"Modern VHF/UHF Front-End Design" (1985)

Impressive. I was wondering how large a dish antenna would need to be in order to obtain the same 35.55dBi gain. Looks like 17 meters (55.8ft) diameter at 0.432Ghz:

2.45 degree beamwidth for the dish, 2.74 deg for the yagi array. I didn't see an NEC2 or NEC4 model of the yagi array, but my guess(tm) would be far more side lobes for the array than for a equivalent dish. However, I can see why your friend selected a yagi array instead of a big dish. The dish would be far heavier, far more difficult to construct, require a large pedestal, and probably more expensive. Nicely done and my compliments to your friend.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Send a PRN sequence and from the received signal search for a match. If you are using separate antennas for send and receive, you can use very long sequences and get good accuracy. If using the same antenna for Tx and Rx, you are limited to 2 second burst, before switching to receive.

At 1Ghz, 15 meters of RG-58a/u is good for: 15m * 60dB/100m = 9dB loss Duz your RF amp have at least 9dB gain? Or, perhaps switch to LMR-240 with only 7.9dB/100m loss?

It might improve sensitivity a little, but with all that 8bit sampling noise in the RTL2832U receiver, it probably doesn't do anything for weak signals. However, an RF amplifier can ruin the dynamic range by lowering the overload point. If I assume that the noise floor is limited by the 8 bit A/D converter, and the overload is limited by when the front end AGC decides to give up, adding any manner of RF gain will simply cause it to overload earlier. If you live in an RF polluted environment, too much RF gain might be a concern.

I guess I should mention that SDR receivers have an AGC (automagic gain control) in the RF input stage before the A/D converter. The idea is to set the RF level in the 820T tuner so that the A/C converter is able to use the largest number of bits to digitize the signal. Most digital receiver chips do NOT use the traditional analog variable attenuator for AGC, but instead use a digitally controlled step attenuator. Those work great for reception while stationary, and potentially horribly when dealing with wildly varying RF signal levels.

Notice the two "variable gain" stages. AGC isn't shown, but it feeds front end variable gain stage and possibly the IF gain stage.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

The need for ranging would justify spreading, but "real" QSOs are made from large antennas, power, preamps and large antennas and power ;-) Did I mention power and large antennas?

73, Gerhard, DK4XP

At 70 cm, you do not need a solid reflector, even a chicken net is enough. However, you are going to need a good support structure behind the net, if you are expecting hurricanes or ice buildup.

No liquid nitrogen required. "Free Piston Stirling Cycle Cryocooler with a cooling capacity of 5 Watts at 77 Kelvin with less than 100 Watts input power."

I've seen a few at various mountain top cell sites. Most of them had some kind of "DO NOT TOUCH" signs plastered on them to discourage nosey techs and engineers like me from playing with it.

The reason to install cryogenic cavity filters on cell site receivers is due to a symmetry problem with cellular communications. On 800MHz, the cell site can legal belch up to 1 watt per channel, which is easily heard by the average handset. However, the handset and smartphones transmit at a much lower power level. My antique LG VX8300 typically shows about 50 milliwatts TX power (in test mode). Smartphones tend to run at about 100-200 mw TX power. To compensate for this 10dB difference in link budget between each direction, a few dB can be gained by reducing losses in the cell site receive system, by using low loss cryogenic cavities. Low loss cavities help, but do not compensate for the entire 10dB difference. For example, it does nothing for coaxial cable losses.

You won't see too many of these in service because they are really only effective on the 700, 800, and 900 Mhz bands. At higher frequencies, the high fashion solution is to install a TMA (tower mounted amplifier), which moves the receiver front end, transmitter power amplifier, and RF combiner to the top of the tower. The trend toward "small cells" and DAS (distributed antenna systems) have also contributed to a decrease in popularity of cryogenic solutions.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Just wonder how many dB he's losing in the combiners for the yagis ...

--

73, Tauno, OH2UG

I used a 100 m reel of RG58 as a dummy load, at 1.3 GHz, it did not have a significant effect if the other end was open, shorted or terminated into 50 ohms. But do not feed too much power into the cable, the first few meters might melt :-).

The 8 bit ADC would be a limit in a single signal environment (signal generator), but in real word all the other signals on the band will function as dither noise, making it possible to receive signals well below -48 dB FS.

However, with only 8 bits, setting the input level is problematic, since the worst case combined crud at input can occasionally add up to huge amplitudes, saturating the ADC.

