FW: [FoxHunt] Turnstile antennas for 2M

[WolfBob]

When I said Adcok, I was referring to the 4 element "stationary" one 
with four dipoles that uses lobing to generate sin/cos and is so popular 
with the LOJAK and marine DF crowd and the Doppler with its bunch of 
antennas which is similar to the Time-Difference of Arrival (TDOA) 
systems like BMG and others but are 360 in measurement. These 360 degree 
systems are more suitable to taking data while running but much harder 
to implement for H-pol. A horizontal Yagi doesnt do well in brush in 
that you have to get it clear to make measurements where other systems 
might be much better. Depending upon an amplitude change due to moving 
an antenna pattern around is just not as neat as TDOA methods that are 
friendly to FM radios.

I wonder about Halos. They are a wavelength in circumferance. about 1/6 
wavelength in radius, and if you space four of them 1/4 wave apart, like 
a cloverleaf, they should have very low coupling, 360 coverage and 
H-pol..I wonder...with either a doppler or adcock receiver...I 
wonder..(You can tell it's getting late here.)

Bob, WB6JPI

Kuon & Dale Hunt wrote:

>>Good points...
>>
>>Except when you expect a runner to carry a pair of turnstiles separated
>>by a ways. I have run my TDOA BMG sniffer with small loops with some
>>success. The LPER is harder to "loopize", but it is possible. Note I
>>didn't say it was not possible, but just difficult. I dunno how to do
>>the Adcock in H-pole.
>>
>>Bob, WB6JPI
> 
> 
> 
>      The L'Per requires a directional pattern, so two loops
>   would have to be phased.  This is actually more common than
>   the L'Per method of parasitic coupling, even for vertical
>   antennas, since it gives the designer more leeway in mounting.
>   The Happy Flyers design in THRDFS illustrates this method.
>   Adjusting the phasing line length and antenna spacing should
>   give you a suitable omnidirectional pattern.
> 
>      The Adcock is even easier:  just mount two identical
>   antennas side-by-side and out of phase.  You can do this with
>   dipoles, but they will tend to interact due to the overlap
>   in elements if the spacing is less than 1/2 wavelength.
>   For full-circle DF you need omnidirectional antennas, such as
>   small loops or halos, but if you just want an accurate bearing
>   over a smaller angular range then you can use dipoles or
>   full wave loops broadside to the null direction.  (The problem
>   with dipoles is that the pattern has a null in the direction
>   of the elements in addition to the usual Adcock null perpendicular
>   to the line of the elements.)
> 
>      If you use small loops they have to be tuned exactly to the
>   same frequency to get the correct phasing.  Generally the best
>   approach is to tune the first for maximum signal and the second
>   to put the pattern null in the right direction - providing a
>   calibrate control.
> 
>      Such a system might be interesting to try, but I think the
>   yagi would still be better for ARDF for sensitivity, ruggedness,
>   and reliability in the presence of reflections. But you could
>   build a helmet with a set of small loops or slot antennas around
>   the outside, then add a digital readout and course correction
>   indicators to a head-up display, and have totally hands-free
>   operation...
> 
> 
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