Time Based Reference in VK3PKT’s Shack

So over the last 12 months the Twisted Shack of Mark VK3PKT has been getting a lot more test gear. Some of it was from the hamfest, some from people that I know and some from eBay.


I first aquired a 550MHz Freq Counter this is connected to a 10MHz GPSDO timebase to lock it to a known reference. It is then connected to a 10 MHz-520 MHz Marconi AM/FM Signal Generator to give an accurate display of the frequency of the RF Sig Gen.

1PTAX0001Marconi RF SIgnal Generator and Philips Freq Counter 


So I have a lot of my gear, 3 Frequency counters and a Time Interval Analyzer hooked up to a GPS Disciplined Oscillator. This uses GPS satellites to create a very accurate 10 MHz signal to use as a reference for the test equipment.  I also have a Rhode and Schwarz Frequency Standard that outputs 5 MHz 1 MHZ and 100 KHz. I use an oscilloscope connected to both the 5 MHz output of the R & S Standard and the GPSDO to get the FRQ standard on spec.


This scope is dedicated to the job of using lissajous figures to monitor the GPSDO and both the R & S as well as my OCXO Ovenized Crystal that runs off 12 volts and has a small SLA battery to keep it running while taking it from the shack to the car then to a mates shack to calibrate gear. I first adjust the transfer standard against the GPSDO using a Scope and then take it to the required location as needed.

transfer2 transferstandard1 transerfreqFrequency Counter showing Frequency of the transfer standard 

Now when it come to calibrating counters and reference standards I start by using the GPSDO as the Master Standard, this is the one that for my shack I trust the most to be accurate. That is what I feed it into a lot of my test gear as a reference. To check the 5MHz R & S I could just use lissajous figures but I have a bit of gear I picked up dirt cheap on ebay. It cost me 160 bucks delivered and new was over US $8000. It is a Yokogawa TA320 Time interval Analyzer. It measures periods down to picoseconds. Here is a histogram of the the 5 MHz signal calibrated against the GPS 10 MHz signal.


As you can see the range of the window is only 2 nanoseconds, from -1 to +1. The average signal is 199.97958198 over 99.999999 Million samples. The gate time is set against the 10 MHz reference. Apart from setting standards what would you use such a beast for ? Well the manufacturer gives a few ideas with one being connecting it to a hall effect sensor counting teeth on a flywheel of a drag car engine it is fast enough to see a stretched pulse at full throttle if the engine misses a bit. It is also used a lot to measure jitter in optical drives for CD’s and DVD’s in a musical recording studio making master discs.

TA320 with Freq Counter permanently connected to it

PTAX0001Here is a photo of the Rohde & Schwarz Freq Standard and GPSDO mounted in 19 inch Rack, there are four 10 MHz outputs on the back of the GPS that break off to test gear in the lab. One comes to the a hole that was in the front of the R & S that had a broken neon lamp in it and was just the right size for a BNC connection to break out the 10 MHz from the back of the GPSDO to the front panel to make it easy to get to it.


DIY RF Adaptor Set

So I was looking at commercial RF adapter kits and the prices shocked me so I decided to make up my own. The commercial ones I saw used a weird connector to join the adapters to each other. I decided I would use female BNC as the interconnect that way i could use male to male adapters to make short connectors or BNC patch leads for longer cables. Here is a commercial kit from element 14 it is pretty limited and is more than US$200.42421688

I put together a much larger kit with two of all the adapters as well as to 50 dummy loads just small ones to use to match the load when connecting to a scope to match the impedance, you use a BNC Tee piece. Anyway here is my kit… It has double of each connector and should cover all my needs it cost me about 120 bucks Australian to put it together.


Dust PC from Hell

So I rebuilt a friend of my sons PC. It was a mess it had water cooling and the radiator was hanging lose. It was overheating from all the dust and when he brought it over in the car the radiator ripped the CPU out and bent dozens of pins.


It was one of the worst PC’s I had seen in a long time for dust and if it had gone to a shop they would have thrown the CPU in the bin and it was an AMD FX 8 core worth 300 bucks

Nearly an hour under a stereo microscope with tweezers that are so fine they are like needles was spent getting all the pins straight.

