[TowerTalk] N or UHF?

[Ian White GM3SEK]

Jim Lux wrote:
>At 02:12 PM 10/16/2006, Dan Hearn wrote:
>>Roger, I have heard of problems with N connectors on the end of long cables.
>>There is reportedly a different thermal expansion  between shield and center
>>conductor which tends to pull the center pin out of the socket. Apparently
>>the UHF jobs are more tolerent of this. 73, Dan, N5AR
>
>
>This would depend on what sort of N connector you are using.  The
>ones with the captive pins won't have the problem.
>
They can have, it the end force is large enough.

>The other connector you might look at is DIN-7/16  (I think that's 7
>and 16 mm, not 7/16").

Yes, 7mm center conductor ID and 16mm shield ID. Those two dimensions 
give almost exactly 50 ohms.

> Better high power handling AND good impedance
>characteristics AND waterproof.

In short - more ruggedness than UHF, more performance than N. Somebody 
sat down with a clean sheet of paper and a list of everything that's 
wrong with existing connectors... and this time they got it right.

I was forced into using 7/16 on the 432MHz moonbounce system because the 
N connectors on the rotator loop started burning out when I upgraded to 
a GS35 amp. Everything had been fine for several years at the 800W 
level, and Ns in the shack were still OK at 1.5kW, but at the higher 
power level they didn't have enough margin to handle the more difficult 
operating condx out at the antenna.

With 7/16, no more problems.

>They're kind of expensive from
>suppliers like RF Parts, but you might find a less expensive
>source.  I've seen them in the $20 range, and you'll find surplus
>jumpers with DIN on both ends for even less.
>
7/16 connectors are widely used in the cellular industry around the 
world, because they have lower intermodulation products than N. As that 
industry continues to expand and upgrade, 7/16 hardware is already 
starting to appear as surplus - often at very low prices, because it's 
"too big" for most people.

This is definitely the one to go for, rather than HN, which has always 
been rare and will only become rarer. 7/16, on the other hand, will 
continue to become more common.

Coming back to K8RI's original question, he should be fine with N 
connectors at 144, up to the US legal limit. But do take the trouble to 
find modern connectors with a captive center pin and pressure-sleeve 
cable clamp; and the same applies to BNC.


-- 
73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek