[amsat-bb] LMR-400 direct to antenna or no?
ko6th.greg at gmail.com
Sat Apr 2 03:45:33 UTC 2016
I understand the desire for minimal use of connectors, but the coupling
between the rigid cable coming from the shack to the rotor, and the flex
cable going to the antenna, is a good place to put a nice little
preamp. Think of it as a barrel connector with attitude. Yes, putting
it at the antenna feed point is better, but unless you're working EME,
the practical difference is pretty small.
Your luck with 9913 and water ingress is significantly better than mine
ever was. I had one 60' run that kept getting worse over time. It got
so bad that I drilled a hole in the lower end connector so I could suck
out the water until I could find some hardline to replace it. Never
used the stuff ever again.
> 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
>> 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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