[RFI] Kenwood TM-D700

[jvpoll at dallas.net]

I would like to get a count of how many active 'loops' (feedback or closed 
loops, also phase-locked loops) there may exist in a transceiver of modern 
design such as the TM-D700.

Figure two or three different regulated 'sources' (voltage regulators) in use 
for the RF (synthesizer/phase-locked loop) and audio portions of the radio, and 
perhaps one more for the digital logic/microprocessor. Today LDO (Low dropout 
regulators) come in SOT-23 packages and can be placed anywhere a clean source is 
needed.

Then we have the Transmit RF chain, any stage of which may be 'blocking' 
oscillating at a low, audible-range frequency and 'helped' along as components 
warm during transmit cycles.

Any one of these could be the source, and I have seen anyone of these 'stages' 
take off and oscillate; just recently we had some LDO regulators 'sing' until 
proper measures were undertaken to bring the 'phase-gain margin' back to a 
suitable point where gain was less than 1 at 180 deree phase shift (effectively) 
from output to input.

As several people have made the same observation, it looks to my trained eye to 
be endemic to this design, to this model. It may be that 'parts' seen in 
production yiekd this phenomonon and the initial prototypes and early product 
runs didn't exhibit this problem buth with a change in both active and passive 
parts (e.g. ESR in caps) this problem has surfaced.

Not *everything* is due to ingress of a foreign signal or energy into a radio .
..

Jim P  // WB5WPA //





Quoting Michael Coslo <mjc5 at psu.edu>:

> 
> On Oct 29, 2008, at 11:48 AM, Hardy Landskov wrote:
> 
> > Not odd at all. The alternator is varying the 12 VDC and frequency
> > modulating the transmitter. Look at the 12VDC line with a scope and  
> > you will
> > see what's happening. I believe a big common mode choke is in order  
> > or try
> > running the TM-D700 power cables directly to the battery as the car  
> > battery
> > looks like a 1 Farad capacitor. Sounds like the TM-D700 is not  
> > decoupled
> > from the 12 volts very well.
> 
> 
> My D-700 will make this noise with the vehicle turned of, and I'm  
> running directly to the battery.
> 
> Actually, if you all could hear the sound, it would be apparent that  
> it isn't alternator or other vehicle based stuff. Whe I first had it,  
> I thought it might be RF getting into the audio, but it isn't that  
> either.
> 
> I'd say it's like a high pitch bronx cheer that lowers in pitch over  
> say 1-2 seconds, then goes away.
> 
> -73 de Mike N3LI -
> 
> 
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