[ICOM] Re: IC-746 w/ No output/high SWR on 6M

[David J. Ring, Jr.]

Loose PL259 - readers are urged to notice the little sharp rises on the 
circumference of the mating surface of the round base (out of which the pin 
sticks out from the middle) on PL259s.  They are 180-degrees apart from each 
other.  These little sharp rises fit into a mating notch in the SO-239 
mating connector - and if they are not correctly mated, the connection of 
the grounding shield is very much impaired as the two circumferences of the 
mating bases of each side is degrated into just the contact of the little 
sharp rounded pin resting on the base of the female connector - 
unfortunately the majority of the bases of the two connectors do not touch.

When the little notches and rises mate, the entire circumference of the 
connectors join - a much better connection for the entire connector 
results - the grounding takes place over a greater area and the center pin 
has deeper and full penetration into the SO239 resulting in less ohmic loss.

I've discovered many such "connections" in service work in the field in 
commercial radio repair.

What often happens is that the SWR becomes intermittant.  There is low SWR 
on low power, but at high power, the SWR increases due to the poor 
connection.

Increasing SWR with power also might indicate failing (or components such as 
in an ATU (Antenna Tuning Unit) which are failing or arcing under the stress 
of the high impedance transformation taking place.  Some antennas produce 
very high voltages when matched to a 50 ohm coax line, and when high power 
is applied to these antennas, the matching units can be under tremendous 
stress due to high voltages.

While I'm offering my "dandy tips for coax connectors" - those problems 
which outsmarted me at first, I'll add another one that baffled me.  Off 
color or carbonized SO-239 / PL259 phenolic insulation - this usually 
happens with non Amphenol connectors.  The yellow turns blackish - as might 
happen if the ATU failed and the tube amplifier tried to "match" the high 
impedance antenna.  The insulation had partially carbonized resulting in 
intermittant and "curious" problems.

73
David N1EA


----- Original Message ----- 
From: "Gary Nichols" <kd9sv at comcast.net>
To: "'ICOM Reflector'" <icom at mailman.qth.net>
Sent: Tuesday, February 07, 2006 10:28 AM
Subject: RE: [ICOM] Re: IC-746 w/ No output/high SWR on 6M


I have also had that same indication (on all bands) that was caused by a
"Loose" PL259 connector on my antenna switch.  Tightened it and problem went
away...de gary, kd9sv

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of gfiber at comcast.net
Sent: Tuesday, February 07, 2006 10:18 AM
To: ICOM Reflector
Subject: Re: [ICOM] Re: IC-746 w/ No output/high SWR on 6M

Mac,

Don't overlook the coax cable feeding the antenna. I once had some coax that
the shield had corroded to black and it was opening under transmit. I would
be chatting along on 10 meters and all of a sudden the rig would fold back
in output power and the reverse power would go to almost full output power.
The antenna was a Mosley 310C.

Took me a bit to figure it out as the Drake W-4 I had always shown a good
match.

Gary K8IZ

 -------------- Original message ----------------------
From: "D C (Mac) Macdonald" <k2gkk at juno.com>
> Right now, it may be a  REAL  SWR problem with the antenna.  It looks
> good on an MFJ Antenna Analyzer, but wouldn't work with my IC-703
> either.
>
> Right now, I'm waiting for Oklahoma winds to subside so it will be
> safe for a younger ham (I'm too old to be climbing around on a steep
> roof) to take the Ringo down so we can check things out.
>
> I also have Drake WV-4, Bird 43, and Heath VHF wattmeters that I will
> use for further checking.
>
> I'll post to the list when I find out something.
> Meanwhile, thanks to all who have offered suggestions.  I don't have a
> low-pass filter in the line and no amp, either; going straight from
> IC-746 to antenna.
>
> Maybe my brain is going soft after 50 years plus of RF exposure???
>
> 73  ---  Mac, K2GKK/5
>
>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net Icom
> Users Net: Sundays, 1700Z, 14.316 MHz Icom FAQ:
> http://www.qsl.net/icom/


----
Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net Icom Users
Net: Sundays, 1700Z, 14.316 MHz Icom FAQ: http://www.qsl.net/icom/


----
Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
Icom Users Net: Sundays, 1700Z, 14.316 MHz
Icom FAQ: http://www.qsl.net/icom/


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