[FoxHunt] Re:HF SSB ADF question

[Bruce]

wolfbob wrote:

> As far as I understand only the Adcock type DF systems work well with 
> SSB. They measure the phase angles in quadrature all the same instant 
> so there is no phase or amplitude shifts due to modulation. You can 
> also use doppler as that measures the psuedo frequency shift, but it 
> requires a FM receiver to work well. Spinning things do not work well 
> as they depend upon either finding the maximum amplitude which is a 
> time variable with SSB or the zero phase which is a function of signal 
> frequency which is ever changing with SSB voice.

Agreed, except the last point. A spinning thing can be made to work 
reasonably well with a bit of time filtering. In my case a I merge together
3 revolutions of signal pattern (dB 'add') to get a much better polar 
plot. Of course this does mean you have to be travelling in the same 
direction for
the 3 turns worth (in my case about 5s), and the signal has to be 
transmitting for at least that time.
The signal level itself is derived from a DSP based FFT frequency 
correlator which rejects a lot of the random noise.
This system works sufficiently well to hunt HF SSB signals on foxhunts. 
It may not suffice for an accurate crossed bearing 'locator' system.

>
> Bob, WB6JPI
>
>
> ----- Original Message ----- From: "John Munsey, KB3GK" 
> <munseyjohn at earthlink.net>
> To: "Radio Direction Finding" <foxhunt at mailman.qth.net>
> Sent: Monday, November 22, 2004 10:31 AM
> Subject: Re: [FoxHunt] Re:HF SSB ADF question
>
>
>> If I understand the problem correctly...
>>
>> The SSB carrier is not there when there is no modulation and then it 
>> varies with the modulation level. Since this system looks for signal 
>> level it can't read "nothing" zero signal level and varies with the 
>> signal level when it is modulated.
>>
>> I suspect this is the cause of your problem.  I don't know of any 
>> "fix" if that is indeed the problem.
>>
>> I have used the Doppler with reasonable success on SSB signals but 
>> even there they can come and go with modulation.
>>
>> It will be interesting to hear from others on this.
>>
>>
>> At 12:29 PM 11/22/2004 -0500, you wrote:
>>
>>> In using a Taiyo CH 338 HF ADF (crossed loop goniometer type with 
>>> polar CRT
>>> readout) I have noticed the following: SSB sigs give no clear 
>>> "propellor"
>>> pattern on the CRT, the sig strength varies with voice and no clear 
>>> azimuth null or
>>> peak can be seen. The exception is when there is a constant audio, like
>>> engine acoustic noise on a boat, then it gives the signal a constant 
>>> strength
>>> background level (analogous to an AM carrier when no speech is 
>>> present) which
>>> allows a good CRT bearing in between spoken syllables. What is the 
>>> basic problem?
>>> Is the goniometer effective rotational speed too slow for SSB? Has 
>>> anyone else
>>> used these Taiyo ADFs for HF SSB?
>>> _______________________________________________
>>> FoxHunt mailing list
>>> FoxHunt at mailman.qth.net
>>> http://mailman.qth.net/mailman/listinfo/foxhunt
>>
>>
>> Sincerely,
>>
>> John Munsey, KB3GK
>>
>>
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>>
>>
>>
>
>
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