[TenTec] KB7OEX: a big plus favoring ORION

[Tom Rauch]

By the way, I don't want selectivity ahead of a mixer...I just don't 
want it back after passing through 10 stages with semiconductors. 
Quite often one or more of those additional stages will not be 
designed correctly, and even the best designs add accumulated 
crud.  

> I'de just like to know where Tom Finds all that QRM. I would think the
> 160m cw test is as bad as it gets. Maybe not. I spent about 4 hours in
> that test and just set my filter on the TS-870 for 50hz to 100hz
> bandwidth. I had 40-50db over 9 sigs on both sides of me and no QRM
> problems.

It all depends on the background noise level, and that of course 
also relates to antenna directivity and what is in front of the 
antenna, as well as how many stations are on around your 
frequency.

On 160 meters, my normal winter nighttime background noise is 
about -130dBm or so, and typically the strongest signals are  -
50dBm with occasional signals reaching -35dBm or stronger. I find 
similar situations on 80 and 40 meters. 

What most people also seem to miss is with multiple signals, each 
signal can be considerably weaker and the accumulation of signal 
power from many moderate level signals can cause IM or blocking 
problems. The IM effect is like listening to a crowded CW band with 
wide selectivity in the AM mode. You hear brief bloops and bleeps 
that really are not there, or have a weak signal pumping in and out 
of the noise with the accumulated power of many stations sending 
CW that just at brief instances all adds up to sufficient power to 
block the receiver.

Of course this problem can be totally masked by noise, so it does 
not affect everyone. It mostly is a problem when you use narrow 
selectivity (because noise power drops proportionally with narrower 
selectivity), have a directional antenna beaming past strong signals 
towards weaker ones, and operate crowded bands.

For example, the FT-1000D is almost useless here when 
stock....yet many people only experience occasional problems. 
Most often, people often don't even recognize problems.
73, Tom W8JI
W8JI@contesting.com