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.

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.

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.

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.

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.