R: [TowerTalk] In Search of 2db

[Maurizio Panicara]

When losses are concentrated in a constrained area (or surface), like a
connector or a joint, that part is voted to suffer an irreversible damage
and become relatively easy to find out when fixing the occurred failure.
When losses are in a short coax jumper, cable heating is a sympton even if
I'm less convinced is always so easy to check by touching what's often not
so easy to reach (ie up to a tower or taped to an antenna boom).
When losses are distributed along a consistent run of cable, the perception
of a noticeable heating is the already the sign of a big loss that's surely
exceeding the "famous" 2 dB amount.
The amateur power levels, the SSB and CW duty cycles (some 30% and 50%), a
different amount of loss along the same cable (i.e. the outside cable runs
age is bigger than inside) togheter the heat dissipation to the external
ambient of a cable that's generally laying straight, may be outside,
contribute to minimize the perception of the actual losses.
My point stay that the best way to define the real losses is always to
measure and not to trust (what?) by individual feelings.
Concerning cable losses, I dont know why but measuring actual losses of long
runs of RG 8 (213, 58, & similars) and same lenght of professional type
coax, the result indicated differences are much bigger than it's reported in
conventional tables.
Also what's the inpact in adding 2 dB gain (or by recovered losses) to an
antenna system can't be discussed and should be experienced before talking
and trusting own point.
As an active contester, I'm very happy a large number of people strongly
believes to extimated cable loss and never test, doesn't believe in cable
loss by aging and considers a 2 dB gain (or the better NF obtainable) always
neglectables.

73,
Mauri I4JMY

(....probably, it was not my self-interest to post last two rows)




----- Original Message -----
From: Fred Hopengarten <k1vr@juno.com>
To: <towertalk@contesting.com>
Sent: Friday, May 26, 2000 5:57 PM
Subject: Re: [TowerTalk] In Search of 2db


> Query. I have a two radio station with a lot of 50 ohm jumpers. It
> works, honest. But some jumpers were assembled in the middle of the night
> by tired operators. Some are 30 years old.  I doubt any of them was done
> as well as W0UN or KC1XX would do it at his work bench. No jumper is
> longer than 10 feet. See configuration below (which should look similar
> to a lot of stations). What method do you recommend to test RG-213 or
> RG-58 jumpers? Any chance I can pick up 1 dB by finding a "bad" jumper?
>



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