[time-nuts] Doppler Design

[David]

On Sun, 01 Jan 2012 18:35:13 -0800, gary <lists at lazygranch.com> wrote:

>This is just a tweak of the older two antenna scheme. Basically it gets 
>rid of the bidirectional nature of the two antenna version.
>> http://www.homingin.com/newdopant.html

Joe has a picture of me on his site if you know where to look. :)

>Signals that are heavily modulated such as trunking control channels 
>don't work well with such schemes. [That part of the experiment I have 
>tried. No problem though with voice modulation.]

I always thought I could improve on the Roanoke design but never had a
need to build one.  I considered using synchronous demodulation to
detect the phase instead of the narrowband switched capacitor filter
they used.  It occurs to me now that varying the switching frequency
to avoid the channel modulation would help as well.

It is possible to use 3 antennas to resolve the direction.  4 antennas
makes for an easy optimization in the design.  I have seen designs
with more than 4.

>My understanding is they use the identical radio scheme feed into a 
>scope XY via demod taps. I haven't tried this since I don't have two 
>identical radios that can be synched. I'm eventually going to hack some 
>cheap scanners, just as the Pro-2035, and simply feed one scanner with 
>the mixers from the other. This would not maintain frequency accuracy, 
>but it would make the XY display possible.

Calibration is easier with a tap to the demodulator but not strictly
necessary.  I installed one on my FT-5100 for the noise meter I used.

>My assumptions is you get a 45 degree line when the antennas are equal 
>distance to the transmitter.

That is what I expect.

>This is like a radio interferometer, though perhaps not in the strict 
>sense. An interferometer, using an analogy to optics, would be mixing 
>the received spectrum prior to any detection.

I would say it is still an interferometer.  It relies on measuring
coherent phase information.

>The AR-One-C is set up for this type of DFing.
>> http://www.aorusa.com/receivers/ar-one.html
>
>
>On 1/1/2012 6:19 PM, David wrote:
>> I think even my old Icom 706 would work that way.  It has the high
>> stability option installed.  From what I remember from the service
>> manual, every mixer has its local oscillator frequency locked to the
>> master oscillator through either a PLL or DDS which makes passband
>> shifting via the IF frequencies very easy.  Since all of the local
>> oscillators except for the first one have very little range and are
>> relatively low frequency, the frequency synthesis was not too
>> expensive to do.
>>
>> I suspect a Roanoke style direction finder with multiple radios would
>> work fine without locking the receiver oscillators but that requires a
>> carrier for FM demodulation.
>>
>> On Sun, 01 Jan 2012 17:55:35 -0800, gary<lists at lazygranch.com>  wrote:
>>
>>> This is an interesting observation regarding the Icom radio that can be
>>> run from one master reference. I would assume any radio which has a high
>>> accuracy option has this feature. Looking at the block diagram of the
>>> R-8500, this appears to be an option. For the R-7100, it looks like it
>>> uses one oscillator for some operating modes. There is a 1GHz mixer on
>>> the front end that can be switched in and out. That mixer is not derived
>>>from the master.
>>>
>>> The only reason I mention this is there are directing finding schemes
>>> based on identical receivers but separate antennas.
>>>
>>> The traditional diode mixer before the radio DF scheme doesn't work well
>>> on digital signals.
>>>
>>> Some of the more recent high end radios from AOR have this one master
>>> oscillator scheme.
>>>
>>> On 1/1/2012 4:14 PM, Magnus Danielson wrote:
>>>>
>>>> So, they essentially did what I did with the heat gun, heat it up
>>>> properly. This technique was not "invented" by me, I in turn had picked
>>>> it from Gerald Molenkamp VK3GJM for the FRS-C:
>>>> http://www.vk3um.com/Rubidium%20Standard.html
>>>>
>>>> Cheers,
>>>> Magnus
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>_______________________________________________
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.