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Author Topic: Need some really good BNC patch cables  (Read 2757 times)
WB2WIK
Member

Posts: 20565




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« Reply #15 on: May 09, 2013, 02:20:22 PM »

The TX antenna is also the RX antenna. (Using a T-R switch to prevent slagging the QS1R.)

I'm definitely getting some QRM introduced through the jumper cables. Receiver minus cables = minimal QRM. Receiver plus cable minus anything else = QRM (at 100W output.)

73, -WX2S


What happens if you terminate the cable in a well shielded 50 Ohm termination instead of an open or short-circuit?

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WB6BYU
Member

Posts: 13143




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« Reply #16 on: May 09, 2013, 07:48:54 PM »

Here is another test you can run:  connect a 6' wire to the ground side of the BNC
connector on the radio, with nothing to the center pin.  Extend it as you would a
jumper cable.  Do you get any interference?  Try attaching the far end to the shell
of the mating jack.

If any of that causes you to hear the interference, then better shielding on your
jumper cables won't help (or at least won't make a big difference.)  You've just
got too much RF around the radio.


Quote from: WX2S

Using a T-R switch...



What type of T-R switch?  Not a relay I presume, because it couldn't operate
fast enough.  So an electronic T-R switch?  Does it allow the QS1R to hear
between the dits when you are transmitting?  While T-R switches are designed
to protect the front end of the receiver, they generally aren't intended to
allow reception at the same time, other than to hear one's own fist in the
receiver.  A fast switch acts as a modulator, so it may well superimpose your
signal on the others it is hearing because of that.

A repeater typically requires 100+dB of isolation between transmit and receive
to maintain normal RX sensitivity.  It isn't trivial:  rigs have to be well shielded,
DC and audio cables properly filtered, tuned cavities in the TX and RX lines, etc.
What you're trying to do requires at least that much isolation" don't under
estimate the measures you may have to take.  Double-shielded patch cables
are a good place to start, but it may take a lot more than that.
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W4PAH
Member

Posts: 67


WWW

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« Reply #17 on: May 09, 2013, 08:27:31 PM »

I recently purchased some cables from this source, after receiving reports of their high quality from Phil Salas AD5X. I am pleased with the quality, although their turnaround time was not the quickest... Genuine Times-Microwave cable, too!

http://myworld.ebay.com/cablebuyer/

I ordered some short jumper cables with specific requirements (e.g., N male to UHF female, N male to UHF male, etc.). They met all of my requests at the quoted price. I was very pleased.

73
-john W4PAH
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AA4HA
Member

Posts: 1386




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« Reply #18 on: May 10, 2013, 09:10:09 AM »

I have a spool of LMR-240 with an assortment of crimp connectors so for BNC I use that as patch cables. It is foil and braid shielded, pretty low loss and easy to work with.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W8JX
Member

Posts: 5640




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« Reply #19 on: May 10, 2013, 11:07:42 AM »

I have a spool of LMR-240 with an assortment of crimp connectors so for BNC I use that as patch cables. It is foil and braid shielded, pretty low loss and easy to work with.

RG 142 is foil and braid and very tuff too. It will handle far more power than LMR240 too.
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WX2S
Member

Posts: 702




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« Reply #20 on: May 10, 2013, 06:23:27 PM »

Here is another test you can run:  connect a 6' wire to the ground side of the BNC connector on the radio, with nothing to the center pin.  Extend it as you would a jumper cable.  Do you get any interference?
Very little. So better shielding might help, I suppose. The problem seems to be frequency dependent -- less on 17m than 40m.

Quote from: WX2S

Using a T-R switch...



What type of T-R switch?  Not a relay I presume, because it couldn't operate fast enough.  So an electronic T-R switch?  
Two kinds, actually. My K3 has a transverter adapter, which allows me to get receiver RF off the antenna. This is the arrangement I tried first. Then a DX Engineering RTR-1A. Both use relays, and both exhibit the QRM.

A fast switch acts as a modulator, so it may well superimpose your signal on the others it is hearing because of that.
Quite possibly, or on top of the normal background noise.

- WX2S
« Last Edit: May 10, 2013, 06:26:05 PM by WX2S » Logged

73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
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