Hello Garey, First of all, let me add my voice to the many well-wishers that have been praying for your return to good health; I hope you continue to make good progress.
You have confirmed things as I thought I understood it; my question was driven by the fact that in your original reply to the post, you specifically mentioned the issue being with the transmitter. Since the chain is the same in both the receiver and the transmitter, it makes sense that the issue is common to both. Thank you for the reminder that various spurs can get through, which means we should be careful as we do our alignments on these radios. 73, Eric KA8FAN ________________________________ From: Garey Barrell <[email protected]> To: Drakelist <[email protected]> Sent: Sun, November 8, 2009 10:37:09 PM Subject: Re: [Drakelist] using the Twins on the WARC bands Eric - Same problem, the R-4/A/B all use the same PreMixer scheme as the T-4X/B, so the same spurious signals are generated. Just Murphy at work. No one ever dreamed that we would get a band at 10 MHz when the 4 Series was being designed. Selection of IF and PTO frequencies is/was difficult. Remember that any mixer has at its output the SUM and DIFFERENCE of ALL frequencies (and their harmonics) present in the output. One of the things that trips up people trying to "repair" a T-4X/B is that the RF TUNE and the PTO frequencies are within the range of the rest of the RF chain. So it is quite possible, in the case of a PreMixer or Band Oscillator failure for the transmitter to be tuned up on either 5.645 MHz or 11.290 MHz and provide full output. So "my T-4X puts out full power, but I can't change the frequency by turning the PTO", syndrome shows up. Only so much selectivity can be achieved in the various tuned circuits so if the PTO is on 5.455 MHz (0.0 on the dial), the Carrier Oscillator is on 5.645 MHz. along with their second harmonics of 11.29 MHz and 10.91 MHz, and the PreMixer output includes 21.1 MHz as well as the desired 26.555 MHz, and the transmitter is tuned up around 10 MHz, you could have quite a few signals at the output of the 1st Mixer stage that would go right through the Driver and Final stages. If you look at the recommended crystal frequencies recommended for the range around 10 MHz, you'll get an idea just how complex this problem is. And just to make it interesting, change the PTO frequency by 10 kHz and get a whole NEW set of spurs. Don't forget, when these units were designed, the engineers were still using slide rules! Today it's not very difficult at all to just plug the various oscillator frequencies into a spreadsheet and let the computer spit out ALL the possible combinations and permutations for the fundamental and say the 2nd and 3rd harmonics of EACH oscillator. You'd get page(s) of frequencies, SOME of which will fall within the bandwidth of successive stages. So my recommendation is to go with the 20.8 MHz crystal(s) and live with the band starting at 9.7 on the dial! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs <www.k4oah.com> Eric Webner wrote: > Garey, > > What, then, are the rules if one wants to crystal the receiver to run 30 > meters, and use it for transceive operation? > 73, > > Eric KA8FAN > > > ------------------------------------------------------------------------ > *From:* Garey Barrell <[email protected]> > *To:* [email protected] > *Sent:* Mon, September 14, 2009 12:40:37 PM > *Subject:* Re: [Drakelist] using the Twins on the WARC bands > > Joey - > > You are absolutely correct. Any of the four line twins will work on all WARC > bands, simply by adding crystals for each band. The only "odd-ball" is 30M, > since it is so close to the PTO and IF frequencies in the transmitter a > "non-intuitive" crystal frequency is required, (20.8 MHz). There is a small > "forbidden" range right at 5-6 MHz and 10.5-12 MHz for the same reason, but > there are no bands affected other than the oddball one at 5 MHz. These rules > apply only to the transmitter. > > Any other frequency range from 1.5 to 30 MHz can be added simply by adding a > crystal cut for 11.1 MHz above the bottom end of the desired range, i.e, a > crystal at 24.6 Mhz would cover from 13.5 - 14.0 MHz. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs > <www.k4oah.com <http://www.k4oah.com>> > > > > Richard J. Fiero II W5TFW wrote: > > I am FAR from an expert, but what Geoff said about the twins isnt > > Correct. I use mine on the WARC bands everyday. for about 40.00 > > for each band You can also, even cheaper if you dont run split. > > all it takes is a set of crystals and tuning the radios by the Manual for > > the band you want to use. > > 73 Joey > > > > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
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