Cliff Bates  KC7PPM    crcwnet.com               1/17/98
     This is a basic primer about getting started in Amateur
Radio Astronomy (RA), and is mostly based on the school of
hard knocks and mistakes I've made over the last 4 years
since I've been interested in RA.  Hopefully, after reading
this, those of you who are up and coming will not repeat my
mistakes and thus save yourselves not only a lot of
frustration, but considerable money.
     Many SARA members who are much more knowledgeable than I
have published papers on how to observe, record, document and
understand what shows up on your chart.  This primer is about
the basic eqipment you'll need, how to set up your system,
and finally how to minimize the dirt on your window to the
     From an email question having to do with some Ham stuff
I met Dick Flagg, (AH6MN), whom come to find out, was also an
SARA member who lived in Hawaii. Dick had acquired RA
experience while working as a electronic engineer at the
University of Florida, and currently is a engineering
     Over the years and hundreds of emails Dick has
inadvertently become my mentor as my interest wondered more
and more toward RA and "The Ultimate DXing".  He has had the
patience of Jobe, and then some.  Though Dick and I have
never met face to face, whatever you may find of use in this
primer is from Dick's patience,knowledge, and editing.

A Little History
     As luck would have it, just before I got interested in
RA I bought a house where they have covanants against
antenna's.  Mistake #1.  Still, I thought if I bought a 10
foot dish and designed it to lay down when not in use, then
planted 6 foot arborvitaes around the area who would care.
Mistake #2.  So I bought a 10' TVRO dish, designed kind of a
neat setup to allow the antenna to be raised and lowered down
to 2 feet of the ground and spent a week planting a forest of
$800 dollars worth of arborvitaes to hide everything when
viewed at ground level.  That done I started to dig the hole
to mount the dish in.  I had about 3 shovelfuls of dirt out
of the ground when the convanence committee showed up and
explained that this was a no-no and I was going to get sued
if I didn't knock it off.
     Several days later I ran into a friend who has an apple
orchard and he mentioned that somebody had stole his
irrigation pump and he needed to put up a structure to house
the pump in.  I explained my problem and that I would build
him a small building if I could locate my RA stuff in it.  So
we ended up with a nice 8' by 10' flat roof structure.  This
is as large a building as we could build without obtaining a
building permit.  The roof was designed to be removed if it
ever became necessary to pull the well pump.
     I then mounted the 10' dish and a Yaesu AZ-EL rotor up
on the roof and decided to try to do RA using the ICOM 7100
scanner audio output into a voltage chart.  It worked, but
not very well.  I could see really big sources, but little
else.  Dick suggested that if I was really going to do this
seriously I needed to put a total power receiver, (TPR), at
the receiving end, instead of a scanner.  A scanner was too
noisy and didn't have the needed sensitivity.  As luck would
have it Radio Astronomy Sales had just come out with a
TPR setup for receiving 1420 Mhz hydrogen line radio
     A Total power receiver is defined as, "any receiver
which measures the total noise power from the antenna and
from the receiver." This explanation when I got started was
about as clear as mud.  How about instead we say, "a receiver
that generates a DC output voltage proportional to the RF
input power".
     RF power is often expressed as equivalent antenna
temperature - that is the "temperature of a resistor" would
have across the input terminals of the receiver that would
generate the same noise level as the antenna is seeing.
     It is important to remember that the TPR is looking at
what the antenna is seeing, and any other noise generating
components including the preamp due to its noise figure,
lossy coax and connectors.  A TPR is simply a radio
thermometer, tuned to the thermal radio emissions in a
particular wavelength.  But when properly setup it is a very
sensitive instrument.
     Anyway, I bought a TPR and I was having a great time
seeing all kinds of interesting things on my chart.  The only
problem was the results of one observation were not
reproducible two days in a row!
     Shortly thereafter in 1995 I went to the SARA Conference
at Green Bank.  If any of you can possibly attend I would
highly recommend it!  Especially if your just getting
started.  For me this established the baseline of what RA was
all about.  Not only did I get to play with a real 40' RT,
but I found that it's results and my results were
considerably different, and not just because of the size of
the dish.  But because of what I was "over looking".  My
window to the universe was very dirty.

     We have to keep in mind how weak some of the signals
we're trying to receive really are.  The sun light falling on
a just one square meter surface at the equator generates
about 1 horsepower.  The radio energy of all the stars
falling on all the radio telescopes in the world has about
the same energy as a fly taking off.  A basic unit used in RA
for measuring this radio frequency power is known as the
Jansky.  One Jansky is defined as,"10 to the minus 26th
power, watts per square meter per hertz."  Or another way,
0.000000000000000000000000001 watts per square meter per
hertz.  A fairly large sized astronomical radio source would
be 200 Jansky at 1420 Mhz, most are much, much less than
that.  The name of the game in RA is WATTS/SQUARE METER/
HERTZ.  The more square meters of aperature, or area of the
antenna, and the wider the receivers bandwidth, the more
     So, unless your system is very clean of noise, power
deviations, temperature changes and signal losses, much of
what you'll be seeing on your chart will be from your own
equipment.  This was what I was overlooking.
     You'll be able to see the Sun, and other large sources,
but the rest will be lost in the noise of your system, or
variations generated by your system.  This can be extremely
frustrating to say the least, and I've been there.  In fact
I'm there most of the time for one reason or another.  It's
also "The Challenge" of doing RA.

Which Frequency
     Most of my experience in RA has been in the 1420 Mhz
range, though I play quite a bit in the 440 Mhz Ham bands as
a Ham Operator.  The needed equipment for RA at frequencies
below 450 Mhz is usually considerably less expensive and
easier to obtain, adjust, and repair than an equal system at
1420 Mhz.  Test equipment is also considerably easier on the
budget at 400 Mhz. At 1420 Mhz and up, cost, (already out of
sight), follows frequency!
     However, the lower the frequency, the higher the
cosmic background noise level.  1420 Mhz is in the pocket of
the Water Hole where things are about as quiet, as far as
cosmic back ground noise, as they are going to get.
     Antenna gain is a function of capturing as many
wavelengths of a particular frequency as possible.  If my 10'
dish has a antenna gain of 30 db at 1420 Mhz and has a
antenna receiving horn 5 1/2" in diameter, at 400 Mhz to get
the same antenna gain I would need a dish 33' in diameter and
a antenna horn 20" in diameter!
     So for two systems of the same gain, what is saved at
400 Mhz in the receiving equipment is lost in the antenna
system, and visa-versa at 1420 Mhz.  Everything being roughly
equal between the two systems as far as total cost per db,
1420 Mhz has a considerably quieter noise level and a smaller
sized antenna system.  Consequently I prefer 1420 Mhz.

Antenna Tracking
     The 40' dish antenna at Green Bank is fixed in azimuth
at 180 deg.  and is only moveable in the elevation mode.
There is nothing wrong with this type of design, except you
have to wait until the object passes through the antenna's
beamwidth by the rotation of the earth before it is
     If this window of opportunity is missed and there is a
need to try again, then a AZ-EL rotor is nice to have to
follow the target object.  They are also expensive, and
unless you design your own system, do not track that well.
     A 10' dish is about as small as you can go and get
good results at 1420 Mhz without undue dish blockage, or
shadowing by the antenna horn of the dish surface.  However
for a rotor a 10' dish is one heck of a sail to hold in
place.  Even with counterweights it is much more than a Yaseu
rotor is designed to handle in both weight and wind area.
The rotor lasted a year before the wind stripped the gears in
the rotor one day.
     I then installed a Emotator rotor which was about twice
as expensive.  This is a fairly husky rotor and has lasted 2
years now without a problem.  However, it does not track less
than 3 degrees in the auto tracking mode.  So if you have
visions of tracking and object and getting a long steady run
on it like the big boys, forget it.  You end up with a
sawtooth chart as the object drifts partly through your 5
deg. beam, then the rotor advances another 3 degrees to
offset the earths rotation.  The big boys RT's are usually
run in a tracking mode when studying a particular source.
But they have a little better system that slowly and
continously drives their dish offsetting the earth's
rotation.  This capability is nice to be able to do, but
requires variable speed motors and very accurate positioning
equipment of where the dish is in relation to azimuth and
elevation.  Plus it needs a computer program able to drive
the dish accurately.  Not impossible, but very expensive and
mostly a do it yourself thing better left until you get
everything else working at its best.
     The Emotator rotor is designed to work to 1.5 deg., but
here the problem is one of momentum.  With a hundred and ten
pounds of counter weight, 45 lbs. of antenna, and 15 lbs.  of
support structure, horn and preamp, when the rotor stops, it
stops!  It doesn't slow down and gently stop.  So with this
sudden stoppage the antenna's torque momentum causes the
setup to twist slightly and then snap back.  This in turn
causes the rotor to think its not pointed where it should be
and energize again to correct.  In short, the whole setup
starts hunting back and forth and shaking the building down.
Therefore the 3 deg. minimum dead band.
     Most of the available rotor systems are designed for
operation using Yagi antenna's, with say 17 degrees of
beamwidth for satellite tracking and such.  A 10' dish at
1420 Mhz properly adjusted is looking at 5 deg. of beamwidth.
The only way my setup will work on tracking is to manually
run the dish around until the object of interest is just
outside the beamwidth, let it drift through, then step ahead
of it and repeat the observation.
     I cheated a bit in the tracking mode by mounting a small
TV camera on the back of the horn in a weather tight PVC pipe
container.  The camera is very small, about 1 1/2" square,
and will see down to .5 lux.
     The light from a full moon will overpower it, and the
sun will burn out the chip during sun shots if it is not
protected with a arc welding filter I have cut out to fit in
front of the lens.  Still it will see the brighter stars and
planets and gives a view of the night sky for some idea of
what the antenna is seeing. It also helps when you get that
big jump on the chart and you look over at the TV monitor and
see those flashing lights of a 747 at 33 thousand going
through the beam.
     With a bigger lens, or connected to a telephoto lens you
could see quite a bit more.  However, don't forget to
consider the extra weight and leverage such a lens will bring
with it hanging out there beyond the focal point, as well as
the extra stress added to your elevation system.
     If your needs are limited by expenses, (and I don't know
anyone's who isn't), go for a fixed azimuth and a manual or
powered elevation system.  Put the rest of the rotor expense
funds into the BIGGEST dish you can afford.  Preferably sized
so that it doesn't allow any sunlight to fall anywhere on
your property!

Antenna Dishes
     Where can you get a large dish?  Of course you can buy
them, 12' dishes are common enough.  But if you have the
property and the experience to handle moving 12' to 16'
dishes, first look around where you live.  Cable TV services,
newspapers, big businesses, hotels, telephone companies.
Many are getting rid of the big dishes and going to the
smaller ones.  Inquire if they are going to update that paint
faded thing on the roof to a newer lower profile model of an
up and coming company.  If they say they are, tell them you
belong to SARA, what SARA is, that you could make good use of
it, and will remove it for nothing.  Don't expect them to
help you in anyway to do it!  They will pay a scrap dealer to
do it rather than send their employees out to help you do it.
Also the scrapper is interested in the metal, not the dishes
condition when it's down.  You on the other hand are
interested in a first rate dish surface, and some of these
dishes are extremely well made, good for use up to 6 Ghz.
With that kind of surface it has to be taken apart carefully,
any bending or dents are bad news.
     Find out what is to be removed and what isn't.  Then
take everything that is supposed to be removed, don't leave
the junk you don't want.  They did you a favor, you return
it.  Most of these dishes are of the fixed type, extremely
well built and cost thousands new.  Once you've got your
prize dish at home it'll be up to you to next come up with a
way to move it either in the AZ and/or EL modes.  Let alone a
mount to put it on that will stand up to the considerable
forces of Mother Nature trying to topple it.
     When mounting the dish, never, never let it rest on one
edge as it will deform it.  Use enough people to control it
into the mount, but not so many as their falling all over
each other.  Dishes are made light, just enough to handle
winds to say 45 MPH.  Beyond that their life expectancy goes
down as wind speed increases.  TVRO dishes will fold up like
an umbrella in a high wind.  And the same with snow or ice
buildup.  Also if the snow or ice doesn't fold it up the
extra weight may spring it out of shape.  Consequently if it
looks like snow is coming I lower the dish and put a infrared
heat lamp at the horn and shine it onto the dish.  This seems
to handle the problem.

Feed Antennas
    The purpose of the feed antenna is to collect energy
reflected from the surface of the dish.  Ideally the feed
antenna beam pattern is designed to see just below the edge
of the dish, or 10 DB down.  If the feed antenna see's beyond
the edge of the dish it will see behind the dish and/or off
to the side, called spillover or high sidelobes.  We only
want to see what is in front of the dish of course, so a
little of the dish collecting area is sacrificed to assure
that what is showing on the chart recorder is from the sky
and not from the ground.
    An antenna feed horn at the focal point is the only way
to go at 1420 Mhz's and higher.  A TVRO dish usually has a
F/D ratio, (Focal Length to Dish Diameter), of 0.35 to 0.4.
In this F/D area a cylindrical waveguide makes a reasonably
effective feed antenna.
    Actually I make my own feed horns out of coffee cans.  At
area's around 1296 to 1420 Mhz these coffee can horns work
pretty well.  When I come up with a good design with the
right length and probe location, I take it to the metal smith
and have one made up in copper.  If it works really good I'll
silver plate it inside with a silver paste plating compound.
I seriously doubt that plating improves anything by very
much, but after all we're after every bit of signal we can
get.  Also silver oxide is conductive, copper oxide is not.
See the yearly ARRL Radio Handbook on antenna horns for
design formulas.
     Aligning the feed horn is critical.  First the horn has
to be centered in the dish.  This can be done by using the
sun's shadow or, more accurately, by drilling a hole in the
very center of the dish just the right size of a laser
pointer.  The feed horn mouth is then covered with white
paper and the laser pointer put through the hole.  The feed
horn supports are then adjusted to center the laser beam in
the center of the horns mouth.
     Fine tuning distance from the dish surface to the feed
horns mouth is unfortunately by trial and error.  One way is
to again use the sun as a noise source.  The feed horn is
first adjusted to the focal point of the dish and then the
antenna is centered on the sun.  A reading is taken, which
can be either voltage off the receiver S meter, speaker
output, or your RT's TPR DC output.  It is then quickly moved
a 1/4" either in or out and another read is taken, and so on,
until the highest level of output is found.  This is best
done around high noon on a cloudless day, as the suns
radiowaves are attenuated by the atmosphere and clouds at
1420 Mhz as it moves toward the horizon and the atmosphere is
thicker and more water vapor is encountered.  By the way,
while taking the readings don't shadow the dish with your
body or any other object or the readings will be affected.
     Though simple, the cylindrical feed horn is not perfect
in its beam pattern, as it tends to create sidelobes.  To
help control the sidelobes of the feed horn it is sometimes
recommended that a feed horn collar be applied.  This is a
round metal disk, twice the diameter of the wavelength which
is being received, with a hole cut in its center the same
diameter as the feed horn.  The collar is slid over the mouth
of the feed horn and assists in keeping the sidelobes
confined to the dish.
    Keep in mind that at 1420 Mhz, a 10' dish with a feed
horn collar 16" in diameter can cause sever problems of over
shadowing the dish surface and actually create worse side
lobe problems.  That is a flaring of the antenna's beamwidth
to the side like a flower petal, instead of the ideal search
light beam pattern for which we are always striving.
Probably a 12' dish is about as small as you can get with a
feed horn collar at 1420 Mhz, and that is kind of iffy.  At
higher frequencies and/or bigger dishes, collars work well.

Coaxial Cable and Connectors
     Only use the best coax cable you can afford, #9913 or
better.  Semi or hardline is even better, but very expensive.
RG-58 should not be used as it is extremely lossy at this
frequency.  Don't even think of using Radio Shack cable.
     Kinks or dents in the cable should be cut out.  These
will change the cables impedance and kill your signal.  Good
enough doesn't apply in this field, we're after perfection.
     Radio waves beyond a 1000 Mhz turns into strange stuff
the higher up you go.  #9913 coax cable at HF radio
frequencies of say 28 Mhz looks like pure water to the
radio waves shining through it.  The same cable at 1420 Mhz
appears more like muddy water when viewed by the radio waves
trying to shine through it.  Consequently some SARA members
add a down converter at the antenna to lower the frequency,
and thus the losses in the cable to the receiver on long
cable runs.  Down converting becomes cost effective around
2200 Mhz as coaxial cable becomes less and less effective and
waveguides come into the picture at big time cost.
     Connectors for cables should be of the "N" type, again
the best you can afford.  Buy these from a good electronic
supplier who also sells good cable.  The cost of good
connectors will help you minimize their use, as each one
causes a loss of signal.  Avoid 90 deg. connectors.  Only
very few of these are worthwhile and consequently are very
expensive.  90 deg.  connectors are a special breed of cat.
Mistake #3.  One of the worst problems I've had was caused by
a cheap 90 deg.  connector that was bad.  Finally I spent
$500 for a wattmeter and a 1420 Mhz slug for it to finally
find the problem.  The connector looked great outside, but
inside it was trash when viewed by the signal at 1420 Mhz.
     Follow the directions to the letter on putting "N" type
connectors on the cable or the impedance will be changed and
the signal degraded.  If you use #9913 cable, get connectors
for that cable size.  Don't use RG-8 connectors on #9913
cable as they are slightly larger and don't hold onto #9913
cable well.  Besides that the connector pin doesn't fit on
the #9913 cable center conductor.
     Seal all the connectors with black silicone that comes
in the form of a tape roll.  This is one of the few things
Radio Shack makes we can use.  Mistake #4.  I thought this
really wasn't necessary as I live in a low humidity, low rain
area.  I paid dearly for it.  I ended up not only replacing
the connectors, but moisture had gotten into the cable as
well.  Once moisture gets in the cable it degrades it and a
new cable run is called for.  Taping the connectors is much

