[time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

Tom Holmes tholmes at woh.rr.com
Thu Apr 21 17:33:02 EDT 2016


Ryan...

I've done a lot of tower work over the years, and have taken down quite a few antennas, which of course meant removing whatever seal was used and separating the connector halves. I have never found an N connector seized. Usually a gentle twist using a pair of pliers will break the sleeve loose. And I should point out that you don’t need to torque the sleeve any more than gently when you mate the halves. Too much torque will distort the internals and possibly damage things, or at least make the inherent SWR bump a bit worse. 

Frankly, I would be concerned about the anti-seize compound migrating into the inner workings of the connector and adding a bit of loss, which is another reason not to use it. I'm not a big fan of the greases that are suggested for use inside of connectors as a way to keep moisture out, again because of their affect on the losses at 1575 MHz.

My observations with various types of coax, such as Belden brand RG-8 and RG-213, as well as Andrew Heliax is that even after 30 years outside in Ohio weather, the outer jacket holds up quite well. Unsupported sections of the RG types of coax that can flop around in the wind sometimes show cracks and splits from years of flexing, however. The occasional punch through from lightning has been found as well near the tops of 100' towers.

Don’t get too uptight about the cabling; just do your best to make it neat, reasonably well sealed (you are putting it in a pipe outside, that's very good), and keep the bend radii gentle and you'll be fine.

Have fun!

Tom Holmes, N8ZM


-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Ryan Stasel
Sent: Thursday, April 21, 2016 1:08 PM
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Subject: Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

All, 

Really awesome answers, thanks! 

For the sealing question, it was more of a “should I bother with something like anti-seize” or the like on the actual thread-thread N interface. The actual connector crimp, was planning on just using a couple layers of the heat-shrink with adhesive. That is all going to be internal to the mast anyway, so direct weather contact should be minimal. It’s also on the side of my chimney, that gets very little to no direct sun, so UV exposure should be minimal. But good note on that regard. 

Pete, thank you very much for the info wrt the antenna and amp, and also the fact the Trimble starter kit came with RG6. I’m going to see what my seller wants for LMR400, but otherwise, I’ll just use RG6. It’s certainly easier to handle. I did find some datasheets on the stuff that Home despot (har har) sells (Southwire (http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM80)). I swear I have a box of Belden somewhere, but I can’t seem to find it. 

Thanks again! 

-Ryan Stasel

> On Apr 21, 2016, at 06:02 , paul swed <paulswedb at gmail.com> wrote:
> 
> With respect to sealing. Everyone has a method.
> I use what I learned in the Navy. I could see how well the connections held
> up in the worst conditions sun cold heat wet humidity...
> Layer of rubber tape
> scotch kote
> Layer of plastic tape
> scotch kote
> If done well the connector releases just fine even after 5 or more years. I
> want to say 10. But then woodpeckers have a way of shortening the life of
> connectors and coax.
> The approach is really layers and the top to deteriorate over time...
> But as I say everyone has their own approach.
> Regards
> Paul
> WB8TSL
> 
> On Wed, Apr 20, 2016 at 9:03 PM, Ryan Stasel <rstasel at uoregon.edu> wrote:
> 
>> Bob/Paul,
>> 
>> Thanks. And there's the rub... Who knows what the specs are on "generic"
>> RG6 QS. I'll see what my seller wants for their LMR400, but otherwise yeah,
>> RG6 is just easier. I have both compression and crimp connectors for it,
>> including some RG6 N-connectors (yeah, they're probably for LMR300, but
>> they work).
>> 
>> Other question: any tips for the exterior N connection? I can
>> "weatherproof" the actual cable-connector crimp, but I'm curious if anyone
>> bothers to "lube" the N connector to keep moisture from otherwise seizing
>> it up.
>> 
>> Thanks!
>> 
>> Ryan Stasel
>> IT Operations Manager, SOJC
>> University of Oregon
>> 
>> Sent from my iPhone
>> 
>>> On Apr 20, 2016, at 17:00, Bob Camp <kb8tq at n1k.org> wrote:
>>> 
>>> Hi
>>> 
>>> RG-6 Quad Shield should be fine as long as it’s meeting the published
>> specs. The advantage of LRM-400 is that you likely *know* where it came
>> from and what the specs are.
>>> 
>>> If you decide to split the antenna between GPSDO’s, a powered splitter
>> is a really good idea. Each time you split another 2 ways, you loose 3 db.
>> Get at least a 4 way splitter ….
>>> 
>>> Bob
>>> 
>>>> On Apr 20, 2016, at 4:41 PM, Ryan Stasel <rstasel at uoregon.edu> wrote:
>>>> 
>>>> All,
>>>> 
>>>> I’m going to be installing a “permanent” antenna at home, and will need
>> a run of about 100ft to get from my workstation, to the mast I’ll be
>> mounting the antenna on (Symmetricom 58532A). I’ve seen some indication
>> that both the antenna and the Trimble Thunderbolt won’t have any issues
>> with running over 75ohm cable, but thought I’d ask the “experts” whether
>> I’d be better off with some RG6 Quad-shield, or LMR400 (I’ve got a local
>> source that doesn’t know what LMR400 is, or what it’s worth)?
>>>> 
>>>> Obviously I’d prefer to run and crimp RG6, but if I’d be better off
>> with LMR400, I’d rather run that now than go back into the crawlspace
>> again. =)
>>>> 
>>>> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near
>> the T-bolt so I can experiment with other GPS(DO)s as well (especially one
>> of the JRMiller boards I bought and built (but never finished) ages ago).
>> Which brings the question, will the T-bolt provide the oomph needed to
>> power that splitter and the antenna over that length of cable?
>>>> 
>>>> Thanks!
>>>> 
>>>> -Ryan Stasel
>>>> 
>>>> 
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