- December 9, 2016 at 8:16 am #7046
I am thinking about getting a small SDR unit, not the dongle but maybe an SDR IQ or SDR Play to use in portable operations. My question is, how can I use one antenna to feed both the radio RX and TX (Icom 7100 or Yaesu 857), and the SDR unit without frying the SDR when I TX on the radio. Any help would be greatly appreciated.
GregDecember 9, 2016 at 8:26 am #7051
It is difficult to use the same antenna for both you main radio and an SDR receiver. The problem come when your your rig transmits. Without protection of some sort, the SDR receiver will likely be damaged. If you have a radio with an IF output or outboard loops for receive preamps or a transverter, you may be able to connect an SDR to one of these ports and use your transmitter’s T/R switching to protect the SDR during Tx. The other thing that you could do would be to implement and outboard T/R switching system and use a sequencer to control it. Note that you’d need to set proper sequencing delays to ensure that an outboard relay was closed and any vulnerable equipment was shutdown before connecting the SDR to the antenna. If you have multiple rigs, you’d have to protect the SDR from any of them transmitting on bands which could damage the SDR.
This probably sounds pretty complicated but its actually not as bad as it sounds. We do it here to protect active receive antennas which we use on the low bands. If you want to hear more about what is involved, give me a call.
73,December 9, 2016 at 10:22 am #7053
As Fred mentions you need a T/R switch. I have a similar setup to the one in the video below, with a MFJ T/R switch, SDRPlay RSP1 and Win3KX3 suite handling the spectrum display with QSY on click etc.
73 de kc1ccr
(attempt #2, webmaster on submit it sent me to a 404 page)December 9, 2016 at 3:45 pm #7067
Thanks Fred and Jwahar, i have been reading up on the outboard T/R switches and I see the MFJ 1708, can anyone comment on the quality? As I understand it receive (in this case SDR) has to go to ground while transmitting so as not to damage the SDR. While the SDR Play RSP2 is not a huge investment I want something I know will reliably work while portable in the field with an android device or laptop.December 10, 2016 at 8:09 am #7079
I use a SDRPLAY with HDSDR software and really like it.
With my Kenwood TS-590SG it is easy as there is a connector on the rear that bring out the antenna during Rx using a internal power divider.
With my Yaesu FT-450D I use two coax switches, a small DC relay, driven with the rig’s amp key output that would normally go to an amplifier. Instead of TX_out think of it as Not_Rx. I use a power divider so Rx is available to the 450D and SDR_PLAY. The key output already has the delay to protect the radios Rx.
While the power divider raises the radios Rx noise floor by 3 dB you will never notice it as the noise floor is dominated by the SNR at the end of the coax from the antenna unless you have Fred’s tower and beams.
With this arrangement I can turn the volume up on the SDR or radio and listen to the one with the best copy.
HDSDR has a built in OmniRig interface and can tune the radio via the CAT interface or be tuned by the radio. I’ve used it with the 450, 590, and my IC-7300. The third option is to let CMD (Commander) in DxLabs tune both the SDR and the radio.
I go back and forth sometimes using the SDR to tune the radio via mouse clicks on the Panadapter. BTW modes etc are also changed. At other times I want to click on DXLabs’ commander or Spot collector to QSY the SDR and the radio together. It’s a quick click box to go back and forth.
Last, if I can hear it with the 590 or 7300, I can hear it was the SDR PLAY / HDSDR combo. I’ve used numerous dongles based on the set top box ICs. SDRPLAY has band pass filters, a selectable preamp, and a ADC and much better performance than any IC based dongle. HDSDR has a nice GUI for configuring SDRPLAY.
SDR Console is not as nice as HDSDR.
Let me know if you want to borrow a SDR PLAY.
Amherst, NHDecember 10, 2016 at 12:20 pm #7096
Great discussion! Greg and Hamilton, I want to expand the goal. Could an SDR dongle/SDR Player, etc be used as a “second receiver” fully integrated into a basic transceiver like an IC 7300 or even a legacy TS450 sat (Yes, I still use the Kenwood and it’s wired to HRD as is the Icom).
1. With the Tr switching issue solved for Greg, are we halfway?
2. Now with SDR Player having found a station on another band and HDSDR having all the settings known (even displayed) how can I send that data to my transceiver as a command line? Can HRD or Dx Suite software do this?
The concept seems an inexpensive way to get that high price dual receiver radio on the cheap??
Dave N1RFDecember 10, 2016 at 3:14 pm #7101
I’m part way to SO2R. By setting HDSDR to “sync to Omin-Rig” a click on the panadapter tunes the SDR and the rig. While listening to the SDR you are free to tune the rig without effecting the SDR. I can monitor the SDR for my call on a net, an opportunity to jump into a pile up, or rag chew while tuning the rig around the bands. When the time comes a click on the panadapter returns the rig to the freq and mode, stomp the foot switch and your on the air. I’m get better at hitting the A/B switch on the rig before clicking the panadapter so I can return to where ever I was before selecting the SDR.
Lately I select both HDSDR sync “to” and “from” Omni-Rig where a click or knob spin tunes both radios. I’ll set VFO A to a 40m freq and B to 20m freq. Now the A/B switch on the rig will toggle the panadapter between the bands. If I see something close by I’ll QSY with the knob, if it is a ways or I want to signal surf I’ll do it on the screen.
You have me thinking about a project……
Here is the switch: Search eBay for “2:1 remote antenna switch DIY cheap SO-239 KIT” These switches are $29 each, you’ll need two. Which a little braid ground strapping the isolation Tx > Rx is 80dB or better.
You must be logged in to access attached files.December 10, 2016 at 9:06 pm #7112
Thanks much Hamilton.
Omni-Rig and the 2:1 RF switch kit look pretty good. What other rig control and logging programs are you using?
So, the idea seems quite reasonable. What’s your new idea project? I need to do more in-depth reading. You’re way ahead of me.
Dave N1RFDecember 12, 2016 at 4:11 pm #7161
Just wanted to mention, instead of using a T/R Switch, DX engineering has a RF limiter that can be put in front of the SDRPlay to protect it. Seems like a simpler solution than keying a T/R switch bringing out the keying line etc. (Please do let me know if i am conceptually missing something and a T/R switch is absolutely necessary). Here is a link to the DX Engineering RF Limiter
73 de kc1ccrDecember 12, 2016 at 4:41 pm #7164
This is a a good safety measure if you have a receiver or receive only port on a transceiver and either one is using a receive only antenna. It protects the receive from “over the air” RF from the TX.
A transceiver sharing an antenna with both RX and TX needs a T/R switch, even at QRP power. The limiter uses diodes that go to a near short under RF drive to protect the receiver. A short across your coax during TX is a problem.
You must be logged in to reply to this topic.