Restoring the Past - The Andrew Watson Holgate Detector

Steve Page from the Hampshire Bat Group is the custodian of Andrew Watson's Holgate Bat Detector, one of the first commercially available bat detectors which was developed in the 1960s. Steve built his own bat detector which kick-started his journey into bat conservation, joining the Hampshire Bat Group which led him to discovering the Holgate Detector. He's currently working to get it restored to a fully working condition and we join him in his workshop as he talks us through the components. 

Chapters

• 0:11 Introduction to Bat Chat
• 0:49 Exploring Historical Bat Calls
• 2:40 A Look at Andrew Watson's Detector
• 7:23 Reconstructing the Holgate Bat Detector
• 17:26 Significance of Bat Conservation
• 25:22 The Legacy of Andrew Watson

Transcript

Steve Roe:

[0:05] Welcome to another episode of this brand new series of the Bat Conservation

Steve Roe:

[0:09] Trust's award-winning podcast, Bat Chat. I'm Steve Rowe, your host, and this is episode 73 of series 7.

Steve Roe:

[0:50] These, of course, are Greater Horseshoe Bat Calls. They were recorded back in 1968. We've heard this recording before on Bat Chat. Back in episode 45 in series 4, we visited the British Library, where an exhibition of wildlife sound was being shown, which included one of the very first commercially available bat detectors. Well, last year I went to visit Steve Page from the Hampshire Bat Group, who first got into bats when he sent off for a build-it-yourself bat detector. It worked well, but he didn't know how to identify the bats that he was hearing. He subsequently joined the Hampshire bat group and did one of their bat detector workshops so that he could identify what he was hearing with his detector. He then took part in some surveys and eventually upgraded to a professional Pettersen bat detector. At one of the anniversary meetings of the bat group, he saw a rather interesting box and we joined Steve as he tells us more about it.

Steve Page:

[1:42] I had been a member of the Hampshire backroom for probably at least 20 years possibly longer and then various anniversaries came round and one of which there was an exhibit in the hall for a box which reminded me of my youth which is a very military looking thing in fact it's drab grey which is how the army used to paint all their stuff and i think it was made by probably a military contractor company called holgates not far from here in totten so it immediately perked my interest now suffice it to say that i don't think anybody will contradict me but there wasn't an awful lot of grassroots interest in electronics in the group so this thing was kind of just sitting there almost unloved but cherished because it belonged to andrew watson who i didn't know anything about at the time but i've since and fortunately been able to learn quite a bit about.

Steve Page:

[2:40] Andrew was a great guy who was with the founder member of the Hampshire Back Group amongst others and this was his personal back detector so for those reasons alone it's I think it's worth cherishing and preserving.

Steve Page:

[2:54] Time went by and over the years I continued to express an interest in it and it's husbandry so to speak and then I was asked if I would like to take over stewardship of it and that's what happened so here it is in front of me in all its glory in bits, now the reason it's in bits is that recently we had another anniversary which was the 40th.

Steve Page:

[3:18] And we laid on quite a good bund fight for that it was uh they hired a village hall in east megan because our local hall wouldn't be big enough and the greater good beat a path to our door one of them was was chris packham who i've met quite a few times in the past um i remember him very well why wouldn't i well i don't expect he remembers me um but anyway chris is a great bloke and i do know that he likes to talk technical but i didn't know he was going to be there so i um i took an exhibit along including the whole gate to try and illustrate how far things have come since this beast saw the light of day, and where we are today. Not the least of which was the microphone that Andrew created, I believe, almost. Anyway, it's a very sturdy thing, it's in front of me now. It's got probably a 2-metre flex on it, which is resemblance of a heavy-duty mains cable. It's got an old 6-pin connector of the military style, made by a company called Bulgins, I expected.

Steve Page:

[4:29] And it's got a cylindrical brass tube with a the business end has got a simple wire grating and you can see there's a silvery foil behind it and this was the detector that they used in conjunction with the holgate back detector to pick up back holes now the scary part about all this is that the microphone is essentially hand crafted by Andrew and I don't have any notes on how he did this but as I unscrew the end cap which has got the grill on it to reveal what's underneath.

