Rick is exactly right, its one thing to be working with two (A+B)
frequencies, with four different sum and difference products in the lab ,
and entirely different for three (A+B+C) frequencies, with nine different
sum and difference products,...... or entirely different for 9
(A+B+C+D+E+F+G+H+I) frequencies with ninety-one different sum and difference
products which may or may not pass through the roofing filter in the real
world during a contest or DX pileup.
73 ES DX,
Gary -- AB9M
-----Original Message-----
From: Rick - DJ0IP / NJ0IP
Sent: Sunday, February 03, 2013 3:13 PM
To: 'Discussion of Ten-Tec Equipment'
Subject: Re: [TenTec] Yaesu comparison
You guys are forgetting one very important point. Radios behave different
in the real world, on the air, than they do in the lab with just two signals
injected.
The roofing filter is there to protect downstream stages from the "SUM" of
all of the signals near the desired frequency, not just that one single
signal that happens to be 2 kHz away. As long as the roofing filter is
doing its job, then the DSP does the rest. So on a given day, you might
clearly see that a radio with a 3kHz roofing filter sounds better than one
with a 1.8 kHz roofing filter. It all depends on how many signals are near
the frequency and what their signal strengths are.
What we saw in that demonstration was a single carrier and we witnessed how
quickly it completely disappeared. That is a function of the downstream
(DSP) filter, NOT the roofing filter! If that test had been run in a CQWW
CW contest weekend, you would have heard at least 5 other signals when
tuning to the side. THEN you could possibly determine if the roofing filter
is making any difference, but that medium strength carrier off the side was
not enough to overload any of these three radios!
What I'm trying to say is, although our lab tests use two signals and we
take a measurement, in the real world there can be tens of signals which
affect how the radio behaves. How can you expect to repeat what the
previous tester did unless you do the test at the same time, same frequency,
and same antenna?
You can run your own test, but you might test one day on your own antennas
with certain band conditions and come to a conclusion.
The next guy tests on another day with different band conditions and comes
to a different conclusion.
Of course you might come to the same conclusion. It depends on the real life
situation, not on just two signal generators.
When I want to test a radio, I put it side by side with another in a BIG
contest and use both for a longer period of time. It is a subjective test,
but I believe it gives you a much better reality check than a lab benchmark
or a quick check on a non-contest weekend.
I will repeat what I said earlier: what we witnessed was a pretty
meaningless test, because we have no knowledge of how each radio was set up.
RF Gain? Attenuator? AGC? Bandwidth? Passband tuning? Maybe it was
legitimate and fair, maybe not. We have no way of knowing because the guy
never said squat about the setup.
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of
k4elo@fastmail.fm
Sent: Saturday, February 02, 2013 3:06 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Yaesu comparison
Wow, this has generated a very interesting discussion with lots of good
points. I do find it hard to believe that a 1.8 kHz roofing filter won't be
better than a 3 kHz one with a strong, clean, signal 2 kHz away. But
unfortunately, as we all know, there are many signals out there that are far
from clean. A quick glance at the external panadaptor spectrum display I
use (LP-PAN on the Yaesu IF output) confirms this.
Going to find out shortly which rig works better for me, as a very generous
member of this list is sending me his O2 with a 1.8 filter so I can do a
direct comparison with my FT5K. I have full one button rig switching set up
so the rigs will be in identical situations. Same antenna, speaker, etc,
just one rig at a time.
Now I just have to figure out how to make a good video of the results.
While I'm at it, I'm certainly open to any suggestions for testing.
I think I can do this without a lot of bias except for the belief I stated
above regarding the roofing filters. But those results remain to be seen.
This Yaesu is the first non-US rig I have ever owned. Other rigs have been
two Flex radios,four TT rigs, plus Drake and Collins.
Stay tuned!
73
Wayne
K4ELO
p.s. Glad to see that John Henry is back at TT.
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