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Author Topic: Recommendations for SDR receiver protection?  (Read 15637 times)
HAMMYGUY
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Posts: 85




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« on: September 06, 2013, 11:37:55 AM »

Most of my operating is with an RF Space SDR-IQ or Pegasus with a TS-2000 slaved to them for transmit.  Currently I as an MFJ-1708 rf switch with a couple of diodes for front end protection.  Now I know this isn't enough as on some bands I still see the internal protection light blink when switching to transmit. 

The antenna switch does ground the receive but obviously the transition time can be an issue.  Its been this way for a couple of years but figured I'd ask the forum for any ideas.

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KA4POL
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Posts: 1978




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« Reply #1 on: September 06, 2013, 09:49:16 PM »

Your problem could be the cable between switch/diodes and the receiver front end. The diodes need to be as close as possible to the front end.
I use a circuit with a lamp (6.3 V 150 mA in series, followed by a pair of antiparallel diodes (1N4148) to ground. The diodes, however are connected to the signal path by a capacitor of 1 µF. Again in series to this follows another capacitor of 100 nF in series.
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WV4I
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Posts: 136




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« Reply #2 on: September 08, 2013, 03:45:52 AM »

Hooked directly to my SDR-IQ, I use an Array Solutions AS-RXFEP front end protector, here in the lightning capital of the US, South FL. So far so good. Obviously, if I have lightning very close or overhead, I still disconnect the antenna if home. Otherwise I run this SDR-IQ online, 24/7, see op SWL/WV4I on http://sdrspace.com/  .....

As to the T/R delay issue, look at your AF Output>Buffer Que Size, audio buffer, if using SDR-Radio, and try a min buffer length. This improved my T/R changeover time dramatically, when my config was SDR-IQ using SDR-Radio and TS-590s as ext transceiver. Also used the MFJ-1708 switch, did not find that to be the issue with changeover time however.

 
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KJ5XX
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Posts: 26




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« Reply #3 on: October 15, 2013, 07:23:59 PM »

I used the TS-590 with an SDR-IQ for awhile with the MFJ-1708.  All three units played nicely together. The only somewhat minor issue was the amount of time it took for the MFJ-1408 to switch from transmit back to receive. Many times I would find  that I had missed the first couple of words of the succeeding transmission.

But, you bring up an. Interesting point here that i hadn't tried.,

In that receive switchover time can be reduced by reducing the size of the AF buffer. Something I'll have to try.

What in particular caused you to choose  the AS-RXFEP over the MFJ-1407?   Design flaw in the MFJ or design feature in the AS-RXFEP

Thanks,

Ron - KJ5XX
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NI0Z
Member

Posts: 560


WWW

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« Reply #4 on: October 15, 2013, 08:01:48 PM »

This thread has another alternative to the MFJ.

https://sdrzone.com/index.php?option=com_kunena&view=topic&catid=18&id=86&Itemid=146&limitstart=6
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ZENKI
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Posts: 934




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« Reply #5 on: October 18, 2013, 08:51:56 PM »

http://www.herostechnology.co.uk/pages/Dual_antenna_relay.html

Nothing that cant be homebrewed. But for those that like everything coming in a box there it is.

Thats the major failing of all the SDR radio makers. They want to sell their products to hams and they cant even included a miserable RX protection ON TX.
Pathetic really.
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SWL2002
Member

Posts: 262




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« Reply #6 on: October 21, 2013, 03:41:17 AM »

http://www.herostechnology.co.uk/pages/Dual_antenna_relay.html

Nothing that cant be homebrewed. But for those that like everything coming in a box there it is.

Thats the major failing of all the SDR radio makers. They want to sell their products to hams and they cant even included a miserable RX protection ON TX.
Pathetic really.

Yes, thank you for posting a very expensive solution to the problem.   Roll Eyes  I would go with the DX Engineering unit at half the price and triple the versatility.

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K9IUQ
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Posts: 1740




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« Reply #7 on: October 21, 2013, 04:55:25 AM »

I would go with the DX Engineering unit at half the price and triple the versatility.

The DXE RTR-1A is an excellent unit. I use it with a QS1R. I sync the QS1R (OmniRig) with a TS-590s and use it both as a RX and Panafall. The DXE works flawlessly. I use Legal Limit frequently in contests and the RTR-1A protects the QS1R with no problem. It is very fast also, much faster than other options.

Stan K9IUIQ
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AB7R
Member

Posts: 128




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« Reply #8 on: October 21, 2013, 07:54:53 AM »

Not as fance as the RTR but I have been using one of these for a few years and it has worked well.

http://www.radio-ware.com/products/fes.htm

73
Greg
AB7R
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KD7RDZI2
Member

Posts: 68




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« Reply #9 on: October 21, 2013, 01:57:49 PM »

what about a sequencer such as http://www.w6pql.com/relay_sequencer.htm to command relays plus a pair of Schottky diodes in parallel and a bulb in series?
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WV4I
Member

Posts: 136




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« Reply #10 on: October 22, 2013, 04:38:10 AM »

Not familiar with MFJ-1407. Also could homebrew front end protector I suppose. And I think the SDR-IQ has clamping protection? But here in the lightning state, and with multiple antennas and transmitters, potential of RF overload, I added the AS-RXFEP. So far so good. Bought a Flex 3000, so now mostly using SDR-IQ as remote receiver, see sdrspace.com and swl/wv4i, easy to forget it's on/there, etc..

Also, to clarify, I thought I had a T/R switchover lag issue, when really it was audio buffer/software induced, far more than my preferred 25ms delay, i.e. when using amp.
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