(meteorobs) Standalone Forward Scatter RADAR Receiver

Jay Salsburg jsalsburg at bellsouth.net
Fri Aug 10 07:12:25 EDT 2012


Hello bob

Thank you for the advice. I looked at the CC222 converter. Even though this
may work for your purposes, I want to create a complete solution where no
other receiver equipment is needed. The idea is to make a receiver that will
work for all three NAVSPASUR Sites and use a PC to record and observe meteor
activity. Since NAVSPASUR is so powerful, I estimate anyone within 400 miles
of the 33rd parallel (North America) will be able to receive forward scatter
meteor activity, unless they live on a mountain.

If the Converter you mentioned were placed in the Antenna and its
Down-Converted Signal fed to a Demodulator/Detector module on the other end
of the signal cable, this output could be displayed on the PC in the usual
manner. There is a technique for demodulating a CW/SSB Signal utilizing the
old SA602 Chip. The difficulty arises with a precise Local Oscillator that
does not drift. But this becomes cumbersome.

My idea is to put the Receiver on the Antenna and feed the demodulated Audio
signal to the PC using Microphone cable to send power to the receiver and
signal back to the PC. There is no Commercially available Receiver for
NAVSPASUR Off-the-Shelf. I want to make one and sell it for less than $100.
This sounds impossible, I know. What is needed is a Direct Conversion (DC)
Receiver, the CC222 may be adaptable to this purpose.

You mentioned being too close to the Gila River site. This may not be. As
you know, all energy reflected from Space Objects is off frequency. I can
understand the receiver being swamped by such a powerful transmitter but
surely you can place the antenna behind a obstruction. If you can get just
20 miles away, the transmitter will be below the horizon. Phoenix Airport is
22 Miles from the Gila River Transmitter. Having close proximity may be an
advantage because of enhanced retroreflection being close to the axis of
transmission.

A DC Receiver uses the frequency of the transmission as the Local Oscillator
(LO) frequency. A Double Balanced Mixer suppresses the LO and Transmitter
freq, leaving the sidebands intact. You can achieve 45 db suppression with
this technique. The problem with the Doppler Energy from Meteors in the
NAVSPASUR Beam is that the frequency difference is very low, only a few
hundred hertz offset. I tune my receiver to a lower frequency than the
transmitter so the Doppler frequencies are near 1000 Hz. This makes them
very easy to hear. There should also be ways of shielding the receiving
antenna from the line of sight of the Transmitter; Buildings, a Corner
Reflector, Cylindrical Beam Formation. etc. You might try just a Simple
Dipole without any other elements, orienting it in parallel to the
North/South direction of the Gila River Antenna. This will mechanically
suppress some of the Energy falling directly on the receiving antenna and
pointing the receiving propagation pattern in parallel with the Fan Beam.
You might also try placing the receiving antenna in a hole in the ground,
using the natural barrier of the Earth itself to block the Transmitter.

Being north or south of the Beam has advantages, it produces greater
textures of Doppler Shift frequencies. I am 300 miles from the Texas
Transmitter, my receiver works very well. Just a few days ago, the ISS went
over Eastern Arizona/Western New Mexico, I got a bounce off the Gila River
Site. The ISS was 880 miles away.

-----Original Message-----
From: meteorobs-bounces at meteorobs.org
[mailto:meteorobs-bounces at meteorobs.org] On Behalf Of bob
Sent: Thursday, August 09, 2012 12:06 PM
To: Meteor science and meteor observing
Subject: Re: (meteorobs) Standalone Forward Scatter RADAR Receiver

Jay - I am interested in your NAVSPASUR receiver.I have built several RF
converters to get meteor foward scatter into my ham band communications
receivers. The converters were easy to make as I used some junk box clock
oscillators for the LO. These converters were used for SNOTEL (40.53MHz) and
TV channel 4. When I decided to try NAVSPASUR my options were very few as my
oscillator/crystal population did not make it easy to downcovert NAVSPASUR
so I used a RF converter from Hamtronics, the CC222. I also did not make an
LNA as I did for my other reveivers as I was getting tired of soldering
those tiny surface mount packages onto cutup copper clad board. DownEast
Microwave had a nice kit(L222LNACK) w/pwb, connectors and housing for $45.
I am not sure if you are making a converter or a complete rx, but I do have
one suggestion, if you can implement it for a complete rx; try to make it
possible to receive the other NAVSPSUR stations at Gila River, Arizona
(216.97 MHz) and Jordan Lake, Alabama (216.99MHz). The Gila River signal is
too strong to be used in the Phoenix area where I live, but I am in the
process of making measurements using the Gila River station up in the
mountains 60-150 miles away; would also like to try it in San Diego. Still
do not know if being 90° to the antenna beam is a problem up North.
I've added the links for the LNA and RF converter that I used if you need
any ideas.
http://www.hamtronics.com/pdf/CC-%28vhf%29%20Converter.pdf
cc222
http://www.downeastmicrowave.com/PDF/l-lna.PDF
L222LNACK



--- In meteorobs at yahoogroups.com, "Jay Salsburg" <jsalsburg at ...> wrote:
>
> I am designing a Standalone Forward Scatter RADAR Receiver for NAVSPASUR.
Is
> anyone interested in my progress?
> 
> Jay Salsburg
> 
> _______________________________________________
> meteorobs mailing list
> meteorobs at ...
> http://lists.meteorobs.org/mailman/listinfo/meteorobs
>


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