[Yaesu] FT-1000D Intermod

[James M.]

Well after playing with my FT-1000 a bit, I notice the same thing
happening.   This intermod is apparently happening in the IF Unit, not
in the front end.  I can eliminate this intermod by cranking back the RF
Gain control, which increases AGC voltage to the IF Unit.  There is no
AGC routed to the front end stages (as far as I can tell) so it would
seem to me that this intermod is in a later IF stage.  My guess is that
there is a stage in the IF Unit somewhere running close to saturation
and if the AGC isn't keeping it below that point reliably, then you get
that intermod.  Especially on narrow bandwidths, where the AGC is a
function of the tuned signal, which could be weaker than a stronger
signal right on the edge of the filter passband.  This is my theory
anyway. Can't say what a fix would be.  Sounds like a design flaw.,  The
QST review article also mentioned this effect several years ago, but
apparently Yaesu hasn't fixed it.  Happy camper?  

Jim N4BE

sellington wrote:
> 
> My FT-1000D seems to hear  CW intermodulation products whenever
> a band is full of moderately strong signals.  Yet the measured third-order
> intercept is normal (and very high).  Also, inserting attenuation ahead
> of the receiver doesn't seem to help eliminate the intermod.  Another
> receiver connected to the same antenna, cables, etc. is clean, so the
> problem is definitely within the FT-1000D itself.  The problem is not
> cause by any extremely strong local signals.  The FT-1000D is a later
> production unit, so it should already have the PIN diode modification.
> 
> Has anyone else seen this kind of behavior?  I'm at a loss to even find
> an explanation of how a receiver can have such a high third-order intecept,
> and still generate intermod products in the presence of only moderately
> strong signals.
> 
> 73,
> 
> Scott  K9MA
> sellington@ssec.wisc.edu
> 
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