Call in a couple of ham radio operators who like to foxhunt and they should be able to point you in the general direction of the problem within minutes. If the effects are as localized as they say it should be able to be pinpointed within an hour.
I would start with just listening broadband with an SDR for a while, just to see what's really going on. Something ought to become visible in the spectrum, at least intermittently.
Once you get the pattern, you could simply move around and measure the relative intensities, map the numbers, and the epicenter ought to become more or less obvious. Then close in with the SDR, watching the levels on the screen, and hopefully you will walk right into the culprit.
An RTL-SDR is a few bucks on Amazon. The software is free. The only other thing you need is a laptop.
For those who need a more concrete example here is a guy who found a power pole that was malfuctioning doing just that, with an odroid, 5x rtl-sdr dongles, and a gps acquisition device.
Would work just fine with a single dongle, a laptop, and a usb gps device or cell phone, just would have to do a few more drive arounds in different frequency bands.
Can you write this up please - I have lived my whole life with these mysterious radio wave thingamijigs suffusing my world and ... I just don't know how to detect them. TV signals get fuzzy, my loudspeaker crackles just before my phone rings, but being able to deliberately reach out and map them seems almost like magic.
If you can, I'd suggest spending a little more on either an RTL-SDR with a built-in upconverter (~$30 on AliExpress) or an SDRplay RSP1A ($120 from Ham Radio Outlet). An upconverter allows the RTL-SDR to operate in the crucial bands below 30MHz; the SDRplay RSP1A has vastly better performance and will pick up all sorts of signals that an RTL-SDR won't. The RTL-SDR is a really cool and very cheap introduction to radio, but I think you might outgrow it fairly quickly if you're technically-minded and have a serious interest in radio.
I'd also suggest seriously considering getting an amateur radio license. It isn't difficult or expensive in most countries, you'll learn a lot about radio in the process and you'll gain the right to transmit on a wide range of frequencies. The /r/amateurradio wiki is a useful starting point.
You don't need an upconverter to receive HF on the version shipped by rtl-sdr.com; it supports it via direct sampling mode. I've listened to plenty of shortwave broadcasters and hams using it with a random wire antenna.
I did recently get an rsp1a as an upgrade once I realized how much fun I was having. It seems better at rejecting noise but otherwise isn't that different than my rtl-sdr. I need to get a windows install so I can use sdruno instead of cubicsdr, though.
While the upconverters are nifty if you're not in a pretty rural area or going to do some serious antenna work you'll be heavily limited by conditions at <30Mhz.
+1 on looking at getting a license though. It opens up a whole new world of experimentation and capabilities. Even on 2m I still get a kick covering 80-100mi with our local repeater network.
Seconding this. Get their kit with the dongle and dipole antennas for VHF and UHF, plus optionally an antenna for HF. Just plug it in, make your antennas the right length for the spectrum you want to explore, and fire up SDR# or CubicSDR to see what signals are present.
In addition to the rtl-sdr site mentioned in a sibling comment, the stuff provided by https://greatscottgadgets.com/ is well worth looking into. I attended his class at Blackhat and it was a blast.
> my loudspeaker crackles just before my phone rings
You can do nothing about it. What you are hearing is the beginning of a GSM transmission. GSM frequencies are well-known to be easily picked up by audio circuitry. Switching to LTE should solve it.
GSM “buzz” occurs with GSM (TDMA) phones,” he said. “It is when the phone is communicating with the tower on the GSM control channel, which is not power regulated and can be as high 1 watt, depending on the phone model. It is pulsed data bursts and does not happen on the LTE side (the reason CDMA phones remain relatively quiet).”
Phones using GSM standards cause most buzzing. Phones using LTE and CDMA rarely do. GSM networks are less common than they used to be, but are still ubiquitous, and even non-GSM phones may “step down” to other networks for various reasons.
The Motorola iDEN (Nextel) protocol was very GSM-like in some ways, but the reverse control channel was even louder, and the modulation even harsher. A Nextel in the audience was every live sound engineer's nightmare.
You got plenty of good advice, so no need for me to add to it.
But once you get the right gizmo plugged in, and the right app running on the laptop, it's literally as simple as walking around looking at a spectrum graph. Sure, you can do more fancy stuff, but for the basic level that's it.
Specifically, $27ish dollars shipped, and basically the cheapest still reasonable way to get into SDRs. Receive only though, so while you can explore the spectrum below about 1.9ish GHz, you can't play with it
For a more capable model, I would recommend the ADALM PLUTO from analog devices.
It's ~$150 USD (if I remember correctly)and has a range of 385 to 3800 MHz @ 20MHz bandwidth, but a very simple hack increases it to 70 to 6000 MHz range @ 56MHz bandwith. Check here for more info on the hack: https://www.rtl-sdr.com/adalm-pluto-sdr-hack-tune-70-mhz-to-...
Having just switched to an RTL-SDR.com from a myriad of cheap ones, I'll say that yours will get you started but picks up a stack more noise. You'll also want a better antenna.
For those of us who have been on an actual foxhunt, it isn't often the matter of an hour for something of this sort. It is operationally tricky to do this.
OP said that the fox would be mobile and not transmitting all the time. You said the fox was static, but had three 10 db steps in power and periods of silence. 10 db steps in power would trick lots of hunters into suspecting mobility and periods of silence is exactly what op said. I can't imagine why something so close would elicit such a dismissive "so no".
