----- Original Message -----
From: "Steve Katz" <stevek@jmr.com>
To: <ron.stordahl@digikey.com>; "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
Cc: <towertalk@contesting.com>
Sent: Wednesday, April 19, 2006 4:30 PM
Subject: Re: [TowerTalk] Power limitation for N-Connectors
> Ron, the Andrew N connectors for LDF5-50 do have captive center pins, they
> don't make them any other way. The problem discussed doesn't occur with
> Heliax, it occurs with flex cables that use connectors having separate
> center pins. You can always use captive pin type Ns on the RG-213/U or
> whatever flex cable you'll be using. Just buy them that way. They're
> available from many sources including Amphenol, Delta, Kings, Trompeter,
> et
> al.
>
> -WB2WIK/6
>
> -----Original Message-----
> From: Ron Stordahl [mailto:ron.stordahl@digikey.com]
> Sent: Wednesday, April 19, 2006 1:31 PM
> To: Ian White GM3SEK
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Power limitation for N-Connectors
>
>
> The consensus is that N connectors are fine at 1500 watts up to 30 MHz
> (and probably beyond but my use is 30 MHz or lower). My problem with
> N-connectors in the past, and it's a distant past, is in assembly..maybe
> I had some bad ones. And I am from the old school...like to use
> solder. But if the compression connection for the shield is good enough
> and long lasting..apparently it must be..then fine.
>
> The cable will be LDF5-50A which is foam.
>
> Is there a certain connector which has a 'captive center pin' as you
> mention?
>
> My plan would be to use female connectors on the heliax, then male
> connectors on the more flexible jumpers at the ends, probably short
> length of 213.
>
> Am I on the right path?
>
> Ron Stordahl, N5IN
>
> Ian White GM3SEK wrote:
>> Steve Katz wrote:
>>
>>> I'd say they're wrong.
>>>
>>> Type Ns flashover at >3000V at STP, and that's a lot of voltage. The
> center
>>> pin can handle 6A continuously, probably 12A intermittently. 1500W is
> 5.48A
>>> in a 50 Ohm system. 1500W is 273.9V in a 50 Ohm system.
>>>
>>> I don't see the issue. I've used type Ns at 1500W output power on 70cm
> for
>>> eme work, and never had one fail...
>>>
>>
>> There is no problem with correctly assembled N connectors at these power
>> levels; but there is a risk of failure if the centre pin is not mated
>> correctly.
>>
>> This can happen when N connectors with a floating centre pin are used
>> with semi-airspaced cables whose centre conductor is free to move
>> inside the cable. A hanging length of cable, and/or some flexing in a
>> rotator loop, can sometimes pull the centre pin partly out from its
>> socket, causing high resistance (especially at UHF where skin depths are
>> smaller) and failures at high power.
>>
>> The solution is always to use connectors that have a captive centre pin,
>> and to take care when installing cables that have a floating centre
>> conductor.
>>
>>
>>
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