PA8W Amateur Radio

Wil, PA8W,  E-mail:           

Building The PA8W Version 2.3 Doppler RDF

The following downloads are made available here:

Main diagram
Parts List
PCB drawing (will help you to assemble the PCB)
PCB and parts service list
PCB artwork (for those who want to home-brew the single sided PCB)

A few considerations before you build the V2,3 doppler.

Car setup:
First of all, if you are going to use the doppler in a mobile setup, you might leave out the 12V voltage regulator and instead put in a 1N4004 diode plus a 10 ohm resistor in series.
This would protect the unit against reversed polarity, and the normal battery voltage of a car (13,8V) is perfectly suited for the doppler.
The voltage regulator is not necessary as long as you don't feed in voltages higher than 15V.
A 12V or 15V regulated  (!)  mains power supply would be the right choice for mains applications of the modified unit.

I found that at a certain calibration point, the doppler showed some degree of instability.
It turned out that the wiring to the calibration potentiometer picked up transients from its surroundings, resulting in sporadic mistriggering.
I replaced the wire by a piece of shielded (pickup-) wire, and connected the shield to the PCB's mass and the other side to the potentiometers casing.
This cured the issue completely.

The front:

First drill the front, using the drill template; best is to tape it firmly to the front and mark all hole positions using a steel nail and a small hammer.
Just make small pits marking the spots where the LED's should be positioned as well as all controls.
Then drill the front, and gently clean all holes using a chamfer drill bit.
Now stick on the vinyl front sticker.

After putting the sticker on the front just cut off the excess with a sharp knife.
Pierce all holes from the front side, and remove any residue.
If you planned to have an integrated speaker this is the moment to glue it in place, since as soon as the pelorus is in place, you're too late!
That's also true for the speaker cable! 

Building the pelorus:
Put in all wire jumpers first, and solder them except for the LED's side.
Then the LED's have to be put in.
Start with LED#1 (RED) at the marked position and follow up clockwise with 3x green, 1x yellow, 3x green.
Note that the long leg of each LED is pointing to the centre of the pelorus.
Just lower the LED's down to about 20mm bottom spacing (if you want to include the speaker in the perosus centre as I did)  from the PCB, and ONLY SOLDER THE INNER LEG!
Work around the pelorus until all LED's are in place.
Now carefully stick the LED's into the drilled pelorus holes. Make sure the 0-degrees LED is a red one!
Since the LED's are soldered with the inner leg only, you can carefully bend each LED into position to fit its hole.
Small deviations in the drilled pattern will be not be a problem.
Once all LED's have protruded the front for a few millimeters, you can solder the outer legs of all LED's.
Then the flatcables can be soldered in position, simply solder them to the copper side of the pelorus PCB.
Apply some contact glue to bond all LED's to the front plate.

The main board: 
The below pictures will help you assemble the main board.
With these pictures and the schematic diagram, you should be able to reproduce the RDF.
(You're a HAM remember?...)
Note that NOT all IC's are oriented in the same direction, and the photo below is not entirely correct.
So take the schematic diagram and the PCB drawing for component values.

If you compare the PCB with the schematic diagram you will notice a similar layout; all IC's are located more or less at the same spot as in the diagram.
So that will make it much easier to understand the layout when troubleshooting or experimenting.
The controls are all wired, so anyone can use his own front layout and even potentiometer and switch size are not critical this way.
Some electronically active HAMs will even be able to build it almost entirely out of the junkbox.

After assembling the board it should be checked for failures.
Leave out the IC's until you've measured a nice 12V supply voltage after the voltage stabilizer.
Then you can put in the IC's and do some simple checks.
Any antenna control output should show a frequency around 500Hz +/- 10%. (not in array test mode!)
If you feed a 100mV tone generator signal into the audio input then you must be able to find a frequency around 500Hz that will result in the LED's racing around the pelorus. (try this with minimum Q and with Threshold at max)
Passing over the central clock frequency will suddenly make the LED's race into the opposite direction.
With no input signal, the LED pelorus should freeze, with the correct Threshold adjustment.

The antenna driver signals should look like this:
(no array attached!)

Note that when not loaded by the array, array drivers 2, 3, and 4 may show a funny type of overshoot at max positive output.
Driver 1 doesn't, because it has a small load formed by the network for the reference output.
As soon as the array is attached these "funnies" will be gone, so they are not important at all.

Now connect the array and calibrate the RDF to a known station.
Then switch to a second known station and see if the new bearing makes sense.
Or, rotate the array and see if the pelorus is nicely following the rotation into the opposite direction!
If you turn the array clockwise, the pelorus should turn counterclockwise!
If it is running the wrong way you may have made a wiring mistake in the control lines.
In that case, swap two opposite lines, for example of the north and south antenna.
This will make it turn in the right direction.

Looking from the top down the antennas should be selected clockwise:

/     \
4         2
\     /

On this website you will find additional information about a Home-Array and a Mobile-Array for your pa8w doppler radio direction finder.