[TowerTalk] connector losses

[Danny Pease]

I have to agree, a connector that has any measurable loss will get warm. I
was told by one of our RF engineers many years ago that at UHF and 900 MHz
we should expect as much as  .1 dB loss for each connector inserted into a
path. Measurements with decent lab grade equipment did not even show that
much at 960 MHz. Any time a connector got warm, it was usually bad. I have
never been able to measure loss on even cheap connecters at HF unless there
was  a problem.

 

I seen some smaller connectors get so hot they would melt the dielectric on
cheap N connector barrels and 90 degree connectors and actually seen BNC and
TNC burn up with several hundred watts of 960 MHz RF, even with a  matched
load. A good quality connector is a must for higher power at UHF and above,
not quite as important at HF. Junk connectors are a different story.

 

We started having N connectors fail after a few years in the field on 500
watts 900 MHz paging systems, so they fix was to use 7/16 DIN connectors on
the 500 watt transmitters.

 

NG9R

 

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Message: 2
Date: Wed, 03 Nov 2010 05:16:58 -0400
From: "Roger (K8RI)" <K8RI-on-TowerTalk at tm.net>
Subject: Re: [TowerTalk] Andrew CNT-240-FR
To: towertalk at contesting.com
Message-ID: <4CD1288A.7020005 at tm.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed



On 11/3/2010 1:25 AM, Jim Brown wrote:
>> Add 0.25-0.50 dB for any connectors/adaptors if used above 50Mhz
> This is another one of those old wives' tales that has no basis in fact
I can vouch for that Jim., I've mentioned a number of times on here
about the number of connectors I have in the system.
Once I leave the tuner, I have the connector on the tuner (1), a cable
to the patch panel (2 more) bulk head connector on the patch panel (1),
LMR 500 to the 6-pack at the base of the tower (2) connectors going
through the 6 pack (2) not counting relays inside.  Jumper to bulkhead
connector on hoffman box (2). Bulkhead connector (1) jumper to Grounded
bulkhead connector at bottom of tower (2), bulk head connector (1) 100'
of coax to the top of the tower (2)  bulkhead connector (1),
pigtail/rotator loop from bulkhead connector to antenna (2) connector on
antenna (1)
Now these antennas can be fed from either the house or shop through the
6-pack for SO2R although it works equally well for 2O2R

That's a total of 20 connectors between the back of the antenna tuner
and the antenna terminals for each run.  I have one run for 160, one for
the 6-meter yagi, one for the 40 meter yagi, and one each for 144 and
440.  That's a total of 5 runs ALTHOUGH there is the side mounted
144/440 antenna at 50' and two remote antenna switches for the sloping
dipoles.

On the air tests between a single run with all those connections or a
nearly continuous run to the tribander that was up there using antenna
switches to switch back and fourth showed no discernable difference on
receive or transmit.

IF there was some difference even a quarter db with each of 20
connectors would give 5 db, or for all practical purposes a full S
Unit.  At a half db each I'd be looking at 10 db difference or basically
the same as turning my amp on or off on transmit which would certainly
be noticeable.  It wasn't!

73,

Roger (K8RI)



 - Release Date: 11/03/10