Using a 18" Dish for Radio Astronomy Demonstrations--Need SimplePower Supply

[W. eWatson]

Somewhere I came across a setup for a simple "itty bitty" radio
telescope a number of years ago. Its purpose is educational. Basically,
it consists of a discarded 18" dish, power supply, and a satellite
signal finder. I happen to have a Channel Master 1004ifd finder, but it
gets its power from the LNB, which apparently gets it from a satellite
rcvr. I have no rcvr. I'm looking for a way to power it.

WEll, lucky me. A small amount of Googling got me to
<http://www.aoc.nrao.edu/epo/teachers/ittybitty/procedure.html>
I'm not sure our local The Shack has a choke. I may have one. My LNB is
different than the one in the pic. It's a Eagle Aspen DTV32+. I'm sure I
have a battery clip and 8 battery holder. This might do it. I didn't
notice the Rx connector on my CM1004, but that is where the power goes.
I may be set.

I constructed the battery pack in the link above, but w/o the coil. I
plugged it into the 1004ifd and immediately got something of a single
note noise from the device. This seems wrong. Any ideas? I did not
connect to the LNB and disk.

 

[Jasen Betts]

Somewhere I came across a setup for a simple "itty bitty" radio
telescope a number of years ago. Its purpose is educational. Basically,
it consists of a discarded 18" dish, power supply, and a satellite
signal finder. I happen to have a Channel Master 1004ifd finder, but it
gets its power from the LNB, which apparently gets it from a satellite
rcvr. I have no rcvr. I'm looking for a way to power it.

13VDC up the coax, center positive.

WEll, lucky me. A small amount of Googling got me to
<http://www.aoc.nrao.edu/epo/teachers/ittybitty/procedure.html>
I'm not sure our local The Shack has a choke. I may have one. My LNB is
different than the one in the pic. It's a Eagle Aspen DTV32+. I'm sure I
have a battery clip and 8 battery holder. This might do it. I didn't
notice the Rx connector on my CM1004, but that is where the power goes.
I may be set.

yeah, 12V may be enough, the connector is probably 'F'

I constructed the battery pack in the link above, but w/o the coil. I
plugged it into the 1004ifd and immediately got something of a single
note noise from the device. This seems wrong. Any ideas? I did not
connect to the LNB and disk.

with the input open circuit unloaded and the output shorted it could be oscilating,
or that could be the base level tone.


--- news://freenews.netfront.net/ - complaints: [email protected] ---

 

[W. eWatson]

13VDC up the coax, center positive.


yeah, 12V may be enough, the connector is probably 'F'


with the input open circuit unloaded and the output shorted it could be oscilating,
or that could be the base level tone.


--- news://freenews.netfront.net/ - complaints: [email protected] ---

Thanks. So I should put the choke in and connect the LNB? Yes, F.

 

[Jasen Betts]

Thanks. So I should put the choke in and connect the LNB? Yes, F.

Yeah, the choke will probably help, for even better termination you could stick a 75 ohm
resistor (82 is probably close enough) in parallel with the choke and a 100pF capacitor parallel
with the battery. But that may not be needed,

Pointing the LNB arm of the dish (which point in the approximate
direction of the focus) somewhere in the general direction of the sun (during the
day) and you should get a big peak on the meter.

--- news://freenews.netfront.net/ - complaints: [email protected] ---

 

[W. eWatson]

Yeah, the choke will probably help, for even better termination you could stick a 75 ohm
resistor (82 is probably close enough) in parallel with the choke and a 100pF capacitor parallel
with the battery. But that may not be needed,

Pointing the LNB arm of the dish (which point in the approximate
direction of the focus) somewhere in the general direction of the sun (during the
day) and you should get a big peak on the meter.

--- news://freenews.netfront.net/ - complaints: [email protected] ---

I hadn't realized that some years ago I had put a choke on the cable. I
happened to remove some of the deteriorating electrical tape.

Now I am at a loss. I hooked up the LNB on the dish, and still get the
squeal. Maybe that's OK. The CM sees a voltage of 10 on it's meter or 35
on signal strength. That corresponds to what I measure across the
battery pack with my volt meter. It looks like gain may jack up the
signal strength. It may change the pitch. Not sure. Things get louder.

I have a second (Aspen) LNB detached from the dish. The LNB on the dish
was part of the original equipment.

OK, I've got something going with the Aspen. If I point it at the
ground, the needle goes up. If I point at the sky, it goes to zero.
Pointing it near the sun doesn't change the sky reading, since I
probably need to use the disk and point it at the sun. I think the link
above gives some clues about pointing.

I'll be back shortly. I went to get my voltmeter, and when I came back
wasn't hearing much of anything. I checked the voltage at it's up around
9v. Interestingly, the sun was getting blocked by some clouds. Probably
not related. I hope the batteries aren't getting drained by this
exercise, AA. They were fresh.

I think some more fiddling is required.

 

[W. eWatson]

I hadn't realized that some years ago I had put a choke on the cable. I
happened to remove some of the deteriorating electrical tape.

Now I am at a loss. I hooked up the LNB on the dish, and still get the
squeal. Maybe that's OK. The CM sees a voltage of 10 on it's meter or 35
on signal strength. That corresponds to what I measure across the
battery pack with my volt meter. It looks like gain may jack up the
signal strength. It may change the pitch. Not sure. Things get louder.

I have a second (Aspen) LNB detached from the dish. The LNB on the dish
was part of the original equipment.

OK, I've got something going with the Aspen. If I point it at the
ground, the needle goes up. If I point at the sky, it goes to zero.
Pointing it near the sun doesn't change the sky reading, since I
probably need to use the disk and point it at the sun. I think the link
above gives some clues about pointing.

I'll be back shortly. I went to get my voltmeter, and when I came back
wasn't hearing much of anything. I checked the voltage at it's up around
9v. Interestingly, the sun was getting blocked by some clouds. Probably
not related. I hope the batteries aren't getting drained by this
exercise, AA. They were fresh.

I think some more fiddling is required.

OK, here's the deal. With the Aspen I have the meter around 30 with it
lying on the table. When I point it to the sky it goes to 0. When I
point it at the ground it goes back up to around 30

With the DTV and dish, the dish is just point to the empty sky, and the
meter is reading 20. When I put my hand in front of the LNB and
immediate vicinity, the meter rises to higher values according to how
close I am to the LNB.

OK, time to read the material about pointing the dish.

 

[W. eWatson]

Ah,I found someone outside the web that had good knowledge of the the
Itty Bitty Tele (IBT), and here's my problem. The voltage needs to be
kept about 12v, maybe 11v, but it's crucial to get this working.
Further, the choke is not needed. As it turns out, the Aspen LNB is very
good, but I should replace the dish with one that accommodates the
Aspen. The Aspen won't fit on the dish. No easy mechanical link.
Secondly, the dish is better in this app if it's circular. Well,things
to do ofter the next weeks.

Thanks for pitching in.