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#3
November 30th 06, 03:40 PM
posted to rec.radio.shortwave
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AM recption notes.
Steve wrote: wrote: I found this web page while looking for a nifty audio filter I found last year. At the very least it gives food for thought. http://www.radiointel.com/phil/phils_radio_tuning_tricks.pdf Terry There are some helpful hints here, though I'm puzzled by the gripe this fellow has with synchronous detection. I personally wouldn't spend a lot of dough on any receiver that lacked it. I think a lot of people are sour on synchronous detection because they've bought and/or used a receiver that had a very poor implementation of it. When sync detection is done right, as it is on Drake's R8B, then it will sometimes do more to aid reception than all of these hints put together. But the good news is that we don't have to choose between synchronous detection and this fellow's helpful hints. We can have all of these tools at our disposal. Steve My first expousre to SAM was with an AOR7030+. My first impression was that "great". That lead me down a long path toward building my own SAM+ outboard detector. Along the way I had a chance to test a Kiwa, MAOP and the Sherwood SE-3. Both are good and both are much better then the AOR. I tried several designs and settled on a variation of Pete's AD607 SAM. Again at first I was very impressed. However after using it for several months the glammor started to dull. For better then 99% of my AM listening, which in truth is a very small part of my SWL activity as I am into utility, I ofund the 3 OpAmp simple "improved detector" to be the equal or the match for any of the SAMs I had on hand. I was not able to compare the MAP or SE-3 for any extened period and while both are great units, they do have differences. On balance I like the sound quality of the MAP over the SE3, but I liked teh SE3's ability to track rapid, deep fades, espcially with nearby AM signals. I had my feet held to the fire for my posts about Dallas Lankfords observations about the utility of a sharp LP audio filter that chops every thing above ~3 or 4KHz. Exact break point depends on individual choice. Now that I have a R8B, I must admit that this is the best implentation of a SAM I have yet experienced. However in many situations it too can benefit from the AF LP filter. Perhaps I expected too much from SAM detectors. They aren't magic and are far from perfect. The home.worldnet.att.net/~wa1sov/technical/sync_det.html page is no longer up, but Peter C. McNulty, WA1SOV, offered an additional OpAmp fitler design that was reported to allow the AD607 to fully reject unwanted signals via I and Q difference and summing. I don;t have my printed copy in front of me so I can't relate the math. The design appeard to be valid, and several other EEs agreed with his reasoning. However I was never able to get that part of the design to work. I wrote if off in part to the 50Hz minimum tuning step the R2000 offers. His design is clearly worthy of study and I suspect that for someone with more time it could be a winner. At this point I am most interested in reducing the local RF noise, improving my antennas and getting to understand how to get the most from my phaser. Oh, and I am still after the Holly Grail" of a perfect 12V audio amp. Terry |
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