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Author Topic: How much loss...  (Read 11185 times)
N8LTD
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Posts: 46




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« on: June 09, 2014, 06:32:36 PM »

I occasionally mount a 2 meter loop for SSB on a tri mag mount with a mast on the roof. Instead of running the cable thru the door, what about this? I no longer use the NMO trunk mount that's still there, so what about a SO239-NMO adapter on the trunk mount and mounting one end of the cable to that to get inside of the car that way? Approx how much loss would that be on 2 meters? I HATE running the cable thru the door!
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N8LTD
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Posts: 46




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« Reply #1 on: June 09, 2014, 06:50:04 PM »

This is what I'm talking about.



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WX7G
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« Reply #2 on: June 09, 2014, 07:21:38 PM »

The additional loss is virtually all from the extra coax and not the connectors.
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KB4QAA
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Posts: 2491




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« Reply #3 on: June 09, 2014, 07:24:54 PM »

http://www.qsl.net/co8tw/Coax_Calculator.htm

Here is a coax loss calculator.  Pick your cable, enter the freq and length and see the loss.

https://web.archive.org/web/20130320182903/http://vk1od.net/calc/tl/tllc.php
here is a more sophisticated one from Owen, ex-VK1OD

IMO the losses will be modest, and perhaps preferable to the unquantified losses from malformation of the coax pinched in the door/window seal.
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N8LTD
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« Reply #4 on: June 09, 2014, 09:27:50 PM »

I was referring to loss in the NMO mount and the NMO-SO239 adapter inline, not the length of coax.
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K5LXP
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« Reply #5 on: June 10, 2014, 06:15:04 AM »

Some NMO mounts are "low loss", others are just the basic large button.  I can't recall ever seeing impedance data on any of them as a connector.  But WX7G is right, I suspect they'll have pretty low losses compared to the coax.

To answer the question conclusively, you could use a PL259 patch cable of similar length as your antenna feed and check the losses directly with a wattmeter.


Mark K5LXP
Albuquerque, NM
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N6AJR
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Posts: 9927




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« Reply #6 on: June 10, 2014, 09:22:55 AM »

It should not be a problem, adding a couple of connectors and a short chunk of coax should be fine. Most of the time,  you will use it on fm repeaters and most any signal will work and on SSB the change to horizontal should help way more than any loss from the  jumper.  I think it will work just fine.  Let us know how well it does in the real world.
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KB4QAA
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« Reply #7 on: June 10, 2014, 02:16:00 PM »

Losses in UHF connectors are minimal for 2m.
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N8LTD
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Posts: 46




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« Reply #8 on: June 10, 2014, 08:30:48 PM »

Mark, that's a good idea to check with a watt meter. I'll do that.
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W5LZ
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« Reply #9 on: June 13, 2014, 05:32:14 AM »

Will there be any loss by doing that way?  Sure.  But not enough to make up for the convenience.  Try it both ways, compare the differences you hear (if any).  Go from there.
 - 'Doc
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N8LTD
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Posts: 46




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« Reply #10 on: June 14, 2014, 10:23:41 PM »

It worked good today. I went mobile with my 2 meter loop and 6 meter whip to make some contacts in the contest. I actually only made 1 contact on 2m SSB about 200 miles away. But 6 was good-it busted open for a little while and I worked several grids(and states). Here are pics.





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