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[TowerTalk] Low Loss Coax

To: <>
Subject: [TowerTalk] Low Loss Coax
From: (Dale L Martin)
Date: Wed, 9 Jan 2002 19:06:21 -0600

 Is it OK to fit a 90 degree connector? What sort of
> loss would
> there be? I have hear mention of 1.5db per connector?
> --
> George Shaw
George (and others),

(I have been waiting and waiting for someone to ask that question)

This is from the April 1988 Bullsheet, newsletter of the Texas DX Society

Coax Fittings Redux
by Bill Schrader, K2TNO

I've always fallen for the old adage that says that UHF coax fittings add
losses and should be kept to a minimum.  Recently, I had occasion to clean
out my tool box (after ARRL Phone at NR5M) and found 5 right angles, 4
barrels, 3 double-males, and several short lengths (1-3 feet) of RG-8X.  I
decided to test this adage by connecting up this wild assortment of coax
fittings into a plumber's delight series arrangement and then checking the
loss and SWR problems on several frequencies.

The test set up consisted of my TS-930S or 2-m rig feeding a dummy load with
a Daiwa power meter as the indicator.  I measured RF power at 14, 28 and 144
MHz using either rig wired directly to the load or when fed through the mess
of fittings.

The connections were made at random, simply to use up as many fittings as
possible.  When done, there  were 17 male-female coax joints in the line, as
opposed to two male-female coax joints when feeding the dummy load directly.
Thus the results below show the additional loss due to the 15 coax joints.

Frequency   Attentuation (dB)   SWR Change
14          Not Detectable      Not Detectable
28          0.3                 +0.1*
144         2.0                 Not Measured

*SWR was 1.1:1 with coax only; this value increased to 1.2:1 when the series
of joints was added.

The results show that UHF coax fittings themselves add negligible loss in
the HF spectrum and are surprisingly good even at 144 MHz.  Thus, for HF
purposes I conclude that addition of right angles, jumpers, etc., does not
add significant additional attenuation or reactance.  Rather, it is
certainly the coax length itself which causes the biggest losses.

Caveats:  Coax joints are deleterious for reasons other than their possible
RF loss characteristics.  These include:
   1) The PL-259s are frequently assembled and soldered incorrectly.
   2) UHF fittings are not waterproof.
   3) The fittings corrode if used exposed outdoors.
   4) They come loose.


dale, kg5u

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