>> Great reflector! Thanks again to all.
>> Bob - W8BOB bobb@smoc.cmhmetro.net
Hi, Bob,
I'm glad you are satisfied with the solutions to your "problems". It gives me
an opportunity to pose something to the group.
Hypothesis: There's nothing wrong with knobs that aren't always exactly at the
12:00 o'clock position. Isn't that why the controls are variable in the first
place, to provide for adjustment? I say that if the passband tuning, or the AGC
delay, or the AF gain, or the noise blanker sounds best when it's set to
something other than the factory default position, leave it there! We need not
apologize for mic gains at 3:00 o'clock, or RF gains all the way up, or RITs at
-0.01 instead of 0.000 kHz.
I realize that if something has changed to cause you to adjust a particular
control to a very different value than normal, that may be cause for concern.
But just because you must tune a control a bit off of what the manufacturer has
deemed the "perfect" setting doesn't mean too much. Bob has brought up an
excellent example of something that will frequently require differences in
receiver settings: headphone response. What if I'm even slightly hearing
impaired? Won't my passband tuning and volume be at different settings than
yours, and if our hearing is very different, perhaps radically so? What if my 9
MHz crystal filter's center frequency is shifted 100 Hz lower than nominal?
(That, by the way, represents a 0.001% error.) To get the same "sound" on my
receiver as on yours, and assuming + and - 1.5 kHz PBT and linear tuning of
that control, my passband tuning control will have to be tuned 10 degrees off
center. Would that bother you, having to leave the passband tuning that far off
center all the time?
Just a few years ago, I had the chance to use an RF communications test set to
measure several 2m/440 MHz HTs at a club meeting. It was very interesting
sampling many different models from several manufacturers. The typical VHF FM
radio is 500 Hz off frequency.Some were up to 1 kHz off frequency, which at 450
MHz represents 0.0002% error. With errors this small, they are usually
represented as "parts per million". That would be 2 ppm. As another example, a
few hams on this reflector not too long ago were bemoaning the fact that their
ovenized oscillators were 20 Hz off frequency. If memory serves me correctly, I
think the oscillator in the Omni VI runs at 10 MHz, so this would be an error
of 2 ppm. To put this error in perspective, the company I work for just
introduced a new $23,000 instrument that has 10 ppm frequency accuracy, but if
you pay $1,500 for the optional high stability reference, you get 1 ppm
accuracy. Yet, most hams would be bummed out for weeks if you told them their
radios had this much error.
If we carry this thinking too far, we begin to grow intolerant of hams who are
"not exactly on frequency". How many times have you heard someone on the air
get balled out because his transmitting frequency is causing someone else to
tune to 7.239.999 instead of 7.240.000, or (God forbid) using RIT? What if my
reference oscillator is only 5 Hz high and yours is 5 Hz low? That means that
when we meet on the air, we'll be (gasp!) a whole 10 Hz apart, causing more
often than not all kinds of grief to us both.
We are to be commended for keeping our stations in tip-top shape and keeping a
close eye on the calibration of our gear. The ham who maintains a practical
perspective on realistic accuracies acheiveable with modern equipment is, it
seems to me, a much happier and efficient operator.
R,
Al W6LX
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