Phase locking a microwave oven for EME use?

The following discussion about the posibility to phase locking a

microwave oven for EME use took place in the Moon-Net
reflector. I found the subject so interesting that I decided to put
together all the messages in this page.
On 12 October 1998 N4IP wrote:
Has anyone tried phase locking a microwave oven for EME use. I've
heard of people using them for AM transmitters and other uses. Where
do I hook up the keyer????
On 13 October 1998 OH2AUE wrote:
Haven't tried it myself, but there has been at least one article on
phase locking a microwave oven magnetron by controlling the cathode
voltage ( anodes are usually grounded ) via a high voltage valve
voltage regulator. The principle is based on the typical power supply
pulling of the magnetron frequency. The tuning range is quite small,
so the magnetron cannot be pulled far off from its nominal frequency
of 2450 MHz. Plenty of CW power though !!!
Keyer ? Thats a tough one. I have used two types of PLL oscillator
modulation to achieve "CW sounding" signals from microwave beacons;
one is to FM modulate the carrier with noise when the "key is up" to
spread the carrier over a wide spectrum and the other is to FM
modulate the carrier with a crystal controlled 10 kHz audio source at
such a modulation index that the carrier power is distributed into
sidebands at the first Bessel Zero. Crude, but sounds good !!!
BTW. If you have a suitable circular waveguide horn with a phase
locked magnetron plugged into the side of it, you can fit a second,
free running magnetron probe onto the opposide side protruding into
the same electric field and this will spontaneously injection lock
onto the PLL controlled carrier for 3 dB more power.....
In fact, you could couple several magnetrons onto a longer section of
waveguide to.....oh boy, I better stop....
On 13 October 1998 G8WRB wrote:
I've not tried it, but in principle a small stable signal at the
frequency of interest, injected into the cavity (small loop), should
cause the magnetron to lock to the stable signal.
I assume you would have to switch the HT on/off to key it. My guess is
that if the HT is turned on, it would take some time to lock to your
stable source, during which time the frequecy could be anywhere.
These are just some ideas - I have not tried any of them.
On 13 October 1998 GM4JJJ wrote:
I find the easiest way to key one is just to open and close the door
:-)
On 13 October 1998 AL7EB wrote:
>Keyer ? Thats a tough one. I have used two types of PLL oscillator
modulation
>to achieve "CW sounding" signals from microwave beacons; one is to FM
modulate
>the carrier with noise when the "key is up" to spread the carrier
over a wide
>spectrum and the other is to FM modulate the carrier with a crystal
controlled
>10 kHz audio source at such a modulation index that the carrier power
is
>distributed into sidebands at the first Bessel Zero. Crude, but
sounds good !!!
BTW this method of producing cw was originated (or at least promoted)
by the San Bernardino Microwave Society, years ago, for freq. locked
polaplexer klystrons (recently gunnplexers). The key was input to a
logic inverter so that (as you stated, above) when the key was up a
tone was modulated on the oscillator control voltage at a modulation
index to produce a nulled carrier and wide sidebands, but when the key
is down the modulation is removed and the oscillator is not modulated
thus producing a pure carrier. The advantage of course is that the
oscillator is not started and stopped thus staying in lock and stable.
The signal to the receiving station is passed thru a narrow filter so
that the wide fm tone is not detected; only the carrier.
>BTW. If you have a suitable circular waveguide horn with a phase
locked magnetron
>plugged into the side of it, you can fit a second, free running
magnetron
>probe onto the opposide side protruding into the same electric field
>and this will spontaneously injection lock onto the PLL controlled
>carrier for 3 dB more power.....
>
>In fact, you could couple several magnetrons onto a longer
>section of waveguide to.....oh boy, I better stop....
My boss, Dick Kolbly, when I was working at the Goldstone Tracking
Facility (NASA), experimented with using oven magnetrons to produce a
cw carrier. He's a member of the SBMS, still, and you may be able to
contact him thru the SBMS web page. As I remember, he was able to
generate a fairly clean signal with them.
