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Author Topic: Ramsey DDF-1 Question/Concern  (Read 30673 times)
W8HDU
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« on: February 18, 2012, 10:56:33 AM »

I just purchased an assembled DDF-1, and I'm having a little problem in understanding it. 

If someone has this unit, perhaps you can tell me if I have a product issue, or I'm not setting it up correctly.

1). Is the DDF-1 intended for you to sit in one location, or for mobile operation? The manual seems to indicate mobile, which has me concerned because of question 2.

2). As I drive north, on a county road with farm fields on both sides, I calibrate the LEDs so they face to the north.  In line with this road I can see a tower owned by a TV station that has a base on 450.2125.   As I make a right turn (east), the LEDs start to rotate counter clockwise then as I conclude the turn and going east, the LEDs snap around showing the transmitter in the opposite direction, (south).

I notice that it seems that when I drive north and south the polarity needs to be normal, while east to west it has to be invert.

If I drive west, so the tower is to the right of me, I can calibrate the LEDs for 90-degrees heading, with the switch in either Normal or Invert mode.  When I make a turn the LEDs start to rotate in the correct pattern, then snap around to the opposite direction from the tower.

As far as antenna placement, when the truck is pointed north, the #1 antenna is to the front, #2 is over the driver, #3 is over the back seat center, and #4 is over the front passenger. Antennas are collapsed for 440 MHz operation, and extended out the cable length from the center, which is approximately 12"

I'm got to try this afternoon to mount the antenna so they are more like front/left, back/left, back/right, and front/right.   But I don't see how that may make any difference.

3). If I can get this to work, has anyone modified the array so the antennas are mounted to sort of a plate that can be attached to the roof of the truck, and instead of using the little telescopic antennas, install BNC connectors.  Since my truck is a dark color, if I come up with some sort of plate that could be attached to the truck, and antennas on BNCs, I could use stubby-duck antennas and be less conspicuous.

This is my first venture into DFing using this gear, so I'm eager to get some good information.
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PA3BNX
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« Reply #1 on: February 19, 2012, 12:41:57 PM »

Hello,

I can give you some advice I think.

Yes it can be used mobile.

But also stationairy.


For 450 MHz the maximum diagonal diameter is about

300/450MHz * .35 = 0.23 Metres

So I think you have ambiguity if the distance is bigger.


So place the whips closer together

And of course the need to be shorter to.

Abt 450/300 * .25 = 0.16 metres

Yes the sequence needs to be 1 2 3 and 4

Front of car
         2

1               3

         4


Pushing the 0 and 180 degrees button swaps
antenna 1 and 3 so to say.



So between antenna 1 and 3 may not be more space than
0.23 cm at 450 MHz.


73's

PA3BNX

« Last Edit: February 19, 2012, 12:46:49 PM by PA3BNX » Logged
W8HDU
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« Reply #2 on: February 19, 2012, 12:54:45 PM »

OK.  Let me try this with antenna height of  16cm, and space the antennas so 1 to 3 is 20 cm.

Is the sequence critical as in your....

Front of car
         2

1               3

         4

The way my device is layed out it would be....

Front of car
         4

1               3

         2
« Last Edit: February 19, 2012, 01:05:38 PM by W8HDU » Logged

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W8HDU
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« Reply #3 on: February 19, 2012, 01:19:37 PM »


Here is how I have my antennas placed.  I though a picture might be better than trying to explain.

http://www.hf-antenna.com/df/T_DF_Antenna.jpg

Antennas = 16 cm
Spacing = 20 cm

Looks kind of ugly.  This array is begging to be put into a flat box on the roof with SMA connectors where the appropriate band antennas are screwed onto them. 
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PA3BNX
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« Reply #4 on: February 20, 2012, 01:55:54 PM »

Hello,

It doesn't matter witch way they are placed

as long as the sequence is right.

You can easy push the 0/180 switch

so left and right turning

and adjust the calibration to the North or front of car.

Remember if you have 1n4148 switching diodes
they have about 4pf capicity so they don't perform very wel on 450MHz
in off situation.

Alo remember that the 4 cables lenght is about

300/450 * .25 * .66 = 0.11 metres

Because open cables electric length 1/4 wave length disconnect the RF also from the switcher
if diodes do not conduct.

Also important is that the undesite of the four whips have very good contact to the ground plate.

Maybe put aluminium foil beneath the magnetic mounts to increase base antenna <> car roof.

Thats why a seperate plate is better because you can ground the coax cables to ground
at the base of the whips.

I think you should find a station on lower frequence to track first.

Suk6

PA3BNX
« Last Edit: February 22, 2012, 10:13:52 AM by PA3BNX » Logged
W8HDU
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« Reply #5 on: February 21, 2012, 05:06:23 PM »

I went out tonight and had a fairly good session of tracking down a QRMer.

I'm still disappointed in the calibration.  As long as I sit still, or drive in one direction, it seems to read correctly.  But when I turn, then the accuracy falls off.  The antenna spacing is still at 20 cm on a side, so I wonder if they should be closed in to say 15 cm?

If I can come up with an ideal spacing that works reliably, I was thinking of taking a piece of sheet steel, and putting NMO mounts at the designated distance.  Then use the Maxrad BMUF4500 antennas, which would blend in with the truck cap, vs the white mounts and silver antennae mag mounted to a dark colored truck.

Quote
Alo remember that the 4 cables lenght is about

450/300 * .25 * .66

Because open cables electric length 1/4 wave length disconnect the RF also from the switcher
if diodes do not conduct.

If I go to an NMO mount, is there any reason not to use RG-58 (instead of the RG174), and terminate the cables for precise 1/4-wave sections?
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PA3BNX
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« Reply #6 on: February 22, 2012, 10:30:43 AM »

Hello Every Body,

Sorry there was an error in my last posting


300/450 * .25 * .66 = 0.11 metres for each cable.


You can try to use better diodes with less capacity if off
like the ba479 or other pin diodes

1n4148 are about 4 pF quite a lot for 450MHz.

You can also try to reverse the off voltage to negative
like Joe Moell K0OV  does.

On 70 cm the cables and the ground plate must be done with more precision.

The doppler readout depends largely on it then.

But the most important part is get the antenna feet Cables earth with short
lead to the ground plate.
Ideal should be at least 17 cm plate after the antenna board

So for 450 MHz I recommend a circle ground plate with diameter off

(300/450 * 0.35) + (300/450 * 0.5) =0.56 metres or larger.

You can very easy adapt the DDF1 to work with a PC and GPS
real time plotting etc...

See our Veron Radio Club Site

http://www.pi4wag.nl/index.php/pseudo-doppler-radio-direction-finder

http://www.eevblog.com/forum/projects-designs-and-technical-stuff/radio-direction-finding/

http://www.homingin.com/newdopant.html

73's PA3BNX
Lodewijk


« Last Edit: February 22, 2012, 10:33:13 AM by PA3BNX » Logged
W8HDU
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« Reply #7 on: February 22, 2012, 12:16:00 PM »

The BA479 diode crosses to a MPN3404.  I'll try getting some.

But let me ask you again, what is the ideal wavelength from antenna to antenna?  Is the ideal with Doppler to be on 1/4 wavelength spacing?   In our thread above we sort of arrived at 20cm, but I'm trying to grasp how that is calculated.

And if I'm trying to D.F. on a frequency of 455.312500 (yes, I know that's not a ham freq), then the cable lengths should be

300/455.3125000 * .25 * .66 = .1087 meters (assuming RG174)  Prop factor is .66

Is this right?
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PA3BNX
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« Reply #8 on: February 22, 2012, 01:12:15 PM »

Hello W8HDU,

Yes for 450 MHz
The cable length for all 4 antenna to switcher is about 0.10 metres
(This is not very critical it just enhances the diode switch off separation)
(The cables do need as close as can be same length)

The wipe distance between adjacent antenna is maximal 1/4 wave length
so about 0.17 metres
              2
           /           
      0.17m
  / 
1 --------0.56m---------3
  \
      0.17m       
        \
             4


The length of each antenna must be about 0.17 m
It's quite okay if all the 4 antenna are not all exact the same length
but are within say 0.02 metres

If the frequency stays at 450 MHz  then you may shorten the
0.56 Meters to about half that length.
Only the amplitude of the doppler-tone will be weaker.

