hi Frank et al.
preparing our last year's CR3L contest activity in the CQWW-CW, we wanted to
try a remote RX-antenna to work in-band multipliers as DM6V in the
WAG-contest at DL5AXX's qth... naively following the formula that quartering
the frequency will half the attenuation Ulf ordered 500m of 75 Ohm CCS -TV
coax promising about 15db loss at 500MHz per 100m... the calculated loss of
about 10db for the Windom 400 m away was expected to be tolerable for our
purpose...
when we didn't hear literally anything on our RX-antenna we first thought of
a faulty connector, but the SWR, totally flat at 1.5 (75 ohms) from 160 to
10m, made us suspicious and measuring the SWR into one (unbroken) 100m piece
(open at the end) showed that the cable was responsible for the high
losses... when taking a 100m bobin home for more exact measurements, at 30
MHz the attenuation was measured as 17db at 14MHz, 15 db and 8 db at 1.8 MHz
... no wonder that we couldn't hear anything at the end of the 400m feed
line... as at 100 MHz the attenuation was 19.5 db, well above the promised
15 db at 500 MHz, we returned the cable to the distributor and hoped for
reimbursement...
to be fair, the cable was very cheap (< 20 EUR/100m) and we simply had to
pay the price for saving the wrong way...
we were almost determined to order 500m of H155 and pay a lot of money when
I found a promising CCS-TV-cable in the catalogue of another distributor in
Germany... at the price of EUR 25/100m the catalogue specified an
attenuation of 5,64 db/100m and I had another try... with 6.1 db at 100 MHz
it was pretty close to specifications and the losses (measured with my
miniVNA ) for 100 m were 4,8 db on 30 MHz , 4.4 db on 14 MHz and 3.3 db 1.8
MHz , not very far away what you listed in the table in a recent e-mail and
clearly better than the expensive H155 we were going to buy at three times
the price...
CONCLUSION: there are enormous differences in the quality of 75 ohms-CCS-TV
cables in the low price segment here in Germany (presumably all made in
China)... TV-cables are very rarely specified as RG-6 here and I wonder if
there are standard specifications for RG-6 just as for RG-58 or RG-213
etc.... furthermore we learned (the hard way) that - obviously due to the
characteristics of CCS-wire - the attenuation/frequency ratio is very
different from that of our common 50 ohm coax with inner conductors of solid
(or stranded) copper... before ordering a long run of TV-cable first I'll
always try a sample...
hoping that our experience will perhaps prevent others from making the same
mistake...
73
Uli, DJ2YA
----- Original Message -----
From: <donovanf@starpower.net>
To: "topband" <topband@contesting.com>
Sent: Thursday, January 24, 2013 3:28 AM
Subject: Re: Topband: Measured RG-6 Loss: Solid Copper vs. Copper Clad
center conductor
Hi Mike,
Obviously I had computers on my mind...
Yes, of course I meant to say quad-shield RG-6 CATV cable. I'll provide
the manufacturers and part numbers in a subsequent e-mail, but its just
typical inexpensive ebay RG-6 CATV cable.
Inexpensive RG-6 with a copper clad steel (CCS) center conductor is much
more widely available than solid copper, especially in desirable options
such as a tough polyethylene (PE) jacket and flooded RG-6. CCS looks like
a reasonable choice except for very long cable runs on 160 and 80 meters.
A copper clad center conductor may be a problem if a device (e.g. a preamp
or relay) is remotely powered through the coaxial cable.
73
Frank
W3LPL
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Topband Reflector
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