I pulled it all apart except for the motherboard, blew all the dust out, mounted the radiator to the top and put a HDD cage in as the hard drives were just hanging by the power cables.



It took Angus and I about four and a half hours to get it from the first photo to the finished product in the last two photos, one of the back which has a case cover over the cables and one of the front side which is missing the cover.

Some people might think it is to much to repair a PC like this and rebuild it but I actually enjoy this type of work, I just wish I could actually do this as a full time job but my health wont let me

IMG_20160114_222123 IMG_20160114_222142


Okay I was a geek at school, .. Nothing has changed… Just ask my wife
I run Linux
I am a licensed Ham Radio operator
I Own 4 Oscilloscopes
I also own 8 calculators including 3 graphing
3 slide rules
I have a glass world globe on my desk
4 Ham Radios in my shack
3 Radios in the car
2 Handheld ham radios
5 Multimeters
My phone and tablet run custom android roms
My bookshelf in my man cave has the following books…
Machine Tool Operation Book 1
Machine Tool Operation Book 2
Taps and tapping by sutton tools
The Australian Amateur lapidary handbook
Meters for measuring water
RCA receiving tube manual
108 uses for an oscilloscope
Audio Handbook No2 “Feedback”
Phillips Valve data book
Electronics Made simple
Oscilloscope equipment
101 ways to use your signal generator
99 ways to use your oscilloscope
How to use grid dip oscillators
101 uses for your Vacuum tube volt meter
Transistor radios Circuits and servicing
The casio PB100 Computer manual
RCA Tube Manual
WIA Handbook Vol 1
Summary of lectures Automatic control systems
Faber castell slide rule manual
Hemi 40RK Sliderule manual
Icom ICT90a Manual
Transistor Transmitters for amateurs
Radio Data Reference book
Program Design
The boys book of crystal sets
ARRL radio Amateur handbook
Electronics Principles Integrated and discrete
GIMP Graphics Package User Manual (Linux)
Tech topics radio handbook
Radiotron designers handbook
High quality sound reproduction with valves
Temperature measurement
Novice Operators Theory Handbook
Tektronics Scope 314 Service Manual
1972 Melways (Street Directory of Melbourne) from my birthyear
The ARRL handbook 1995 (Theory)
Sourcebook of electronic circuits
Yaesu FT707 Service Manual
Ford Falcon EA-EF Factory Manuals (We own 2 falcons)
Running Linux
Linux Sys Admin
HEMA World Atlas
Oh and I own two domains, twistedsouls.com and hamshack.org
Geek and proud

Low Cost 10Mhz Frequency Reference

I was looking at a low cost way to build a 10Mhz frequency for my electronics lab. I had a few options that I could pursue, these were…

  • GPS Disciplined Crystal Oscillator (GPSDO)
  • Rubidium atomic standard (RbXO)
  • Caesium atomic Standard
  • Oven Controlled Crystal Oscillator (OCXO)

So to make a choice on what I should use I had to come up with design parameters for my frequency standard, these were as follows.

  • Had to be low cost
  • Had to be portable
  • Had to work inside of a building
  • Had to be stable, better then +/- 0.5 hertz drift over 2 minutes

The preceding criteria ruled out a GPSDO as that requires an antenna that has a view of the GPS satellites, this would be ok at home but I didn’t want to have to make sure I had a outside view of satellites if I was taking it to someone else’s shack or like the club shack with no windows this would have been impossible to get a GPS lock.
I next looked at atomic standards. The Caesium standards were out of the question due to the cost, second hand you could expect to pay upwards of USD$5000 for one, certainly not low cost by any measure. The rubidium standards were a lot cheaper at around USD$200 so that was an option. This raised the question, did I need the accuracy of a Rubidium or could I get away with a cheaper option ?
This led me to investigate OCXO’s to see if they would suit my needs. First was to see if they met my stability requirements. A typical 10Mhz OCXO has a stability of 5×10-10 This is ±5 mHz drift per second on a 10Mhz signal, well within my requirement of 0.5hz over 2 minutes. The reason I need this stability is for WSPR digital which requires a very stable clock signal.

