ACCURACY OF GB4000

[Guest guest]

After Bil Green¹s post on the accuracy of the GB4000, I e-mailed Jeff Garrf,

maker of the this machine [which I own] to question him about it. This was

his response:

Hello Lee, A few instruments that were the rev A (rev A will show in the

LCD) had problems. The higher you when in frequency the greater the error.

We have tried to replace all of these instrument that have come to our

attention. The Rev B is right on frequency and we have not had any problems

with it. We test each instrument before it goes out. In order to test the

instrument for accuracy you have to put it in audio mode. If you try and

test it in RF mode you will be trying to measure a modulated frequency (the

carrier and the audio). Frequency meters cannot read RF and you need to have

an oscilloscope to do this. A frequency counter will work In audio mode but

you must remember that the instrument may be running several frequencies at

once and the counter doesn't know which frequency to read. This is why you

must put it in audio mode and test a single frequency at a time. This will

tell you if there is any problem with accuracy. Also, in audio mode, some

frequency counters do not measure a 90% duty cycle well so you should change

it to a 50% duty cycle to make sure it will work. We do not use frequency

counters to test with because of this problem. We always use an oscilloscope

so that we can be sure we are getting an accurate reading. The type of

oscilloscope we use has an auto find feature and this accurately tells you

what frequency is being put out. I have had some people who had older

oscilloscopes that did not have this feature and they had problems reading

the frequencies correctly. This fellow (maker of the mag pulser) may have

read a rev A. If you know of anyone that may have a rev A we will replace

the board in at no charge. I hope this helps. If you have any problems let

me know.

>

> Jeff