no mod monitors available to me so I did a little experiment with what I had
on hand to check my FM occupied bandwidth.
this is what I did.
Tools:
Atenn AT5005 spec analyzer
Carver TX11b with aftermarket IF Tap
RG 58 with BNC connectors
hookup:
Spec An set to 88.9 (my operating frequency) set for 0.200 scan width and
video filter enabled connected via RG58 to the IF out of the TX11b which was
also set to 88.9
is this the proper setup and settings to read my occupied bandwidth for FM?
it looked to me that I was slightly under 200khz total occupied bandwidth if
I did everything right.
Hi, Robert,
What you describe is correct in theory but there is a "gotcha". The signal you view on the spectrum analyzer is tapped from the tuner IF and it will be limited in bandwidth by the tuner IF bandpass characteristics. Many receivers do not have 200 kHz bandwidth since the lower the IF bandwidth the higher the selectivity of the tuner.
Your tuner may be OK but it is likely that you are not seeing enough bandwidth to allow an accurate measurement of your transmitter bandwidth. It is possible that higher frequency components are being filtered out by the IF bandwidth.
A search on the spectrum analyzer you listed shows an operating frequency range up to 500 MHz so it appears that it can be used to directly observe the transmitter output. This would eliminate questions about the the tuner bandwidth. This connection could be via a pickup wire near the FM transmitter antenna. If this doesn't give a usable signal then a direct connection possibly through a series resistor to somewhat isolate the analyzer input from the transmitter to avoid loading effects may work.
Connecting to the transmitter output would also allow you to check for harmonics up to the fifth.
Neil
What a great tuner. I've read about it
in the FM DX blogs.
I have a tuner with a deviation meter,
but the tuner is 30 years old with serious
problems. Anyway, it's a Kenwood KT-8300.
A beautiful piece of gear. It just fails every
once in a while, so it's not dependable. I've
had a lot of really good people check it out,
and they haven't been able to find the problem.
But it does have a meter marked FM deviation
on the front panel. Just thought I'd mention
it for fun.
Good luck with your project.
Bruce, Mon. Stn., CT
I was an FM deviate.
Oh, woops... maybe I misunderstood the subject.