What about the cost of an OCXO ? Well a quick search of eBay led me to a Double Oven OCXO from a Russian company called Morion. I could get a second hand unit for less than $40 delivered. This particular unit listed stability of better than 2×10-12 over 1 second which is 0.005 mHz and stability of ±5×10-10 per day at 10Mhz. These figures were well within my requirement’s so I ordered two units from eBay.ocxo
I now started to put some thought in to the design and construction of the complete unit and what I would need.

I had an old car computer case that I could use for the project so I ripped out the old motherboard and found some rubber feet in my junk box to put on it, this gave me an idea of the size case I had to work with so I grabbed a ruler and measured it up to see if the OXCO would fit. It would fit with heaps of room for an internal 240 to 12 VDC power supply and a battery.
I was thinking about the power requirements for the unit and how I was going to power it. I needed about 1.5 amps for the oven while it is warming up with that dropping to about .5 amps once warm. Wrapping the oven in insulation should drop that even lower. I had an old 4 amp 12VDC power supply from a computer monitor that I could use so I dug that out as well.
At this stage I put the project aside for a couple of weeks while I waited for the OXCO’s to arrive in the post. When they had arrived I put one in the case with the power supply and soon realised I actually had the space for both of the OCXO’s.

top view
I had originally bought two so I had a spare but I quickly decided at the cost of them I could just run both so I would have two units that I could compare against each other to make sure they were still within specification and also It meant I could connect it to more than one device at once. The signal quickly attenuates if you are splitting it.
I then got all the other stuff together to assemble the unit this consisted of the following.

  • Trimpot’s to adjust the OXCO
  • SLA 12V Battery
  • Switches to switch power and outputs
  • Veroboard to mount it all on
  • LED’s for status indicators
  • Volt Meter for battery level
  • IEC Socket for Mains input
  • DC Barrel plug and socket for 13.8VDC to charge battery
  • DC-DC Buck/Boost converter to level out battery voltage
  • BNC Sockets for the output
  • Current limiting resistors for the LED’s

veroI soldered the two OCXO’s on to a bit of veroboard and then connected 25 turn 2KΩ trimpot’s with the wiper to the calibration pin with one side of the trimmer to GND and one to the 5VDC reference output on the OCXO, this forms a voltage divider to calibrate the oscillators. I measured the output of the power supply I was going to use and it was 12.3VDC which is within the spec of 12VDC ±5% that they require.

The next problem I would have was to power it while travelling, I didn’t want a huge battery so I used a 1.3AH SLA battery that I would charge off the car while travelling. I needed to keep the battery voltage at 12VDC into the oscillators while I would see between 14.2VDC while charging and 11VDC if the battery was a bit flat.

dcdcTo get the nice 12VDC I used a cheap $2 buck boost DC-DC converter from eBay. They wont supply the 3 amps I need to warm up but it would handle the .5 amps that I had measured once warm. I had managed to get the 400mA current per OCXO down to around 500mA for both once warm by wrapping the ovens in neoprene foam from a stubby holder.

I adjusted the DC-DC converter to output 12.3VDC so it was the same as the mains power supply, this prevents instability of the 10Mhz signal due to supply differences.

I have each oscillator feeding a DPDT switch, one pole switches the signal the other switches an LED on to show the output state, I can feed either the A or B signal to a common N Type connector or to their own BNC connector. A cheap LED volt meter was added to the front panel to show the battery voltage, these are available on eBay for a couple of dollars.

frontIf you were building the unit with one OCXO and had to buy everything instead of raiding you junk box for parts you would need to invest around 80 to 100 dollars. This includes a case the OCXO and the needed hardware. It took me around three hours to assemble.

Freq ref FLIR 02So what is it useful for ? Well some of the things you can use it for are as a stable reference to calibrate test equipment like frequency counters and signal generators. With a divider board to generate a one pulse per second signal to sync your PC time. This is useful for the digital mode WSPR that requires no more then ±1Hz drift over two minutes. With a general multiplier/divider DDS you can produce signals from 1 hertz to around 100Mhz from the 10Mhz input. This is useful for calibrating rigs to see if they are on frequency.

All in all I am very happy with the resulting unit and it makes a nice addition to my test bench.