[Flexradio] 5000 X-MIT AUDIO DEGRADATION

Tue Apr 7 00:10:10 EDT 2009

Hi Jim,

Yes, perhaps a complex EMC problem. I did(and still do) many EMI
investigations on my Flex 5000C (eham /my qrz.com) mostly around CW issues.

My general rule is any radio that is EMC ok on the inside, but allows
penetrations of un/shielded cables ( not 360 degree terminated shield on the
outside) will show sooner or later some strange EMI/RFI effects. And yes, in
digital electronics these effects are harder to trace to the causing source
due to being digital. A number of variables need to be met before something
happens, e.g. change of logic state or RF rectification/AM mod effects. The
metallic chassis should be a "complete" barrier to RF not a Swiss Cheese.

Where are these weak spots in the F5K?

E.g. the RCA connectors on the rear (not EMC terminated)and the firewire
etc.

Solution without opening the Flex.
Put Flex +PS over a metallic ground plane (station ground) and bond it
shortly to that(- 1 to 2 inch max-). All coaxes should be bonded here as
well. Wind front mike/earphone cable through high permeable ferrite (8turns
2000-4000 mu)directly at the socket/Flex
Insert the same type of toroid ferrite cores onto the critical cable e.g.
PTT PA etc before it hits the RCA..rear....
In extreme cases I inserted 100uH and 4,7nF to 10nF Low Pass into the
control lines.

I did prior some RF sniffing with EMC instruments.
If you have more questions , I have pics to send directly.

A very good source of EMI trouble shooting in Audio Systems is
http://audiosystemsgroup.com/publish.htm

gl
73 Andy HB9CVQ DK2VQ
www.qrz.com/detail/hb9cvq

-----Original Message-----
From: flexradio-bounces at flex-radio.biz
[mailto:flexradio-bounces at flex-radio.biz]On Behalf Of Jim Menefee
Sent: Tuesday, April 07, 2009 5:24 AM
To: flexradio at flex-radio.biz
Subject: [Flexradio] 5000 X-MIT AUDIO DEGRADATION

While hearing outstanding audio from many on the 5000, they're those of us
who are experiencing some very real audio degradation issues from
something..  perhaps R.F.  I work several people daily who have the same
issues on the 5000 and all of us seem to get a "head in the sand"
 response when ask about it... Coming from the R.F. industry I
understand frustration with issues like this, but we need some answers.  I
have applied every reasonable method I know to find the problem.
The best description of the annonimaly is that it sounds like the noise gate
is on, and set at a threshold point, being most noticeable at lower voice
levels.  Another person described as choppy, like an analog noise blanker
being on at the receiving station.  I might add, I don't hear it in the
monitor mode.
To my ear along with the quasi-intermittancy of the problem, it acts like
R.F. is getting into something, but doesn't sound like a normal issue of
R.F. getting into an analog radio. It comes and goes on all the stations
from day to day.   Everything is very well grounded and the antenna is 150'
away and the power supply is iron, non switching. R.F power levels have very
little or no effect for any of us. Level of audio shows very little
difference.
I know someone out their has experienced this issue and has an answer of the
source of the problem.

--
     Jim  Menefee - W4JWM
  James W. Menefee, Jr. P.A.
         (904)  685-2218--
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