Phase difference detector, 433.92MHz

[AndyPLL]

Cool. I really appreciate the help. I'll have to do some more reading about PLLs and DBMs - non trivial subjects, I feel. I'll be back...

 

[AndyPLL]

Just playing with broad block diagram..

(Antenna 1)                  (Antenna 2)    <signals         *easy*
     |                            |
(Bandpass 1)                (Bandpass 2)    <pass 433.92MHz  *easy*
     |                            |
(Sens. PLL 1)               (Sens. PLL 2)   <lock carrier    ?possible?
     |                            |
     |------(DBM PHASE COMP)------|         <compare phases  *easy*
                   |
              (Audio AMP)                   <boost for use   *easy*
                   |
                 OUTPUT                                      *DONE!*

About 1/2 dozen ICs and a bunch of Rs & Cs might do it? Maybe frequency dividers can help bring freq down to PLLable level and reduce antenna back-intereference? But freq. division removes sensitivity and introduces other problems right..?

 

[G8RPI]

Hi,
Interesting post. I agree with RadioRon on all his posts. The DBM method will give good results on a strong signal, it has been used in radar warning receivers on aircraft to give a quick indication of the presence and direction of a very short burst (literally just a few pulses a couple of microseconds wide) of attacking radar. A narrowband receiver or pll would not settle in time. What bandpass filters were you going to use? The narrowband SAW types might work or even minature helicals like the one Toko make.

G8RPI

 

[AndyPLL]

Good point. I am indeed planning to use SAW B3555 Filters (433.92MHz, 2dB, 0.57MHz bandwidth) before and after a Motorolla MBC13619 pre-amp. All 4 SAW filters will be impedance matched by usual inductor/capacitor combo either side of each filter.

This will give good but low level signals for product detector (mixer). Only problem is that DBM mixers can't take two low level signals, at least one must be of sufficient level (7dBm) to bias DBM diodes (RadioRon made me aware of this - thanks!). Looks like I need another 70dB of amplification if I am to use DBM mixer for phase comparision.

OK, so this kind of amplification is not realistically possible. Thus, We have 2 options, unless we use a completely different approach (OR FIND SUITABLE MIXER..suggestions?):
1) Use PLLs to produce phase/frequency synchronised VCO outputs that can be used as input of DBM mixer.
2) Use hetrodyne method to produce strong IF frequency signals that can then be used in DBM. Would require single LO (local Oscillator) to preserve relative phase diff (thanks RadioRon). Then DBM phase detection could be done on the downconverted signals. And if I wanted to use the circuit to send data aswell as directionfinding, then this is 2/3rds of a FM demodultor circuit anyway! Not sure how downconversion would exactly affect phase difference calculation performance tho, probably just reduces sensitivity, but this can be calibrated for on the output right?

I'm tossing up both methods. I think I could get a pair of monolithic ICs that could do all of 2), plus extra stuff for FM demodulation. However, If PLL method 1) is possible (I can't see why not?), I _think_ it might be more sensitive as it operates on the original RF signals at original frequency... Of course a LPF is also required after DBM/mixer to complete phase diff detector.

ANY SUGGESTIONS?

I plan to post the exact cct/components when done. It will be very low cost, only a few ICs, NO EXPENSIVE RADIO REQUIRED, complete homing capability!! (That is _IF_ I get it done!) Anyway, it should be useful for many beacon-tracking / direction-finding / rocket-eering projects where miniturisation/mobility/autonomy is important, and for those who want a better cheaper option. Ain't I a giver!

(Thanks again to RadioRon for enlightening me more off-line!)
(And thanks G8RPI re SAWF!)

 

[AndyPLL]

**broken link removed**

 

[jawadbakhshi]

Hello, Iam working on a similar task as that of AndyPLL, I need to know some information regarding the approach as told in thge article, "A Companion Tracker for the Miniature UHF Fox Transmitter" by Dave Bowker K1FK; QST May 2006, page 32. Kindly reply if you can help me.