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

Mon Oct 13 02:04:07 EDT 2008

Hi guys:
I'm usually not much of a writer but this time you hooked me.
Years ago we ran tests of the kind Bob did at Tadiran Communications with
basically the same results.
Somebody explained to us at the time that there is a physical phenomenon
that causes rigid wires to absorb part of the bending or vibration energies
and cause the structure of the wire to change from amorphous to crystalline
and brittle. His dicta was:" if it doesn't droop from its own weight, it's
not flexible enough!"
Sooo, according to the gospel, it you can, use VERY flexible sections for
the last stage! I assume you wouldn't like to climb the towers every few
months to replace those sections. I would consider buying a few pieces of
flexible cable a good investment. BTW, they don't have to be the absolute
best, since only short sections are involved.
Alex	4Z5KS
-----Original Message-----
From: antennas-bounces at mailman.qth.net
[mailto:antennas-bounces at mailman.qth.net] On Behalf Of Bob Nielsen
Sent: Monday, October 13, 2008 5:41 AM
To: bonddaleena at aol.com
Cc: antennas at mailman.qth.net
Subject: Re: [Antennas] Feedline question (please bear with me,this might
get long)....
I recommend that you use a coax with stranded copper wire for the 
part of the run which flexes a lot. Many years ago (for a military 
application) I ran a bunch of tests comparing RG142B (copperweld 
center conductor) with RG400 (stranded copper center conductor) and 
after few thousand flexes, the copperweld broke into a number of 
small pieces. I'm not sure how solid copper center conductor would 
hold up, but it would probably handle the flexing better than 
copperweld.
Bob, N7XY
On Oct 12, 2008, at 4:10 PM, bonddaleena at aol.com wrote:
>>> 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.
>>> Your opinions, PLEASE?????
> To save bandwidth. you can reply to me 'off line':
>> bonddaleena at aol.com
>> or
>> n4ue at arrl.net
>> thanks!!
>> ron
>> N4UE
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