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Build it yourself?
Just curious,
Has anyone here built their own shortwave receiver? Something comparable to a low-end commercial receiver, (perhaps no FM though) no audio amplifier section either. (Just pre-amp) Something very modular so you could experiment with filters and things along the stages. Years ago.. I had a ton of books on the subject, but they were tube-technology and in all the moving I've done.. most were thrown away. Is it possible using these tools: Cheap, crappy oscilloscope. (old tube-type, basic, it drifts as it warms up) Circa 1955-1965'ish RF generator. (analog tuner, tube based, might not even work) TTL puls gen. High-voltage power supply. Clunky soldering iron. That is what I'd have to work with if I tried it, the reason I discarded so much of that old stuff is that it's just too expensive to experament. (and all the math gave me a headache!) Something a little better than those "spring kits", should use crystal oscillators NOT regenerative. Ideally a web resource some place that I haven't already googled, with "alternate plans". Can't really justify spending much $$ on something like this. Jamie -- http://www.geniegate.com Custom web programming (rot13) User Management Solutions |
wrote in message . .. Just curious, Has anyone here built their own shortwave receiver? Something comparable to a low-end commercial receiver, (perhaps no FM though) no audio amplifier section either. (Just pre-amp) Something very modular so you could experiment with filters and things along the stages. I tried to reply off list- but looks like you have an anti-spam address. Lots of people are building their own receivers- and many of them above average designs. I have posted this before, but here it is again for those that may have missed it: http://www.parelectronics.com/pics/w7zoi13jpg.jpg http://www.parelectronics.com/pics/w7zoi14.jpg http://www.parelectronics.com/pics/w7zoi15.jpg http://www.parelectronics.com/pics/W7ZOI11%20copy.jpg 5/2.5/.5 KHz homebrew xtal filters; selectable and defeatable AGC; tone; audio notch filter; preset BFO for USB/LSB/CW; AM detector; S meter Loosely based on W7ZOI Progressive RX from the late 1980's. Look also at Pete KE9OA's neat receiver on his site and many others. 73, Dale W4OP |
Many radios have a 455khz output. Building your own demod might be the
place to start. These days you could even do a digital demod. For AM, you could phase lock your sample clock (oversampled) to the carrier and do a decimation demod. Nothing obvious pops into my mind for a digital sideband demod. |
In: _I7ge.7551$hb1.3677@trnddc05, "Dale Parfitt" wrote:
Has anyone here built their own shortwave receiver? Something comparable to a low-end commercial receiver, (perhaps no FM though) no audio amplifier section either. (Just pre-amp) Something very modular so you could experiment with filters and things along the stages. I tried to reply off list- but looks like you have an anti-spam address. Yea, I do. Anything to this address gets a higher "spam score". Lots of people are building their own receivers- and many of them above average designs. I have posted this before, but here it is again for those that may have missed it: http://www.parelectronics.com/pics/w7zoi13jpg.jpg http://www.parelectronics.com/pics/w7zoi14.jpg http://www.parelectronics.com/pics/w7zoi15.jpg http://www.parelectronics.com/pics/W7ZOI11%20copy.jpg 5/2.5/.5 KHz homebrew xtal filters; selectable and defeatable AGC; tone; audio notch filter; preset BFO for USB/LSB/CW; AM detector; S meter Loosely based on W7ZOI Progressive RX from the late 1980's. Look also at Pete KE9OA's neat receiver on his site and many others. I couldn't find Pete's web site? (I did a google for KE9OA) Would you say it was rewarding to do something like that? What were the costs and such? Did you build the case yourself too? Seems like it would be fun to do something like this, but whew! where to start? Jamie -- http://www.geniegate.com Custom web programming (rot13) User Management Solutions |
On Tue, 10 May 2005 19:12:58 GMT, "Dale Parfitt"