     Mount the preamp as close to the horn as possible
without further blocking or shadowing the dish.  At 1420 Mhz
and higher inches of coaxial cable make a difference.  Until
the signal is amplified from the horn by the preamp, every
connector and inch of cable we put between the horn and
preamp is creating a loss of signal.
     Down East Microwave makes a fairly good receive only
preamp for 1420 Mhz.  It is a 2 stage preamp that is small,
light weight and has a reasonable noise factor.  Radio
Astronomy Supply has come out with a 2 stage 1420 Mhz preamp
that is supposed to be the best on the market with the lowest
noise factor around.  I have both kinds, but I personally
think the RAS one is slightly better than the DEM one.  Both
are relatively broad banded and can be used for other things
besides RA, such as SETI.  However keep in mind the bandwidth
gain of each is peaked at, and the noise factor is the lowest
at 1420 Mhz.  In short, both will work over a pretty broad
range, but less so and noisier than at 1420 Mhz.
     Mistake #5. It is also a good idea to use the old black
silicone tape again on the preamp as well.  Both preamps come
in a weather resistant case.  Notice the word "resistant",
not "weather proof." Taping the seam, screw holes, and power
feed thru will keep the moisture out of the box.  The stuff
inside is extremely sensitive to moisture and if it gets in
you will find you have your own universe in a box, as it
turns into a noise source and there is no reclaiming it.
Again I found this out the hard way.
     While you are at it with the black silicone tape, cut
two holes in the sides of a Zip Lock Bag for your coax cables
to go thru.  Put this over the preamp and run the cable in
and screw them on the preamp.  Next seal the coax where it
goes through the bag with black silicone and leave the open
end of the bag down and open for things inside to breathe.
This rain shield lasts for quite a long time and yet is easy
to work with.
     Mistake #6. I cooked one of my preamps last summer on a
hot day doing sun shots.  It seems that a dish "really" does
focus infrared as well as microwave energy, even with holes
in it!  Shading the preamp will also keep the preamps noise
level down, besides protecting it from a heat stroke during
hot sunny days.

First Receiver
     When it comes to the type receivers you will need, I
would suggest first you get a very good quality scanner such
as ICOM or other top brand.  The reason is you need a test
source for many things.  Testing of the antenna horn, coaxial
cables, preamp, and such.
     A scanner produces a sound, a TPR produces a voltage
reading on a chart.  It is very difficult to determine from a
chart recorder what it is you are receiving.  However your
ear can quickly determine whether that pulsar signal your
seeing on your chart is coming from "out there" or is a
radar, satellite, pager system, or a high voltage line
insulator flashing over, to name just a few.
     There are a few other good uses for a scanner.  I use
radars in the 1200 to 1350 Mhz band to determine attenuation
in the atmosphere caused by inversions, or water vapor.  Most
FAA air traffic control radars run at a fixed power level and
it is amazing how atmospheric conditions can affect their
signals.  If the atmosphere is affecting these radars, they
are affecting signals coming from "out there" as well.
Especially the lower the source is to the horizon and the
more atmosphere it has to shine through.  If you have any
doubts about these affects having an effect on your
observations, turn your RT toward the sun and watch what
happens when a cloud goes through your beam.
     The scanner can also be used to tell whether a large
source is coming toward earth or receding by scanning at 15
second intervals and 50 Khz steps from 1400 to 1440 Mhz in
the "AM" mode and recording the output, (S-meter, or audio
output), to a voltage chart to show doppler shift.  A word of
caution!  Receiver stability is a must here.  So allow the
scanner temperature to stablize and then keep it out of
drafts.  These doppler shifts are very slight.  If the
equipment isn't stable what you see will be variations of
your equipment due to temperature changes.  A minimum size
dish to detect doppler shift is 10'.
     Finally if you are into SETI you can use your scanner
for that as well.  I don't want to discourage anyone in
pursuing this field as I think it is an interesting
challenge, and very worth while effort.  I have read several
articles on how to use ICOM's 25 to 2000 Mhz scanners to
automatically scan the heavens and record any ET events as we

