I've always wondered how well a parabolic mic works. Here is my experimental setup for testing such
DIY parabolic microphone. It is a great weekend project and will let me experiment with high-gain / low-noise audio amplifiers. The heavily wooded area off my back yard is plentiful of singing birds.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnKCz2tLX_vt8Iq5mip8cQKAbWZzE8k1F7TLa9xrRQcb4NfEHgMz36secL2WIJYy9aSVclfi9GJz8ZGbu4qP1vkmKlGgi49jUCubUr9ffMWblHJBQSV2YHWbfYL3WLj0uMOiSzvMCRNw8/s400/IMG_6523.JPG)
Photographic tripod is used as mount for the parabolic dish. I had to construct a simple mounting bracket and a "focusing" contraption that will let me use different size and shape microphone elements.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIb7YqCiYDWs4bSLL3_41xX_pw87M3LRXAkOHHE4tQ9aJrj7wXLbJVE5knD3Y4CzpA3cXIT6TMPNSRwbSUUUYpeF0o6v7uvxP9BqOix9gVh4BC_Kyc_CRlVzS6GAdFvYtjY8dIoU7SVaA/s400/IMG_6527.JPG)
I got the actual parabolic reflector from "the place where you can find anything" -
eBay. The parabolic reflector is made out of polyethylene plastic. The diameter is 21 inches with focus point 4 inches from the bottom. It came as one solid reflector - I had to drill the mounting hole. I had a few ideas for mounting the dish - I wanted to be compact and simple so I decided on a single hole in the center.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEie5wrbpAQ_9AhR2zgJW3lBE8J2pKnpVUi13YqUS4fatG44wSB2gc1eFLWGN_m75_W3asq2YXIgR1oF-gOCFAgSXNb-FGQ51CmWAdTfDSLJeyHqnmdH8cyYvCQiP7DFAe4zYKcSEejSwu8/s400/IMG_6524.JPG)
The microphone mounting frame is made from semi-rigid coax (
RG-402) and small PCB board for attaching the mic element. I used a threaded cable feed-
thru to both - attach the dish to the bracket and mount the
RG-402 frame with the microphone. A "sandwich" of metal and rubber washers - including two large and thick rubber washers provides "shock-mount" for the dish. The mic frame is fed through the threaded feed-
thru using silicone cemented inserts.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgSmCxWebmY-gs9G8CFjvXS0FAe6WzzhyFauJB5dVhWIS2sgOzHZXlqawHA_3VlXOc-tPx0imcqmjoKkMTt0reyZFdwPDq7M7i88gy_K7C3d7LFNc2F-JYRCrWH61hXvp1fzIIj9VwNhWA/s400/IMG_6525.JPG)
The "focusing" rig lets me move the microphone element to the exact focus point of the dish. The focusing range is about 2 inches. Normally, the mic can be fixed in the focus of the parabola, but I am planing to experiment with different mic elements and they all vary in size and shape so I wanted to be able to adjust the mic frame with no hassle. Two spring-tensioned wing nuts fine-tune the mic frame.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhapO4pRceVzZdRmU6_SoG5501BIZkEEXCO6bjMt37IqFEdBa1vC5DoHCGHhlVme50KYQQS8X8mBmAPMPKiL9o7rpjr6vMydKMD_NdKq9hXc4PkgDXmPiYMRyqnyUAPiEMBG8fBJKg1qxU/s400/IMG_6528.JPG)
Small plastic container is holding the battery pack, microphone preamp and 900 MHz FM transmitter (a.k.a Baby Monitor - For the initial testing and to validate the concept I just modified a baby monitor and then used my
IC-R20 scanner to listen and record). Currently, I am working on my low-noise/high-gain preamp. The radio-channel link sort of works but the noise levels are way too high. Proper mic
pre-amp and better (broadcast grade) FM transmitter are planned for the next stage.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIprwdl6e8WeMMdDwBA7yAQk9qdwXMldQ9O2Iew_9Y6A02vDC1e7tOB3wR8D1vi-KKlkggE1oFNdMSd09-3-KP5LtABsg8lM_bKDzIdFyB9dCLmJsJucfbs2disSMLGTBSo4rmROInHYo/s400/IMG_6530.JPG)
Hand-held mode. Large plastic handle salvaged from old angle-cutter provides comfortable grip.
A word of warning - the surface reflectivity of the polyethylene dish is high enough to produce smoke from the
mic's wind guard while I was playing with the dish and decided to verify the focus by pointing it at the sun. It took less than a second! I was able to act quickly and saved the guard from catching on fire :) (stupid move but the damn thing looks transparent :-)