[Boatanchors] Crystal Holder Pressure

[Gary Peterson]

Bry,

I will attempt to answer your questions and comments in some semblance of order.

Our station frequency monitor was manufactured by General Radio.  It contained a high precision crystal and thermostatically-controlled oven, with a mercury thermometer that enabled one to know that the oven temperature was correct.  Once a month, after midnight, we would modulate with a 1 kc tone, to enable Commercial Radio Monitoring Company to identify our signal and measure the frequency with equipment traceable to the NBS.  We would talk to the measuring service, long distance, and set our GR monitor to agree with their measurements.  

In the ‘60s, and before, meter readings were taken every 30 minutes.  Plate voltage, plate current, antenna currents and phases and frequency deviation.  There were five transmitting equipment inspections required for each calendar week.  Auxiliary transmitters were required to be tested, weekly.  Tower lights observed, daily.  A full audio proof-of-performance was required, annually.  If the station employed a directional antenna system, an operator had to be present at the transmitter site.  Monitor points, out in the field, for directional antenna systems had to be measured and logged at regular intervals.  Back then, FCC inspections were fairly common.  As you can imagine, all of this generated a lot of paperwork.  It was a great job for anyone in possession of a first class radiotelephone license, as these were required to sign most of the paperwork.  This job and license paid for my college degree.

Your engineer friend was probably interrupting modulation to obtain an accurate antenna current measurement.  Back then, antenna currents were made with thermocouple-type RF ammeters.  These meters read the power in the sidebands, in addition to the carrier.  The FCC wanted only the carrier power logged.  It was computed, using I-squared-R.  R being the resistive part of the antenna impedance.  Because the meter reading was derived from a heated thermocouple, there was a bit of a time lag.  There was often a push button that would kill modulation, in order to get an accurate reading.  When the audio was killed, it took a second or two for the thermocouple to cool a bit and for the meter reading to drop to the unmodulated carrier value.  It was easy to get antenna current readings during Paul Harvey, as he was well known for his pregnant pauses.

Needless to say, things are much different now!

Gary
KzeroCX 


“That is very interesting, Gary!
I wonder what you used to check the frequency?
Of course these crystals were probably in an oven too right?...
I remember hanging out at WFOM Marietta, GA in the late 1960s and chatted quite a bit wit he ENhgineer who was a full time employee I believe. I could be wrong but he was there at the station a lot. It was a 1000 watt local AM station on 1230 kHz. He would take and log a LOT of meter readings and antenna measurements. Occasionally they would take the station off the air for a few seconds to make some measurement or adjustment. I forget what that was now. Interesting times, to say the least....
Bry AF4K”