Parabolic mic questions

[zachtheterrible]

Hello, I got me a couple questions about parabolic mics. First off, what kind of amplifier is used? One like the one in the transmitter pic here? With this amplifier, I can hear myself wisper from across the room. Is it possible to build a parabolic mic w/ out IC's? cuz i would kind of like to try and design my own amplifier n stuff, and am not good w/ IC's. I posted a question about parabolic mics before, and someone said they would give me their email adress . . . I think it was chemelec? They said that they had built some in the past. Thankee

 

[chemelec]

chemelec@hotmail.com

YOU MUST PUT THE WORD: "ELECTRONIC" In the Subject Line

 

[ante]

Chemelec,

If you make a post of it instead of answering by mail everyone whit an interest in the subject can also benefit from it. That’s one of the reasons for being a member of a forum. Unless of curse it’s something illegal or in any another way unsuitable to post in the forum.

Ante :roll:

 

[zachtheterrible]

Thats a good idea ante, i think that i will just ask my questions in this forum. So . . . hwo bout those questions in the first post? 8)

 

[audioguru]

Hi Zach,
Your transmitter already has an electret microphone amplifier, so why do you need another one for a parabolic dish? Just connect the electret microphone to the transmitter with some shielded cable and mount the mic at the focal-point of the dish.
Your transmitter will probably work much better, especially when the battery is low, by adding a 0.01uF capacitor and a 100uF capacitor, both connected from +9V to ground.
The mic amplifier will have more gain so that the mic is even more sensitive, by adding a 100uF capacitor across R5.

 

[zachtheterrible]

Thx!! So howcome wen i search for parabolic mic circuits on the net, i always get fancy ic circuits? What is the purpose of the 100 n .01 uf caps? Thanx

 

[chemelec]

The Problem with Answering in this Forum is I visit Many Forums and answer Many Questions on Many subjects. Than I can never remember which ones (Messages and Forums) to go back to. mostly just find them by chance, sometimes.

So if you want specifics from me, E-mail me or you may not always get an answer. I always reply to ligitmate E-mails.

Gary

 

[chemelec]

Here is a Closeup of that Preamp.

 

[Dean Huster]

Back in the "old days" of satellite TV with the big 10'+ dishes and such, I was listening in on an installation seminar where the instructor was cautioning the techs to be very careful of what they say when they're working at the focus of the dish where the LNA was. At that position, they could hear with amazing clarity what folks in the line where the dish was pointed were saying, even if they were hundreds of yards away; and those same folks could hear you quite well!

The "Omniplex" science center in Oklahoma City had two such dishes set up on opposite corners of the huge auditorium and two people could talk to each other in a whisper over all the ambient noise of the center.

Dean

 

[zachtheterrible]

alrighty than, ill do that chemelec. that whole thing w/ the huge satellite dishes is REALLY COOL!! So from what you said Dean, i guess that really good amplifiers arent really needed, just ones that can hear about as good as the human ear.

 

[chemelec]

The Amplifier and the use of Headphones helps a lot. It Needs to be Low Noise. If all you want to do is Talk across a Gym, than you don't need it.

An Adjustable Bandpass Filter or a Low Pass Filter are VERY Useful to Eliminate Unwanted stuff, like WIND NOISE and Cars passing by.
Filters can also "Tune IN" if for example you want to listen to a Bird. (Set it for Higher Frequency Tones Only)

I also use a 6 foot Satellite dish, But Its a bit big to move around easily.
Also Very Obvious as to what your doing.

I have the PCB layout for the amplifer/Filter I designed above and I could also take a picture of the parts layout of it. But I never actually drew the entire schematic when I made it.

Gary

 

[Dean Huster]

10-foot dishes aren't clandestine, that's for sure. I'm certainly not advocating the large dish, just illustrating the power of a large dish.

As Gary said, it's the electronics that really makes for a versatile and powerful long-range microphone. By that way, parabolic dishes aren't the only way to go. Bundled pipes was another popular type of mic and simple to aim. In that system, 1/4" aluminum tubing was cut into graduating lengths with the longest about 4 feet long and the shortest around 4 inches as I recall, graduating from smallest to larges in 1/4" or 1/2 in increments. The whole mess was bundled together and one end of all the pipes lined up into a funnel where there was a microphone at the small end and an amplifier. It was a construction article in Popular Electronics back in the 1960s.

 

[ante]

Dean,

Is it this device you referred to?


Ante :roll: