Dave Typinski ) writes:
On Sun, 21 Oct 2007 01:01:19 -0400, "Jimmie D"
wrote:

"Dave Typinski" wrote in message
. ..
Anyone have any ideas about what one might do with a television
receive-only (TVRO) antenna? The thing is 10' diameter and it's mine
for the price of dismantling it and hauling it out of the present
owner's back yard.

I'm thinking radio astronomy. Might be nice to make my own radio map
of the galaxy. I'm guessing that this would work okay somewhere
between 1 and 10 GHz... which means making a feed horn... which is
easy enough to do.

What else could I do with this antenna? Other than covering it in
polyethylene sheet to make a really big bird bath...
--
Dave Typinski
AJ4CO

I know of a couple of guys that took two of them, one for rx and one for tx,
tx was a microwave oven mgnetron. He and his frined talked to each other via
troposcatter. I do know if a maggie operates within a ham band or not but it
didnt matter too much for these guys because they didnt have a ticket
anyway.

Jimmie

I thought about magnetrons... but not for communication. My idea is
to set it up as a radar station to measure the distance to the Moon. A
microwave oven magnetron operates at 2450 MHz, which is right at the
upper edge of the 13cm ham band. Unfortunately, magnetrons produce a
really dirty, wide output. Worse, being right at the edge of the
band, half the RF energy would be out of band.

How do you think the higher bands were conquered? It was always with
simple equipment that was cheap and easy (relative speaking), with
the more serious work coming later.

So before WWII, it was modulated oscillators and superregen receivers
on 56MHz and 112MHz. After the war, new equipment was available, and
there was a desire for pushing the limits (and laws came in at some
point to require better signals), and there was a move to crystal
controlled transmitters and better receivers. Well, they really
went together, since if you changed one, the other had to follow.

So that equipment got pushed up further, helping to stake out
220MHz and 420MHz. A lot of work was done on the 1215MHz band
after WWII and even through the early sixties with the venerable
APX/6 (I suddenly realize I may have gotten that wrong), which
was a modulated oscillator for the transmitter, and it was often
debated whether it was amplitude of requency modulated. The receiver
was a superhet, but had a nice broad IF bandwidth, so it didn't matter
how much the transmitter drifted. I seem to recall that the APX/6 was
intended as an IFF unit, it gets triggered by radar and identifies
itself as a friend, so nobody shoots at the airplane.

Newer techniques came along, more desire to push the limits, and that
sort of thing was slowly phased out on the band.

But hey, it moved further up. In the late seventies, a lot of hams
played with the 10,000MHz, using garage door openers, modulated
oscillators and broadband receivers.

The further you go up in frequency, the more such cheap and
simple equipment can be tolerated, since the bands get wider (well,
until they get narrowed as bits are allocated away from amateur
radio). So there is long history of both wideband simple equipment
and narrowband DX'ing going on at the same time, albeit at opposite
ends of the band.

But in reality, you dig up that article that was in "73" years ago
that was about adding a phase locked loop to a microwave oven, which
gives a nice narrow signal.

Michael VE2BVW