[amsat-bb] LMR-400 direct to antenna or no?

w4upd updwrb at bristor-assoc.com
Fri Apr 1 13:40:45 UTC 2016

As I mentioned before, I used 9913 (rigid) for years without a problem. 
After taking the arrays down, I was able to reuse some of the 9913. The 
9913 I had, had a large solid center conductor. By doing a loose spring 
type of installation around the mast and boom, there was very little 
flexing of the cable. This only adds about 2 - 4 foot to the length of 
the cable.

I did this to keep the number of connectors and connections down 
(especially on 70cm) to reduce cable loses. The more turns (for example 
maybe 4) the less flexing of the cable will occur.

Again, just my 2 cents, but the installation mentioned above was very 
successful for years. If I ran into any problems it was due to the 
"known" problem of water getting into the 9913. However, I had little 
problem with that as well.

If the runs are short (less than 50') you could use other methods which 
requires additional coax fittings and barrel connectors. My goal was to 
prevent that. I would still recommend a preamp on 70cm at the mast to 
over come any installation. I found it to be a good addition, especially 
if we get any HEOs up or for near AOS or LOS operation, trees or weather.

Reid, W4UPD

On 3/31/2016 11:33 PM, Glen Zook via AMSAT-BB wrote:
> Use LMR-400 around the rotor if you want to have to replace the cable every few days!LMR-400 has a solid center conductor and it will definitely break after being "flexed" for not that many times!Frankly, for short runs like around rotors and to most antennas, plain old RG213/U works fine and the loss is very low.  Run the LMR-400 up to just below the rotor and then install the RG213/U the rest of the way.I use either 1/2-inch Heliax or 7/8ths-inch Heliax for almost all my antenna runs from 160-meters through 70 cm.  Where a rotor is involved, the Heliax goes up the tower to just below the rotor and then RG213/U the rest of the way.  Most of the antennas have been "up" for a pretty long time (decades) and they are working just as well today as they did when first erected. Glen, K9STHAMSAT 239 / LM 463Website: http://k9sth.net
>        From: Scott <scott23192 at gmail.com> To: amsat-bb at amsat.org  Sent: Thursday, March 31, 2016 8:35 PM Subject: [amsat-bb] LMR-400 direct to antenna or no?   I hope to put up my first rotating antenna soon and just received a nice length of LMR-400 to use. (regular, not "super-flex")
> Having never seen LMR-400 before, I did not know how flexible it would be.  I would call it "medium"... not stiff as a pipe but not floppy, either.
> My question is whether anyone using LMR-400 can recommend whether I should attach it directly to my antenna (with slack loops, of course)?
> Or, should I get a few meters of something more flexible to attach to an antenna that needs to be free to rotate 360 degrees?
> If a jumper is recommended, I would appreciate suggestions on what cable would work best for the task.  The frequency for this project is 70cm.
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