Double sideband demodulator  mk3  squaring loop

After having tried the dsb demodulation using the MC1496  divide by two and the  Andren frequency doubler  I thought i would marry up the bits of circuit that gave the most performance gain and build up what I call the mark 3  dsb demodulator , Hopefully this will cut down the complexity of the circuit  and enable a simple PC board to be  produced .
I used the Andren frequency doubler as a squaring generator as it gave the most gain to produce the dsb squaring output' from the DSB supplied .  The NE592 application with a crystal as the the  frequency selective feedback element  , gave the most gain with the minimum frequency bandwidth to enable one to pick the wanted carrier from the mixer( squarer) output  ,Its output was enough to feed   the synchronous oscillator and  with its ability to lock to subharmonics ,  enables one to achieve a "divide: by two " function and at the same time derive a suitable level of rf output at the correct frequency  for the NE612   DSB  product detector .
The components were assembled together to enable the required results , a double sided PC board was made  as per the photo  below .  Once again i used the 1.84 Mhz  crystal to achieve the narrow  bandwidth to filter the  wanted  synthesised carrier ,  the filter bandwidth was very narrow which in this receive situation will not allow a lot if drift to occur before the circuit looses lock , Im sure an IF  Frequency of 5 MHz or more will perform equally as well and enable a larger tolerance of drift in the receiver and still provide adequate demodulation performance ..
The circuit rail was  12v  however the Dc feed to the NE602 had to be limited to 8 v max with a series resistor and a zener diode  bypassed with a tantalum polarised  capacitor .

I am not sure of the input impedance of the frequency squaring circuit so have transformed the 50ohm signal generator output to 450 ohms to approximate a match  for circuit evaluation purposes , with a homebrew 9:1  trifilar wound transformer   transformer design could be somewhat more  relaxed if i was running the circuit at 5Mhz  rather than 1.8 MHz . The other minor inconveniences I had was the use of 6 mm neosid  slug tuned  coils requiring rather a large number of turns and capacitance to achieve resonance at such a low frequency  85 turns of fine wire and 220 Pf to get me near 1,8 Mhz .  . and much larger values of capacitance to achieve resonance at 912 Khz in the synchronous oscillator ..

The Finished  product

 

                                                    
                  9:1 input transformer             squaring mixer        ne592 xtal filter             synchronous osc           ne592  prod detector

 

 

more to come later    

Double Sideband suppressed carrier demodulation  ,  MC1496 as squaring means

 DSSC    demodulation by the squaring means     diode doubler technique

The next   DSB  demodulator I want to try is the switching  inverting alternate audio type  which sequentially inverts the  demodulated audio  and thus assembles it in the correct sequence , the phase changes in the  carrier RF at Zero Crossings on modulation , trigger the alternate switching action This type was patented  in 1957  ( applied 1952) by Leonard Khan of am stereo fame . he of  course used valves !!

Double Sideband   suppressed carrier Demodulation   Patents

These are all the References I can find on Double sideband suppressed carrier demodulation , there are bound to be more ,  they are all US patent Office registration No..  The E  ones are European Patent office ,
Have a look on the application of File dates and the Granting dates and some people had to wait a long time before their patents  were granted .

2924706 ,2992326, 2999155, 3047659,  3060383, 3088069,  3108158, 3141066, 3151217, 3252094, 3286183, 3345571, 3457513, 3537017, 3593149,  4253066

 4821322, 4475218, 4642573,  4862098, 2979611,2397961, 4130839, 4430620, 4485487, 4510467, EP0291826B1, EP0293828B1, 2193801, 2276863, 2784311,

3375453 , 3430151,

3719903, a  novel dsb modulator ,

  references   :          http://adamkar.republika.pl/spread_spec_rx_en.htm                            http://www.tapr.org/ss_g1pvz.html#part_two-receiver      see squaring loop demod

 

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