Gentlemen,
In the current thread one of us mentioned real-time situations versus
theoretical circumstances. For me, this discussion is very apropos because of
the project I am involved with currently.
In the course of investigating pulsed HF effects on nearby microwave equipment
whose low-voltage D.C. supplies might be unable to filter such hash from the
feeds through the low impedance battery plants an HF exciter and tetrode
amplifier running at 3KW to a "noisy" resistive load at 5ØΏ+jØ was pulsed
at 1 PPS and at 10 PPS. A spectrum analyzer monitored the surrounding 50KHz of
the transmitted signal whose frequency was changed from 1MHz. through 20 MHz. A
second test was conducted with a 55Ώ load to cause some reflection.
The point now being that we used a currently marketed amateur-band tetrode
amplifier whose power supply was based on a single frame transformer supplying
the unregulated HV, regulated Screen and regulated Bias voltages.
The power line supplying the primary of the transformer was 212 vac (!!!) at 60
Hz., single phase. Please note that the 3,025 VDC HV would sag 18%, down to
less than 2,500 VDC upon application of minimal drive and Grid Bias to the
final.
Tuning the amplifier using AØ versus 10PPS was the only way we could get near
true resonance, as indicated on the Ig meter bargraph. Several times we noticed
reverse current in the Ig metering.
Most notably, the spectral display of the transmitted signal with a
1.5:1 mismatch, from 15 through 19 MHz., at the 3KW rating of the 4CX3000E1
(GU-78B) PA, showed IMD products throughout the 50 KHz around the center
carrier frequency to a maximum of 5dB down! The collateral result was noticed
when pilot lights of the telephone radio equipment were noticed to be pulsing
in sequence with the keying.
Lastly, the Ig display during this test was seen to be illuminating roughly 50
percent of its Positive Grid Current display and 25 percent, (one LED segment),
of its Negative Grid Current display. At this point the test was immediately
concluded because we could not verify the correct tuning of the amplifier
output circuit on a pulse-by-pulse basis, and as such, need to replace the test
equipment completely with a regulated and better-shielded power supply that
does not succumb to its own distortion products.
Thank you, gentlemen. This discussion was so important to more folks than you
can imagine.
Hal
KA1XO
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|