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Author Topic: We just need the hardware.....SDR sat ops  (Read 4851 times)
W4HIJ
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« on: April 02, 2013, 05:31:49 PM »

Still experimenting here with my $20 DVD-T stick and a old omnidirectional scanner antenna I had lying around. I can copy VO-52 reasonably well but haven't had much luck with SO-50. I haven't really been able to catch and good passes though. It's quite fun to watch SatPC32 and HDSDR track doppler together especially considering they are using the aforementioned cheapie DVB-T stick.  It would be nice though to have something a little more sophisticated that could both RX and TX in all modes via SDR. The software is out there for free and being developed more each day. We just need the hardware. A 2M/70cm SDR kit designed especially for satellite ops would be very cool!
73,
Michael, W4HIJ
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KQ6EA
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« Reply #1 on: April 02, 2013, 08:57:54 PM »

Have you considered adding a filter and a preamp?

From my experiments with the "$20 Dongle" they seem to overload pretty easily from strong stations.

Jim
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K5LXP
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« Reply #2 on: April 03, 2013, 06:34:31 AM »

This will get you half way there (RX only):

www.funcubedongle.com/


Mark K5LXP
Albuquerque, NM
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W4HIJ
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« Reply #3 on: April 03, 2013, 01:37:29 PM »

Have you considered adding a filter and a preamp?

From my experiments with the "$20 Dongle" they seem to overload pretty easily from strong stations.

Jim
I'm working on the preamp. I have a MAR-6 and just need to acquire the rest of the components and figure out how to make a circuit board since I've never done any etching and need an alternative. Haven't thought about any sort of filter besides  maybe a diplexer setup to combat desense but with that or any other filter I will have compromised my ability to receive both bands on one antenna.

As far as the funcube dongle pro, I'd love to have one but I can't afford it. Right now I'm just playing around on a very miniscule budget. Still I think it would be cool to see a kit for a sat optimized SDR. Sort of the funcube taken one step further. I wish I had the talent to design it but my radio knowledge doesn't reach quite that far.
Michael, W4HIJ
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KQ6EA
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« Reply #4 on: April 03, 2013, 03:44:30 PM »

If you have the foil pattern, like from the new AMSAT preamp, you can use it as a guide to cut away the foil on a blank board with an Xacto knife.

There are also special papers made for a copy machine/laser printer, that can be used to reproduce the foil pattern. You then "iron" the pattern on the blank board, peel away the paper, and your pattern, made from the toner, is on the board, which you then etch in the usual way.

I've built some preamps "dead bug" style on double-sided board, and they worked quite well at UHF.

One thing you'll want to do is to connect the front-side ground foils to the rear-side ground plane with a series of drilled holes connected with jumper wires.

Far Circuits might also have some premade boards that will work for you.

http://www.farcircuits.net/

Jim
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W4HIJ
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« Reply #5 on: April 03, 2013, 05:37:49 PM »

If you have the foil pattern, like from the new AMSAT preamp, you can use it as a guide to cut away the foil on a blank board with an Xacto knife.

There are also special papers made for a copy machine/laser printer, that can be used to reproduce the foil pattern. You then "iron" the pattern on the blank board, peel away the paper, and your pattern, made from the toner, is on the board, which you then etch in the usual way.

I've built some preamps "dead bug" style on double-sided board, and they worked quite well at UHF.

One thing you'll want to do is to connect the front-side ground foils to the rear-side ground plane with a series of drilled holes connected with jumper wires.

Far Circuits might also have some premade boards that will work for you.

http://www.farcircuits.net/

Jim
I have the PDF of the amp article that has the circuit board pattern. I'm embarassed to admit though that I can't tell what is supposed to be the copper and what is supposed to be cut or etched away between the black and the white! The pattern is confusing to me when I look at the actual photo of the assembled board. It's also not clear what size SMD's are used. My experience is with hand soldering 1205's, I don't know if I can handle much smaller than that.
Michael
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KQ6EA
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« Reply #6 on: April 03, 2013, 06:12:10 PM »

Generally speaking, the magazine will publish a positive image of the foil, where the dark is the copper foil.

If you want to make your own board using photo-sensitive PCB material, here's an excellent guide:

http://hackaday.com/2008/07/28/how-to-etch-a-single-sided-pcb/
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W4HIJ
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« Reply #7 on: April 05, 2013, 09:26:40 PM »

Generally speaking, the magazine will publish a positive image of the foil, where the dark is the copper foil.

