Modernized Drake FS-4 for the Drake R-4 and SPR-4 Receivers


By: Steve Hageman


The construction article was published in the June, 2004 issue of QST.


Reprints are available from the ARRL for a nominal charge

Search the ARRL Website - at one time the article was posted for free downloading.



Picture of the Crystal Eliminator mounted in a MS-4 Speaker Enclosure for my R-4B



Picture of the Crystal Eliminator built in a small Hammond enclosure for my SPR-4


Note: This is a Do-It-Yourself project. All the information required to build one of these on your own is in the article - please read the article first to answer any questions you may have. At the present time I can supply some small quantities of the MC145170 PLL chip and pre-programmed PIC Microcontrollers just as a help to people (feel free to contact me for availability information). The PIC code is free to download on the ARRL Website. FAR Circuits did at one time supply a partial kit of components - contact them directly to find out their current status. I have no business connection with FAR Circuits in any way so I cannot answer directly for them. Thanks for your understanding and have fun with your "Full band" Drake receiver!

*** Below is a current FAQ for the project as published in QST ***


Drake made a great series of receivers over the years. The best were called the R-4 series and even today some 35 years after their first release they are very fine radios. My personal collection consists of a R-4B and a SPR-4 (The solid state version). These radios were advertised as "Programmable" -- That is by adding a crystal they could tune any 1/2 MHz segment of the HF bands from 1.5 - 30 MHz. They came configured for the Ham bands (80-10 meters) and always had extra crystal positions for shortwave frequencies or utility bands, etc. But you could never add enough crystals for full coverage of the HF bands. The SPR-4 had the most bands available - 23, but even that allows only less than half of the available HF tuning spectrum. Drake also had a synthesizer (I call it a crystal eliminator) called the FS-4 that allowed full band coverage from 1.5 - 30 MHz. These are still available today on places like ebay, but they are very expensive. I decided to build a modern version of the FS-4 that I could actually afford to own. My version allows full HF band coverage but with the modern elements like a 2 line LCD or very pretty VFD display, single knob tuning, etc. This project is fully documented in the June 2004 issue of QST. Reprints of the article are available from the ARRL. Other sites on the web have more information on the original Drake FS-4, so "Google" away!

Project FAQ:

1) Big Oops! The MC145170 part number specified at Newark is for the WRONG package type. The proper Newark part number is: 01C4669, for the proper Freescale (formerly Motorola) part number MC145170D2R2. I'm really sorry about any inconvenience this may have caused anyone, this was totally my fault. For all the different package types check out the data sheet for the MC145170 at If you bought the wrong part from Newark - they will give you your money back on an exchange - they want you to have the correct parts and be happy! :-)

The MC145170D2R2 part number decodes as follows:

MC145170D2R2 = The base part number

MC145170D2R2 = The package type, SOIC here

MC145170D2R2 = Means revision 2 (or -2) of the part

MC145170D2R2 = Newark has this designator on their website, but it means tape and reel. You will be buying the part as bulk so this doesn't matter or really apply.

In April 2005 Motorola (Freescale) finally obsoleted the last part I wanted to buy from them - yep the MC145170. There are still thousands in the supply chain and I secured about 30 of them for this project. If you are having problems finding the chip, feel free to contact me and I can get you one of the ones I have for my cost plus shipping.

2) If you bought a kit from FAR circuits and have not assembled it yet, please contact FAR Circuits for updates since there were many 'Startup' problems getting this project going. I believe that the problems were taken care of by July 2004.

3) The VCO can be bought from or you can purchase the short kit from FAR circuits that contains this part. Contact FAR Circuits at: Minicircuits has changed their minimum order quantity to 5. This was done in the last six months and follows years and years of being able to buy just one of anything. Things just keep on changing! I was told however, that if you call your local Mini-Circuits rep they would be able to let you place an order for just one. Thanks for the info Jim.

