[BC] FM Harmonic Measurements

[Len Watson]

I've been through one of these and a couple of things can bite you in 
the backside.

First, if you're measuring while feeding an antenna, the sample point on 
the line makes all the difference since the SWR will be different for 
any harmonic compared to the fundamental (evens through the roof and 
odds relatively low but still varying).  That was proven with a slotted 
line.  We could almost pick our carrier:harmonic ratio by sliding the 
probe.  Into a good dummy, it's more constant - if the dummy will 
respond up that high.

Second is the rejection/pass characteristics of the antenna since the 
commission isn't concerned with what's in the line but what's leaving 
the antenna.  That's the real fun part since you never really know what 
the antenna do at 9f.  The directionality definitely changes - like 
feeding 33 megs (about 9f) into an 80 meter dipole and getting an 
endfire.  I only mention that because it means that you can measure the 
carrier:harmonic ratio in different places and get different results.  
In this case, the complaintant (is that the word?) had "shopped around" 
for a location where the signal was less than 80 dbc and used that as 
his benchmark!  That happened to be on a hill about 1000 yards from the 
tower.  Anywhere else - including at the base of his tower - everything 
but the fundamental was in the noise.

The station GM took a stand and, for whatever reason, they went away.  
He also rebilled the complaintant for my time.  I don't think he ever 
saw his money.

Len Watson