BAT DXing or noise hunting ….

[WA2SQQ]

Some of us have used ultrasonic directional mics for hunting down power line noise. I came across this and decided I’m going to order a few of these. You can use your SDR for both RF and audio noise hunting.

https://youtu.be/-ikeMSn35T0?feature=shared

[W1ITT]

That ultrasonic microphone is available from Chinese sellers on Ebay inexpensively, like 10 or less than $10 at one vendor.  It's a different sort of SMD than what I'm used to.  I'm guessing that you use paste and cook it in a toaster oven or under an air soldering iron.  Does anyone have any experience with this particular package.
I have used an SDR-IQ with a run of the mill 30-something khz sensor with limited success.  Without a preamp it was a bit numb but I could hear my fingers rubbing.  The unit listed in the video seems to have an onboard preamp.  It looks as if it would be swell at the focus of a plastic punch bowl to listen to power line insulators.
What's the special magic to dealing with that particular SMD  package?
73 de Norm W1ITT

[W1NB]

Norm,

Yes, you use a solder paste which is solder suspended in a flux paste. There are reflow ovens that you can buy but unless you are doing a lot of boards I recommend using a rework heat gun. I purchase my paste from Amazon but you can get it at most electronics supply houses like Mouser or Digikey. Usage is very easy. You simply place a small droplet of paste on each pad to be soldered, set the component, then heat it with the gun until the paste turns into solder. As long as you don’t put too much paste on a pad, the solder will pull into the pads and component tabs and give you good results. The paste works great with just about all SMD components. It will actually align the components on the pad when it’s heated to the activation temperature. Keep the airflow low on your heat gun. Just enough to heat the pads you are soldering. If you’re using it on rework, get some heat resistant tape and use it to cover the surrounding components so you don’t accidentally float them.

Bob, thank you. I’ve been battling power company line noise all winter. This may be just what I need to track it down. With the amplified version shown on the video, I think it can be mounted in one end of a paper towel roll to make it highly directional.

[WA2SQQ]

The element featured in the video has a built in preamp. They aren’t expensive. Going to order one or two.

[W1ITT]

Scott
I have a rework hot air soldering tool and I'm passable with it on components with insect-style feet that stick out.  This one scares me a bit because the pads are hidden.  I suppose the device must be made to take the heat, so to speak.  At the 10-fer cheap prices on Ebay we could afford to spoil one or two in the learning curve.
I got a cheap plastic punch bowl at the party goods store to use as a parabolic (more or less) dish with the idea of getting some gain as well as directivity..  MFJ sells a unit like this already made up but it costs more money.  I think Rick K1BQT did the design work.  But I think I can do better on the QC that the folks in Starkville.    And besides, this little unit looks to do most of the work for us.
73 de Norm W1ITT

[W1NB]

Norm,

I purchased a couple of the microphones identified in the video. They are mounted on a circuit board that has connection points for output and source voltage. It works quite well. I found a squirrel baffle at Home Depot for a parabolic reflector. It’s a bit shallower than I’d prefer but I think it will work fine. It’s 16” in diameter and made of rigid clear plastic. I’m working on the hub and button hook focal mount for the mic. I hope to have it completed in another week or two.

[WA2SQQ]

What is a squirrel bafflle? Photo?

[Jim, W5JO]

What is a squirrel bafflle? Photo?

Don't have a picture but around here they use a stainless steel circular device that sits on the output insulator that is spiked to keep the little buggers from getting on the output of the transformer.  They, also, have begun to nail a brown plastic looking sheet that is about 2 ft. long around the pole to keep them from climbing it.

The best thing has been the shift to metal poles.

[WA2SQQ]

I figured out what it was. Please share details of the mount you will use. Have you calculated the proper focal point?

[W1NB]

I have calculated the focal point, 6.1 inches. The baffle came with a hub assembly that I think I can modify to support a button hook strut on which I will mount the mic. I’ve ordered some 4mm round aluminum stick and a 4mm shaft coupling. It should be here Friday.

Here is a picture of the squirrel baffle

[W1NB]

Here is a quick summary of the conversion from squirrel baffle to ultrasonic mic:

The hub section of the baffle has a steel rod running through it with hooks bent into both ends. I cut both hooks off so that the remaining rod was straight. On the inside end I attached a shaft coupler, then cut the plastic hub length so that it is flush with the inside of the dish and filled it with epoxy. The opposite side of the rod serves as a mounting stud to which the handle grip, a Danco universal shower valve lever, is attached. The hub is attached to the dish with epoxy glue.

The focal feed is a plastic end cap and it’s mounted to a 4mm strut with a screw hub. The strut is bent to provide an offset so that the mic, which is mounted inside the plastic cap, is centered on bore site. The mic is powered by a three AAA battery pack mounted to the back side of the dish. The battery holder conveniently came with an on/off switch. I added a connector so it can be disconnected. The strut is easily removed for storage.

I’m using a Malahit DSP2 receiver. It will tune down to 10KHz.

I finished it early this morning and had a few minutes before work to take it for a test drive. So far, it appears to be working well. It is quite directional and its bore site appears to be accurate. You’ll note in the pictures that the strut is considerably longer than is needed. I left it long to experiment with the focal length if it did not perform well. I don’t think that will be necessary but the added length helps in siting.

[W1NB]

More pictures

[W1NB]

And more pictures

[WA2SQQ]

So during your testing what did you find, bats, arcing or ??

[W1NB]

I only had a few minutes. I checked the pole at the corner of my lot and didn’t detect any arcing. The power company had found an issue there in January and did some work on it. Most of my testing was around the house. I can detect garbage at 11KHz coming from my computer monitors. I plant to check all the poles in my area this weekend subject to the weather.