Radio testing.
I agree that the standard numbers we have been seeing for 30 years are not
enough information, especially with the advent of DSP-base radios. I have been
harping on serious AGC problems with newer radio designs for two years. I just
finished up lab testing the FT-2000. Its numbers will be on my web site soon.
What is not yet being published by either my web site or the League's data is
an impulse noise test. I gave a talk at Dayton this year on the subject, and
the Power Point slides are on my web site. Unfortunately there is no audio
recording to go with the slides. Hopefully I will find time to write up some
text to go with the PP presentation.
The owner of the FT-2000 I tested (he had two of them) found that on the air,
the FT-2000 was basically useless in QRN. Poor QRN performance of my IC-7000
was what prompted my study into the subject and resulted in my 2007 Dayton
presentation.
On the impulse noise issue, I finally took the time to setup something
repeatable in the lab using an HP pulse generator. In effect it approximates
an electric fence. One pulse per second, fast rise time, and a reasonable
duration of about 1 usec. Since I had the Flex 5000A for such a short time,
this test never was run on the radio. I did, however, feel the AGC did not
over-react to impulse noises like the FT-2000, FTdx-9000, Orions, IC-7000 or
IC-7800.
With an IC-781 as a reference, and the FT-2000 setup for similar AGC readings,
such as the AGC threshold = 3.5 uV and S9 = 50 uV, the pulse generator caused
the following on these radio:
FT-2000: S7 reading on the impulse. Icom 781: just barely moving the S meter a
needle's width. The effect of this problem is for a very short impulse noises
to poke holes in the desired signal.
This is the problem with so many new radios. An impulse noise, (click, tick,
pop, or QRN) causes the AGC to be captured by the impulse. Older radios do not
get captured by the pulse. So as Lee said, no only do we need to compare lab
numbers, someone needs to listen to the radio on the air who can distinguish
problems. When I asked Mike Tracey, KC1SX, of the League about their findings
on this subject, they have nothing to say, as they never noticed the problem.
Could the League afford to say that most of the new big dollar radios from the
main OEMs don't perform satisfactorily in impulse noise or QRN?
73, Rob Sherwood, NC0B
>>> Lee A Crocker <[EMAIL PROTECTED]> 9/20/2007 6:06 AM >>>
I'm not even sure the "old" way of analyzing receiver performance is entirely
germane to SDR because the radio is very different in system concept than a
standard analogue radio. Yes there are points where the system can be made to
break, but the points of "breaking" in a test are simply definitions not
necessarily real things.
Part of the "problem" with numbers is the manufacturers have learned to
manipulate them. They build their systems in order to beat the numbers. It's
why every friggin radio in the universe except the Flex now has a "roofing
filter", but the numbers are in some respects artificial and not complete.
Like Rob says its the radio that you turn on when you go in the shack that is
the radio for you. This being driven by the numbers is not necessarily smart.
When Polio was endemic people were kept alive with iron lungs. If we did not
explore outside of the box ideas and were simply engineering driven, we would
not have come up with vaccines. We would have come up with real efficiently
engineered iron lungs. There is no "test" of an iron lung that is germane to a
vaccine.
We have seen in this very thread the problem. At some point the "numbers"
devolve to a Ford v Chevy kind of thing, a competition of trivialities. I
think the W4TV post has some of that kind of tenor. Others claim to believe
Rob over the ARRL. I can't say I disagree with that because my knowledge of
Rob is that he is interested in honestly advancing the state of the art. I
believe the ARRL is interested in selling advertising, but the point is a test
is merely a way to compare some limited aspect of function across systems and
as such may not really inform you about the system. An automotive example:
You can test a rail dragster's turning radius and compare it to a Honda, but in
the end who cares what the turning radius is of a car that is made to go real
fast in a strait line? All you need is "enough" to keep the lateral forces
balanced as you scream down the strip
73 W9OY
____________________________________________________________________________________
Shape Yahoo! in your own image. Join our Network Research Panel today!
http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.asp?a=7
_______________________________________________
FlexRadio mailing list
FlexRadio@flex-radio.biz
http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/
FlexRadio Knowledge Base: http://kb.flex-radio.com/
FlexRadio Homepage: http://www.flex-radio.com/
_______________________________________________
FlexRadio mailing list
FlexRadio@flex-radio.biz
http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/
FlexRadio Knowledge Base: http://kb.flex-radio.com/
FlexRadio Homepage: http://www.flex-radio.com/
