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Radio friends,
It’s been a while since I posted here but I have been so busy with managing my “major market” radio systems, maybe can relate! At any rate, I just wanted to report on an old method of getting very good fidelity out of an AM signal.
I decided to use a crystal radio for a Hi Fi tuner for reception of my AM broadcaster (a Talking House Two) and have had fantastic results. The received signal bottom lows to top highs, sounds as good as FM to me, although I know top end may be limited to 5Khz, but then I’m not sure what the limits are on the Talking house transmitter either, it may be higher than that.
From the crystal radio output, I connect to the auxiliary inputs on a Bose Wave radio, but any stereo with aux inputs will work. You don’t need much of an antenna on the crystal radio, since the signal is very strong in the house, and I’m only interested in receiving my signal. In this environment, selectivity in not an issue, because the wider the received audio bandwidth the better.
The voltage output of the crystal radio is a very nice match level wise for an aux input (.5 to 1 volt) so the audio signal is nice and strong.
I know JW Miller had a Hi Fi AM tuner out some time ago and I think people used to use a crystal radio output for better quality local reception in the earlier days of audiophile history, when radio had a broader interest than it does now.
At any rate, I was pleasantly surprised by the results, so passing this along to the rest of my radio friends for possibly renewed interest.
Radio Joe
Total posts : 45366Radio Joe I thought it was my imagination when I heard the awesome sound quality when I listened to a crystal AM Radio years ago at the School For The Blind in Lansing, Michigan. I did have to ask myself if I was actually listening to FM. The station was only a mile away, but man WILS sounded good and very pleasing to the ear.
Total posts : 45366Fidelity of AM always sounded great over a crystal set.
Having grown up in the Cleveland,Oh area my first receiver was a crystal set built from one of those Radio Shack crystal radio kits. The tiny crystal ear piece that came with the kit had tinny sound, but after messing with some junk amplifiers i was able to get a 5 watt amp to amplify the audio to a decent speaker.
WOWO sounded great.
Barry of BBR World Wide
Total posts : 45366Nice writeup of your experience with a crystal set and a good amp/speaker. Not surprising since the bandwidth of the crystal set is quite wide. It seems that since the introduction of transistorized radios in the 60s that the IF stages are tuned too narrow to produce the high frequencies in the audio.
I have a military tube set which has an adjustable bandwidth and when set to maximum the audio sounds as good as FM mono when tuned to my transmitter , but not so much on broadcast stations. The audio response of my transmitter is from 20 to 17000 Hz and though anything over 10 Hz is probably wasted it gives bragging rights.
AM receivers which use IF transformers can be “stagger tuned” to provide wider bandwidth with some sacrifice in sensitivity. I recently did this when I recapped a 1936 model radio and despite the rather small speaker the audio sounds very good, nice clean and crisp highs, when tuned to my station.
Neil
Total posts : 45366When my youngest daughter was in the 6th grade I helped her build a crystal set for a school science project- complete with galena/razor blade/safety pin/pencil lead/oatmeal box coil form…the one “local” station was a 1kw about 7 miles airline distance away…..I remember listening and thinking: “Gee…the station sounds better with this crystal earpiece than the studio monitors!!”:)
That was over 20 years ago….!
Total posts : 45366The razor blade with graphite lead and safety pin sounds like a fox hole radio from war time. I’ve seen those in old junior science books a lot. That and the galena crystal radio with cat’s whisker probe make point contact diodes.
I’ve heard of staggered tuning, and Heathkit did something like it with putting complimentry IF bandwidths together, normally coupling one transformer so it produced a single hump resonance, and overcoupling the second transformer so it caused two humps with a trough in response in the middle, that when combined would make a single wider bandwidth, that still had steep selective sides, pretty slick idea on their part, oh and adding a 10 khz audio notch filter since the bandwidth was that wide.
You might want to check out infinite impedance detectors, I’ve built these and they really do work well. It’s true you can’t always tell the real fidelity of a station on an average radio, but something like this with a good amp or amp and headphones can be a help around your station and a pleasure to listen to.
http://sound.whsites.net/articles/am-radio.htm
Look at this guy’s other articles, he’s my kind of radio tech, lots of fun, presenting and no lecturing.
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