70cm? When RF test equipment is calibrated in meters and centimeters, I might try referring to the bands by their wavelengths. Meanwhile, I much prefer using the equivalent frequencies and suggest you do the same. Or, would you prefer instead the 2.30 foot or the 1.53 cubit band?

I didn't mention anything about dish construction.

The problem with big dishes is rigidity. The nature of the beast requires that it be mounted using a pedestal, making the dish a cantilevered affair which is subject to bending under its own weight. In order to obtain the maximum theoretical gain, the dish must be an accurate parabola to within about 1/10 wavelength or in this case 7cm. At 430Mhz, that's fairly easy for small dishes, but more difficult for a 17 meter wide dish. It can and has be done with a rigid frame, but it's still more difficult to build and stabilize than a yagi array.

Here's an 8 meter dish. Now, imagine what a 17 meter dish would look like:

Personally, I was thinking in terms of an inflatable dish. Dirigible style contruction with a aluminized mylar flexible frame. Basically, air pressure keeps the dish rigid. However, at 17m diameter, it's much too large a project for me.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

The distance to the moon varies between different points on the ground, at different times of the day, and to different points on the moon. The orbit of the moon is not a perfect circle. You might end up taking measurements on different days or at different times, and obtain different results. You might also read something on RADAR theory as you're going to have resolution problems with a rise time limited RF pulse and a bandwidth limited receiver.

Use a pulsed laser and you don't need to worry about EME political correctness.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Look up libration fading which mangles a long pulse quite radically.

Not only that, you must also consider the rotation of the Earth and the Doppler shift caused by it and the daily distance variation.

Why use a single pulse instead of a coded sequence of pulses (such as PRN) and a matched filter in the receiver. Use a pulse sequence shorter than 2 s, if you are using the same antenna for both Tx and Rx so that you have time to switch from Tx to Rx.

half a dB per 1:4 stage IIRC. He has given the exact numbers on the web site.

Jeff Liebermann wrote

Like I showed from rtl_test: Found Rafael Micro R820T tuner Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6 That is enough for most if no tall AGC situations IMNSHO. Steps are really small for high gains. I 4 sure never had a problem with that.

Libation? Offering alcohol to the moon gods was known to work in the distant past. Oh, you must want something else.

"Frequency-Dependent Characteristics of the EME Path"

I seem to recall (but am too lazy to lookup) that most EME software calculates the various Doppler shifts and adjusts the receiver frequency accordingly. It's much the same as working ham radio satellites, but with two Doppler shifts.

Why make it complexicated when a CW pulse is sufficient? Traditionally, it was done with Morse Code, mostly to guarantee that you're hearing the real moonbounce, and not another station or alien replies from the far side of the moon. These daze, it's done with WSJT software and JT65 protocol. For example: See part III I guess using a computer to run everything is the ultimate form of EME "doping".

Just about everyone uses the same antenna for TX and RX. Round trip delay is about 2.5 seconds, which is plenty of time to switch direction.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

You'd need your own nuclear power plant to run it, though, or else a metre-class telescope. The photon budget for lidar to the moon is pretty heartbreaking, mostly because the photon energy is too high and the reflection is diffuse (it goes into pi steradians). Apollo left a corner reflector there, so if you can hit it, you can do the measurement with a kilowatt-class pulsed laser.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Ok, bad idea. Perhaps a lunar laser rangefinder is rather ambitious for this project and RF would be easier.

"Mythbusters Moon Hoax Retroreflectors"

"Lunar Laser Ranging experiment"

"The Apollo 15 Lunar Laser Ranging RetroReflector"

"Want to measure the distance to the Moon yourself? Now you can!" Uses a digital camera and a smartphone, but no laser.

"Lunar Laser Ranging Experiment (about 1972?)

"Amateur moon laser ranging"

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Here's a radar moonbounce, done in 1946.

Probably a megawatt or so transmitted power, a mediocre crystal diode receive mixer driving a vacuum-tube IF strip, and not too tight antennas.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Which the Chinese will no doubt be producing in less than 10 years for under a dollar.

-- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

With 24dB gain the EIRP was about 750kW with 3kW output so a megawatt wasn't that far off.

I wonder how they identified the source so positively. Maybe accurate transmit frequencies of the transmitters were published? I sort of remember that the analog transmitters were always at some offset (a multiple of the scanline frequency) from the nominal frequency of the channel.