[Drake] TR4C 80m hum

[Paul Manno]

Hi John,

Antenna is a Hustler 6-BTV showing a low SWR and station ground appears 
good.  Same antenna, ground and feed line work fine with an old Johnson 
Valiant 1 on AM at varying power levels up to its full output.

Yep.  Using a Hallicrafter's SX-110 to monitor audio with the RF gain 
turned down so it's showing around an S7 on the 110's meter.  Same used to 
monitor the Valiant on antenna or dummy load with no such hum evident.  
Several stations on 80m have reported hum/distortion in the signal - same 
as I hear on the monitor I'll guess.

The TR4C works fine on 40-20-15-10 all modes into either a (Drake) dummy 
load or the antenna.  But, the TR-4C hums that NA power grid hum like an 
ungrounded audio cable only on 80m tune-up or key-down, with a key in or 
out, different microphones and cables and at different power levels.

Good suggestions for a real head-scratcher.  I'll try with the mic cable 
out and see what it does.  Usually run the rig on SSB with no key.

Thanks and 73,
-- Paul, kg4uvu



On Fri, 15 Aug 2003 W4AWM@aol.com wrote:

> <<on 80m, the receive works fine but transmit has a 
> very pronounced line-frequency hum in all modes (CW, AM, LSB, USB)>>
> 
> 
> Hi Paul,
> 
> A good thing to check for since the problem is only on 80 would be that you 
> have a good ground and low SWR.  It is also possible that RF could be entering 
> the rig through a resonating mic cable or key line.  Easiest way to determine 
> this, since it is an all mode problem, is to disconnect both cables and try 
> keying with a dummy plug inserted in the ksy jack, if a kay is needed in the 
> tune position.
> 
> Also, are you determining that there is hum by monitoring in a local receiver 
> or are you getting reports from another station?  RF can easily overload a 
> local receiver and cause you to believe that you have all kinds of problems than 
> don't really exist! I had a problem like that when I was hooking up the 
> PSK-31 interface and tore the shack completely apart before finding that the 
> problem was the receiver!  (Red face!)
> 
> Hope you find the problem and please post your findings to the list so that 
> all may benefit from your experience.
> 
> 73,
> 
> John,  W4AWM
> 
> 
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