[Milsurplus] BC-230 harmonics

[Jack Antonio]

Hi all

As I mentioned, I just got an SCR-183 set running, and in communicating with
Hue M, we got started talking about harmonic levels.  So I measured the harmonic
levels out of the BC-230.  

Test setup.  Transmitter out through a 100 pf transmitting mica, to a 1:4 (impedance)
step up transformer. Then to a Motorola coupler, which is just a short section of
line with a capacitive probe on the side, then to a Bird 43 and finally a 50 ohm load.
Frequency is 3870, with 3 watts out to the load, 0 reflected. The antenna current
is .5A, which is 3 watts into 12 ohm load, so the figures tend to support each other.
The plate current is 32ma at 300 volts, which is 9.6 watts DC input. This works out
to an efficiency of only about 30 percent, which does seem a little low. The analyzer
is a Tektroniz 7L12 in a 7623 mainframe. The analyzer input comes from the capacitive
probe.

Possible inaccuracies are the Motorola coupler, being capacitive, probably tends to
emphasize the higher frequencies, so the actual harmonic levels are probably lower.
Also, at these low levels, the various meter readings are in the lower third of the scale, so are 
probably not as accurate as they could be. However, the figures do tend support each
other.  Don't take these as laboratory values, there is no NIST traceability here!

Fundamental 3870kc 
2nd Harmonic   28db (relative to fundamental)
3rd Harmonic    35db
4th Harmonic    35db
5th Harmonic    33db
6th Harmonic   >50db(surprising, is there some stray 24 mc suck out somewhere?)
7th Harmonic    42db
8th Harmonic    33db(surprising)
9th Harmonic    40db
10th Harmonic  42db

Some questions

1. Do these numbers seem reasonable, or is my test setup needing some fine tuning?
I do plan on making a resistive divider to feed the analyzer, making sure the analyzer
sees a 50 ohm source.

2. Even if these numbers are meaningful, would they be applicable to a transmitter running
a short wire antenna(instead of a stepup transformer into a 50 ohm load).

Thanks

Jack

Jack Antonio WA7DIA
scr-287@sbcglobal.net