What kind of losses do you expect to sustain with a couple of connectors,
Gordon?
I think you may have more to worry about with the feedline loss than with
the insertion loss from a couple of connectors. LMR-400 at 1000MHz shows
4.3 db loss per 100 feet.
Check this out...
73, dale, kg5u
This article appeared in the July/August 1988 National Contest Journal and,
before that, in the April 1988 TDXS Bullsheet newsletter.
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.
==========================================
>
> Another question...I know it may not be ideal, but with a
> generous loop, can I use this type of cable around a rotator
> and avoid the losses from a set of connectors and the
> flexible jumper? My total runs are about 40-60 ft and below
> 1300 MHz. Alternatively, should I use the flexible version
> of LMR400 instead?
>
> Thanks &73,
> Gordon, w2TTT
> 201.314.6964
>
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