[TenTec] Accuracy (long)

[al_lorona@agilent.com]

>> 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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