[Elecraft] loss of RX sensitivity

[Drew AF2Z]

I used that trick to keep my DSL line running for a couple of years when 
Verizon was abandoning copper and no longer interested in doing 
maintenance. Placing a resistor across the telephone line would draw a 
constant small current, not enough to off-hook the line but enough to 
"seal" the poor connection, wherever it was, and improve the noise margin.

Regarding the PL-259 center pin-- it's also important to check the 
connection between the threaded shell and the body of the plug. That is 
a common and overlooked connection point subject to poor connection.

Note that there is no electrical connection through the threads on the 
plug body and the threads on the shell; these threads are merely a stop 
to keep the shell from sliding down the cable when not connected to the 
SO-239 on the equipment.

The electrical connection occurs through the lip at the back of the 
shell which butts against the threaded region on the plug. The area of 
this thin ring of contact is pretty small so it's important that the 
mating surfaces are entirely clean and free of corrosion.

It may help to disconnect the cable, then hold the back of the plug in 
one hand (where the cable enters it), then pull on the shell with the 
other hand, toward the pin end, as if trying to pull it off the plug; 
while maintaining this pressure, twist the shell vigorously. That will 
help clean the mating surfaces, especially if the plug is not silver 
plated but that cheap "shiny metal" stuff a lot of plugs have now. Also 
do this with all jumpers between SWR meter, matchbox, etc.


73,
Drew
AF2Z



On 09/17/18 01:44, Frederick Dwight wrote:
> Scott,
>       The problem you describe is actually quite common in electronics.  In the telephone industry, especially in the “good old days” with wire cables, sometimes with many splices it was common to get drop outs.  These could be due to a splice, wire wrap connection, oxidized relay contact or whatever, especially with only low level signals.  If the circuit also had a DC voltage on it, the problem often did not exist.  In fact it was common on critical circuits for the FAA or military, or whatever to sometimes just put “sealing current” on certain circuits just to be sure it was reliable.  Often we used 24 volts DC or less with only a few ma of current.  At one time I had many phased verticals which were controlled by many relays.  Occasionally the received signal would drop by many S units.  Sending a single dot, even with QRP or QRPP power always cleared the problem, sometimes for weeks or months.  So it could be a connection in the antenna system, a plug on a circuit board, or even a relay.  I have never experienced trouble with Elecraft relays personally.  Sometimes PL-259 center pins are not correctly soldered, and can present similar symptoms.  You could try a random wire, or even something like an 80 meter dipole on 30 meters, just to see if it was anywhere in the antenna system.  Even a volt or two is often enough to punch through a poor solder or oxidized connection, but even something like a 0 dBm signal is just not enough.  I have identified problems with BNC connectors and adaptors purchased at ham flea markets which are just not reliable and are probably factory rejects.  So look into your antenna system before you dig into your rig.  You could also hook a signal generator to the rig and see if it receives OK on all bands with something like less than an S9 signal.  Be sure to not transmit into your generator, and/or set your tx to very low power.  Good Luck   Rick  KL7CW
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