Steve Page:

[5:09] There is a as I said a silver diaphragm of sorts and then there's six small screws present themselves and if you take those off there is a similar diaphragm behind it which is the business end of this detector and what I believe it is is an early form of capacitor microphone whereby you've got two essentially electrical plates and with a charge across them and these days these are very common these days just about everything that we own has one of these things in it but the modern ones only need something like the battery voltage to make them work whereas this contraption was clearly more hungry and this threw a light on the other half of the conundrum for this bat detector which is the power supply.

Steve Page:

[6:01] Which was contained within it now i've got now a bag in front of me which has got a see-through front on it and it's not a pretty sight there are various old but in fact there's many of the same type of old battery in there which you've got the label on the towing ever ready battery 15 volts.

Steve Page:

[6:21] Blr121 now i know this beast because it was the battery that was used in the early, analog volt meters that we used to use in the days of yore but this thing doesn't use one of these batteries it uses two four six eight ten twelve of them so i think if my math is correct that's about 180 volts and they're all joined in series so this detector attracted a charge or received a charge of 180 volts from these batteries in order to work.

Steve Page:

[6:59] So not only was the guy using this standing up in the elements trying to pick up a small brown furry mammal, he was also holding a potentially life-threatening device while he was doing it. But I exaggerate because it's only batteries. And this was some of the adventure that I've been involved in,

Steve Page:

[7:17] trying to get to the bottom of how the Holgate Bat Detector works. And so I was pleased actually to discover the circuitry that involved these batteries was limited to the microphone.

Steve Page:

[7:34] And basically the voltage or the connection goes straight into the microphone circuit and doesn't venture any further. So that means that all the rest of it is powered by the other battery. The only clue about which i had was the two connectors which aren't like anything that is available these days but a bit of sleuthing in fact in fairness to your listeners they resemble a pp3 connector on steroids they're about twice the size of today's nine volt battery connector diameter-wise and the same style but much much bigger so i uh thanks to the wonders of the internet i had a look around and discovered the batteries that were in the uh ever ready catalog contemporaneously with the holgate which is in the 1960s and found that there are about six designs that use this particular connector.

Steve Page:

[8:34] Barring one which i can't remember what was special about that they all were nine volt batteries so that was good so we're talking almost certainly about a nine volt supply, the next clue was the hole or the cavity within the detector to receive this animal and it turned out that the only battery that fitted that hole is the battery i've got a copy of here which i've just lost which i've just found which is a pp9 so pp3 pp9 so it's just a big pp3 battery, quite a substantial animal as anybody who's um prone to taking things to bits will know that the pp3 inside it has got a little stack of leclanchey cells not very big not very powerful they're all linked together and with a bit of luck you get nine volts out the end, this thing although i'm not going to take it to bits because it's the only one i've got is the same sort of thing, I think, only much bigger. So larger area, more material, bigger chemical reaction, more power as they used to say.

Steve Page:

[9:40] And so I got hold of one of these, and it was only about £9 I think, so not too bad. Plugged it into the hole gate and turned it on, having done a few other checks to make sure that there wasn't anything going terribly wrong. And the little light came on, which is always a good sign. It means the man's in, and we may have some joy. However just before the arrival of steve here i thought well i'll get it going again to make sure nothing untoward has gone and the positive lead went all floppy and just broke off so i was in the process of reconnecting that when you arrived so we can make a bit of smell and some heat if you like and try and get that reconnected if you like okay so.

Speaker3:

[10:29] While steve's doing that i'll try i don't know how to describe the detect that's something to me there's no case on it it's just a couple of metal boards with lots of electronics on it and not electronics that i'm familiar with there's something that looks

Steve Page:

[10:43] A bit like what they call discrete component stuff so whereas today you would have a chip this has got individual transistors one there one there there There are, I think about a dozen others, mostly in this little box down here and inside here. There's a hefty speaker on it, which would do your granny's radio proud. There's some coils, which are to do with the beat frequency oscillator, which is the magic which turns the high frequency we can't hear into audio frequency that we can hear. There's a robust, of its time, volume control with switch on it down the bottom there. Oh, that's all fat, this hasn't got a switch, sorry. Sorry, I haven't revealed the front case to Steve yet, but a nice bit of rexine fretting on the front there. And indeed, there's even a socket so you can scope the output from the microphone, which is a very sensible innovation for this kind of thing. There's a thing there called the beat frequency oscillator, which you can fine-tune, presumably. We haven't got to that giddy stage yet.

