Last night I was surveying for emerging bats that didn't emerge, so I had plenty of time to think about life, the bats and everything. It occurred to me that the detector I was using, a Bat Box Duet is of the most popular detectors on the market, and rightly so. It's sensitive, selective, ergonomic, robust and sensibly priced.
As with any piece of equipment, there are hints and tips that help the user, some of which I've picked up from other users and some I've worked out myself. So here are my ten top tips for using a Bat Box Duet:
1. Try plugging your headphones into the tape socket, instead of the headphones socket. You will hear the heterodyne detector in your right ear and the frequency division one in your left. Whatever frequency the detector is set to, you will still be aware of bats on other frequencies. The audio level is fixed, so the volume control has no effect: if you're beside a road or river you may struggle to hear over the background noise.
2. If you want to try this technique somewhere where there is some background noise, try plugging the detector into a minidisc machine and plugging your headphones into the minidisc. You should hear the audio from the bat detector and the minidisc volume control will allow you to hear it louder. This is good practice when recording, as it allows you to be confident that the detector output is being recorded properly. It's very frustrating to get to the end of a survey and find you've recorded nothing because you accidentally knocked the stop button or a plug has come out.
3. When the low battery BAT warning appears on the display, don't panic if you haven't brought a spare battery: the detector will continue to function for a short while. Eventually the frequency indication will go haywire and then the detector will switch off the display to save power, but the detector will still operate for a little while longer.
4. Even in that situation you can by without the frequency display. Although you don't know what frequency you're tuned to, if you rub your fingers together, this sound will be loudest at 40kHz, giving you a very rough frequency indication. Of course, its a lot easier just to carry a spare battery!
5. Have you ever wondered why a seemingly random digit appears when you first switch the detector on? This is the software version.
6. If you have a childish sense of humour (like me) you can convince gullible people you have a very clever detector. Using a worn battery, turn the volume high, without headphones. The loudspeaker is the most power-hungry part of the detector so, when a bat is picked up, the extra current consumption will cause the word BAT to appear. When the call ends, the word disappears again. Fun for all the family!
7. Fed up tuning up and down, to ensure you don't miss any bats? Try tuning to 42kHz. You'll hear Myotis calls as a regular machine-gun type call, Common Pipistrelles as an irregular, thudding and Sopranos as an irregular squeaky sound. Noctules can be hear when close, as this frequency is close to the first harmonic of their call. For heaven's sake don't try this for anything important: you will lose a lot of sensitivity, and you may miss something important (especially Horseshoe bats) but it's handy if you just want a general idea of what's happening. I sometimes do this when I set up a Duet on a tripod to record the frequency division output. In that situation I know everything is being safely recorded, so missing the odd call is less important.
8. Did you know there have been some subtle changes in the design of the Duet since it first came out? Earlier versions had a less sensitive microphone, which looks like a small black plastic grille. the later, more sensitive microphone looks like a tiny metal disc, surrounded by a rubber grommet.
9. Another change is the function of the REF button. In earlier versions this produced a steady reference tone. With more recent Duets, this button shunts the microphone to normal audio. This is handy for taking field notes, as anything you say into the detector will be picked up on the left-hand stereo track and recorded (assuming you are recording the survey). Be sparing in it's use: whilst you are talking the frequency division detector is inactive.
10. I only had nine things, so for number ten I'll mention that the Bat Box III has now been revamped into the same style of case as the Duet. I have yet to get my hands on one, but I suspect it will be a very good heterodyne detector. The original Bat Box III was excellent, but it's only weaknesses were poor ergonomics and difficult frequency indication. The new version (Bat Box IIID) fixes both of those issues and will probably be a really good little brother for the Duet.
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