I recently purchased a used but freshly calibrated service monitor and have been enjoying testing the radios I have around the house. I have not previously used a service monitor, so I'm learning as I go.
A local group gave me a pile of 20 year old vertex 400U handhelds to test.
FCC Part 90.213 says for mobile transmitters in the 421-512Mhz range, 12.5 kHz channel bandwidth must have a frequency stability of 2.5 ppm. If my calcs are correct, using an example frequency of 460Mhz, that would be +/- of 1150hz.
Most of these 20 year old radios are testing at around 600hz off frequency. Some are testing as high as 2100hz off.
I can't find a service manual for these radios, and the programming software I have for them does not have an alignment mode, like many of the newer versions of this series.
Any thoughts on acceptable tx frequency error, what limits to take them out of service absent ability to repair, is much appreciated. I just don't have any experience to know what is normal.
Thanks!
A local group gave me a pile of 20 year old vertex 400U handhelds to test.
FCC Part 90.213 says for mobile transmitters in the 421-512Mhz range, 12.5 kHz channel bandwidth must have a frequency stability of 2.5 ppm. If my calcs are correct, using an example frequency of 460Mhz, that would be +/- of 1150hz.
Most of these 20 year old radios are testing at around 600hz off frequency. Some are testing as high as 2100hz off.
I can't find a service manual for these radios, and the programming software I have for them does not have an alignment mode, like many of the newer versions of this series.
Any thoughts on acceptable tx frequency error, what limits to take them out of service absent ability to repair, is much appreciated. I just don't have any experience to know what is normal.
Thanks!