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Author Topic: Need some really good BNC patch cables  (Read 2928 times)
WX2S
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Posts: 735




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« on: May 08, 2013, 07:25:49 PM »

I have some Belden 6-foot BNC to BNC patch cables that double as pretty good receive antennas. Result: self-inflicted QRM.  Angry Does anyone have any recos on PNC to BNC patch cables about 6 feet long with really good shielding?

73, -WX2S
« Last Edit: May 08, 2013, 07:28:02 PM by WX2S » Logged

73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
WB6BYU
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Posts: 13286




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« Reply #1 on: May 08, 2013, 09:00:02 PM »

Pasternak Enterprises will sell you just about any sort of patch cable you want if you
have the money.  Start by choosing one of the double-shielded coax types like RG-55
or RG-223 (RG-58-sized) or RG-214.  I suspect that most of the standard ham cable
suppliers may have something suitable available by the foot and could make up such
cables for you.


You might think of how much you are willing to spend first:  we use 5' cables with
SMA connectors at work and they run a few hundred dollars each.  And we still
have to add heat shrink tubing on the ends to extend their useful life.  The manager
has been complaining about the price increases, but we can't count on everything
still working correctly if he swaps to a cheaper cable that will have higher loss at
5 GHz.
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W8JX
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« Reply #2 on: May 08, 2013, 09:39:12 PM »

For best there for its size try RG 142. It is 58 size with Teflon dielectric and braided and foil sheild. We used it on patch panels into ghz range. Second choice would be RG 223 which was already mentioned.
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N0IU
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« Reply #3 on: May 09, 2013, 04:00:23 AM »

I have always had excellent service from DX Engineering.

http://www.dxengineering.com/parts/dxe-8xdb006
« Last Edit: May 09, 2013, 04:02:26 AM by N0IU » Logged
TANAKASAN
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Posts: 933




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« Reply #4 on: May 09, 2013, 05:44:51 AM »

Holy smokes, have you seen the prices at Pasternak?

Heart stopping!

Tanakasan
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N3DT
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Posts: 536




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« Reply #5 on: May 09, 2013, 06:06:33 AM »

Yeah, I was going to suggest some RG-8X and some connectors and DIY.  The 8X is very reasonable.
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AA4PB
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« Reply #6 on: May 09, 2013, 06:54:15 AM »

What are you doing (frequency, etc) with the patch cables that leakage through the shield is an issue? You **could** have common mode current issues that is causing RF to flow on the outside of the shield that would not be corrected by a more effective shield. Over the years I've used a lot of patch cables with a variety of test equipment up through 900 MHz and can't say that I've ever experience problems from excessive leakage through the shield.
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WX2S
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« Reply #7 on: May 09, 2013, 07:07:33 AM »

What are you doing (frequency, etc) with the patch cables that leakage through the shield is an issue?
Connecting a second receiver (QS1R) that seems to be extremely fussy about RFI on transmit. Frequency range is 3-30 MHz. I'm trying to run a skimmer on the QS1R; the issue is that the skimmer doesn't stop on transmit and my signal splatters across the received subband. So I get a lot of spots of myself.

With the antenna connection to the QS1R disconnected, the RFI is minimal. With just one of the Belden BNC jumpers connected to the receiver input, I get pretty serious RFI on transmit. This happens whether the end of the jumper is open or shorted.

- WX2S
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73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
AA4PB
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« Reply #8 on: May 09, 2013, 07:26:08 AM »

If you are transmitting CW at the 100W level and the transmit antenna is not far away from the skimmer receiver then preventing pick up by the cables could be a tall order. I'd suggest that the best test of the jumper cables would be with the cable terminated with a well shielded 50 Ohm termination rather than an open or short. You could also have common mode currents flowing on the transmit antenna coax, bringing the RF back down into the shack and coupling into the receiver connections.

I'd be really surprised if a better quality jumper cable solved the problem unless there is something wrong (like a poor shield connection on one end) with one or more of the cables.
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WX2S
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« Reply #9 on: May 09, 2013, 07:34:37 AM »

The transmit antenna is about 50 feet away. Not much I can do about that.

I've got some Type 31 ferrites on the antenna coax. Maybe not enough?

- WX2S
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73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
W8JX
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« Reply #10 on: May 09, 2013, 08:35:35 AM »

The transmit antenna is about 50 feet away. Not much I can do about that.

I've got some Type 31 ferrites on the antenna coax. Maybe not enough?

- WX2S


RG142 would stop it. Not cheap though.
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K5LXP
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« Reply #11 on: May 09, 2013, 08:52:53 AM »

Double shield coax like RG-142 will have excellent shielding at HF.  So does single shield for that matter, as at HF shielding isn't that hard to effectively do.

You can't beat a solid shield like Superflex:

http://www.tessco.com/products/displayProductInfo.do?sku=95371&eventPage=1

I think your "leakage" is coming in from the receive antenna, not through the patch cables.


Mark K5LXP
Albuquerque, NM
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AA4PB
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« Reply #12 on: May 09, 2013, 09:08:08 AM »

Remember, what you are essentially trying to do is operate two stations side by side, running on the same band. It's really tough not to overload the receiver while the other is transmitting. It would be like putting two active 20M CW stations in the tent during field day without having any interferrence between them.
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K5LXP
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« Reply #13 on: May 09, 2013, 09:51:29 AM »

I think this is a key parameter:

QS1R RevD Receiver Specifications:
Input ADC Clipping Level:       +9 dBm ( 8 mW )


So the overload level will depend a lot on power level, TX and RX antennas and the distance between them.  At 100W and good antennas on the same site you can easily be above +9dBm.


Mark K5LXP
Albuquerque, NM
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WX2S
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Posts: 735




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« Reply #14 on: May 09, 2013, 12:51:55 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
« Last Edit: May 09, 2013, 01:09:34 PM by WX2S » Logged

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