[Scan-DC] Jeff's recent observations

[Mike Agner]

   Hi Jeff and list; Jeff, I would be very careful about thinking that one 
scanner has an edge in overload and intermod resistance, based on your 
recent logs.  To be honest, I'm wondering if you're observing more a 
sensitivity issue - that is to say, that the 780 is VERY sensitive - vs. 
some actual receiver fault.

   Let's take the first 2 logs you reported as harmonics in last nite's 
batch as an example.  There's no such thing as a perfect repeater or 
transmitter - EVERY transmitter will put out harmonics, though they should 
be attenuated way down to the point that they're not detectable.  Is it 
possible that, with your setup (particularly with any amplification in 
place), that it's TOO sensitive, and is picking up even the faint harmonics 
from other systems?

   The 3d log you supplied with the ham repeater mixing in with other 
signals is a clear indication of an overload or intermod product.  In point 
of fact, this report, combined with the other 2, suggest that you are 
possibly pushing the 780 too hard - if you have some amplification ahead of 
it, which I think you had mentioned that you do.  Your recent observations 
about hearing more 'harmonics' and 'false hits' on the 780 adds 
circumstantial evidence to this observation.

   Remember, a harmonic does not have to be generated by some fault in the 
scanner/radio; if it's an even multiple of the base frequency, the chances 
are good it's the transmitter at fault, not just the receiver.

   I have mentioned this before in other forums, but it bears repeating - 
using any kind of amplification can cause all sorts of headaches if used in 
an area that has a high RF density.  Sometimes you're better off NOT using 
amplification of any type.
   I should also stress that comparing a 780 (which is not a DSP based 
scanner) to a PCR1000 (which is, at least in part, DSP) is like comparing 
apples to oranges; both fruits with very different characteristics.

   73s for now...Mike