PTS Synthesizer Programming Info
There are lots of PTS (Programmed Test Sources) synthesizers available on eBay. They go for reasonable prices because they are usually set up for remote control and don't have any front panel at all.
These are nice units because they have low phase noise and the spurious outputs are way down in the mud. The best place to find details is on the PTS website) where they have a fair bit of technical info and a PDF catalog. However, the web site doesn't provide info on how to program the units via their rear panel connectors. This page fills that gap for two units that I've worked with: the PTS160 and PTS250 units (I also have a 40MHz PTS040, but it has the direct digital synthesis option and some other quirks that I haven't fully figured out yet).
Mix-and-Match
The PTS synthesizers are very modular in design. They offer various frequency step sizes from a minimum of 100kHz down to 0.1Hz. If you happen to find yourself with more than one unit, you can mix and match the divider modules to get the resolution you want. Looking down at the unit with the front facing you, the right-hand seven slots may or may not be populated with boxed modules. These are the "digit modules" that provide the resolution settings. If all the slots are full, the unit has 0.1Hz resolution; each missing box (from the right end) drops one digit.You can add additional digit modules from another unit. However, you need to tell the unit that they're there. To do that, open the bottom of the box and look at the long PC motherboard that's nearest the front of the unit. There will be a wire running from pin 3 (from the front of the box) on the right-most slot over to pin 3 of the last slot that has a module installed. Simply plug in the extra modules and move that lead to so that it now connects to pin 3 of the last slot that you've filled (still leaving the right-most end anchored), and you're all set. I modified a PTS160 unit to go from 1kHz to 1Hz resolution this way.
Performance
The PTS synthesizers have very clean output spectra and low phase noise. Here is a screenshot of the phase noise of my PTS160 taken from an Agilent E4440A PSA Series spectrum analyzer:
PTS Programming
The 50 pin connector on the back of the unit is a standard Centronics male plug. The connector carries BCD programming lines for each digit as well as a few other signals. All the logic signals are TTL level and are tied high internally; to activate, ground the appropriate pin on the connector. Looking at the back of the unit, pin 1 is at the lower left, pin 25 at the lower right, pin 26 at the upper left, and pin 50 at the upper right of the connector.Pin 42 is the "remote enable" pin and it must be tied low before you can program the unit.
NOTE: The PTS250 pinouts below are in error. I believe the PTS160 pinouts apply to both units.
The PTS160 and PTS250 have some differences in pinouts, so make sure you use the proper column from this table:
| Pin | PTS160 | PTS250 | Pin | PTS160 | PTS250 |
| 1 | 100kHz | 200kHz | 26 | 400kHz | 800kHz |
| 2 | 200kHz | 400kHz | 27 | 800kHz | 1MHz |
| 3 | 10kHz | 10kHz | 28 | 40kHz | 40kHz |
| 4 | 20kHz | 20kHz | 29 | 80kHz | 80kHz |
| 5 | 1kHz | 1kHz | 30 | 4kHz | 4kHz |
| 6 | 2kHz | 2kHz | 31 | 8kHz | 8kHz |
| 7 | 100Hz | 100Hz | 32 | 400Hz | 400Hz |
| 8 | 200Hz | 200Hz | 33 | 800Hz | 800Hz |
| 9 | 10Hz | 10Hz | 34 | 40Hz | 40Hz |
| 10 | 20Hz | 20Hz | 35 | 80Hz | 80Hz |
| 11 | 1Hz | 1Hz | 36 | 4Hz | 4Hz |
| 12 | 2Hz | 2Hz | 37 | 8Hz | 8Hz |
| 13 | 0.1Hz | 0.1Hz | 38 | 0.4Hz | 0.4Hz |
| 14 | 0.2Hz | 0.2Hz | 39 | 0.8Hz | 0.8Hz |
| 15 | 10MHz | 20MHz | 40 | 40MHz | 80MHz |
| 16 | 20MHz | 40MHz | 41 | 80MHz | 100MHz |
| 17 | 1MHz | 2MHz | 42 | REM EN | REM EN |
| 18 | 2MHz | 4MHz | 43 | ||
| 19 | 4MHz | 8MHz | 44 | ||
| 20 | 8MHz | 10MHz | 45 | ||
| 21 | GROUND | GROUND | 46 | LATCH EN | LATCH EN |
| 22 | REM LEVEL | REM LEVEL | 47 | LATCH EN | LATCH EN |
| 23 | LATCH EN | LATCH EN | 48 | +5V | +5V |
| 24 | LATCH EN | LATCH EN | 49 | ||
| 25 | LATCH EN | LATCH EN | 50 | GROUND | GROUND |