[Milsurplus] Hum (long)

[James M. Walker]

Questions,
Hum is not too descriptive, but let me try a shot at it.
BC-614-E OK what Mic/audio input device are you
using? Next what power are you running, and is it to an antenna
system or a dummy load? If to an antenna, and you are tunning
around 350 watts to the antenna, how much RF is getting back into the shack?

Regarding the BC-614(*), the connecting cable type between the BC-610
and the BC-614 is significant. The original was a shielded cable with the 
shield held
under the cable clamp inside the shell at both ends, has the shield 
connection
come loose? Without applying RF output to the antenna (rig in standby)
take a VOM (set on 250 VAC) check voltage between the BC-610 and the
BC-614 cabinets, if there is a reading they are NOT grounded to each other.

With my BC-610 and using the BC-614 with the proper cable and good
ground connections, and using the Dynamic mic input I get no hum into the
dummy load at 400 watts output. When I transmit into a dipole cut to the
proper frequency, I get a small amount of RF in the shack (direct 
connection)
to the antenna. When I use my long wire antenna through a Johnson KW match
box I read about 5 volts peak to peak on an oscilloscope when probing the
chassis at either end, as in BC-610 or BC-614. The signal does not have a 60
cycle component however, as in it is not noticeable on the scope.

I run several configurations of audio input to the BC-610(*) depending on
the operating mode. When I run just CW, I use a HB metering arrangement
with keying to the remote panel, and relay contacts with a switch to mute 
the
HQ-129(X) in CW mode. There is no noticeable 60 cycle hum, on the CW
signal. I can also feed 600 ohm level audio into the BC-610 through this
interface, using an EICO 730 modulator W/600 ohm output selected. No
noticeable hum, However grounds have to be connected and secure.

As an aside, what type receiver are you using to monitor this hum, and
is the receiver actually detecting hum, or is it Front End Overload? When
using just AM operation, I usually have the HQ-129(X) antenna feed coming
from a Johnson TR switch, with the probe connection coming from there also
I have provisions for muting the HQ-129(X) to minimize audio feedback
while transmitting.

FWIW
YMMV
Jim
WB2FCN

----- Original Message ----- 
From: "Rick Brashear" <rickbras at airmail.net>
To: <milsurplus at mailman.qth.net>
Sent: Tuesday, March 14, 2006 11:54 PM
Subject: [Milsurplus] Hum


>I have a 60 cycle hum in my BC-614-E that has me scratching my head.  All 
>filters, chokes, bypass caps, line filter caps, etc. either check good or 
>are new.  It seems to be a shielding issue.  When out of the cabinet the 
>hum is very loud, however, when I put it in the cabinet the hum is almost 
>gone.  I have double and triple checked all grounds and they are good.  Has 
>anyone encountered this with the 614-E?  What am I overlooking?  I know 
>it's something starring me in the face, but I can't seem to see it.
>
> Thanks for any advice you can offer.
> Rick/K5IZ
>
>
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