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[aprssig] Kenwood D700/D710 RF Problems

Dave Baxter dave at uk-ar.co.uk
Thu Jul 22 14:00:28 UTC 2010


> -----Original Message-----
> From: Stephen H. Smith
> 
> 4)      Finally, analog DC power supplies tend to be 
> susceptible to low levels 
> of RF, because their voltage-regulator systems typically work 
> with milli-volt 
> level control signals.    On the other hand, switching-mode 
> supplies tend to be 
> less affected.  The same RF filtering and bypassing that 
> keeps the supply's internally-generated switching noise from 
> leaking out (and causing RFI to nearby receivers) also works 
> to help keep external RF from getting into the supply.


Funny, I've had exactly the oposite experience with nuisance trips of
analogue (Linear) and switching PSU's.  Generaly, I find linear designs
are much more forgiving when under threat.

SMPS regulator systems also work with the same mV analogue signal levels
by the way....
The RF filtering they have, is to meet EMC regulations, not to co-exist
by design with any RF equipment they may be powering, or be co-sited
with.   They still leak noise and crud, just not as much as without any
filtering.  We have to add extra filtering to the AC line, and DC load
leads, for use in our RF amps (at DC and RF power levels up to many kW!)
But they do have active PFC that is nice, but noiser....

Have to ask, why there is enough RF in the plant room to cause problems
in the first place?  Something's leaking!

Check any DC cooling fans too.  I've seen a SMPS trip due to
overheating, as a result of it's cooling fan almost stopping in the
presence of unexpected RF (108MHz) the rest of the PSU was fine (no
trips or wobbles) otherwise.


Others have said about the Kenwood built in TNC's.  Bit of a disaster
waiting to happen, in unatended site situations sadly.

73.

Dave B
G0WBX.



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