Steve Page:

[11:53] But basically that that tunes the oscillator which is part of the protect detector which as i say allows you to hear the audio signals coming or calls coming from the bats in our own spectrum so that's it and there's a dinky little switch there which is panel light and that does work sometimes so anyway we'll try and reconnect this thing interestingly this is almost a sacred moment because i am reworking andrew's handiwork the wire that they use i can almost certainly say is a mil spec cable military spec cable which was good quality stuff and you can tell that because when you hit the end with a soldering iron as you have to when you're soldering iron soldering a metal connection the insulation doesn't run back down the cable which it does with a poorer quality or lower quality jacket anyway we'll stick that on there for now.

Steve Page:

[13:00] It's got a bit of modern heat shrink the original connection of these what they call hellerman sleeves which are rubber and that had all perished and so it's lost support and that's in the bin somewhere. Anyway, it's all in bits now, but that just fell apart. So age is taking its toll. A nice little bit of acoustic side effect with nothing.

Steve Page:

[13:28] Just melt the heat shrink to make it look official, a modern innovation there and now we should be good to go as they say, now then bear in mind that this is a device that needs the microphone to make it work, the microphone is not connected so it's not going to detect any bats partly because they're aren't in the workshop but mainly because it hasn't got a way of doing at the moment the scary part about this is connecting the two connectors because they are not joined so you've got to get the right one on the right battery or you will reprise your smoking experience from, we were discussing earlier and then if we i did this earlier we've got no oh that's right turn it on there is a soft noise coming from the speaker which tells me that the audio stages, which amplify the signals are working and the little light on the dial comes on so you can see what you're doing in the dark always useful as a bat detector and the basic thing seems to be in quite a reasonably good state that dear leaders is as far as i can say at the moment and.

Speaker3:

[14:50] How old is how old is this detector do we think

Steve Page:

[14:52] It's 1960s 1960s i would think probably being worked on before that maybe because of development cycle this is a a product of academia and industry and industry would have been making these things by the thousands for whatever purpose that they were used originally i believe this is possibly a converted design maybe it was a long wave receiver or something where they've taken the aerial out and put this circuit in its place i don't know for sure with a view to replicating these.

Steve Page:

[15:28] I touched a spring that's what the noise of these ever ready batteries i don't propose that we, use these unless we get a lottery grant to buy some more because i think we're looking well over 100 pounds worth there so what i've done is i made a simple inverter converter circuit which basically is the sort of thing that you would use if you wanted to run a heater in your warm a cup of coffee in your car or something like that or run a run a.

Steve Page:

[16:04] Mains device from a smaller battery so this basically takes in low voltage dc there's an oscillator in there and a simple oscillator which and a transformer in this instance and that turns that low voltage into a high voltage at low power and sends it out through that pair of wireless and this one i've made comes out that i think about 160 volts anyway that's the idea that we provide a second source or an alternate source rather, to charge the diaphragm on the microphone and then we've just got to get the microphone to work, what kicked me into doing this rather than just putting this in a box and looking after it for posterity was at the 40th meeting that we had as i said chris packham was there, and i know chris likes to talk techie stuff he came up he saw this thing and he made a beeline and one of the things i was trying to do was to show people what it looked like inside contrast it with our modern back detectors which just about everybody else there would have been familiar with if there are any experts out there who know how to make mylar.

Steve Page:

[17:27] Microphone diagrams then I'd be grateful for a DM as they say but anyway that's kind of where we've got we've got that lot we've got, that's the technical details of the little tiny MEMS microphone which shows you how that works that was part of the exhibit, and then we've got the i think these might have been samples that you got from somewhere sheets of mylar for constructing condenser microphones to receive ultrasonic signals, brilliant and this has been cut off the roll the roll was probably a meter and a half wide and we've got i don't know probably a reasonably long run of mylar sheep, more than you could ever need for the lifetime of the equipment. We've also got.

Steve Page:

[18:29] Something here called ditafran material and also a sample here which is an industry sample and it's different weights of melanex as this proprietary name for this polyester film is called made by a company called ICI now I think that must have outlasted ICI actually because I'm not quite sure what's happened to them now so they went from being Britain's biggest chemical industry mainly making munitions during the war and um seemed to have sunk without trace but maybe i've just missed it anyway so there are some samples and i don't know which weight oh here we are 25 gauge someone has conveniently put a label on here saying um what does that say.