4) The VFD specified at Digikey is obsolete - Digikey now carries the Noritake CU16025ECPB-W6J. This new part is a drop in electrical replacement. However the replacement VFD draws a bit more power than the original and to keep R100 cooler you can fashion a small clip-on heatsink as shown here. Use a small piece of scrap aluminum and make the fins as long as will fit in your enclosure or you can wrap them over and attach them to the die cast metal shielding box or your chassis. Even the short 1" fins shown here will sink off quite a bit of excess heat.

Hey guess what? The LCD specified at Digi-Key is now obsolete as of August 2004. Mouser has P/N HDM16216H-B-S00S, which is a drop in replacement - Same with the Jameco # 171715 It will also work fine, although it is slightly smaller that the pictures of my units show.

5) The PIC16F876A may be getting easier to find than the non A version. The same bits work for either part - BUT your programmer must know the difference from an A to a non A part. This is because the programming algorithm is different between the two parts. You may be able to get samples of this part for free from Microchip. Try them at

6) Many suppliers and distributors sell the other parts so check around.

Jameco, Allied, Radio Shack

Mouser, Newark, Ocean State Electronics

TI, Analog devices, Maxim, National, Microchip and others also offer free samples in many cases.

If you have any trouble with a specific part - call the manufacturer. They don't care who you are or who you work for - really! All they want is for you to be able to get their parts and be happy! They will sample parts in many instances and they can tell who has stock of the particular part instantly - over the phone.

7) Digikey may not have the original OP27 that was specified, but recently they had over 3000 OP27GP and OP27EP devices. These will also work in the project.

8) The Grayhill rotary encoder specified was a 25LB45-Q. Other substitutes that will work are the,

25LB10-Q, 25LB15-Q, 25LB22-Q

These are the same switches, except they have a different number of detents than the original. Newark carries several of the others.

9) Please note that we are coming out of the worst technology downturn ever. Approximately 25% of the worldwide manufacturing capability was taken off line in the last 4 years. Now that the economy has improved - lead times are increasing. This has resulted in 8-12 week lead times on many parts in the industry, perhaps even some of the ones specified for this project. If you let me know what you are having trouble finding, I will do my best to help you out.

10) A number of folks have asked how I make the front panels and labels for my projects - I make them basically the same way Neil does at AADE, in fact he has some good ideas I didn't even think of -> So check out his site at: Scott Edwards also makes some really clever little stick on bezels (great when you can't cut a straight, square hole - like me!) Look for them at Digikey also sells plastic, stick on bezels (That's what's on my SPR-4 version face plate as shown above).

11) Where's Waldo part 1 - Jim let me know that C23 was mislabeled on the ARRL schematic. The parts list is correct however and C23 is really a 120 pF capacitor. To tell you the truth - I looked at a simulation of the filter with a 82 pF capacitor like the schematic says and I believe the unit will work just fine either way.

12) A chap asked about using sockets for the IC's. You should not need sockets for any of the parts. I only use sockets for the PIC when I am developing code as this allows me to remove the part for programming. So a socket for the PIC is optional.

13) Where's Waldo part 2 - Somehow I mistyped "Orion" instead of "Omron" for the relay manufacturer ( ). My typo...

14) Where's Waldo part 3 - The parts list printed in QST lists C31-C36 for 0.1 uF capacitors. However C33 and C35 are not used. It should have said C31, C32, C34, C36.

15) Apparently FAR circuits has substituted a "House Numbered" device for U6. I have no idea what this device originally was, however the one I saw appeared to have a 1985 Date Code on it. I have seen one case where there were huge 4-5 kHz sidebands on the output which manifested itself as an AM modulated tone on the receiver audio output. The cause of these sidebands was because the substituted regulator was oscillating. If you have this problem, replace U6 with the specified part. Radio Shack, DigiKey, Mouser and Jameco carry suitable 7805 regulators. You can spot this problem with a DVM: Set the DVM to AC RMS, 200 mV Full Scale and measure the output pin of U6 and compare this reading to the reading of the other two regulators. If U6 measures appreciably more ripple on it's output than the other regulators - it is probably oscillating.

