[Drakelist] TR4 Filters
Good Morning Friends Thanks for respond to my question about mic level. I have other question , some try change the cristal filters of TR4 for More Width (example 2.8 or 3 Khz) what is the result is possibly work with these filters?. Its possibly maybe switch T/R for transmit with 2.8 and receive with original or viceversa? Thanks in Advance 73 lw3ewz Gus Andrada (Sorry For my English) ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR4 Filters
- Original Message - From: mail.speedy.com.ar lw3...@speedy.com.ar To: drakelist@zerobeat.net Sent: Thursday, June 30, 2011 6:49 AM Subject: [Drakelist] TR4 Filters Good Morning Friends Thanks for respond to my question about mic level. I have other question , some try change the cristal filters of TR4 for More Width (example 2.8 or 3 Khz) what is the result is possibly work with these filters?. Its possibly maybe switch T/R for transmit with 2.8 and receive with original or viceversa? Thanks in Advance 73 lw3ewz Gus Andrada (Sorry For my English) Your English is OK Gus:-) The TR-4 uses the same filters for receiving and transmitting. I don't think is possible to use different filters for each function without some very complex modification. The main difference in using wider filters is that the voice quality is a little better. Personally, I think the very narrow filters that became popular at about the time the TR-4 was made are _too_ narrow. The theory is that they provide greater discrimination of the wanted signal from QRM in reeiving and concentrate transmitter power in the frequency range of speech that carries intelligence in transmitting. However, after reading a lot of the research papers on which this idea is based I have decided that its based on a mis-understanding of that material. Its interesting to me that Bell Labs and the Bell System found that if they made the bandwidth too narrow speech sounded un-natural. They decided to have a low frequency limit of around 250hz. On the high frequency side it turns out that for best intelligibility, even in the presence of noise, that the high frequency limit should not be much less than about 4 khz but around 3 will still give good results. The narrowest limit used by the phone company was 250hz to 2750 hz, a 2500 hz bandwidth. This was used for the filters in carrier telephone service and was just about the minimum possible in commercial telephone service where voice quality is important. It _is_ possible to transmit intelligible speech with a narrower bandwidth but its a matter of diminishing returns as the band is reduced from around 3khz. Nonetheless, many ham and military circuits have only about 2khz bandwidth. The filters used by Drake have very steep skirts so are good at eliminating nearby signals. The original Collins mechanical filters were six-pole filters, that is they had six resonators in them. These were _very_ much better than the typical communication receiver selectivity at the time but advances in crystal and ceramic manufacture allowed more complex filters to be made economically so Drake and others used 8-pole filters. The additional resonators can be used either to increase the rate of cut-off beyond the desired pass band (that is increased skirt selectivity) ot to improve the amplitude or phase flatness of the pass-band. BTW, ATT was using very complex filters, some with twenty poles for carrier telephone purposes. These were exremely difficult to make and very expensive but were justified by the application. This has gotten a little off-topic. The point is that if you change the filters they will work in both transmit and receive. I think the difference may not be worth the cost and effort. We will see what the real experts have to say about this, I may be completely wrong, wouldn't be the first time. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR4 Filters
Replacing filters and using different set of filters for T/R. They are all possible if you have right parts and do some electrical/mechanical mod. But why would you do that? The filters in TR-4 are not very narrow/sharp anyways. If you want to change the TX audio, try doing something on mic and mic amp first. You can achieve a lot there. For example, take a look at what W2PA did: http://www.w2pa.com/Home/articles/drake-t-4xb-audio-improvement Kihwal, K9SUL From: mail.speedy.com.ar lw3...@speedy.com.ar To: drakelist@zerobeat.net Sent: Thursday, June 30, 2011 8:49 AM Subject: [Drakelist] TR4 Filters Good Morning Friends Thanks for respond to my question about mic level. I have other question , some try change the cristal filters of TR4 for More Width (example 2.8 or 3 Khz) what is the result is possibly work with these filters?. Its possibly maybe switch T/R for transmit with 2.8 and receive with original or viceversa? Thanks in Advance 73 lw3ewz Gus Andrada (Sorry For my English) ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] SOLD: L4B/L7 power supply rebuild kit