Receiving A Possible "WOW" Signal
     Let me say that if you have a 10' dish as I have, a very
good preamp, good cable, and a Yaseu 736R transceiver, which
is considerably quieter than my ICOM 7100 scanner.  And in
France you have a Ham running 600 watts at 1296 Mhz into a
25' dish, bouncing his morse code signal off the moon and
back to earth, EME, (Earth-Moon-Earth), I can very faintly
hear him and then not get a very accurate copy of what he is
sending.  One trillionth, (that's correct with a "T"), of the
power he sends out at his antenna will fall back to me!
     Besides that, it took me a year of polishing my system
to hear him.  This is the same system I use for RA except for
the receiver.  I therefore have real doubts when the next
"WOW" signal is heard that it is going to break the squelch
on any of the hundreds of ICOM scanners listening during the
night and record the event!!
     But using a good FFT program such as Mike Cooks FFTDSP
42, the same Ham in France left a nice track of his signal
down the computer screen.  So there is hope.  And the
FFTDSP42 program does automatically save it's screens while
everyone is asleep.  However the squelch of the receiver has
to be off for it to see anything.
     I think a better way would be to have one computer step
the scanner though the interested frequencies using a
computer/scanner interface.  A stereo recorder continuously
monitoring what comes out of the sound card in one channel,
as well as recording the frequency voice chip as the scanner
is changed through the frequency range, all the while
recording through a cheaper shortwave receiver WWV at 10 Mhz
in the other channel for a time reference.
     Then if something unusual shows up on another computer
running and continuously recording the FFT program during the
night, the time of the event could be noted and the stereo
recorder advanced to the time hacks of WWV and the sounds of
the event and at what frequency could be studied.  The Bambi
Group, (they have a Web Page under SARA Links), is apparently
using this approach.  Unfortunately I have been unsuccessful
in getting their freeware software to run.  However it looks
very promising and a lot of work has gone into it.

Checking Out The System
     Back to the RA stuff.  Using Ham EME morse code signals
as a test source can be an excellent way of testing out your
RT system.  If you can hear these kinds of signals you have a
VERY GOOD system.  A change of the antenna horn may or may
not be needed.  It will depend on the bandwidth of your 1420
Mhz horn.  A properly designed horn will have maximum signal
strength at 1420 Mhz and will drop off to either side in a
curve.  Very much like a bell curve.
     However a 1296 Mhz horn is easy to make out of the
trustly coffee can.  Simply take two 36 ounce cans and solder
the open ends together. This will take a large soldering gun.
This produces a horn that is to long for the frequency, so we
then cut the can very carefully with a very fine blade saw to
a length of 10 1/8".  Be sure the cut is square to the bottom
of the can.  Don't use tin snips as they distort the metal
too much.  The probe is made out of #14 solid wire 2.128"
long soldered to a female "N" type chassis connector.  From
the bottom end of the can measure out 2 3/4" and lightly
center punch the mark.  Drill a hole 3/8" in diameter and
place the chassis connector, probe end first, in the hole.
Drill out the 4 little screw mounting holes.  I use very
small sheet metal screws.  Keep screw length to a minumum
inside the can.  The wire probe picks up the signal, not the
sheet metal screws!
     Align and adjust the horn as recommended before and your
in business.  The best time for listening is during a EME
contest.  When these are going to occur is published in the
Ham magazines and there are several Ham EME Web Pages.

What Total Power Receivers Can Do
     To really do RA with any seriousness a TPR is required.
The only commerically available one I know of for the amateur
radio astronomer is through Radio Astronomy Sales.  I
purchased mine several years ago and I have returned it twice
for updates in the circuitry.  It has worked extremely well,
is highly sensitive, and is "on" continuously for temperature
stability.  The gain is adjustable between 5 and 50, as is
the integration time from .01 to 10 seconds.  It also comes
with an offset adjustment to adjust the receiver for various
     To give those of you who may not have used one before an
idea of how sensitive these units are I'll give a couple of
     I was making an adjustment on the rotor one night and
had the dish in the down position. It had snowed the night
before and down inside the shack I could hear the chart
recorder pen slide suddenly zipping back and forth.  I
stopped what I was doing thinking I'd shorted something.  The
chart pen continued zipping back and forth.  I looked out to
where the dish was pointed toward a mountain side 5 miles
away and I could see a small red light of a snow mobile
heading up the mountain.  I thought, "No way!", and climbed
down and went inside.  You could see the ignition trace as
the driver got on and off the gas.  Still disbelieving, I
stood and watched until the red light went out at the ski
resort.  The pen settled down immediately.
     Unfortunately the unit has the same attraction to piston
powered airplanes, relay contacts, or any spark no matter how
small, such as produced in a mercury switch in a thermostat.
     In the summer to do a sun shot at high noon I have to
put 6 db of attenuation in the antenna feed line and set the
gain to its lowest setting which is 5.  At that setting the
sun will drive the unit to 10 Vdc.  The units voltage output
limit is 11.2 Vdc.  Normally while doing RA I run the unit at
its highest setting which is 50 with no attenuation.  At a
gain setting of 20 it has no problem detecting the moon.  A
full moon will drive my 6" chart recorder pen, when set on a
0 to 2 volt scale, 2" across the chart at a gain setting of
50.  Not to shabby for amateur equipment and a 10' dish.
     I noticed that Radio Astronomy Supply has a new version
of the TPR out now that has several built in features that it
didn't have before.  And appears more convenient to not only
operate, but set up and test. If this unit is anywhere as
sensitive as my older model, and I don't see why it shouldn't
be, it'll be like getting your drivers license and taking a
tour of the neighborhood in a top fuel dragster compared to
using a scanner!
     I have seen some plans now and then for building your
own TPR, but most I don't believe will come close to one of
the RAS units.  I'm not selling RAS stuff, I have no
financial interest in it.  To me it is just a fact.
     Some of you may want to try your hand at designing and
building your own.  I say have at it.  That is how things are
improved, and SARA members could use the competition.

