[Elecraft] BNC connector oddity on KX3

[Don Wilhelm]

Rich,

Since you have traced the problem to the contact between the female BNC 
and the male (yes your twisting and applying pressure confirms that is 
the problem).

It is entirely possible that if you had some old cables made with old 75 
ohm BNC male connectors, that they could have enlarged the female pin 
causing it to become marginal when used with the 50 ohm male connectors.

You may have success with a very slender tool to bend the 'fingers' of 
the female connector toward the center, but the best cure is to replace 
that connector.

Before we get into another long discussion of 50 ohm and 75 ohm center 
pin diameters, let me say that modern BNCs use the same diameter center 
pin for both.
That was not always true, so beware when buying older BNC jumpers at 
hamfest flea markets - the old ones could be old 75 ohm BNCs with the 
larger center pin.  Those less than 10 or 15 years old are OK.
It may also be that *some* imported BNC connectors do not have the 
proper diameter.  For best results, buy only Amphenol connectors or 
other trusted brands.

73,
Don W3FPR

On 3/9/2018 11:13 AM, rich hurd WC3T wrote:
> I've pretty much exhausted most of the permutations of my cables and
> connectors.  The only persistent behavior is that if I apply slight
> pressure to the side of the BNC connector where it plugs into the jack on
> the KX3, or sometimes if I twist it and then apply slight pressure just so,
> I see a jump in the noise floor and instead of the internal ATU wearing
> itself out and giving up with a 9:1 or 7:1 SWR, it immediately tunes to 1.0
> or 1.1.   I have removed/swapped all my the antenna leads.  I have four of
> them, all Cables On Demand (Amphenol) manufacture.  I also have a number of
> BNC to banana plug jacks, and even an MFJ-1899T.  If I replace the leads
> without doing the twisting-and-slight-pressure thing, I lose the RF
> connection; the S meter has no indications on it, and the noise floor is
> nonexistent.
>