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ubitx calibration

terryhugheskirkcudbrifght@...
 

hi

i have calibrated my ubitx to a medium wave station on 1485 k hz.

can anybody tell me if the calibration will be good up to 40 mtr

i cannot hear www hear in scotland

terry gm4dso

Tom, wb6b
 

I believe that what you did, calibrating to a medium wave signal is a suggested alternative in the uBITX calibration instruction. It should work OK.

The higher the frequency you use to do the calibration, the better the accuracy will be with a given amount of zero beat as accurately as can be determined by ear. Of course, the signal you calibrate to, whatever frequency, should be accurate themselves.

Tom, wb6b

 

Alan de G1FXB
 

In addition to choosing a higher frequency carrier to zero beat, remember the Human deficiency......
The "perfect" Human hearing is generally specified as 20Hz to 20KHz so will not directly hear the zero beat (0Hz error), in a perfect world you should get to within 20Hz........
It's hit or miss to manage to get closer by ear.

Observe the zero beat using the S meter wobble / use a scope to look for the resultant 0Hz trace
Also the response of the IF, filter(s) / skirt, demod and audio stages will all play a part especially if the VFO is off when looking for zero beat?

The workaround for precision is to choose a convenient audible beat tone say 500Hz or 1KHz to make the measurement and some arithmetic to get the true carrier freq.
Best check the methods of the ARRL FMT / K5CM, even an SDR dongle can make the grade.....


Alan



On 08/08/2019 23:51, Tom, wb6b wrote:
I believe that what you did, calibrating to a medium wave signal is a suggested alternative in the uBITX calibration instruction. It should work OK.

The higher the frequency you use to do the calibration, the better the accuracy will be with a given amount of zero beat as accurately as can be determined by ear. Of course, the signal you calibrate to, whatever frequency, should be accurate themselves.

Tom, wb6b

?

Clark Martin
 

Years ago I zero beat (although I didn’t call it that) an NE555 running at 60Hz to the AC line by connecting an analog voltmeter between them. As it neared zero beat the meter started swinging back and forth and then slowed down to a stop when I was on frequency.  I say it started swinging back and forth as at higher frequencies the meter didn’t respond.

Clark Martin
KK6ISP

On Aug 8, 2019, at 4:48 PM, Alan de G1FXB via Groups.Io <g1fxb@...> wrote:

In addition to choosing a higher frequency carrier to zero beat, remember the Human deficiency......
The "perfect" Human hearing is generally specified as 20Hz to 20KHz so will not directly hear the zero beat (0Hz error), in a perfect world you should get to within 20Hz........
It's hit or miss to manage to get closer by ear.

Observe the zero beat using the S meter wobble / use a scope to look for the resultant 0Hz trace
Also the response of the IF, filter(s) / skirt, demod and audio stages will all play a part especially if the VFO is off when looking for zero beat?