On 13 October 1998 K2LME wrote:
Communications Quarterly's Winter 1991 issue has an article by WA6EXV
describing his 13 cm magnetron implementation.
On 16 October 1998 S57UUU wrote:
Many years ago, I came across an article (I think it was in the IEEE
proceedings) about orbiting solar power stations. One of the ways
considered to transfer power to Earth was an active phased array of
millions of KW class phase locked magnetrons. In this article, the
author(s) wrote that a cooking magnetron produces quite a clean
signal, when fed with smooth DC. This made me think, but I haven't had
the required rectifier, WG couplers, QRO loads etc etc.
About a year ago, Pavle S57RA upgraded his 'Frankenstein laboratory'
with some HV transformer brutes, so we decided to try this out.
The basic circuit was a 5kV conventional rectifier with an improvised
constant current source made with an GI-7 russian triode. The
magnetron was a Toshiba 2M240, connected to a standard waveguide with
tuning screws.
For phase locking, we tried to use the circuit from the S53MV 13cm
satellite receiver. It has about 2MHz reference frequency with a few
hundred kHz of loop bandwidth. The magnetron was used as a 'CCO'
(current controled osc).
The results:
(Note that this magnetron has 2460 MHz nominal frequency, so results
would be better with a 2450 MHz type)
The frequency can be changed both by the impedance that the magnetron
'sees' and by the current. (DC-wise the magnetron is almost like a 4kV
zener diode, so it must be connected to a current source, not a
constant voltage supply!) By both methods, single or combined, the
frequency can be pulled down to abt 2415..2420 MHz where the magnetron
starts to 'mode' (the single line spectrum changes to a forest of
crazy dancnig lines). We haven't tried to change the DC magnetic field
of the permanent magnets.
At the 2424 japanese band, it gave abt 100W of power at 50..60mA, at
2434 abt 250..300W at cca 150mA and at 2460 it gave 800W at
350..400mA.
The spectral line width of the unlocked magnetron was abt 1..2 MHz,
sitting on a wideband (10's of MHz) 'noise hill' some 30-40dB down.
The noise gets worse as you pull the magnetron away from its design
frequency. The noise seems to be generated inside the magnetron, you
can see it if you monitor the DC current through the magnetron with an
oscilloscope. The height of the grass on the 'scope grows as you
insert the tunning screws.
We weren't able to get a phase lock, the magnetron was simply jumping
around too fast for our PLL circuit to catch it. The circuit we used
is a 'divide down' PLL, and it was to slow. With a 'mixdown' PLL with
a MHz or so loop bandwidth things might have worked. Also the current
source should have very high impedance and fast regulation. A choke is
probably no solution, since it would slow down the PLL. Also, removing
the heater filter caps in the magnetron case base might help.
About modulation:
The best solution is to use FSK. If the shift is a kHz or so, the
receiver can be tuned to hear only the 'mark' frequency - it will
sound exactly the same as a 'real' CW transmitter. If tuned to 'space'
frequency, the receiver would hear 'inverse morse', but I think that's
no problem. In fact, the communication theory says that a receiver
using BOTH frequencies could gain up to 3dB in sensitivity. (if we
don't switch the TX off between dots and dashes, it is better to USE
that energy than to throw it away by
spreading or noise modulation.)
I had some slides and circuits with me at the Paris EME conference,
but the time schedule was so tight, that I forgot about it...
On 19 October 1998 AL7EB wrote:
This was the project we were involved in, that I commented earlier
(10/13/98) about. One thing I remember: Dick (Kolbly) experimented
with the magnetron by turning off the filament supply after initial
oscilation began with a resulting narrowing of the output noise
spectrum (apparently the filaments continued to be heated by back
bombardment). I was a jr. engineer at the time and my part was
designing and building a w/g transition to couple the Litton
magenetron to our (NASA-DSN) standard WR-430 w/g. Soon after I was
transferred to the Microwave Receiver Group and wasn't involved in the
tests. Could you list the IEEE article/proceedings issue? I would be
interested in obtaining a copy of them.