16) I saw a unit with a 74AS74 substituted for the 74AC74 part specified. It worked amazingly well - however the AS part draws considerably more power than the AC part specified and causes the PLL to loose lock at the higher frequencies. The AS part is also not nearly as well behaved driving the LC filters as the AC part is. I suggest that the originally specified AC part only be used. Also ACT parts are not the same as AC and I don't recommend them either, please stick to the parts specified.

17) Crystalfontz ( makes some wonderful LCD displays in many colors for very reasonable prices. If you are looking to make a 'fashion' statement with your unit you should check them out. Their 16x2 character modules work just fine with the Crystal Eliminator code as is. You may find that some of their displays need to have a contrast adjustment. This is not to fault their displays as they are excellent - however you may want to connect a 10 k trimpot between pins 1 and 2 with the wiper going to pin 3. This will allow the contrast to be adjusted - see their data sheet if this doesn't make sense.

18) I found a few errors on the schematic as published by the ARRL. I have attached the original schematic here for your download. The original schematic was in the ARRL download package also. As far as I know the PCB's have always been correct, these were transcription errors from my schematic to the ARRL publication.

19) I have seen people with PLL problems, mostly these problems have been solder joints at the PLL IC. Use a microscope and be very careful. A short or an open here and the PLL won’t work.

20) As the article stated - the FAR circuit boards do not have plated through holes, so everywhere there is a trace on the bottom side and the top side there needs to be a solder joint on BOTH sides! Use an ohm-meter to trace the circuits. I have seen many instances of this around the 74AC74 flip flop. It is hard to see the traces on the top side the way I laid them out (sorry 'bout that) put a jumper on the backside if you need to. If the 74AC74 is not working then the PLL will not work. Use an ohm-meter to trace the circuits.

21) People seem to be getting confused by the negative supply to the OP-27 not being regulated. Here is the full story on this. As long as the negative supply is below about -4 volts AND the total supply voltage across the OP-27 is less than 40 volts, the OP-27 will work. The OP-27 has more than 80 dB power supply rejection ratio at 120 Hz. So ripple on these lines does not affect the PLL at all. If the PLL is tuning and stable, then these power supply voltages are probably OK.

22) The PIC must have a clock signal to run. If the PIC appears not to run, then check to be sure that it is getting a clock. The clock to the PIC initially starts out at 10 MHz / 8 = 1.25 MHz - this is the way the PLL IC defaults to on power up. One of the first things the PIC does is program the PLL IC to make this 10 MHz. If the PIC clock never changes to 10 MHz, then the PLL IC is not getting programmed.

23) All of the errors I have seen so far are with the wrong parts being used (one even had a 7905.2 negative regulator where there should have been a 7805 positive regulator - also see above) and soldering. After 35 years or so of soldering I know how frustrating this can be so have someone else check your work if possible and keep at it you can figure it out. It might be best to only work on a section at a time and carefully checking with an ohm meter. Too much time spent looking for a problem is counter productive, take a break and try again tomorrow.

24) People seem to be getting confused about the 10 MHz clock needing to be right on - while that is a worthy goal, step back and think how the Drake originally worked. The crystals weren't specified to be exactly on frequency, nor were they trimmed. The R4 series had a slip calibration on a knob and the cross hair was movable to make up for this error. Once the dial has calibrated out any PLL error the error tracks to the other bands because the PLL is locked to the same crystal. The accuracy of the synthesizer between bands is better than the Drake originally had with it's many crystals. Certainly better than the PTO accuracy which on my drakes is about +/- 500 to 800 Hz across a single band.

