Use SDR while transmitting

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Harry
Posts: 35
Joined: Mon Nov 02, 2015 9:47 pm

Re: Use SDR while transmitting

Postby Harry » Sat Jan 14, 2017 2:15 pm

dsalomon wrote:That really depends on your definition of Nearby, how close the transmitting antenna is from the RSP receiving antenna, and the amount of power being transmitted.

In general it is a VERY BAD IDEA to have a receiving antenna attached to any energized radio when a transmitting is nearby. Many companies sell RX/TX switches that automatically switch the radio out of line when transmitting so the radio is not damaged. It is also very easy to build such a switch. Google it and you will find LOTS of answers.

There are several approaches to protecting your precious RSP (or any receiver, for that matter). There is also a very wide range of costs associated with these approaches. Once such exaxmple is the DX Engineering RTR-1A: https://www.dxengineering.com/parts/dxe-rtr-1a. This device has a number of useful functions, none of which I will discuss here except the one that addresses your concern. It has a circuit that limits the input to a safe level, which allows you to continue to use the attached receiver safely while transmitting. This protection does not come cheap: $170 USD. Read their documentation to find out all the details: https://static.dxengineering.com/global ... rtr-1a.pdf. This is the best of the best when it comes to protection (IMHO). There are many much less expensive alternatives. Here are a few examples:

Yet Another Front End Saver (yep, that is actually the name): http://www.ok1rr.com/index.php/technica ... -end-saver. This site details instructions for a homebrew switch

AY Technologies RIP-1: http://www.aytechnologies.com/TechData/RIP-1.pdf. This is a simple XMIT/RCV switch.

DX Engineering Receiver Guard: https://www.dxengineering.com/parts/dxe-rg-5000

These are just a few examples. Google for lots more.

Bottom line - you MUST have some protection for your RSP if you're going to use it near a transmitter. Even ONE test without some protection can damage the front end of the RSP.

73 - David, AG4F


One thing to consider with the various "RF front end protectors" is rectification of strong signals and creating considerable overload and intermodulation. For example, I used one of these devices (a passive until requiring no power) between my SDR and a TS-990. In this application I was using the SDR as a panadaptor connected to the rig's RX IN/RX OUT ports and wanted to protect both the transceiver and SDR from any potential overload. Unfortunately, at various times and bands I would get all sorts of unwanted products both displayed and fed back into the transceiver. Once I removed the front end protector the problem went away. A google search produced a number of hits about users of these devices having similar experiences with panadaptor applications as well as those having their SDRs relatively close to strong broadcast stations (not "nearby" but miles away).

Now one may ask why use such a device if the transceiver's RX/TX relay should provide sufficient isolation to the RX ports when transmitting? The correct answer is you shouldn't need one assuming (a) there is sufficient isolation, (b) the RX port has sufficient protection and (c) the relay doesn't fail. Unfortunately, some of the earlier transceivers (say 5 years and older) have a history of faulty protection of their RX In ports. In these cases a front end protector would be highly recommended.

After removing the device from my TS-990 I have seen no adverse effects on either the transceiver or the SDRplay for the past year.

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vk4dcm
Posts: 2
Joined: Sat Jan 14, 2017 12:20 am

Re: Use SDR while transmitting

Postby vk4dcm » Sun Jan 15, 2017 4:43 am

Yes you are correct I have found the problem and i was finger trouble not the unit a asuned it wsas faulty after giving up on it for a while going fine now but i want to give it some front end protection. Im looking for an easy solution so i wont blow it up.
Last edited by vk4dcm on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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wb7tim
Posts: 1
Joined: Fri Feb 03, 2017 8:55 am

Re: Use SDR while transmitting

Postby wb7tim » Fri Feb 03, 2017 9:04 am

I just purchased a rsp pro 2 and I love it. Has anyone ever hooked it up in line with a yaesu ft 991. It sucks because I have it plugged into a extra antenna line that is high impedance and ever time I have to transmit, I have to remember to switch the frequency on my sdr so I don't blow it up. Thanks for any tips.
Last edited by wb7tim on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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K9TEN
Posts: 1
Joined: Mon Feb 13, 2017 11:49 pm

Re: Use SDR while transmitting

Postby K9TEN » Sat Feb 18, 2017 12:02 pm

Need simple directions, say step by step on getting several programs to work together. I accendently had it working but now its not. Equipment/software. IC-7300, SDRplay reciever, Omnirig, Free version HRD and HDSDR for panadapter display. I have the SDRPLAY running in parallel with the IC-7300 to a recieve only antenna through te DX Engineering recieve switch device. As I said, I have already had it working, but I changed something and don't know what combination works
Last edited by K9TEN on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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W2DLC
Posts: 41
Joined: Tue Apr 04, 2017 1:51 pm

Re: Use SDR while transmitting

Postby W2DLC » Thu Apr 27, 2017 5:52 pm

I am using an automatic QSK antenna switch so I can use the same antenna between my transmitter and receiver. The switch mutes the audio output from the computer and attenuates any signal coming back through the receive line by -80db. However, the SRD1 still desensitizes and hangs long enough to be a problem when I'm on CW. It's not as bad if I tune off frequency when I'm transmitting, but the main waterfall really lights up.

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Tech_Support
Posts: 202
Joined: Mon Jun 01, 2015 7:00 pm

Re: Use SDR while transmitting

Postby Tech_Support » Thu Apr 27, 2017 6:37 pm

I don't know what power you transmit at, but 100W is +50 dBm, so 80 dB of isolation still gives you -30 dBm at the RSP input which is a very strong signal. The problem will be that the RF AGC will react to your Tx signal and will need to re-acquire the receive signal and this takes time. You could try manually using the IF AGC to acquire the correct gain setting for your receive signal and then turn it off and see if that helps.

Sincerely

SDRplay Tech_Support

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W2DLC
Posts: 41
Joined: Tue Apr 04, 2017 1:51 pm

Re: Use SDR while transmitting

Postby W2DLC » Fri Apr 28, 2017 12:53 am

I'm using 5 watts and the AGC is manual. I really want to be able to use the RSP1 as my main receiver.

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W2DLC
Posts: 41
Joined: Tue Apr 04, 2017 1:51 pm

Re: Use SDR while transmitting

Postby W2DLC » Sat Apr 29, 2017 7:14 pm

I solved the problem! Since the time I bought the SDR1, I've had problems with my QRP transmitter overloading the receiver, even though I have it connected through and automatic switchbox. I tried all kinds of isolation techniques, and each helped a little with other types of interference, but not with that problem. Finally, I bought the $15.00 aluminum box that's being sold on eBay, and the problem is solved. I can finally use the SDR1 as my main receiver.

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