[time-nuts] RG 6 U couplings

Mark Spencer mark at alignedsolutions.com
Mon Dec 7 16:58:36 EST 2015


Yep.   I used to worry about eliminating potential error sources such as that from my home lab.   On the flip side the Teflon cable I used did have a defined spec vis a vis behaviour in a fire that gave me some comfort when routing it thru my house on the way to the roof mounted antenna.   I also had it on hand.

Many items to consider.

If I was doing it again I'd probably just use 75 ohm RG6 CATV style cable with an appropriate fire rating for indoor / in home installations.   The local electronics store sells nice F female to (apparently 50 ohm) N male adapters that ease the interconnection issues if you can live with the impedance miss match.

Sent from my iPhone

> On Dec 7, 2015, at 11:23 AM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
> 
>> On Sunday, December 06, 2015 10:02:43 AM Mark Spencer wrote:
>> I've seen data re delay vs temperature for high end 50 ohm cables.  I've
>> never seen it for 75 ohm CATV style cable.
>> 
>> Back when I was into time nuts pursuits this was one of the main
> reasons I
>> was contemplating switching my GPS antenna feed line to hardline.   I
> never
>> made the change but still have the hardline.
>> 
>> To this day I still use Teflon RG58 style cable (purchased surplus from
>> Boeing decades ago) for my GPS antenna fee line to the splitter.   I
> doubt
>> I will ever change it out.
>> 
>> Sent from my iPhone
>> 
>>> On Dec 6, 2015, at 4:21 AM, Attila Kinali <attila at kinali.ch> wrote:
>>> 
>>> On Sat, 5 Dec 2015 17:06:03 -0800
>>> 
>>> Mark Spencer <mark at alignedsolutions.com> wrote:
>>>> Over the years I've used a number of CATV style 75 ohm patch cords
>>>> with F connectors, F female to female couplers and F to other
> connector
>>>> adaptors to distribute gps signals from my GPS splitter to various
>>>> receivers.   I've never been able to notice any difference in reported
>>>> signal strength vs using "brand name" 50 ohm coax with N
> connectors.
>>> 
>>> Well, putting the numbers into a calculator gives:
>>> VSWR: 1.5
>>> Load Return loss: -14dB
>>> Load Mismatch Attenuation: -0.2dB
>>> 
>>> I'd say that for a receiver, this is quite negligible. Heck, even 1dB
>>> loss wouldn't hurt too much. I would suggest, that for all practical
>>> purposes, the use of (good) satellite coax cable would be more than
>>> good enough for most of us. The only thing i'm not sure about is how
>>> the delay through the cable behaves over time (aging, temperature,
>>> humidity). If anyone has some data on that, for different types of
>>> cables, I
>>> would appreciate getting a copy :-)
>>> 
>>>           Attila Kinali
>> 
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> Teflon has a phase transition around 20C or so.
> Consequently its phase stability isnt stellar near the transition.
> Polyethylene insulated cables are superior in this regard.
> 
> Bruce
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