Modify AM radio receiver to pick up radar-like ping?

I have a 173.5 kHz radio animal-tracking transmitter and a new radio receiver. But reception is terrible even at point blank range so I want to modify the receiver by simplifying it.

The transmitter doesn't output AM but outputs an even simpler signal, a ping, 50 milliseconds of carrier wave. It emits this ping 40 times a minute.

According to the transmitter manufacturer, the ping ought to be able to be picked up 40 km away but my VHF receiver (Baofeng) doesn't even pick up every ping at point blank range. The signal is totally lost at a mere 50 metres (or less) line-of-sight from the transmitter. I suspect that's because the receiver can't handle such a short pulse because it's optimised for AM voice communications.

So I want to simplify the receiver by adding and bypassing electronics (such as a big capacitor) to give the loudest ping sound. Help?

Or failing that build my own ping detector using components (such as aerial, tuning, and speaker) out of the Baofeng receiver. Something like this perhaps? http://www.high-voltage-lab.com/105/economy-radar-detector, but with a proper aerial and tuner?

 

> firstly ... did you err in the frequency you quoted ? is it really 173.5 kHz ?

Oops, sorry. 173.5 MHz.

> But the problem that I see is that you have a 50 msec burst of detectable energy every 1.5 seconds. So you will need to add external circuitry. A comparator monitoring the output (where ever you can get to on your receiver, maybe even at the speaker). The output of the comparator going into a pulse stretcher. So every blip of detected energy now results into a .5 to 1 second long pulse. The output of the pulse stretcher drives an LED, a sonalert, a toy monkey that claps its hands together, whatever it is that you want to have alert you.

A "pulse stretcher". Great idea. Ideal output for me would be a signal strength meter, so I can tell how far away I am from the source, but failing that a sonic ping.

> You will need some test equipment to determine the ambient noise level of your radio receiver, so that you know what to set the comparator detect level at. Or perhaps just make it widely adjustable and then try dialling it in by test and error to see what works best at various ranges.

Trial and error looks good.

 

So, would the simplest solution be Aerial to Tuner (from Baofeng walkie-talkie) to rectifier-amplifier transistor to capacitor to store up the power from the signal to a buzzer? Then the duration or loudness of the buzzer would give proximity to the source. There are buzzers that run off 3 to 16 Volts, 15 mA max 90 dB. The Baofeng runs off a 7.4 Volt battery.

I can't see how to do anything else because a 50 ms pulse is too low for the human ear to hear and 173.5 MHz is far too high for the human ear to hear.

 

They do sell one, but at $800 per receiver it's more than I can afford, and has a three month delivery time. I thought I could get away with the $46 dual band VHF/UHF receiver I bought - but on trying it out I can't, hence the idea of modification.

Have just bought a buzzer to try out with capacitor.