wrote: wrote in message ... Just curious, Has anyone here built their own shortwave receiver? Something comparable to a low-end commercial receiver, (perhaps no FM though) no audio amplifier section either. (Just pre-amp) Something very modular so you could experiment with filters and things along the stages. I tried to reply off list- but looks like you have an anti-spam address. Lots of people are building their own receivers- and many of them above average designs. I have posted this before, but here it is again for those that may have missed it: http://www.parelectronics.com/pics/w7zoi13jpg.jpg http://www.parelectronics.com/pics/w7zoi14.jpg http://www.parelectronics.com/pics/w7zoi15.jpg http://www.parelectronics.com/pics/W7ZOI11%20copy.jpg 5/2.5/.5 KHz homebrew xtal filters; selectable and defeatable AGC; tone; audio notch filter; preset BFO for USB/LSB/CW; AM detector; S meter Loosely based on W7ZOI Progressive RX from the late 1980's. Look also at Pete KE9OA's neat receiver on his site and many others. 73, That's bad-ass. Dale W4OP |
Some radios already output the signal after the IF. This is what feeds
a Sherwood synch demo: http://www.sherweng.com/indepth.html I'm not saying I'ev done this myself at 455Khz, but I know the theory and have done phase lock decimation demodulation in voice band data modems. In this particular application, all the multiband tuning has been done by the radio. All you are doing is the final demod. I'm not sure I can explain it better than that. The oversampled decimation demodulation sounds more complicated than it is provided you understand a bit of digital signal processing. If you know about the concept of aliasing, then what you are doing to demod the 455KHz signal is to alias it back to baseband. Let's say I sampled the 455Khz signal at 4*455Khz. Now I have this stream of samples. Label the stream 1 2 3 4 1 2 3 4 etc. where the numbers correspond to the sample clock phase, which is 4 times the 455Khz signal. Now make two stream of data such that they are 1 -3 1 -3 1 -3 etc and 2 -4 2 -4 2 -4 etc. This effectively beats the signal down to baseband and at the same time derives the signal in quadrature. WIth the quadrature signal, you can isolate the sidebands. The phase lock loop is used to generate the oversampled clock. A PLL basicly does what the name says, i.e. locks its oscillator to the reference oscillator. To get the 4x oversampled signal, you insert a divide by 4 after the oscillator. Now the oscillator will run 4x faster to lock to the reference. Probably the only reason this hasn't been done is there are numerous patent "mine fields" on this scheme. I found this paper on decimation demodulation: http://www.ntnu.no/~htorp/Undervisni...modulation.pdf Section 3.5 explains the procedure. A similar scheme is used in digital demodulation of the chroma signal in color TV, except they phase lock to a multiple of the color burst. |
In: _I7ge.7551$hb1.3677@trnddc05, "Dale Parfitt" wrote:
http://www.parelectronics.com/pics/w7zoi13jpg.jpg http://www.parelectronics.com/pics/w7zoi14.jpg http://www.parelectronics.com/pics/w7zoi15.jpg http://www.parelectronics.com/pics/W7ZOI11%20copy.jpg Where would a person find the mechanical parts for the tuning assembly? Is there a good source for the small pulleys, chords and weighted tuning wheel? (I'd go to a hardware store and ask, but I'm not sure what one would call these parts) Jamie -- http://www.geniegate.com Custom web programming (rot13) User Management Solutions |
In: .com, wrote:
Actually, you want to work backwards if you are going to fiddle like this. The 455Khz signal is pretty low frequency so the board layout skills are not very difficult. Starting from the front end can be annoying, especially when your home made amp oscillates and oscillator won't start. Sounds like a wonderful idea, however.. I don't want to tear apart my radio to experament. If I stumble across a cheaper, older one perhaps. (Or, maybe muck around with a cheap MW radio) This weekend (when I get home) I'm going to take a stab at Mr. Andersons circuit: http://www.tricountyi.net/~randerse/regen.htm But.. I'd like to adjust it a bit. One thing I'm having some difficulty with is locating the formula for calculating turns to inductance and inductance to frequency. This was a problem last time I built a tube-based regen receiver, I just did what they told me to do w/out finding out how the number of turns was determined. (I got lucky I guess, because it worked..) :-) For frequency, I've seen 2 formulas: F = sqrt(25,300 / L*C) And: F = 1 / 2*pi * sqrt(L*C) I don't know which way is correct? (where is the 25,300 coming from?) I'm still searching for the formula for calculating the inductance of turns on a toroid coil. (as that is what Mr. Anderson spec'd out) http://www.radio-electronics.com/inf...e_am_demod.php Wow, didn't they used to be a magazine? Thanks for the URL! (I'd forgotten all about them) Jamie -- http://www.geniegate.com Custom web programming (rot13) User Management Solutions |
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