25) Pin 21 of the PIC is labeled "Debug PLL". Normal operation is to leave this pin open. If you ground this pin and power-up the crystal eliminator the PLL IC is programmed to make three pins active (See article page 29, 2nd column). The reference frequency (Fr) to the phase detector is put out on Pin 9 - should always be 200 kHz for a R4 version or 20 kHz for a SPR-4 version. The output of the N counter (Fn) is output on Pin 10. If the PLL is locked this should be the same frequency as pin 9. If the VCO frequency is too high then Pin 10 would have a frequency that is greater than Pin 9, etc. In Debug operation The Lock detector output is also active. When the PLL is locked this pin will be at a high level with negative going pulses if the PLL is locked. If the PLL is unlocked (Fr and Fn are at different frequencies) then this pin will be low. More information on these pins can be found on the MC145170-2 Data sheet which can be found via a Google search of the web.

26) On the schematic: Pin 26 of U101 it says: "VFD OFF... No Function with LCD" Actually this pin will blank the LCD also. This will manifest itself with the display going blank after a power on message. So if your display works for a second, then goes blank make sure that this pin is open.

Here is a list of some of the units I have fixed and the problem found...


Symptom: Works fine, then just stops after a few minutes to a few hours.

Problem: Bad solder joint on a topside trace - component was not soldered on top - intermittent. (This was one of my units! - Very embarrassing....)


Symptom: Multiple parts get red hot.

Problem: Multiple PCB shorts. 7905.2 installed where a 7805 should have been. That's a negative regulator! Pull all the regulators and put them back in one at a time until the problems (shorts) are resolved.


Symptom: PLL doesn't seem to lock. Looks like PLL loop is oscillating.

Problem: Voltage regulator oscillating. Unknown regulator part type installed where a 7805 should have been. Who knows what that part really was?


Symptom: PLL won't lock at highest ranges.

Problem: 74AS74 installed where 74AC74 was specified. "AS" part does not work at high VCO frequencies, also draws too much supply current causing V+ on OP-27 to get below minimum for operation.


Symptom: PLL does not work.

Problem: Pins at PLL IC are shorted with solder, clean pins - unit works.


Symptom: OP-27 output is at -6 volts or so, never moves.

Problem: Pin 7 of OP-27 is at -6 volts (should be +17 volts or so). Bad solder joint on capacitor C31 and C36, no positive supply on OP-27.


Symptom: U5 is hotter than the sun.

Problem: Using my highly calibrated finger I found that Tantalum capacitor C14 was hotter than the sun too! Ouch that hurts! C14 was found to be backwards. Fix C14 and what do you know? U5 is now cool as the morning air in Switzerland! :-)


Symptom: Unit does nothing.

Problem: Crystal not soldered (bad solder joint), resulting in no clock at PIC. The PIC must have a clock to run. This is one of the first things to look for if the LCD display does not light up - check the PIC clock.


Symptom: Unit works, but The OP-27 Seems to be stuck at the positive rail most of the time. The PLL seems to sortta lock at the lower frequencies - but then get's stuck.

Problem: 74HC74 used where 74AC74 was specified. The HC part is only rated to 30 MHz! Also a 20 MHz crystal was used where a 10 MHz unit was specified. Both these errors make the PLL operation very iffy. Troubleshooting consisted of first looking at all the parts for proper values. This unit took about 15 minutes to fix because the problems were all in plain sight.


A general tip: If the unit doesn't work, check all the IC's voltages right on their pins. This will show where the bad solder joints are.


A general tip: If one of the regulators or an inductor in the power supply lines gets hot - feel around to see if some component is hot - if it is in backwards it will likely get hot too (like a Tantalum capacitor). If nothing else gets hot then there is a solder short to ground somewhere on the output of that regulator. You can trace this out with a voltmeter.




This is what the engineering prototype looked like. Fully functional breadboard used to verify PLL operation, spurious levels and to develop the PIC firmware. 



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Modified - 25Sep07