Project  Up  Previous  Next

The Transtronics
Heterodyne Detector

Vincent Goffin
Last updated Sun Jul 16 10:51:55 EDT 2000

The Detector

The Transtronics SK-207 Ultrasonic Translator is an heterodyne detector kit. At $20 this is the cheapest bat detector I found for sale on the web, and with both volume and tuning controls it is certainly a good value.

This unit is a bit harder to assemble than a division detector, owing to the fact that it has many more components. The PC board is well done, if a bit cramped. The assembly instructions are clear and an excellent diagram is given. The circuit description genuinely tries to explain how the unit works, and scucceeds. This is indeed a "smart kit"!

Schematic diagram and parts list.

The additional tuning control is a bit intimidating at first, because one doesn't really know where to set it when looking for bats. I detected my firt bats by placing this control in the second quarter of it's range.


July 16, 2000. Lake Surprise, Union County, NJ. i
Just after a big rain; bats were pretty sparse but fireflies abundant...

sample 1 (2.2 s, 19 kb mp3).
amplitude and frequency plots
The pulse rate is about 10 per second, but the pulse constituent frequency is unknown.

sample 2 (2.2 s, 19 kb mp3).
amplitude and frequency plots.
The pulse rate is about 5 per second, and the pulse frequency appears to be higher than in the previous sample.

As in the case of the division detector, all sound and image processing was done with linux-snd, gimp and bladeenc.


For this detector the bat sound frequency is hard to get with any accuracy because the tuning and audio frequencies have to be added together. The audio frequency can be read off the tape with processing software, but there is no easy way to readout the tuning frequency. The detector should first be calibrated: the frequency tuning knob marked for select frequencies; then when making a recording the tuning frequency must be noted.