[Elecraft] AC hum on tune

[Tom W8JI]

Sam,

First, you may be on a wild goose chase or you may have a 
problem. I would like to hear a recording of the "hum".


Second, never rely on any "I can't hear it" report. Too much 
of hearing a problem teeters on the skill of the person 
doing the test, his equipment, his noise floor, your signal 
level at his house, and so on.

The entire process you are involved in now is notoriously 
unreliable because you are depending on very poor test 
setups run by others with unknown experience or skills to 
determine the problem.

Mike WA8BXN suggested: "Did you try running your monitor 
receiver on battery?" and I agree with his suggestion. No 
one knows you monitor setup is clean, especially for local 
signals.

Like I said earlier. Virtually every rig I run on my shop 
test bench without a closed sampling system, like running it 
into a dummy load with a high attenuation line tap, has hum 
induced by all the lights or something in the shop. I can 
move coaxial cables around and hear the hum change, and that 
hum really is not on the signal at all. It is some multipath 
artifact.

Understand I'm not saying they are wrong, but no one could 
say they are right with the information now.


73 Tom




----- Original Message ----- 
From: "Sam Morgan" <k5oai.sam at gmail.com>
To: "Tom W8JI" <w8ji at w8ji.com>
Cc: <elecraft at mailman.qth.net>
Sent: Sunday, May 16, 2010 8:03 PM
Subject: Re: [Elecraft] AC hum on tune


> Well at this point I have:
> gone on battery power
> nothing is hooked up to the K3
> except the 12v power lines from the battery
>
> all reports of a hum on my tune signal
> have come from stations 1/2 mile to 3 miles away
> my output power was varied from 1w to 100w
> only difference was the hum was louder with more power
>
> one station 75.5 miles away did not hear the hum however
> the 80m band was QRN with storms and local noise at the rx 
> station
>
> clues?:
> hum is louder on 80m than on 17m
> nothing different if I go to battery or on ac/dc power 
> supplies
>
> at this point I think for my next try
> (since I have been using it on SSB only so far)
> I will get on cw and see if I can get any R5 S9 T(1-6) 
> reports
> If I don't I will quit freaking out and be satisfied for 
> now.
>
> If that is successful I will start adding things back to 
> the rig
> ground, serial cable, line out, (external) tuner, IF 
> output cable,
> amp and keying line to amp, ground to amp, coax switch,
> ground to coax switch, other antennas to coax switch, etc 
> etc etc.....
>
> hmmmmm lots of *stuff* involved when you get back to that 
> point
> hopefully somewhere along the way,
> something will show it's self as the culprit
>
> Thanks to all who have offered suggestions on and off 
> list.
> -- 
> GB & 73
> K5OAI
> Sam Morgan
>
>
> On 5/16/2010 3:03 PM, Tom W8JI wrote:
>
>> It is common for me to hear hum or buzz on local 
>> receivers very near a
>> transmitter. Even on perfectly clean transmitters unless 
>> I use a line
>> tap to sample signal all sorts of stuff mixes in. I've 
>> never really
>> looked into why. My guess would be it is some nasty 
>> multipath being
>> modulated by something. Just a guess.
>>
>> I'm not saying you don't have hum, but just cautioning 
>> you to be careful
>> when listening on a local receiver near a transmitter. I 
>> can replicate
>> hum on my shop receivers even with a very clean 
>> transmitter on the bench.
>>
>> That aside, did you try disconnecting everything except 
>> the K3 antenna
>> and power supply?
>>
>> Switching supplies do not normally cause 60 or 120 Hz 
>> problems.
>>
>> 73 Tom
>>
>
>