Authored by VE3EFJ3.4 R4ANY RECEIVERS
 | Mixing Scheme First mixer injection on all T4/R4 is premixed from the PTO and the band crystal. The crystal is always 11.1 MHz higher than the low end of the band edge in question. For example, the 80 meter band will have 3.5 + 11.1 = 14.6 MHz crystal. The PTO is mixed with the band crystal and the difference is used and injected into the first mixer. A lower PTO frequency correlates to a higher received frequency in the band range. Using 160 meters with a 12.6 MHz band crystal for example, the 0 scale band edge is 1.5 MHz. The first mixer injection frequency is Fin + Fif = 1.5 + 5.645 = 7.145. This is made from the difference of the PTO = Fxtal - Finj = 12.6 - 7.145 = 5.455 MHz. If you apply the above scenario to a 2.0 MHz incoming signal you will see that the PTO oscillator frequency tuning is inverted. Both the R4any and SPR-4 are remarkably low in spurs and mixing pro- ducts once aligned properly. On all of these receivers, I've always noticed a quickly tuning spur at 3.897 MHz. This tunes very fast, so a VFO harmonic is involved. Because of the PTO frequencies and mixing scheme there are some forbidden zones of operation on some band segments that will produce very foul mixing products. Obviously the band range covered by the PTO is a no-no. 10 MHzoperation is possible, but pay attention to the transmitter manual, for the PTO second harmonic is an important consideration when the twins are set up for transceive operation. None of these zones fall into current amateur band assignments. This also explains why strange settings of the preselector control produce receive peaking - you are likely finding a mixer output that could be PTO, crystal or the sum of the PTO/crystal product that coincides with the rack slugs for the front end tuning. |
| R4any and T4any Transceive Operation Transceive selection and muting is accomplished through the INJ line. This is done by supplying a high negative voltage along this line from the unit with the active PTO. This line is routed to the link on the preselector and to the control grid of the PTO/xtal LO premixer. There is also a diode on the preselector mixer more or less from screen grid to plate. This forms an electronic switch to kill the premix on the unit that is having the external PTO premix signal. On the R4C/T4C there is also a separate BFO line. The oscillators on both units will fall into sync with each other naturally just from being linked together, providing they were pretty close together to begin with. If the BFOs won't sync, make sure you are using RG/62U cable and that the oscillators individually are pretty close. Since it is the receiver that syncs to the transmitter, failure to sync or an off frequency BFO is likely caused by the transmitter. If you find that the receiver acts funny when the BFO line is linked - there is a sub audible beat note and the S meter cycles up and down, this is a sure that the injection level is wrong, likely from the transmitter. The BFO line is being mixed, rather than sync'd. Check the BFO level from the transmitter. You should have 1V P/P, minimum, open circuit, at the receiver input plug of the cable. |
| Digital Dials Once in a while I have had requests for digital dials for the older transceivers. This also applies to Atlas and some Japanese units such as the Kenwood 520. I bought an R4C once that had a Yaesu DYC-221 hooked into the PTO. It worked, but this is not the way to go. What you *really* want to do is to read the INJ line and count the RF signal on the line, accounting for the IF frequency before dis- play. If you do it this way, you get a true read out in MHz, real time. After doing considerable research for a related product, I found such a device that is near perfect. Out of all the units on the market, the Radio Adventures A2K is without any doubt THE way to go. It will interface with almost anything and is programmable for just about any offset. And, it will work with the inverse PTO tuning Drake without a hitch. "All ya gotta do" is, once programmed, is connect the A2K into the INJ line of the transceived B's or C's with a Radio Shack Y cable. Since this line is hot with INJ no matter who is slaved, Bob's your uncle. When you build the kit, do not install R1. I have not tried the A2K with the TR4, but it will work even though 20 tunes backwards. It will/should work because the A2K contains programmable memories. On 20, you'd use a different memory setting and tell him to count the other way. The website is at www.radioadv.com or call 814-437-5355. |
| Noise Blanker Set Up Both the R4C and TR4 noise blankers are very effective. The alignment of either is not difficult except in the case of the TR4 where access to some tuning adjustments can be a challenge. You'll need a 'scope to completely set one up and/or an analogue meter. Digital meters are OK, but they don't show relative measurements very well. The components in parenthesis are TR4 part tags for the 34PNB. Turn equipment on (what else?), turn noise blanker and calibrator on. Tune calibrator in on 10 meters and misadjust preselector for about an S3 reading. Adjust C3 and C6 (C10 and C19) for maximum S meter reading. Place a 'scope probe to the base of Q12 (Q12) or a volt meter to the emitter of Q14 (Q14). Peak preselector. Adjust C19 and C25 (C8 and C21) for maximum. Turn off calibrator. Set the 'scope probe for 1/10 (low capacity probe). All tuning adjustments are finished. No more trimmer twiddling from this point! Place 'scope probe to drains of Q7 and Q8 (Q6 and Q7) and adjust R28 for minimum. Finally, on the R4C only, adjust the gain balance for similar S meter reading on the calibrator with and without the noise blanker and the jumper plug. If you do not have a 'scope to adjust R28, leave it alone or more or less centre the control. |
| Crystal Filters - Hope Section deleted. Consider your sources today to be either the used market or International Fox Tango in Florida. *** They are the only supplier that I know of for Drake filters. If you decide your R4C, TR7, R7 etc is a keeper and an additional filter is desirable, then what ARE you waiting for? *** The June issue of QST states that IRCI has been bought out. |
| R L Drake Inc Drake has in stock replacement parts for most of their equipment. For items that are in excess of 15 years old, this is very good. In most cases their prices are good. One can obtain coils, crystals, tubes, meters and relays. Final variable capacitors are available, but expensive. Most front panels are available for around $15.00 but Drake won't sell you a new one unless you return the old one. I do not know why, but Drake is adament on this policy. If you write Drake a letter they will ship off a computer listing of current parts stock for a particular radio. As of the Summer of 1995, considerable parts were available for the 4 line et al. Parts for the TR7 were few except for ICs and transistors. There are no accessories available of any consequence. You will not be able to buy noise blankers or crystal filters for any of the C Line. If you want crystal filters, there is only one known source - International in Arizona. Their filters are at least equal to what Drake supplied and expensive. Well, maybe not that expensive con- sidering current KenYaeCom prices. Essential parts are still available (until the stock is gone) at reasonable prices. If you need accessories for your R4C or TR7, best to get them with the radio. Drake still services all of their amateur equipment, but they do not stock the PA tubes. They charge by the 1/4 hr. The current rate is about $19 US. I have heard some 'mutterings' about the labor cost, but have yet to hear ANY complaint about the quality of the work done. Consider Drake your only commercial repair service area, especially in the case of the TR7. The TR7 (and possibly other equipment in the '7' series) requires a fairly high skill set to service properly. Most, if not all 'dealers' of the, uh, other equipment won't touch it. Use this as a warning also for some Drake equipment on the dealer shelves, again, especially the TR7. Most are consignment sales. Consider its status as 'indeterminate'. R L Drake Manufacturing |
