[NLRS] Re: (LONG)10GHz Operating procedures ?

[John P. Toscano]

Donn Baker wrote:
> [I'm cc:'ing the entire NLRS list on this.  There is sure to be experience
> there that is useful, but won't get captured with just the 10GHz list.  Donn]

I will send my $0.02 there, assuming that all the other individuals on 
your original distribution list are also subscribed there.

> 9) Don't follow the other guy by changing your TX frequency.  Use RIT or
> split VFOs...

This one stumped me at first.  Of course, I have ZERO first-hand working 
experience on any frequency above 1296.x MHz with the exception of a few 
QSO's on 10 GHz WBFM, nevertheless I will try to offer some ideas that 
may hopefully be constructive.

My first take was, "the problem is drifting LO's", inherent in starting 
with a lower frequency crystal oscillator and multiplying it an enormous 
number of times to get up to 10 GHz, so a little original drift causes a 
large drift in final frequency.  If that's the case, I imagine it to be 
unlikely that the Tx and Rx frequencies would drift *apart* from one 
another significantly, so why not just tune the main VFO up or down and 
be done with it?  (This sentiment seems to be shared by Jon's reply.)

But I have too much faith in Donn's experience to assume he would be 
conjuring up a unique solution to a problem that didn't exist.  What 
could cause a disparate shift between Tx frequency and Rx frequency? 
The one thing that came to my mind (probably from my past satellite 
experience) was Doppler shift.

Imagine KM0T is at his home QTH with his dish pointed due East.  Imagine 
N0DQS is due East of Mike, in his rover vehicle, and Gene is driving due 
West at 100 Kilometers per Hour (62 MPH or thereabouts).  Mike transmits 
on 10.368000000 GHz.  Assuming that Mike's and Gene's transverters and 
I.F. radios are precisely on frequency, where does Gene hear Mike? 
Based on the Doppler effect, at 10.368000961 GHz, or 144.000961 MHz on 
his IF radio.  So Gene tunes to 144.000961 MHz (peaks up on the signal) 
and transmits back to Mike.  Where does Mike hear him?  10.368001921 
GHz, or 144.001921 on his IF radio.  So Mike tunes up to that frequency 
to acknowledge the transmission.  His signal is heard by Gene at 
10.368002882 GHz, so Gene peaks up to 144.002882 MHz on his IF rig, and 
send back his acknowledgement, which Mike hears best at 10.368003843 
GHz, or 144.003843 MHz on his IF rig.  Because each of them is adjusting 
both transmit and receive frequencies each time, and because each of 
them is hearing a signal Doppler shifted HIGHER than it is transmitted, 
they keep "walking up the band" to stay in tune.  If they each left 
their transmitter frequency alone, and adjusted only their receive 
frequency, they would have stayed in place (other than oscillator drift).

OK, so why should any of this matter if both stations are in fixed 
locations?

I guess that the answer lies in reflections.  Granted, on a direct path, 
or with a reflection from a non-moving object (e.g., the Downtown 
buildings), there should be no Doppler effect.  But airplane scatter 
involves velocities much higher than 100 Km/hr, and so the Doppler shift 
would be much higher, and complicated by the fact that the shift at each 
end of the path is in different directions!  Cloud scatter?  Rain 
scatter?  Tropo scatter?  These reflective objects are not likely to be 
stationary, so Doppler effects may come into play.

And talk about good timing, I just received the July/August issue of QEX 
in the mail yesterday, and on page 3 is an article entitled "Microwave 
Propagation in the Upper Troposphere".  The authors demonstrate several 
instances where 10 GHz signals *ARE* received with significant Doppler 
shifts.  Looks like my imagination isn't so bad, in spite of zero 
practical experience on 10 GHz weak-signal equipment.

Hope that helps.
73 de W�JT