     Now we need a recording device to keep a record of the
observation.  Chart recorders are nice things to have and a
fairly good one will be expensive.  It should be able to
record over various voltage ranges from 200 millivolts to 12
volts, as the TPR output is varied over different voltage
outputs depending on the gain and what you are observing.
     If possible it should have two recording pens.  I've
found that having two pens is worth while.  An immediate
backup pen is available if one starts to go dry, or as a
second channel for tracking outside or equipment temperature.
This ability at times is very helpful when comparing unusual
recordings to temperature changes.  I also use mine for
adding time hacks on the hour.  This saves a lot of effort in
going over a long chart figuring out what time it was when
that interesting observation happened, verses counting off
and marking inches or centimeters of chart speed per hour.
     Chart paper is permanent, can be photocopied easily, and
is not subject to erasing the wrong computer file
     On the downside chart recording paper is a little
costly.  My 6" recorder uses folding paper charts that run
about $5.00 a chart.  Though a chart lasts quite a while if
run at a slow chart speed of say 6 cm. per hr.  I often rerun
a chart using a different color pen sometimes if the
observation isn't critcal or I'm testing something, to save
paper.  How long a chart pen lasts depends on how fine a
scale you run it on.  In other words if it is drawing a
straight line it seems to last forever.  If it is set to a
sensitive scale showing each and every deviation of the
signal, resulting in a wide tracking path, it will exhaust
itself much sooner.  Probably within the length of the chart.
     However I haven't found much use for a chart looking
like an electrocardiogram.  They may look impressive to show,
but as far as what the overall trend of the source is it is
worthless in my opinion.  I prefer the pen to be set at a
sensitivity level that it responds mostly to the source, not
background static.
     Finally I see very few used chart recorders for sale
unfortunately.  But this maybe also be an indication that in
the digital world, the old pen chart recorder still has its
place.  If you do find a good used one, be sure you can still
get chart paper for it.  I've found that just about every
brand of recorder uses a different size paper, or has a
different size chart feed system.  Very few have
interchangeable chart paper with other brands.
     An alternative is to use a digital software program
through a computer interface and your detectors output to
view and/or record on your computer the observations.  This
works pretty well and is considerably less expensive than a
chart recorder.  It has the potential benefit of also being
shipped around as a text file on email to others, besides
being able to be used for data processing directly for sky
charts and other processes you might want to do.
     Radio Shack makes a digital multimeter, (Cat. No. 22-
168A), that I have used that comes with the computer
interface built into the multimeter and the software for your
PC.  It comes with several recording programs and has a print
capability of your observations.  I does a pretty fair job of
recording, especially for the price and the fact that your
getting a multimeter in the deal as well.
     On the downside of digital recording, if the computer is
in use recording it is not available for other things.  If
you live where electrical power is very expensive, leaving
your machine on all night or for several nights to record may
not be appealing.
     The data files generated can and do become fairly large.
In an 8 hour run, recording output reads of the mulitmeter
every 5 seconds I generate a text file in the neighborhood of
250 K.  In a few nights of running you have a million bytes,
and so on, until storage becomes a bit of a problem.  Running
the recording at 1 second intervals of course increases the
output size of the files 5 times.  But there are times when
you will want greater detail in the recording for closer
     Finally is the battery problem.  The 9 V battery in the
multimeter lasts about 4 days of 8 hour recordings. This
expense somewhat offsets the chart paper expenses.  A battery
eliminator is a consideration here.  However I have not tried
it as the eliminators output voltage is not polished and will
follow the power line variations.  This in turn may produce
outside influences affecting the multimeter reads, and for
the moment I have enough problems with those from other
System Stablity
      My problem right now, and since I've gotten seriously
interested in RA, is not how to make my system even more
sensitive but continually battling the forces that block the
use of the sensitivity I already have.  Heat, voltage
deviations, noise, and interference!  The view through a
telescope is only as clear as the glass your looking though.

