A superb polycarbonate (Lexan) 32" parabolic dish fitted with stereo microphones, for bird and wildlife recording.
Sadly, my disability has taken a turn for the worst and I am forced to offer the dish and (maybe) mics for sale.
Open to offers around £100, or swap for a large SATA Hard Disc Drive (500GB ?)
contact info
A few MP3 song files and sonograms at the bottom of the page.
The system as it stands is very sensitive, with about 30dB gain at HF, down to zero gain at 500Hz and negative below that.
I have worked out an Excel spreadsheet to show Gain Vs Frequency, which may be downloaded HERE
In fact, high frequency sensitivity is so good, I have even picked up the 15625Hz from the line transformer in a TV
in our house, from the bottom of the garden !
This is a 32" (812mm) active diameter 2mm thick polycarbonate (Lexan) dish. There is an outer rim of about 2" all the way the edge,
enabling me to hold it, and to bolt other bits onto it. It is fitted with two single point electret microphones, to form a stereo pair.
EDIT : the mic support structure has changed slightly, and now has a clear sighting hole through the centre.
Here you can see the 3mm threaded rod, which I bent into a hairpin shape. I then bolted into onto the dish, and attached
the microphones with tie-wraps. They are oriented horizontally to give a true left/right setup.
This is my iRiver 20GB HDD MP3 player/recorder. It is capable of recording WAV as well as up to 320kbps MP3s.
As I have now discovered that MP3 files cutoff at 16kHz, I am only using WAV format to record, as some sonograms
have proved that songs can reach 20kHz. Currently I have about 6GB free, which is more then enough for any field recording
I will need to do (works out at about 12 hours!). The iRiver also provides limited phantom power for the electrets.
This is my own idea ! A hole, drilled in the exact centre of the dish, which acts (rather nicely) as a visual sight. I line
my target up with the end of the threaded rod, and centre everything in the hole, and it is spot on ! The line of focus is
quite small, only a few degrees, so extraneous noises are REALLY kept to a minimum. The amplification factor at 1KHz
is about 30dB, and even if my maths is off, the available amplification is more then enough for me :)
The whole thing including dish, mics, MP3 player and headphones weighs in at under 2.5KG (5.5lbs)
OK, it's been up and running a few weeks now, but so far, I've only managed a few decent recordings.
This is a duet between a Dunnock and Coal Tit from the back garden.
The song sounds good, and the
sonogram looks even better. The seee-wee is the tit, and the low suee is the
dunnock. There is also a robin
chipping at the start along with an unidentified cluck - possibly a pheasant,
as they often visit.
MP3 of duet (thanks to Geoff for the ID corrections)
This sonogram shows time along the X axis Vs frequency up the Y axis. Volume is shown by brightness.
Bandpass filtered from 2kHz to 16kHz, no discernable song outside of these limits but plenty of wind and noise is reduced.
Dated 4th Sept 2006
Another Dunnock, this time a single peep, note how the harmonics go up to 20kHz or so !
Dated 7th Sept 2006
This time a juvenile Robin "pips", quite a short MP3 file, but a fascinating sonogram with lots of harmonics again.
Dated 7th Sept 2006