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Beacon Reception -- Any Interest?

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Dave Marshall

Fri Nov 24 2006, 02:39PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Chris Russell has a source for programmable oscillator modules that are sufficiently stable enough.

All it requires is some filtering to clean up the output of the oscillator, and you're set.

It should be noted that the receivers for QRSS/Slow Heil have to be extremely stable. Even a +/- 3Hz shift would keep you from receiving effectively.

I'm definitely interested in listening in, and I'm seriously considering my own beacon as well.

Dave

Steve Conner

Fri Nov 24 2006, 11:34PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hi guys

I managed to set up my old computer with Spectrum Lab and a decent sound card, and have it upload a screenshot of the Spectrum Lab waterfall plot to my web server every 30 seconds. So with any luck, anyone with a web browser can see what I'm receiving as it comes in. If you've got a transmitter you might even be able to see your own signal appear.

I just ran it for a few hours as a test, and I still need to hook it to the radio, but so far it looks good

Chris Russell

Sat Nov 25 2006, 02:43AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Excellent, glad to see there's some interest!

Avalanche: That looks excellent. I would prefer to stick to 30m anyway, so you shouldn't need to even change any values. If you wanted to use the mic line of your sound card, you could even leave out the op-amp and just sample the output from the mixer directly. The important thing is stability. You're going to want to make sure the circuit is enclosed in a case that's going to provide electrical and thermal shielding. In fact, if you were really insane, you could probably submerge the whole thing in oil, to ensure that the temperature only changes very slowly.

WaveRider: I don't have a plan for any particular time yet, just when I have enough interested people. I can certainly run the test again if it turns out that there's anyone interested who missed out.

Anyone who doesn't have a receiver will probably want to look at the circuit that Avalanche linked to, unless you have some specific plans already. I am planning on operating right around 10.141MHz, so a 10.139 or 10.140MHz crystal is what you'll want (causing my signal to appear at either 2khz or 1khz on the output, respectively). You could also replace it with an SG-8002 programmable oscillator, available at Digikey. Specifically, you'll want this part number: SG-8002DC-PHB-ND, and specify 10.139MHz in the comments. They're $5.15 each, and since there's a $5 charge on orders less than $25, it would be smart to either do a bulk buy with someone, or order a fistful for various frequencies -- they're damn useful.

If anyone is *definitely* interested in going this route, and *promises* to complete the project and listen for my signal, I have two SG-8002 modules that will be sent free via postal mail. Just PM me your mailing address and I'll get it in the mail ASAP. One is 10.135MHz, one is 10.140MHz. The 10.135MHz one will work fine, but my signal will appear at 6khz, so the penalty is that you'll have to use a higher sampling rate on your sound card, thus requiring more computing power. The difference isn't huge, but it's something to think about if you're using a computer that runs at less than, say, 500MHz.

ShawnLG

Sat Nov 25 2006, 06:21AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

What electronic equipment would most likley have these crystals?

Dave Marshall

Sat Nov 25 2006, 07:13AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

I have yet to stumble on a useful crystal in a common electronic appliance that fell within a ham radio band. I would imagine thats largely because hams are more likely than most other RF spectrum users to experience interference from such devices. Most crystals I've seen in the 10Mhz range are well above the 30m ham band, or on the very low fringe, between 10 and 10.1Mhz.

You can sometimes find the QRP calling frequency crystal at 10.130Mhz, but those programmable oscillators are really the most practical solution.

Dave

Steve Conner

Sat Nov 25 2006, 10:15PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The only ones I can think of even vaguely ham-related are the NTSC colour burst (3.579MHz) found in many VCRs and games consoles (basically anything with a composite video output) and the old IBM PC bus clock (14.318MHz) that still appears in a lot of PC motherboards and expansion cards.

If Chris's transmission is a success, and I guess even if it isn't, I'm up for trying another one myself, so you guys can try tuning into that. I have a 100 watt rig and a 33' dipole in the attic, and so far I've not been able to get signals into the US, but some of our European members might be able to get it. Or maybe it'll finally make it across the pond by the magic of DSP

Avalanche

Sat Nov 25 2006, 10:59PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

As for crystals, I remember reading something on the net a few years ago describing a method by which crystals could be 'doped' to reduce the frequency on which they operate.
It was something along the lines of: cut open the can, use the ink from a permanent marker(?) to add impurity to the crystal, then solder the can up again (using pieces of copper clad) when it is nearer your required frequency. However, I cannot find the article. I just wondered if anyone else had heard of this and if it would be worth trying. I don't know how good the temperature stability would be with the added impurities, that would be a bigger problem than the crystal being off-frequency by a few Khz.
I have a bag of 10.240Mhz crystals on my eBay watch list, so if I win them i'll probably give it a go.

Marko

Sat Nov 25 2006, 11:08PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I'm completely lost in this thing, but, regardign crystals, 3.57Mhz one can also be found in old telephones (I have some of them here.)

You could probably change crystal's frequency by just dropping something on it, like superglue (caring not to bind it to case) wich would elongate it and lower the frequency; but I really doubt you can get something precise that way!

ShawnLG

Sun Nov 26 2006, 01:51AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

I did find two of my crystals 18.1Mhz and 7.966Mhz when mixed together would give me 10.134Mhz. This would require much more circuitry.

UPDATE:

I have found a better crystal being 20.2752Mhz. When the frequency divided, this would give me 10.1376Mhz. So when Chris transmit on 10.141Mhz. I should see him around 3400Hz on spectran.

1164771808 286 FT1630 Qrss 101376

I am ready for contact!

Is it normal to hear interferance from TV on this frequency? It sounds like the RF from the TV video driver.

Chris Russell

Wed Nov 29 2006, 10:01PM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

ShawnLG, that looks perfect. Just remember that you'll want some thermal insulation there, too.

***UPDATE***

The first beacon test will be Sunday, December 3rd. I will start transmitting at 1200 UTC (0700 EST, 0400 PST) and keep it up for 24 hours, barring any technical difficulties. Transmissions will be centered on 10.141MHz, and will be sent in QRSS10 mode. Message will be in three parts: chirped-hell, dual frequency cw, and standard cw. It will loop every 30 minutes.

Note that if conditions are very poor, but not terrible, you may not see the chirped-hell part of the message, but will still be able to copy the cw and dfcw portions. So don't despair or start hunting around right away; wait at least ten minutes before concluding that you're not receiving anything. After ten minutes it's safe to either reposition your antenna, or hunt up and down the band for the signal. If you're still not getting anything, try back later, and hopefully band conditions will have improved. If you're able, leaving your program running, taking screencaps, would be a good idea, in case you can't be near the receiver when band conditions do improve.

I will transmit a second message later on this month, if there's anyone who is interested but isn't going to be ready with such short notice.

For those who want to know what the signal will look like, or for those who want the fun of trying to receive the beacon but don't have a radio, I'm attaching an mp3 with a message similar to the one I'll be transmitting. I've buried it under enough white noise to simulate poor band conditions, but your software should be able to recover it if you're going to have any hope of recovering the actual beacon.

Please post your screencaps and/or results here.

]1164837714_1_FT18313_4hv_beacon.mp3[/file]

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