Fellow enthusiasts, Thanks for all the nice emails. Wish I had a hundred kits available for all the Drake enthusiasts. Have a safe, enjoyable, holiday weekend. Please remember the price that has been paid for our freedom. 73, Evan, K9SQG ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] R-4C PTO Hum
I spent a part of the afternoon isolating the PTO audio fuzziness I described when the VFO dial is moved from 0 then upwards to 500 when listening to a CW carrier. I hear a pure, clean CW carrier at the 0 VFO position but then progressively gets worse, ending at 500. Based on how the fuzziness behaved, I guessed that it was more than likely related to a magnetic field -- either the power transformer or filament AC currents in the chassis. So, I completely disassembled the entire PTO and dial assembly and placed it on the bench, about a foot away from the R-4C. I ran RG-174 from the PTO to the R-4C. Sure enough, the problem is completely gone when the PTO is external to the receiver. After about an hour of testing, here's what going on: As the dial changes from 0 to 500, the PTO's ferrite core moves toward the back of the receiver. As the core moves rearward, it is also coming nearer to the AC power transformer. PTO cores are especially susceptible to magnetic fields. To prove to myself the AC power transformer is the culprit, I took the PTO assembly in my hands and moved to and from the transformer. When the PTO is within about three inches of the transformer, the CW note starts to become fuzzy. The degree of magnetic coupling is highly dependent on the orientation of the PTO to the flux field of the power transformer. The current orientation of the PTO with the transformer core (i.e., PTO core in-line with the laminate core direction, produces the worst results. By contrast, there's no fuziness whatsoever if I take the PTO and run it right up to the transformer when the PTO core is 90 degrees perpendicular to the orientation of the transformer core. If a were a bettin man, I would say a great number of R-4Cs (but NOT R-4Bs - see below) are affected by this -- some to a greater degree than others. I noticed this mainly because I've upgraded the entire path from the product detector to the final AF amp. Audio fuzziness on both CW and SSB that were previously masked by mediocre audio performance are now clearly audible -- but only when the PTO is on the top of the band -- like when I'm listening to 75m around 3950 kHz. Down on the CW band edges, all if fine. Some ideas on where to go from here and I would like input from others: 1) Investigate a real Mu-metal shield for a PTO cover. The stock PTO shield is aluminum and is fine for RF shielding -- but wholly useless for low frequency magnetic fields. This is where Mu-metal shines. Mu-metal is composed of 75% nickel, 15% iron, 15% copper and/or molybdenum; 2) Turn the power transformer 90 degrees. Easier said than done because there are no service loops in the transformer wiring. Would take extending the leads -- or purchasing a NOS transformer, subject to availability. I'm also unsure if the Xtal Cal board interferes with the transformer in that orientation. More measurements needed; 3) Bolt the AC power transformer to the back of the R-4C and get the flux field out of harm's way. Here's the kicker. When I replaced the power transformer in my R-4B with an R-4C transformer to gain some advantages previously discussed here, I oriented the transformer 90 degrees from the R-4C mounting scheme as the R-4B's transformer is 90 degrees turned from the R-4C orientation. I'll bet R-4B PTOs are probably cleaner than that of the stock R-4C when the VFOs are tuned up to 500. My R-4B with all the audio mods and new R-4C transformer does not exhibit this problem. I'm glad I conclusively found the root cause but I'm a bit bummed-out over what this next level of refinement is going to take to fix. There, I said it. This is a fix to a design problem. Sure, the R4 receivers are meant for communications and not audiophile use -- but the problem could have been managed better in design. It seems more proximity testing of PTOs to the magnetic field of the power transformer was in order. Or, perhaps Drake did run these tests with the older A and B series but became complacent when they changed the transformer orientation in the C series. Pointless to guess, I suppose. Paul, W9AC ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4C PTO Hum
On Thu, 30 Jun 2011 21:09:05 -0400, Paul Christensen wrote: As the dial changes from 0 to 500, the PTO's ferrite core moves toward the back of the receiver. As the core moves rearward, it is also coming nearer to the AC power transformer. PTO cores are especially susceptible to magnetic fields. To prove to myself the AC power transformer is the culprit, I took the PTO assembly in my hands and moved to and from the transformer. Ecellent work, Paul! This one is going in my file. 73 -Jim -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime. HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R-4C PTO Hum
