hi Rys,
I have been using exactly that kind of twisted wire for most of my
(unidirectional) contest beverages in the past, because of its excellent
strength (and its low price)... as untwisting comes close to the punishment
of Sisyphos I have always used the twisted pair connected together at both
ends... this gave me the chance to simply check with an ohm-meter if the
line was broken...
I have often considered to try the twisted wire in a bi-directional
configuration, but in the usual haste before the contest weekend I got stuck
with the simple version...
the controversial discussion about this type of wire caused me to find an
answer by some practical experiments with it this afternoon... a
(well-weathered) length of telephone wire left from some previous beverage
happened to be 67,25 m long (abt 220 ft.)... first of all I determined the
half-wave resonance as 1.510 MHz and a VF of abt 0.68 for that frequency...
the fact alone that the input impedance was raised to abt 75 Ohms when the
line was terminated with a 50 purely resistive load at half-wave line-length
raised first doubts... it actually didn't make any (significant) difference
if the line was suspended or lying on the (tarmac) ground... at two lambda
(6,130 MHz) the "transformation" yielded about 100 Ohms and a SWR of 2 (with
the same 50 Ohms termination)...
the quarter-wave resonance was difficult to determine with my AEA CIA-HF,
but the input impedance showed a maximum of just over 400 Ohms on 0,705 MHz
hinting at a characteristic impedance of about 140 Ohms, a value that I had
already obtained in previous measurements... at 3/4 wavelengths (2,230 MHz)
the transformation resulted in about 330 Ohms (due to the higher losses) and
a Zo of just under 130 Ohms...
the line-loss was determined by feeding a constant 10 Watts into the line
and measuring what was left of it at the far end... my IC765 does not
transmit as low as 1,5 MHz, but on 1,6 MHz 5 Watts (-3 db) were indicated...
the higher half-wave resonant lengths yielded 4,2 W (-3,8 db) on 3, 3,4 W
(-4,7 db) on 4,5 MHz, 2,5 W (-6 db) on 6 MHz dropping to 1,3 W on 12 MHz
(-8,8 db)...
without claiming scientific accuracy the attenuation of this twisted line
amounts to about -4.5 db / 100m (-1.4 db / 100 ft)... thus in a 200m (600
ft.) bi-directional beverage using this type of wire you should be prepared
to put up with a loss of almost 10 db in one direction... using RG-58 the
difference would (ideally) be about 2.5 db, while the difference with
"window-line" should be close to 0.5 db or even less (esp. with open
wire)...
for my part, I have buried the idea of using this twisted telephone wire in
spite of its excellent mechanical properties... I'll either do the job of
Sisyphos or make an open wire line of two twisted pairs...
BTW I did the tests in bright sunshine... as several others have pointed
out: rain will not help...
good luck with your experiments, Rys... it was nice to meet you personally
in Friedrichshafen... CU soon
regards
Uli, DJ2YA
----- Original Message -----
From: "Ryszard Tymkiewicz" <rtym@ippt.gov.pl>
To: <topband@contesting.com>
Sent: Wednesday, July 28, 2004 8:08 AM
Subject: RE: Topband: two wires Beverage
> First of all I would like to thank very much for all e-mails and advices.
> A few were trying such beverages and they were satisfied with them.
> Tom...wires I have got are with very thick jacket and I hope it " prevents
> water from disturbing the line".Additionally they are twisted very
tightly
> so I hope there will be not too much infuence of water.
> Well if I understand correctly even if moisture will change an impedance
> /of course not too much/ it will result mainly in not the perfect matching
> what will cause mainly in "slightly" weaker signals but if push pull
matching
> transformer is still balanced it will still works for both directions..?
> I know its not a perfect system but I have too many houses around to
> build bigger/better aerials.
> In the past /hmm..30 years ago/ I was using G5RV with 300 ohm TV line
> and it was very dependent of a moisture and mechanically rather not strong
> so maybe its worth to try this twisted wire.
> THANKS again and I let you know about results I get.
>
> 73
> Rys
>
> SP5EWY
> rtym@ippt.gov.pl
>
>
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> Topband@contesting.com
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