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Obsolete old buzzard receivers?




 
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Author Topic: Obsolete old buzzard receivers?  (Read 6426 times)
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Tom W2ILA
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« on: March 01, 2005, 11:51:31 AM »

I am hearing more and more digital broadcasting on the SW bands.  That noise at the top of 75 every night sends each of my old buzzard rigs into a tailspin.
Will our gear be completely useless for SWLing in the next few years?  How do you demodulate those stations?  I assume you need a stable ricebox.  Anybody listening to it?

TM
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WA1GFZ
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« Reply #1 on: March 01, 2005, 11:59:27 AM »

Tom,
I would love to see a DSP interface to a common IF like 455 KHz or better yet programmable IF input to keep the analog machines useful.
All my old stuff went down the road after I discovered  the Racal RA6830
and other fine mil machines of the 80s and 90s.  The collectors will have a hey day buying all the old stuff when it becomes useless.
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K8SWL
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« Reply #2 on: March 01, 2005, 02:25:40 PM »

Quote from: WA1GFZ
Tom,
I would love to see a DSP interface to a common IF like 455 KHz or better yet programmable IF input to keep the analog machines useful.
All my old stuff went down the road after I discovered  the Racal RA6830
and other fine mil machines of the 80s and 90s.  The collectors will have a hey day buying all the old stuff when it becomes useless.


Most stable receivers with a 455Khz IF can receive Digital Radio Miondale. Convert the 455 Khz IF dowen to 12 Khz and feed it to a computer soundcard. The front end receiver should have a wide bandwidth of 10-15 Khz. There are a couple companies that are making converter boards for such applications. If anyone is interested I'll find a source and post it here. The registered DRM Software runs $60-70, however theres a freeware program called "dream" avaiable.

I use a more modern TenTec RX-320 that has a 12 Khz IF availalbe and it works quite well. The fidelity is very near Broasdcast FM.

There are also some hams playing with Amateur DRM. I havn't had the time to really investigate it, but it sounds interesting.
Regards
Mike K8SWL
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W1RKW
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« Reply #3 on: March 01, 2005, 02:52:50 PM »

digital vs. analog.  I'll take an analog signal anyday. It irritates the crap out of me when I lose lock on my satellite and cellphone.  You get no warning whatsoever. With analog at least you can hear the signal begin to fade. And I dislike hearing aliasing.
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Bob
W1RKW
Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
WA1LGQ
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« Reply #4 on: March 01, 2005, 05:31:20 PM »

Here's a simple down converter schematic that I found on the Yahoo R75 group. I can't vouch for it, have'nt tried it out. Looks very easy to do.
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WA1GFZ
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« Reply #5 on: March 01, 2005, 09:47:39 PM »

Larry you can get I/Q out of a ne602 check WA1SOV site.
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W1DAN
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DRM
« Reply #6 on: March 02, 2005, 01:26:32 PM »

I have been extensively playing with DRM. You can homebrew a converter and use the software below to listen to DRM.

There is free software available for DRM and HamDream for us experimenters:

If you want, here is the main software:

http://drm.sourceforge.net/

or...
http://pessoal.onda.com.br/rjamorim/dream.zip

Another site:
http://www.qslnet.de/member/hb9tlk/

And another version:

http://www.n1su.us/windrm/
 
Here is a users guide:
http://www.mynetcologne.de/~nc-keilje/drm/dream/index.htm
 
FAR circuits makes the simple DRM converter board that uses an NE602.
http://www.farcircuits.net/convert2.htm#9convert

Receiver mods site
http://www.drmrx.org/receiver_mods.html


Also see the ARRL article “International Digital Audio Broadcasting Standards: Voice Coding and Amateur Radio Applications” at:
http://www.arrl.org/tis/info/pdf/x0301049.pdf


You need a 455kc output with a pretty flat bandpass about 12-15kc bandwidth. I Use a Yaesu FRG 7700 with good results. I tried an HRO with poor results (I think the IF has too much fhase shift).

I built a converter using the NE602 and a crystal oscillator provided by KE1GF that is much more stable.

Nearby interference will kill reception quickly.

73
Dan
W1DAN
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K8SWL
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« Reply #7 on: March 03, 2005, 01:01:59 PM »

Dan,
  What frquency are you experimenting with DRM on. I'd love to listen in. Sounds like a fun project.
Regards
Mike K8SWL
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W1DAN
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« Reply #8 on: March 03, 2005, 03:42:57 PM »

Hi Mike:

I listen to SW broadcast statons that I can hear the "noise" from. Usually Germany on 3.995 and Sackville Canada on many frequencies.

There is a schedule here:

http://www.drm.org/livebroadcast/globlivebroadcast.htm


73
Dan
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W1DAN
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« Reply #9 on: March 03, 2005, 03:46:28 PM »

Here is an article I wrote for my club's newsletter:

Dan Dreams!
By Dan W1DAN

OK OK, I tend to get caught up in the excitement of technology. This is a blessing and a curse, but I feel life is more fun when you are playing with some new piece of hardware or software. This last month I did both with Dream.

All this started when a fellow ham (JT, WA1TDH) got interested in a PC software application called HamDream. HamDream is a software program that allows two hams to chat via HF, but using digital audio instead of the usual SSB. The result is no fading, noise or distortion. This program is the grandchild of Digital Radio Mondiale (DRM).

DRM has been used by a few shortwave broadcasters for a couple of years now. DRM sends digital audio over the big shortwave transmitters such as Radio Canada’s Sackville site and is received by a special radio, or a modified radio, a converter and some PC software. The end result is that you can listen to Radio Canada, the Voice of Russia, Deuche Welle, or Radio France with no interference, noise, fading or distortion. DRM also can pass stereo audio, images and text information as well.

Well, Some friends of JT started looking into HamDream, but JT really wanted to listen to DRM. Until recently, DRM software was sold for about $100.00 from the DRM web site and equipment manufacturers like Ten Tec. JT kept asking people he knew in the industry whether they could give him a copy of the commercial software. Not receiving any results, and asked me to see what I could do.

I looked around the web a lot and finally found a web site (http://drm.sourceforge.net) that two graduate students at a German university had. They created software that ran on Linux that decoded DRM. Later a compiled a version of this code for Windows, called Dream was created. I had struck gold!

Once I told JT of this find, Harry KK4QK and John K9FB started building converters (from a FAR Circuits PC board) to allow their standard shortwave radio to feed their sound card so the Dream software could decode the digital stream. John was the first to get the whole lash-up to work. He discovered that the converter drifted and designed a crystal oscillator to eliminate the drift.

I got exited, and gathered up an old box, a perf board and most of the parts to build a converter (my junk box really paid off as I only had to buy one connector). I was on 75 meters a couple of weeks ago talking to Bill KE1GF who played with Dream for Linux about a year ago and had limited success. He offered to send me a crystal oscillator and a couple other IC’s, which I promptly installed.

I downloaded the software, modified my Yaesu FRG 7700 receiver to get an IF signal out of it and plugged in the converter. Once I ran the software and tuned in a station, I heard music from Germany!

 
We have been comparing notes via e-mail and making further small improvements to our reception. This all has been great fun!

Dan
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