Temperature Stability
     One of the big problems I've been battling is
temperature stability.  When I first got my TPR I had it
setting out and it didn't take long to notice that as the
room temperature cycled a few degrees from the heater going
on and off, so did the pen on my chart recorder.  And I don't
mean slightly.  A 10 deg. change in TPR temperature will
change the output up to 8 volts!  Not a good thing when the
TPR is set at it most sensitive setting and the chart
recorder is on a 5 volt scale.  So I put the entire setup in
a large Coleman Picnic Cooler, drilled a hole large enough to
get the antenna feed, output and power wires in.  I also
drilled another 1/4" hole opposite the TPR's offset
adjustment and extended a wooden dowel out of the cooler
attached to offset knob to adjust it.  Just popping the lid
for 10 seconds to make a quick offset adjustment took the
unit a minimum of 10 minutes to recover from it's lost
     This helped considerably with the stability problem.
The temperature in the cooler averages about 85 degrees F
from the total power receivers own internal heat.  As long as
the temperature inside the cooler is higher than the room
temperature things are fairly stable.  However I began to
worry about the heat shortening the life of the equipment.  I
had a small Sears refrigerator in the shack to keep me
supplied with pop and such as there is no drinking water.  I
decided to put the TPR in the refrigerator where it would be
cooled and have a fairly stable environment.  So I drilled a
hole in the side of the refrigerator, being careful not to
drill through a cooling coil.  (Wouldn't recommend doing this
to the wife's refrigerator.)
     All in all it didn't work out that great in my opinion.
I noticed that I ended up with a very slow sine wave on the
chart output as the temperature inside the refrigerator
changed as it cycled on and off about every hour and a half.
I have since moved the TPR back to the picnic cooler where it
seems to be more stable, and the heat apparently is low
enough that it hasn't shortened the life of anything.
     Along this line it has been suggested to me that putting
dry ice in the cooler and cooling the TPR down to
approximately -120 deg. F. might handle the problem at a
reasonable cost.  I haven't tried this yet as I don't want to
rush into it and create Mistake #7, and some really expensive
repairs.  Cooling the TPR down to -120 deg.  F will probably
put quite a bit of strain on the circuit boards and
components.  I also don't see or hear of any amateurs doing
any super cooling, so this again sends up another flag of
caution to me.  I think I'll wait on this one until the next
SARA conference and talk to some of the Green Bank engineers
about it first.  However for those of you who prefer to go
where no amateurs have gone before, dry ice is reasonable to
purchase and can be had at some of the larger super markets
if you ask the manager.

Voltage Stability
     The next source of problems in my system is getting an
accurate voltage reference.  As the total power receivers
temperature changes, so does the electrical components inside
vary in their abiltiy to conduct electricity.  The same holds
true if the power supplied to the TPR is varied.  It will see
a change in reference as to where it was set and will duly
record it on your chart as a bump, a dip, or a slow sine
wave.  You of course not being plugged into the wall outlet
think everything is cool and the TPR is seeing something "out
there" and congraduate yourself on how sensitive your
equipment is.
     Not to be outdone, the preamp is out there by the horn
subjected to much greater temperature deviations that are
also affecting its components in the same manner that those
in the TPR are experiencing, but on a lesser scale because it
isn't as sensitive.  Added into these variations are any
preamp supply voltage changes, which instantly affects the
preamps output level.  All these little variations are then
fed to the TPR, (which from our earlier definition is looking
for any outside, as well as internal changes), they are
greatly amplified, and then deposited on your chart as
garbage!  Yes, the world of RA is a cruel, cruel world!
     The only way to handle this problem is to obtain the
best regulating power supply you can afford or make, to
polish out the dips and surges in the supply line voltage.
The extra expense is well worth the effort in your systems
stability and consequently in the reliability of your
     My system requires 15 Vdc for the preamp and 24 Vdc for
the TPR.  The wattage requirements of the power supplies to
supply the preamp and TPR is relatively low and this helps
considerably in lowering cost.
     The temptation to add other loads needing these voltages
to these power supplies is tempting, but these two power
supplies should only supply the preamp and receiver.  Other
loads are subjected to the same outside and internal
influences as the preamp and receiver, and consequently will
change the stable voltage the preamp and receiver require and
show up on the chart.
     Finally I would recommend one last piece of test
equipment, and that is a "good" 50 ohm resistive load rated
for 1420 Mhz.  Installed in a thermos bottle to protect it
from the winds and temperature changes and connected to the
cable connector that would attach to the antenna horn probe,
it will quickly show any nasty influences in the system below
the antenna.
     Once you have a stable, reliable system the sky has no
limit.  It is a good hobby, challenging, and never ending.
Take it from one who gets bored easily, and has yet to with
this one.

Cliff Bates  KC7PPM    crcwnet.com               1/17/98