[TenTec] A/B rig testing

[Jim Brown]

On 1/29/2013 9:46 AM, Paul DeWitte wrote:
> I just hooked the same coax to each rig, so it was a few seconds 
> between each one. He was not always solid copy on the Omni VII, but 
> was Q5 on the Corsair II. 

Several thoughts.

First, I've spent a LOT of time trying to evaluate the differences 
between antennas that are predicted by NEC models to have definite, but 
small (3-6 dB) differences in their directivity. My station is set up so 
that I can switch instantaneously back and forth, but even with that 
ability, signal fading often overwhelms the differences in the antennas. 
The same thing could be affecting your evaluations. 160M has a LOT of 
QSB, the peaks can be strong, the dips can be deep, and can coincide 
with the switching.  I've seen exactly this effect watching reverse 
beacons using JT65 on 160M to the east coast from California, and 
switching between two antennas on alternate transmissions.  If one 
antenna  coincides with the timing of QSB peaks it looks better, but a 
difference in that timing can make the other one look better.

Second, the setup of the radio can have a very strong effect on our 
ability to copy a signal.  Is the preamp on?  Is anything getting 
overloaded?  What roofing filters?  What IF bandwidth?  What audio 
filtering?

To do tests like what you want to accomplish, a switching system is 
required that simultaneously switches the antenna from one rig to 
another t the same time that headphones are also switched. And this sort 
of test MUST be done with headphones -- differences in how speakers in 
radios interact with the acoustic environment in the room, whether those 
speakers are partly blocked by equipment stacked on top, etc. can affect 
how well we copy a signal.

73, Jim K9YC