[Drake] Re: FS: Frequency Synthesizer for Drake R-4 Series

[Bob Stein]

Barry L. Ornitz wrote:
> Bob, W6NBI, offered his frequency synthesizer for the 4-line 
> receivers for sale and wrote:
> 
> 
>>This frequency synthesizer for the Drake R-4 series 
>>receivers was designed and built by me and was published in 
>>the August 1972 issue of "ham radio" magazine.  The 
>>synthesizer provides complete coverage from 500 kHz to 30 
>>MHz.  When the Drake receiver is used as the controlling VFO 
>>in transceive mode, full operation is possible from 1.5 to 
>>30 MHz, including the WARC bands.  I will supply an original 
>>issue of the magazine (torn cover), as well as schematics of 
>>all the circuits which improved performance but were never 
>>published.
> 
> 
> It has been quite a while since I remember reading the article 
> in Ham Radio Magazine.  Does this synthesizer output in 100 
> KHz steps (I think it does) or in 500 kHz steps?  
> 
> I ask because while the receivers can cover 1.5 to 30 MHz with 
> the exception of 5 to 6 MHz, in nice 500 KHz bands, the 
> companion 4-line transmitters have a number of frequency 
> segments where they should not be used, and a number of other 
> frequency segments where only portions of the dial range are 
> acceptable and crystal frequencies ending in other than 0.1 or 
> 0.6 MHz are needed.  These segments are, of course, where 
> spurious emissions are likely because of harmonics of the PTO 
> or because of the high probability of tuning the radio to the 
> incorrect mixer products.  They are all listed in the 
> transmitter manuals.
> 
> Fortunately only one WARC band is affected, the 30-meter band, 
> where a 20.8 MHz crystal is normally needed rather than a 21.1 
> MHz crystal.  Sadly the proposed new 60-meter band may not be 
> possible with this series of radios.
> 
>>From memory again (and since it has been quite a while since I 
> read the article, I may be mistaken), I believe this design 
> had spurs spaced 100 KHz away from the desired output that 
> were of a high enough level to cause some problems with false 
> signals.  Do your modifications specifically address these 
> spurs?
> 
> Please note that this is not to fault Bob's design in any 
> way.  I think the Drake FS-4 may have suffered from some of 
> the same problems.  Perhaps someone who has owned a FS-4 can 
> address this.
> 
>         73,  Barry L. Ornitz     WA4VZQ     ornitz@tricon.net
> 
> 

It outputs in 500-Hz steps to correspond to the crystal frequencies 
that would be required.  There are three frequency controls marked 
according to the receiver frequency, not the synthesizer output.  For 
example, to set the receiver to tune 24.5 to 25.0 MHz, which would 
require a 35.6-MHz crystal, the synthesizer TENS dial (3 positions: -, 
1, 2) would be set to 2, the UNITS dial (10 positions: 0 to 9) set to 
4, and the TENTHS dial (2 positions: .0 and .5) set to .5.

I has been many years since I made any changes to the synthesizer, 
although I used it up to about a year ago.  However, I did reduce the 
spurs to more acceptable levels.  One thing that I never mentioned at 
the time was that my first attempt was made using the PLL chips being 
produced at that time by a manufacturer who shall remain nameless.  I 
proved to them that their design was suitable only for very low 
frequency use.  There was just too much coupling from the reference 
frequency to the VCO control voltage.  Talk about spurs!

Bob, W6NBI