Paul - Interesting. Something to try. A piece of copper wire, as big as will fit, looped around the outside of the transformer in the same plane as the transformer winding. Short the ends together, forming a complete 'shorted turn' around the transformer. I suspect a sheet of mu-metal stuck vertically behind the PTO, (don't forget the extension of the guide pin!,) might also help. Hopefully a combination of small 'fixes' can take care of the problem, rather than go through the pain of re-orienting the power transformer! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Paul Christensen wrote: I spent a part of the afternoon isolating the PTO audio fuzziness I described when the VFO dial is moved from 0 then upwards to 500 when listening to a CW carrier. I hear a pure, clean CW carrier at the 0 VFO position but then progressively gets worse, ending at 500. Based on how the fuzziness behaved, I guessed that it was more than likely related to a magnetic field -- either the power transformer or filament AC currents in the chassis. So, I completely disassembled the entire PTO and dial assembly and placed it on the bench, about a foot away from the R-4C. I ran RG-174 from the PTO to the R-4C. Sure enough, the problem is completely gone when the PTO is external to the receiver. After about an hour of testing, here's what going on: As the dial changes from 0 to 500, the PTO's ferrite core moves toward the back of the receiver. As the core moves rearward, it is also coming nearer to the AC power transformer. PTO cores are especially susceptible to magnetic fields. To prove to myself the AC power transformer is the culprit, I took the PTO assembly in my hands and moved to and from the transformer. When the PTO is within about three inches of the transformer, the CW note starts to become fuzzy. The degree of magnetic coupling is highly dependent on the orientation of the PTO to the flux field of the power transformer. The current orientation of the PTO with the transformer core (i.e., PTO core in-line with the laminate core direction, produces the worst results. By contrast, there's no fuziness whatsoever if I take the PTO and run it right up to the transformer when the PTO core is 90 degrees perpendicular to the orientation of the transformer core. If a were a bettin man, I would say a great number of R-4Cs (but NOT R-4Bs - see below) are affected by this -- some to a greater degree than others. I noticed this mainly because I've upgraded the entire path from the product detector to the final AF amp. Audio fuzziness on both CW and SSB that were previously masked by mediocre audio performance are now clearly audible -- but only when the PTO is on the top of the band -- like when I'm listening to 75m around 3950 kHz. Down on the CW band edges, all if fine. Some ideas on where to go from here and I would like input from others: 1) Investigate a real Mu-metal shield for a PTO cover. The stock PTO shield is aluminum and is fine for RF shielding -- but wholly useless for low frequency magnetic fields. This is where Mu-metal shines. Mu-metal is composed of 75% nickel, 15% iron, 15% copper and/or molybdenum; 2) Turn the power transformer 90 degrees. Easier said than done because there are no service loops in the transformer wiring. Would take extending the leads -- or purchasing a NOS transformer, subject to availability. I'm also unsure if the Xtal Cal board interferes with the transformer in that orientation. More measurements needed; 3) Bolt the AC power transformer to the back of the R-4C and get the flux field out of harm's way. Here's the kicker. When I replaced the power transformer in my R-4B with an R-4C transformer to gain some advantages previously discussed here, I oriented the transformer 90 degrees from the R-4C mounting scheme as the R-4B's transformer is 90 degrees turned from the R-4C orientation. I'll bet R-4B PTOs are probably cleaner than that of the stock R-4C when the VFOs are tuned up to 500. My R-4B with all the audio mods and new R-4C transformer does not exhibit this problem. I'm glad I conclusively found the root cause but I'm a bit bummed-out over what this next level of refinement is going to take to fix. There, I said it. This is a fix to a design problem. Sure, the R4 receivers are meant for communications and not audiophile use -- but the problem could have been managed better in design. It seems more proximity testing of PTOs to the magnetic field of the power transformer was in order. Or, perhaps Drake did run these tests with the older A and B series but became complacent when they changed the transformer orientation in the C series. Pointless to guess, I suppose. Paul, W9AC ___ Drakelist mailing list
