[Antennas] Feedline question (please bear with me, this might get long)....

Sun Oct 12 20:09:14 EDT 2008

The mismatch at HF and 6 is not worth bothering about.....EVEN AT UHF, we
did that YEARS ago on a 440 rptr site with 3/4in CATV line (which has lower
loss than same size 50ohm stuff!)....Dont feel like Al Bundy (I feel like
Charlie Brown a lot of times...and share his initials! ;) As to connectors,
I used BRASS Union compression fittings....1/2in to the PL259 and whatever
size of the hardline was on the other end of the compression...just make
sure the center conductor is CAREFULLY cleaned...it is copper clad
aluminum.....I used a BIG soldering iron (200+ watts) and heated the center
conductor after using a tubing cutter on the shield.....then as the center
heated up, the foam glued to it let go and the whole thing pulled off....a
wipe with a solvent to remove the remaining glue/foam and you're set for the
connector...
OR Gilbert Electronics in AZ sells AL Type N and UHF connectors for CATV
hardline...they aren't cheap though...forget the RG6......I would not use it
if I have the hardline....besides the power handling/lower loss of the
hardline is a win hands down!
GO FOR it and enjoy!! Your gear likely wont see any difference....if it
DOES, you somehow HAVE hit the wrong spot where the SWR may be max
(1.6:1).....if so, trim, recut, reconnect and you're back to the airwaves...
A lot of the folks on eham have egos bigger than their pants size....and
that's BIG!!!!!!
Chris
WB5ITT
PG-9-5322 FCC Commercial
Society of Broadcast Engineer member
(and a ROLM tech to boot....so I have a connection with you at IBM :)
-----Original Message-----
From: antennas-bounces at mailman.qth.net
[mailto:antennas-bounces at mailman.qth.net] On Behalf Of bonddaleena at aol.com
Sent: Sunday, October 12, 2008 6:11 PM
To: antennas at mailman.qth.net
Subject: [Antennas] Feedline question (please bear with me, this might get
long)....
Hi. Long time subscriber, first time poster (I think...) I got about 
1/2 way through my 'question, when my 'el cheapo keyboard decided to 
stop producing the letter 'e'.....
I swear, sometimes I feel like Al Bundy, trying to use this bloody 
computer. AND, I retired from IBM!
So here goes. By the way, when I ask these kind of questions on eHam, I 
usually get insulted or 'flamed'.
I am in the process of re-erecting 2, or maybe 3 towers here in North 
Florida. I have had these towers in many different locations (used to 
work for IBM) (I've Been Moved).
So putting the towers up, is actually fun, even at 62 yrs.
My 'main' tower will have a M2 6M7JHJ at about 100' (we have some TALL 
trees here!). Above that, 5' or 6', will be a single KLM 16LBX for 2 
Meters. OK, simple so far.
Here is my 'question'. The feedline for this tower (as well as my 
others) will be CATV Hardline. I have (believe it or not) THOUSANDS of 
feet of the stuff. All brand new, made by Commscope. Never been off the 
spool. It ranges from 5/8" to 1 1/4' diameter. I have used this type of 
cable in the past and it is excellent. It is non-hygroscopic, so water 
ingress is no problem.
In the past, I have run 7/8" hardline to just below the rotor and then 
went to 9913 around the rotor, to the antenna connectors.
OK, let me make some statements. (no boast, just fact).
- I have a complete Machine / Welding shop here. I make 'adaptors' to 
mate the CATV stuff to coax. I had them swept back in the EMC Lab in 
Lexington Ky. There were good through 1296.
- I understand the different impedance 'bump' going from 75 ohm to 52 
ohms below the rotor and to the antenna. This is NOT a problem! 
However, I do NOT want to get in the hassle of measuring exact 1/2 
wavelenghts of coax, etc.
- Barefoot, the Drake TR-6 and the tuner in the 756PRO handle this 
perfectly. So far, so good.
- I also have a HUGE 6M Linear that can also handle a wide mismatch.
- NOW the question.... I have access (free) to some VERY high quality 
Commscope RG-6 Quad coax. Brand New. This stuff is rated to 2+ GHZ. I 
was thinking today, as I was assembling the above antennas, why can't I 
use the RG-6 to go from just below the rotor, to the antenna feed 
point? That way it will be 75 Ohms all the way... I had been 
contemplating buying some NEW Belden 9913F7. I have a lot of the 
original 9913 (from the 80's), but don't want to do this twice!!! It's 
old and has been stored outside. I have the 'professional' tools to put 
the connectors on and waterproofing is easy. Even thought about buying 
RG-11. However, I am on a limited budget and would prefer to use the 
available (free) RG-6 Q.
- Now you're asking yourself, what is the power handling capacity of 
the RG 6 Quad? Well, let's consider this.... M2 uses RG-59 and 'F' 
connectors on the JHV and it's rated at 1500 Watts.
- The 2 Meter antenna will only have to withstand 200 Watts. However, 
on 2 Meters, I will be putting my mast mounted GaasFET preamp just 
below the rotor. I have not yet decided if 2 Meters will use 7/8" or 
5/8" CATV Hardline...
The stuff is really easy to work with.....
My questions are: will the RG 6 cable handle the repeated flexing 
around the rotor? I can put in a LARGE loop. Would I be better off 
getting some 9913F7? LMR is out, 'cause I don't see the advantage for 
such short runs, versus 'special' connectors.
- all the antennas use 'N' connectors......Easy.
Post: mailto:Antennas at mailman.qth.net