This item is a scarce Drake FS-4 frequency synthesizer used as an accessory by many pieces of RL Drake equipment manufactured in the 70s and early 80s.  It has been tested and works beautifully.  Cosmetically, the unit is used, but any marks are minor and this is one of the nicest FS-4 units to pass through our hands the past 17 years of selling such equipment on Ebay.  As is common with these FS-4's, we want to mention that the center lamp is slightly brighter than the side lamps, but this does not affect operation and we suspect was a characteristic of the FS-4 as it was sold.  We also want to mention that a previous owner has removed the ground from the AC cord (see picture).  Please observe the HD pictures that we have supplied to view cosmetic detail and use them to supplement this written description.

We rarely have an FS-4 to offer for sale here on Ebay and it has been nearly 3 years since we offered the previous FS-4 for sale in our Ebay store.

The FS-4 comes with a copy of the manual that contains connection information, operating instructions, and a schematic. The FS-4 does not come with an injection cable, but this is easy to construct from a common RCA male 3' patch cord.  

During the time of manufacture in the 70's, many of the Drake receivers were crystal controlled and the user was limited to about 500 KHz within each crystal range.  Because the receivers had a limit on the number of crystals that they could use within the receiver, the Drake receivers were not full coverage and the owner had to prioritize which bands they wanted to be able to tune to and sacrifice listening to other bands.

However, eventually Drake also offered the FS-4 frequency synthesizer for sale and this allowed for full coverage on its equipment.  According to price lists from that era, the original cost for this unit was around $250 or so making it quite an expensive accessory item at the time when the receiver sold for about $400 to $700.  This explains why the production was limited and why these FS-4 units are not that common in consideration to the proliferation of other 4 line equipment.

The unit was specifically designed to interface with the "4" series of receivers like the SPR-4, the R4-C, and the T-4X. (R-4, R-4A, R-4B, R-4C. SPR-4, T-4, T-4X, T-4XB and T-4XC) For example, with the SPR-4 receiver, the operator can tune from 500 KHz on up to 30 MHz. The frequency on the FS-4 in MHz is added to the frequency on the PTO in KHz for the proper frequency reading.  Thus, if the FS-4 reads 3.5 MHz and the PTO on the receiver / transmitter reads 450 KHz, the frequency being received is 3.950 MHz.  Yes, some simple math is required to know the operating frequency.  Once you are on a specific band, you do not need to mess with doing the math as you tune around the band.

The FS-4 requires the proper injection signal using a cable that connects into one of the crystal sockets.  The center conduit of the RCA style coaxial cable plugs into the socket and the coax shielding fastens to the chassis of the receiver as a ground.  We have tested this unit on an SPR-4 and there was a nearby screw to attach the shielding so this connection was easy to accomplish.

While not designed specifically for the "2" series receivers, the FS-4 will work with them.  However, it is not full coverage as you have to add 7 MHz to the scale and this makes the FS-4 usable from 7 - 30 MHz on the "2" series units.  There is a very slight possibility that the unit may need to exchange the crystal inside the FS-4 with another one that is available online, but our experience has been that the calibration travel on the unit that the FS-4 is connected to is enough to generally allow for use the crystal as installed.

Here is information found at the Drake site regarding this unit:

https://web.archive.org/web/20110113185052/https://www.dproducts.be/drake_Museum/fs-4.htm  (copy and paste link into your internet browser)

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