I am using a much simpler detector than that: Clip it to give a square wave, integrate to give a triangle wave, rectify the peaks of the triangle wave and recover the modulation as A.M.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
On a sunny day (Fri, 5 May 2017 09:05:02 +0100) it happened snipped-for-privacy@poppyrecords.invalid.invalid (Adrian Tuddenham) wrote in :
Old analog video was put on tape with FM modulation (say 5 to 7 MHz carrier), where black was 5 MHz and white was 7MHz. In consumer recorders (like old Umatic) lower frequencies were used. the Umatic FM detector worked like this: Every zero crossing a one shot was started. The pulses were low-passed and that gave the video again. Problem was that if there were tape dropouts causing a missing pulse, then that was taken 1/2 f, as less than black, causing the video amps to go into saturation and produce a spike from black to white... So it depends on what your transmission path can do to the signal what sort of detector can be used safely. I remember designing a work around for that problem long ago, that was actually sold.
The requirement is to communicate mic signals on the 100v loudspeaker line of a temporary outdoor public address system. The mic is connected to the modulator, which can inject a carrier signal into any point in the system. The receiver is located at the main control point, where the recovered mic signal can be fed into the P.A. amplifier, along with other sources, and raised to 100v line level.
The cable is approximately 100 ohms characteristic impedance and the leakage inductance of the matching transformer at each loudspeaker point is high enough to ensure that there is no significant loading at frequencies above 50 Kc/s. There may be long unterminated branches in the system, so the wavelength of the carrier needs to be long enough to avoid problems from their reflections causing standing waves - hence the choice of 450 Kc/s.
Wide deviation (at least +- 50 Kc/s) is not a problem, as there is nothing else on the system above audio frequencies. The passive input filters have to be flattish over this range but able to reject 100v audio signals up to 20 Kc/s. by at least 40 dB, so that the receiver pre-amp is not overloaded ahead of some further filtering.
The mic pre-amp and modulator have to work from a 9v battery (PP3) and I would prefer the reciever to do the same, although a 12v supply from a car battery may sometimes be available.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
so why not use conventional FM modulation if you choose 10.7 MHz there are plenty of receivers ready made
why do you have to send the mic signal back over the speaker wires?
hand held radio mics are readily available that work well over 100's of feet, what is the distance? m
On a sunny day (Fri, 5 May 2017 14:40:22 +0100) it happened snipped-for-privacy@poppyrecords.invalid.invalid (Adrian Tuddenham) wrote in :
450 kHz triggers my radio receiver IF (intermediate frequency in an AM super heterodyne) alarm... There was always 450 kHz around if AM radios were on... In your case your signal will likely be strong enough, most AM MW is gone here..PMR radios not good enough?
Standing waves on unterminated branches. There must be no constraint on the flexibility of the system, loudspeakers and long lines may be added or removed during the event and terminating boxes would be a nuisance.
The particular event which triggered this idea was one which took place in a long field (500 metres or more). The control point had to be situated at one end of the field and the hand-held radio mic became unreliable at maximum distance, so I moved the receiver to the mid point of the field and brought the signal back to the control point at mic level on screened cable.
The proximity of the mic cable to the 100v speaker line (and the lack of proper earthing facilities) meant that the system was liable to instability, so I looked for an alternative way of carrying the mic signal. One way would have been to raise it to around 0 dBm and use balanced line, but I realised that it would be very convenient if I could just inject it into the existing loudspeaker lines by means of a carrier. Experiments with the amplifiers and speaker matching transformers suggested that they would not load down the line at any carrier frquency above 50 Kc/s.
To avoid the use of R.F. coils (the formers and slugs are difficult to obtain nowadays), I planned to use a very low I.F. and a pulse-counter discriminator; but when the need for a low carrier frequency became apparent, it made sense to send the I.F. directly down the line instead of taking it up to R.F. and back down again.
This then led to the design of a 450 Kc/s wide-deviation inductorless modulator which happened to give "period modulation", so I could see no reason why I should not use that instead of true F.M.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
On a sunny day (Fri, 5 May 2017 16:37:15 +0100) it happened snipped-for-privacy@poppyrecords.invalid.invalid (Adrian Tuddenham) wrote in :
PS I did something similar in the eighties. I uses a CD4046 audio on pin 9 VCO in. On the RX side I used a CD4046 in PLL mode locked to the FM, and took audio from the PLL control voltage.
Not HiFi, but worked very well, look up datasheet for how linear it is. maybe these days uses a 74HC[T]4046. hehe I still have those around for all sorts of things, cool chip.
But also there exist special intercom ICs made to interface with the mains, dunno any type number, google.
multiple receivers near the mic and bring the audio back over line level XLR cables sounds like a winner.
Most wireless mic receiver already have the option to output line level audio,,,no?
or build two yagis and low noise preamps and use a good diversity wireless mic Rx.
then you don't need anything at the far end, just the mic
m
That is what I originally tried, but the cables are long and probably 'hot' with some of the 100v of audio output turning up on the screen. Things that work nicely in a studio or theatre have a habit of misbehaving in the field (literally in a field!). A balancing transformer got me over the problem, but I was looking for a more flexible solution.
Perhaps, but mine doesn't.
It's easier to build the carrier injection system ...at least, I hope it is - I haven't got it fully working yet.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
If you have receivers local to the mics, why can't you convey the audio from there to the central point wirelessly with a point to point RF link? That can use directional antennas and have a calculable link budget to assure proper performance. No more wires to fight.
-- Rick C
** Mic a speaker signals on the same 100V audio line sounds bonkers.
Have you really proven the set up will never oscillate ?
You peak detector is sensitive to audio.
..... Phil
That was another possibility I considered. I do have wireless link equipment but unfortunately it works on the same channel as the radio mic.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Since when was this sort of equipment not switchable? It all works on exactly one frequency?
-- Rick C
Yes, there are switchable types and fixed-frequency types, mine is the latter and so is the mic.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
I can't imagine ever buying a device like this that can't be switched. One interfering source and it becomes useless.
-- Rick C
Think back 20 years when multi-channel systems were an expensive rarity, that was when I bought it. I hardly ever made any money on these events, so there was no point in buying expensive gear to cope with a rare eventuality. How many other radio mic systems were likely to be sharing the field with me?
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Draft of the circuit at:
It probably contains a few wrong values and incomplete component numbering, but it shows the direction I am developing it. The chip is a CD40106. The receiver is still on the test bench, so that circuit isn't finalised yet.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
On a sunny day (Sun, 7 May 2017 21:49:41 +0100) it happened snipped-for-privacy@poppyrecords.invalid.invalid (Adrian Tuddenham) wrote in :
Interesting. Nice how you do most with discrete.
I did it something like this:
With one-off designs it is often easier and quicker to use discrete components that are in stock, rather than spending days trawling through data sheets and ordering some special part (which often turns out to have some unexpected snag).
What was the transmission medium?
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
On a sunny day (Tue, 9 May 2017 08:59:08 +0100) it happened snipped-for-privacy@poppyrecords.invalid.invalid (Adrian Tuddenham) wrote in :
Long cables that had differential data and audio pairs. But lower voltage than a 100V system.
Combined with your coupling transformer it should work. Note that if you use a 74HC4046 you can set that to many MHz, and likely get away with just a small coupling cap and inductor. Not sure about FCC limits for RF radiation here, if one side of the 100V system is grounded then it is no longer differential, and should radiate.
But.. in the EU these days low power FM is legal, I have one of these is use:
I wrote PIC software for that module:
There are many ways to solve this problem....
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