[Lowfer] Re: lowfer/ham QRM and Q

[Tom Rauch]

> It may not be as much of a problem as you think.  After all, if an
> antenna is any good at these frequencies, its Q will be high enough so
> as to pretty well eliminate any out of channel garbage by itself.  And
> since the antenna would present a high reactance off frequency, a TX
> that is putting out serious spurs and trash would quickly find itself
> in trouble - it might even let the magic smoke escape!

The high Q antenna will help bandwidth on the desired frequency, 
but watch out for harmonics!! 

Low frequency NDB beacons at airports run low power through 
"high Q" loading coils. The transmitters are mostly low power. 
The manufacturer "thinks" the loading coils act as filters, and 
depends on the loading coil for final harmonic reduction. The 
manufacturer forgot at some higher frequencies the coil looks like 
anything but a high impedance inductance, and may even look like 
a good matching system.

160 meters is full of harmonics from LF NDB beacons at airports, 
for example I can hear 20 watt NDB BCK on 1813 (and the CW 
keying image of BCK on 1811). That NDB is in Black River Falls 
WI, nearly 1000 miles.
73, Tom W8JI
W8JI@contesting.com