If you want to make your own board using photo-sensitive PCB material, here's an excellent guide:

http://hackaday.com/2008/07/28/how-to-etch-a-single-sided-pcb/
I had figured the dark was the copper which is what confuses me looking at the PCB graphic vs. the actual etched board in the photo. http://store.amsat.org/catalog/docs/preamp.pdf  I may just order conventional lead parts and  perf board it but that will drive up the cost. Either that or come up with a pattern of my own based on the circuit diagram. I think etching is out of the question anyway. I will probably cut it with an X-acto knife and remove copper with an iron as you mentioned. I know I can hand solder 1205 sized SMD's, I built an HF amp kit that used them.
Michael
« Last Edit: April 05, 2013, 09:30:09 PM by W4HIJ » Logged
KQ6EA
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« Reply #8 on: April 05, 2013, 10:27:28 PM »

The copper foil is tinned, or solder-coated, which makes it look silver/white. The dark areas are the actual circuit board under the foil.

Guess I've been doing this so long that things that are "obvious" to me aren't so obvious to other people!
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W4HIJ
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Posts: 367




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« Reply #9 on: April 05, 2013, 11:37:01 PM »

The copper foil is tinned, or solder-coated, which makes it look silver/white. The dark areas are the actual circuit board under the foil.

Guess I've been doing this so long that things that are "obvious" to me aren't so obvious to other people!
Dang! With all my reading on PCB's lately I ought to have seen that. As soon as you mentioned it and I looked again, it was clear as a bell. My amp kit board was done by a PCB house and had a blue/green coating over it. Only confusion I have now is the notation for 33 uh at the top of the PCB mask. I see a .33 uf cap in the circuit but no inductor of any type which is what the uh would indicate.  Strange..... am I missing something?
Michael
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KQ6EA
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« Reply #10 on: April 06, 2013, 11:59:23 AM »

The green coating is called a solder mask, and is used to keep solder from going places you don't want it to go. It's nice to have when hand-soldering a board, and is almost a MUST have if you're "wave soldering" batches of boards in a production environment, especially if you have small traces close togther that will tend to "bridge" with solder.

A lot of PCB vendors include it at "no extra charge".

From looking at the board layout, schematic, and built board, it appears that the 33uH inductor is not used. Perhaps he was thinking of using it if power-over-coax was desired, in which case it would block RF from getting on the DC feed of the circuit.

Looks like he just bypassed it on the built board with a glob of solder.
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W4HIJ
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Posts: 367




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« Reply #11 on: April 06, 2013, 01:54:57 PM »

The green coating is called a solder mask, and is used to keep solder from going places you don't want it to go. It's nice to have when hand-soldering a board, and is almost a MUST have if you're "wave soldering" batches of boards in a production environment, especially if you have small traces close togther that will tend to "bridge" with solder.

A lot of PCB vendors include it at "no extra charge".

From looking at the board layout, schematic, and built board, it appears that the 33uH inductor is not used. Perhaps he was thinking of using it if power-over-coax was desired, in which case it would block RF from getting on the DC feed of the circuit.

Looks like he just bypassed it on the built board with a glob of solder.
Thank you for all the help Jim. I think I got it now. I'm pretty sure now that I understand the PCB pattern that I can cut it with a knife and not have to etch it. It looks relatively simple. I looked into the parts at Digikey and all are 1206 or larger so I can hand solder them. This will be a fun little project.  I'm thinking about simple filters to put ahead of the DVB-T stick now but if it ends up not working I will still need the preamp for a dual HT setup.  I actually have a WA5VJB "cheap yagi" dual band antenna setup built already. It was to go on a camera tripod but I never quite finished it because I didn't want to stand out on my deck to work the sats. Might just hit the wood boom with some spar varnish and slap it up above my HF mini beam! I may be on a miniscule budget but I'm having fun experimenting and that's all that counts!
73,
Michael
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KQ6EA
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« Reply #12 on: April 06, 2013, 02:33:47 PM »

The only thing to be careful about when hand-cutting a board (besides not slicing a finger or two!) is to try your best to maintain the WIDTH of the conductors from the input, through the active device, and on to the output.

The conductors are more than just "a piece of flat wire connecting things", and are actually a transmission line with a design impedance, 50 Ohms in this case.

If you change the width too much from the design, it could affect the gain of the circuit. The MAR series of devices are "unconditionally stable", so your chances of turning your amp into an oscillator are pretty small, so it's not "super/ultra/double secret probation" critical, but why throw away any gain when you're building a "gain block" for your system.

You can find the data sheets for the MAR-6/7 at this link, about half-way down the page:

http://www.minicircuits.com/products/amplifiers_smt_gpw.shtml
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