[Towertalk] Coax Connecter Losses - Dose anyone know?

[Dale L Martin]

>From NCJ, July/August 1988

Coax Fittings Redux
by Bill Schrader, K2TNO
(Reprinted from the TDXS Bullsheet, April 1988)

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.

==========================================

> Dose anyone know what the loss introduced into the circuit  is
> from the use
> of these connectors?
>
> My interest is in the RF range from 1.8 to 30 MHz.
> The connectors all nickel plated.
> I would like to information about a:
> PL-259
> PL-258
> SO-239
> 85-877
> PL-259 90 degree (Can't find the stock number)
> PL-259 Tee (Can't find the stock number)
>
> As a side note I called Amphenol for this information. The person
> I spoke to
> was very friendly but unable to provide me with any information.
> The comment
> from someone he spoke to was that the loss was insignificant within the
> frequency range up to 300 MHz. The connectors were tested many
> years ago but
> the results are not available.
>
> If it hasn't already been done this might be a good project you someone
> going to MIT.
>
> Rich AA2MF
>
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