Re: Long range (high power?) 433MHz, 916MHz, 2.4GHz transceiver for data comm

1uV

suggest

no

one of the first lunar probe transmitters was 0.1w at 108 mhz.

"Dave VanHorn" wrote -

Yeah, and to receive it, they used steerable dishes that were as big (and likely cost as much) as your whole neighborhood!

i don't know that to be true, but i have the schematics for the transmitter.

moonbounce is done by hams all the time, on the 2 meter band. given that the moon is a really lousy reflector, and also the wrong shape, it seems entirely reasonable to me that a low noise receiver, with a reasonable antenna, could pick up a tenth of a watt from that distance.

Are those available for download somewhere?

Cheers,

Andi

--
If Mr. Edison had thought smarter he wouldn't sweat as much.
   - Nikola Tesla

\

here's the seti league's antenna. this is probably about 8' across and about

3' high. four antennas transmit, and the other four receive. notice that the antennas are wound in different directions. when the signal reflects, it is changed to the other rotation direction.

here, they describe the system.

power up the pipe is 150 watts.

given the large path loss, the signal coming off the moon will certainly be much less than 100mw

Thanks for the reference, Dave. I couldn't figure out what interest SETI had in the moon (which most of us believe to be uninhabited!) Until I read further that it is a "reference standard" for radio-astronomy calibration. Ingenious!

big kind of awful reflector in the sky.

The date of the photo might be crucial.

The first amateur moonbounce took place in 1953 (the first moonbounce ever, by the US Signal Corp, was in 1946), though they never tried to contact anyone (obviously); they just hear their own signal back from the moon.

That was before parametric amplifiers (Sam Harris is credited with making the first practical paramp, he was a ham and did moonbounce), and transistors. They had to use either fairly noisy diode mixers (I forget what frequency they used) or fairly noisy tubes in the front end. I suspect the transmitters were fairly effective, but still they likely needed every bit of ERP they could get.

And large antennas had to be the norm in the old days. Not many doing moonbounce, and still not so great receivers. I'm not sure how many put their equipment right at the antenna, rather than facing the losses of the feedline.

But once enough got on with those big antennas, and other factors improved, it became easier for others to do it. A guy in Australia did it in the sixties from Australia, and they had something like a 150watt power limit. But, he had a lot of space on the farm, and he had big rhombics. I thought he had a section to allow some directing, but basically he could only do moonbounce when the moon was in the right place for the antenna.

When Sam Harris started working at Arecibo, he worked it so they used the antenna for moonbounce one or two times in 1964 or so. That thing had so much gain that it made moonbounce feasible for a lot of people during the brief time it was tried.

So there's a balance. The guys with the big arrays enable people with much smaller systems to do moonbounce.

Along the way, the receivers got better. First, they used paramps, and then solid state devices started getting better. I remember one review of a fairly early FET converter, and the writer said it compared well with his 416 (or was it a 417?) converter, and the 416 was considered basically the best front end tube for VHF/UHF at the time. He admitted that it meant his tube converter needed adjusting, but considering there was no finicky adjustment of the FET converter, it bode well for the future.

So if someone wants to hear their own echo at this point, they may find they still need a fairly good system. But because there people with good systems, others can get by with less.

Michael

"Michael Black" wrote ...

This one was on the cover of QST just 2-3 years ago at the most.