Hi Rich, 

Your problem is almost certainly caused by using obsolete 75 ohm 
BNC male connectors on your coaxial cables. 


During the 1960s, the easiest way to manufacture 75 ohm BNC 
connectors was to significantly reduce the center pin diameter from 
the 0.053 +/- 0.001 inch diameter specified by M IL - C - 39012. 
The problem is that the non-standard smaller pin does not fit properly 
into 50 ohm sockets or modern 75 ohm sockets using the standard 
0.053 inch center pin opening. 


Modern 75 ohm BNC connectors now use the standard 0.053 inch 
center pin diameter. Unfortunately some cheap import BNC connectors 
and inter-series adapters still use non-standard small diameter center 
pins. 


If you have any obsolete 75 ohm BNC connectors (male or female) 
its best to throw them in the trash before you accidentally introduce 
them into your station, causing unreliability exactly as you describe 
in your email. 


Some readers will insist that BNC connectors were never manufactured 
with small diameter pins, but I have a few that I keep on hand 
-- that I clearly marked as "do not use" -- just to prove the point. 


73 
Frank 
W3LPL 





----- Original Message -----

From: "rich hurd WC3T" <r...@wc3t.us> 
To: k...@yahoogroups.com, elecraft@mailman.qth.net 
Sent: Monday, February 19, 2018 4:54:37 PM 
Subject: [Elecraft] BNC connector oddity on KX3 

Hi, 

I had an oddity with hooking an antenna to the BNC connector on my KX3 that 
happened enough times to be chalked up to something other than random 
chance. Looking for opinions on whether my solution aligned to your 
experience(s). 

I have a complete station - a KX3, a PX3, and a KXPA100. The KXPA100 is 
connected via a Cables On Demand connector with a PL259 on one end and a 
BNC connector on the other end. All other interface cables are Elecraft 
standard. 

This is NOT the first BNC connector that I've used. Prior to this last 
acquisition I had a couple of other BNC to PL259 jumpers that I was using, 
and the usual smattering of connectors and adapters in the junque box. 

No matter which one I used, If I removed the BNC connector from the rig 
(maybe to go portable, for example, or the last time it was because I 
installed Eneloop Pro batteries to the internal battery holders) I would 
put everything back together, and then would have severe - almost 
debilitating - signal attenuation when I got the rig fired up. If I 
twisted and spun the BNC connector on the jack, it would improve, and then 
get bad again more often than not. It could take up to 20 minutes to get 
everything "dialed in" so that the signal was appearing again. God help me 
if I accidentally moved something after that. And of course, while all 
this was happening the ATU was having fits, with 99:1 SWR readings and the 
amp was going offline; all kinds of weirdnesses. After things calmed 
down. the ATU behaved itself, the amp stopped being pouty, and all was then 
good. 

Thankfully, now that I have the Cables On Demand product, things seem to 
have quieted down - although I still don't disconnect without provocation. 
:) Though I'm desperately afraid of when I start to go mobile after the 
snow melts and the weather gets nice again. :) Hope I can get my IC706 
fixed and back in service as my base station before that occurs. 

My question was going to be in desperation more than anything else if this 
last cable didn't work, but thankfully, that's been the only cable vendor 
that I trust for any of my specialized cables and they haven't failed me 
even with this one. 

Are BNC connectors that finicky? Is it possible that I just had a bad 
batch of low quality jumpers? I'm just wondering if anyone else has had 
excessive fiddling with their BNC connections. 

--- 
72, 
Rich Hurd / WC3T / DMR: 3142737 
PA Army MARS, Northampton County RACES, EPA-ARRL Public Information Officer 
for Scouting 
Latitude: 40.761621 Longitude: -75.288988 (40°45.68' N 75°17.33' W) Grid: 
*FN20is* 
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