[AReU] <---- February, 2006 meeting report.

[Ron Youvan]

Hi all:                                                                [AReU]

   I had a grand time at [AReU] last Tuesday, as usual.  I hope you did too.

   I would like to explain "the dog Tony was chasing" to our new friends/members.
   Originally the only way to determine transmitter frequency was to feed it's output down 
two parallel feed lines (open wire feed line, called leecher wires) at waist height (or 
so) and slide a indicator along these wires and measure the distance between  maximum 
indications, in METERS.
        (that's where that came from)
then wave meters were developed
then frequency meters were developed
then frequency counters were developed

   Before sometime in the '60s, transmitter (and receiver) dial accuracy was + or - 
hundreds of cycles per second.  Once digital readouts on our "VFO's" came into use, the 
accuracy has improved to under 10. Hz or so error.

   None of the Heath SB and HW series and most all Japanese made HF equipment of that era 
do not possess "state of the art" dial accuracy.  (with mechanical dials)
The procedure, with these radios, is to tune to a "frequency standard broadcast" and 
adjust the DIAL to read the "known frequency" nearest to where we want to operate, at the 
time.  If your radio (or receiver) covers the HAM bands only you may only have one 
frequency to choose from.
   With your own "frequency standard" at 1.0 mHz (or at 10.0 mHz with a one IC frequency 
divider you can divide by 10 and you will have a little carrier every 1.0 mHz along your 
dial.  (in all bands)
Some HF radios have a built in "marker generator," from the 60's to the development of 
"digital read outs" it operated on 100 kc/s and was not very accurate, in my Yaesu 
FT-757GX II (with a digital readout) it is every 25 kc/s and I presume it is a bit more 
accurate and more temperature stable.

   All quartz crystals used as frequency "standards" (sources) are temperature dependent, 
they mechanically vibrate and this vibrating speed (speed is frequency) depends on the 
temperature of the vibrating medium, usually a wafer of pure crystalline quartz.

   Two methods improve the stability if quartz crystals used as frequency "standards."
   The first is called TXO, a temperature controlled oscillator.  The quartz crystal/s 
(and possibly the oscillator circuitry) is within an insulated "chamber" referred to as 
"oven."  A system controls the added heat (from a heater) to maintain a constant 
temperature which must be above any ambient temperature that might be experienced. 
Usually 130. degrees f. or higher.  (This reduces component lives as a rule!)
   The second is called a TCO, a temperature compensated oscillator.  Here there is no 
oven, the components are selected (and tested at varying temperatures) so the various part 
values, mostly capacitance, changes in the reverse direction to the changes in the 
crystal, to the point that the frequency remains unchanged over quite a wide range of 
temperatures.  This is the "standard" oscillator (meaning supplied with the equipment) in 
most modern HAM equipment, frequently an optional TXO is offered.
   Which is better?  The TXO usually produces a better accuracy, but at the expense of 
having to warm up for about half an hour before "the" stable temperature is reached.   In 
fact the TXO equipment will be way off frequency when cold.  Normally the oven circuitry 
is kept operating  with the switch turned off, but if you unplug it (from AC or 12 Volts) 
the oven will go cold.

   Any questions?
--
Ron   KA4INM