Steve Page:

[19:17] Lapidex i think that is metalized melanex 25 gauge coated both sides are an overall thickness of 80 millimicrons so it's a pretty good ruler that can measure that now but was that the one they use though we don't know the soup thickens another envelope brown paper envelope no it's not it's a buff folder sorry diaphragm material obviously this diaphragm for these microphones was a key part of this development and was revisited many times anyway an interesting conundrum an interesting puzzle there are other opportunities we've got a basic receiver here which.

Steve Page:

[20:09] To all intents and purposes stands a good chance of working it's making the right sort of noises it's not overheating we could try and put a conventional modern microphone, into the front end of this see if we get some signals going through it doing that but i haven't got that far yet we've got a graveyard of early bat detectors here which, as you see in various states of disrepair but anyway there could well be some components in there that are in a good enough shape state rather to do something with perhaps so job for the long winter evenings i think and.

Speaker3:

[20:55] Just tell us why it's so important to keep this stuff catalogue documented and working you know what what is its significance to future bat

Steve Page:

[21:04] Conservationists i think we are possibly looking at the first commercial bat detector, that is viable in the hands of the what trained observer so this contraption that we've got here the Holgate-backed detector. And this is the Mark IV, which is a very military sort of oriented way of saying it's the fourth iteration of this design. Could be the first viable.

Steve Page:

[21:44] Backboardable back detector and this belonged to the guy who as far as i can see was the prime mover in making that happen with he was local he lived in basingstoke holgates were in totten which is down near on south near southampton water on the other side from southampton and so it's all local and there was a guy again name escapes me from sussex university who was involved in it to what a great extent i don't know but anyway he deserves credit as well but anyway it was andrew that pushed this and they did make some and they were expensive i don't know how much but in today's money we're probably talking thousands and they did mostly go out to academia and they you can come across articles on the web written by people who use them in far-flung lands so they got about, and then andrew was quite a character in his own right he was definitely a batterholic.

Steve Page:

[22:50] He traveled to various places in the world and collected bats and brought them home in his pockets apparently and he used to walk around with a bat in his pocket and he also had vampire bats as well which i'm not sure whether they were the same bat they used to walk around with, there's a story that says that he used to go down to the local butcher and get fresh, blood from the butcher to keep his bats sustained so he's definitely well into bats but anyway he had a passion for them and he wanted to see that they were better understood and, people had the opportunity to get to find out about them and so he was one of the people's instruments oh that's right he was a secretary of the mammal society and i believe one he was using this bat detector and it was under the auspices of the mammal society of great britain at that time and then he uh i guess he must have thought well bats need their own.

Steve Page:

[23:54] Conservation groups so he started bat groups and he started the hampshire bat group which is where we are now he also started the one up at Reading which becomes the Bucks and Barks back route he probably started many others as well and the in the first minutes of the first Hampshire back route meeting he's recorded as being there and taking a leading role in encouraging but not being part of the organization itself so he said he would train people on doing bat surveys and this kind of stuff but he didn't want to take over being i assume he didn't want to take over because other people were being secretary and chairman and all that other stuff so there you go yes fascinating chap i wish i'd have met him but um the only time i was in the room with him he was quite elderly and quite infirm and i didn't sadly know who he was but it wouldn't have been my place to get to talk to him anyway so there you are so that's why i think it's important that it does get conserved and i don't know of another one in existence there could well be somewhere but um whether the people that have got it know the significance of these things but this was andrews so i think that's what makes it special although that's only come down to us because the bat group inherited his chattels with regard to bats but from my point of view.

Steve Page:

[25:22] The journey continues in Hampshire.

Speaker3:

[25:26] Fanstastic bit of history, Steve Page thank you very much

Steve Page:

[25:28] You're welcome.

Steve Roe:

[25:31] And my thanks to Steve for taking the time to show me Andrew's Hullgate detector. As we heard at the start of the episode, the recordings made on this device are of their time and we've come a long way in technology. Well next time we're off to Wales to visit one of the most well studied bat roosts in the country where detectors have been used to uncover previously unknown communications between bats.

Maggie Andrews:

[25:51] And he lived in a caravan outside at the archway here where the bats come out.

Paul Culyer:

[25:56] He was probably the UK's first paid bat worker.