[TowerTalk] Narrow Band Filters

[Jim Brown]

On Sun, 4 Jul 2004 22:19:02 -0700, Michael Tope wrote:

>An interesting test would be to measure
>broadband noise for various rigs at 50 to 500 KHz offset to see if
>any rigs would be standouts for this kind of same band different
>mode operation.

Yes, I had thought of that but have not taken action on it yet. We're going to 
try some more informal tests as well, using some of our rigs running mobile, 
parked in the driveway of a fellow ham's QTH, and see how much phase 
noise different rigs have comparatively. 

The rigs we used on CW this year were my K2/100 with KAT100 (an 
EXCELLENT CW contest rig), and a TS-850SAT. We also had two dipoles 
for each band (for CW alone), and they were at right angles to each other. I 
think I may have been having less QRM from the SSB and GOTA stations on 
my K2 than the 850 was. Nearly all of the QRM was broadband noise. 

The SSB station was roughly 600 ft away, with an antenna at roughly 70 
degrees to our antenna location.  The GOTA antenna was more like 200 ft 
from one of our dipoles, but 400 ft from the others. These two stations used 
higher priced ICOM radios, but I don't recall model numbers. 

Someone suggested that stations on the same band should use dipoles that 
place their null in the direction of each other. Certainly that's a good thing. 
Having a good balun on each antenna is important if you're going to get full 
benefit from that, and I'm convinced that the DX Engineering baluns are the 
only way to fly. 

But when you work with only a single antenna (as opposed to two at right 
angles), you will miss a lot of lower strength stations (poorer antenna, lower 
power, weaker path). You quickly learn that if you have two and switch 
between them on receive (which is VERY easy to do with the K2's tuner). Our 
dipoles for 20 and 15 were good enough (and high enough) that the nulls 
were pretty pronounced. On more than one occasion, I would call CQ and get 
answers there were in the mud one one antenna but 579 on the other. This 
was less true on 80 -- our dipole that was broadside E/W had a shorted 
balun, so I had to use only the one broadside N/S. I still managed to work a 
lot of guys on the west coast. 

Jim Brown  K9YC (at K9OR on FD)