If you take the 0.56 meter smaller lets say 0.40 it will also increase
probally the accuracy of the heading from the pelorus a bit.



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N0ZYC
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« Reply #9 on: April 19, 2013, 02:03:01 PM »

reminder that if you're using the mod that disconnects the antennas at the switcher and the antenna bases, (commonly referred to as "frequency independent switcher mod") then coax length becomes unimportant.  Just make sure your antennas are being rotated in the correct order and keep whip separation under 1/4y on a side.  I'd strongly recommend doing the frequency independent mod, although my mod list for my doppler is somewhere around 4-5 pages of stuff I've done to it, so there's a lot of room for improvements.  (I see now that I look around, a lot of foxhunts are now banning dopplers?  wow.  I could see that for the "bought a black box and turned it on" users, but for those that worked hard and built them with loving care and attention... we've earned the right to use them)
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W8HDU
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« Reply #10 on: April 26, 2013, 06:46:54 PM »

@N0ZYC:  Where do I find the mod you're talking about? 

Now that the weather is getting better I would like to fix up my system better.

One question still remains, and Ramsey says they can't answer it.  How do you check the antennas for proper rotation?  The instruction are sort of vague on the theory and how to check this part of the system.

Fred/W8HDU

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WB6BYU
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« Reply #11 on: April 26, 2013, 09:09:03 PM »

Ramsey is pretty vague on a number of things.  They often seemed to copy circuits
from other sources without doing much design work themselves.

Here's a link to the article that Joe Moell K0OV published in 73 magazine in 1995:

http://www.homingin.com/newdopant.html

The HomingIn website has a lot of good information and links about transmitter hunting.
And K0OV has been known to haunt these boards on occasion.
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W8HDU
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« Reply #12 on: April 27, 2013, 05:35:43 AM »

Thanks for the link to the page with the information.  From the description in the text, this might work well.

My thought is to use a short 1/4 whip, attached to a magnetic bases.  This way upon knowing the frequency, I can measure and set the spacing of the array to what I desire.  A small box (1.5 x 1.5 x 1) with SMA connectors, sitting in the middle of the array would be the breakout point.  I found some black, low profile magnetic bases, and black Laird antennas.  When mounted on my Silverado's roof, they are not that noticeable.

Again, I appreciate the info and link!

73,
Fred/W8HDU

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AG1B
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« Reply #13 on: May 04, 2013, 06:10:28 PM »

I just used black non-gloss spray paint on the white parts.
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N0ZYC
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« Reply #14 on: May 25, 2013, 08:20:21 AM »

@N0ZYC:  Where do I find the mod you're talking about?

I have information on my doppler HERE

One of the modifications I made on my box was the row of yellow lights with the switch to the right.  That switch is a DPDT MOMENTARY (with no center off)  It is set to toggle the switching step off the oscillator.  You set the unit to hold (instead of scan) and then tap the switch.  Since it's two /2, you have to toggle four times to move the antenna once.  The yellow led indicates which antenna is selected currently.  When scanning, all four leds appear to be on since they are switching so fast.

With the frequency-agnostic mod, the antennas can be directly tested with a voltmeter.  The ground reference at that point up on the platform will be +3. The selected antenna will be at ground, the other three will be at +5.  The antennas should be selected in sequence, in clockwise order as viewed from above.  It doesn't matter where the first antenna is.  You will be adjusting the calibrate anyway, and that combined with the phase switch will allow 360deg adjustment.

You need to make sure that (A) the antennas aren't being switched counterclockwise, and (b) you don't have them out of order.


front

4   1

3   2

that is the order I have mine in.  If you were to switch any two antennas, they would be out of order and wouldn't work right.  If you switch adjacent antennas, you jam the signal.  If you switch opposite antennas, you flip the rotation direction and your display will be mirrored.

The yellow LEDs are driven off the switching lines.  You could use an LED driving IC to run them.  I did mine the hard way with transistors and resistors.  Don't load down the switching line.

The antenna mod you are looking for, as well as a lot of other good information, is HERE
« Last Edit: May 25, 2013, 08:39:54 AM by N0ZYC » Logged
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