Home |
Search |
Today's Posts |
#27
![]() |
|||
|
|||
![]()
In article , wrote:
John Byrns wrote: 3. TRF receivers have been mentioned, and everyone seems to assume that a TRF receiver would consist of cascaded single tuned resonators with RF amplifier stages between. There is no reason why double tuned circuits, similar to those used in the IF transformers of a superhetrodyne can't be used in a TRF receiver, with all the selectivity/bandwidth benefits that brings to the party. For examples see the Western Electric No. 10A receiver, the J.W. Miller TRF receiver, the early Altec AM receiver, as well as others. I did a cursory check on the Internet, but did not yet find any schematics for the mentioned receivers. Are they online somewhere? Anyone? I also found the following article from John posted back in 2000, where he talks about the double tuned TRFs, such as WE-10A, J.W. Miller, Collins (which I assume is the same one Volker Tonn mentioned today), Meissner, and the Weeden (the last of which John noted to be the best designed of all of them): http://groups.google.com/groups?selm...&output=gplain Unfortunately the URLs to the TRF schematics at John's site are not working. Try this URL: http://users.rcn.com/jbyrns/BP-TRFs.html Another bandpass receiver which uses J.W. Miller coils is the Altec 101(B), the schematic for the 101(B) is available on the "Nostalgia Air" web site. After reviewing this thread, and considering that the proposed tuner is to be an audiophile tuner, and given the great affinity of audiophiles for Western Electric audio equipment it is clear to me that the tuner of choice would be an updated version of the Western Electric No. 10A receiver. The tubes used by Western Electric receiver are obsolete and should be updated to more modern tubes in the revised design. The detector in the Western Electric design is also inadequate having high distortion, and due to the square law characteristic it modulates the AGC voltage at the syllabic rate of the audio signal. Modifications to update the tubes, resolve the detector and AGC problems were available by the early 1950's, or earlier. There is one remaining problem with the W.E. 10A that hasn't yet been addressed to the best of my knowledge, and that is the aperiodic antenna input circuit, that is likely to be a source of RF 3rd order IM problems which will wipe out some weaker signals if you live near a number of 50,000 Watt flame throwers, or even 5,000 Watt stations. This problem could be eliminated by deleting the first RF amplifier stage, which is probably serious overkill with modern tubes anyhow, and making the first bandpass filter a tuned antenna circuit. This is the reason that I prefer the Weeden and Altec designs, they both have tuned antenna circuits to minimize RF IM problems. If one wanted to duplicate an existing circuit the Altec is probably the best choice as it has a tuned antenna circuit and uses modern 7 pin miniature tubes. One addition that would be necessary for any of these tuners today would be the addition of a "NRSC" deemphassis network to compensate for the preemphassis that is used in AM broadcasting today. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
FA/FS: High Power Antenna Tuner | Equipment | |||
FA/FS: High Power Antenna Tuner | Equipment | |||
High school radio stations alive and well | Broadcasting | |||
KE9OA's High Performance MW Receiver | Shortwave | |||
High performance MW receiver | Shortwave |