone hooked up an SDR with a TX/RX switch to your transceiver?  (Read 327 times)

AK4YA

  • Member
  • Posts: 196

I've got this really slick setup now with Omnirig + HDSDR + FT897D + WSTJX whereby my rig, HDSDR (controlling a QS1R), and my JT9 stuff are always in sync.

Just got my TX/RX switch in and as a little added bonus here, you can monitor your TX signal via the SDR during your TX operations.  I noticed these odd sidebands, whats going on there?
Logged

K6AER

  • Member
  • Posts: 7159
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #1 on: October 17, 2022, 06:54:55 PM »

Is their a question here?
Logged

AB6RF

  • Member
  • Posts: 95
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #2 on: October 17, 2022, 07:32:44 PM »

Is their a question here?

From the OP, “ I noticed these odd sidebands, whats going on there?”
Logged

KD6VXI

  • Member
  • Posts: 1022
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #3 on: October 18, 2022, 07:00:04 AM »

Those aren't sidebands.  Those are you are driving the living snot out of the SDR.

--Shane
WP2ASS / ex KD6VXI
Logged

K9RJ

  • Member
  • Posts: 159
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #4 on: October 18, 2022, 08:34:04 AM »

S9 +72dB Hmmm :)
Logged

AK4YA

  • Member
  • Posts: 196
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #5 on: October 18, 2022, 09:22:41 AM »

so this mfj antenna tx rx switch is junk then?  its supposed to short the SDR ports center pin to ground when the radio keys up, and I made for sure have the SDR on the correct port of the switch.
Logged

KD6VXI

  • Member
  • Posts: 1022
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #6 on: October 18, 2022, 10:00:42 AM »

so this mfj antenna tx rx switch is junk then?  its supposed to short the SDR ports center pin to ground when the radio keys up, and I made for sure have the SDR on the correct port of the switch.

Generally, yes.  *(MFJ)=junk / Mighty_Fine_Junk

But, you can be seeing the phenomenon you are (with so much RF on the shield of the coax) due to common mode current.

Chokes can be your friend here.  Judicious use of type 31 and / or type 43.  As well as a good ground, bonded to the service panel of the house (or wherever else your service drop bonds the ground to neutral).

I used to get a nasty AC hum on my RX recovered audio.  Found out common mode current was causing it.


You can always try an external antenna.  Short antenna to ground right before you go to TX.  Do not have the SDR antenna connected to any coax or anything else.  If this fixes your problem, you know your coax ground isn't 'ground'.


--Shane
WP2ASS / ex KD6VXI
Logged

AK4YA

  • Member
  • Posts: 196
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #7 on: October 18, 2022, 12:24:43 PM »

so this mfj antenna tx rx switch is junk then?  its supposed to short the SDR ports center pin to ground when the radio keys up, and I made for sure have the SDR on the correct port of the switch.

Generally, yes.  *(MFJ)=junk / Mighty_Fine_Junk

But, you can be seeing the phenomenon you are (with so much RF on the shield of the coax) due to common mode current.

Chokes can be your friend here.  Judicious use of type 31 and / or type 43.  As well as a good ground, bonded to the service panel of the house (or wherever else your service drop bonds the ground to neutral).

I used to get a nasty AC hum on my RX recovered audio.  Found out common mode current was causing it.


You can always try an external antenna.  Short antenna to ground right before you go to TX.  Do not have the SDR antenna connected to any coax or anything else.  If this fixes your problem, you know your coax ground isn't 'ground'.


--Shane
WP2ASS / ex KD6VXI

Thanks much for this!  OK so I've backed up a bit.  took out the SDR switch and just have the ft897d connected to my balanced tuner with rg214 (and 2 ferrites with multiple loops each ferrite) and my tuner has ladderline out the wall to the antenna.  the SDR itself has nothing connected to its RX antenna port now.  its physically located next to the transceiver and when I key up the TUNE button in wstjx my hdsdr shows a signal at -32db.  with the sdr a foot away from the transceiver the signal drops to -42.  Im just not sure what would be "normal" given my actual dipole antenna itself is right above my head, so I suppose SOME amount of leakage into any receivers even with no antenna connected could be expected.
« Last Edit: October 18, 2022, 12:40:36 PM by AK4YA »
Logged

N2DTS

  • Member
  • Posts: 1368
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #8 on: October 18, 2022, 05:31:18 PM »

What I do is short the antenna to ground close to the SDR receiver with a shielded box and some small relays.
I use the sdr as a 2nd or 3rd receiver and also to monitor my transmit, so I disconnect the sdr antenna and short it to ground, and open up the audio path from the computer and ground that also (as a mute) when I transmit.

Logged

WB8LBZ

  • Member
  • Posts: 285
Re: Anyone hooked up an SDR with a TX/RX switch to your transceiver?
« Reply #9 on: October 19, 2022, 07:15:26 AM »

I get the same output from my 7610 and  I added the only the I & Q cable. TR swiches too.

Larry in El Paso
Logged
Pages: [1]   Go Up