2.4 Ghz Field Strength Meter With Sound Output

[Flaps 30]

Hi guys.. Someone has talked me into giving a talk on aerials (antennas to some people) later in the year. Using 2.4 Ghz will enable me to build a nice bonsai aerial farm to demonstrate the characteristics of various types of aerials without having huge arrays of metalwork around me.

The ideal would be to use the DJT module (on the 9x) as an RF source. It is fairly easy to knock up a simple 2.4Ghz sensor system. The ideal would be to feed the output of the sensor into an audio amplifier so the audience can hear the signal. This depends upon the form of modulation that is used of course. So has anyone actually listened to the output of a Frsky DJT module and if so is it usable in this situation?

Of course any other suggestions are welcome.

[jhsa]

The ideal would be to use the DJT module (on the 9x) as an RF source. It is fairly easy to knock up a simple 2.4Ghz sensor system. The ideal would be to feed the output of the sensor into an audio amplifier so the audience can hear the signal. This depends upon the form of modulation that is used of course. So has anyone actually listened to the output of a Frsky DJT module and if so is it usable in this situation?

Of course any other suggestions are welcome.

Take a Taranis instead. You can hear the RF very well on it's speaker. And no need for an extra amplifier as it is already quite loud

[Bill]

I was going to recommend wi-spy which used to cost about £50-60 but now I see the price has gone up to over £200+.
I bought one a couple of years ago it displays the spectrum on a PC, listening to the signal would probably be nothing but a hiss or buzz, not terribly useful.
I could probably loan you mine if its just for a club demonstration.

[Flaps 30]

Yes it is for a club demo at the back end of this year. Thanks for the offer Bill it's much appreciated. I do have enough time to construct something from the junk pile that is full of failed and unfinished projects that can be put to good use in this project..

I keep thinking that somewhere on a Frsky receiver there might be an RSSI/AGC output that could be tapped for use.. Yet another line of investigation to take up my time.

Looked inside the old Turnigy RX that was supplied with the 9X which is now spare. It uses the A7105 transceiver chip which happens to have an RSSI output on pin 1. Further work on this in a day or so. Could be interesting. All I have to do is to find the Turnigy TX module that was last seen under my bed, which will complete the system.

[Kilrah]

I keep thinking that somewhere on a Frsky receiver there might be an RSSI/AGC output that could be tapped for use.. Yet another line of investigation to take up my time.

I'll save you some time, there is none.
RSSI is only available digitally as a register you read through the RF chip's SPI interface.

You could use an arduino and simply base yourself on the RSSI/TSSI value available on the serial port though. Or modify the Taranis' vario code to put out tones based on the RSSI value instead of the vario

You can do anything you want but will have to do it programmatically, no way with "good old" analog techniques.

[Flaps 30]

Ohh!! ,,, The data sheet says - "A7105 has built-in 8-bits ADC do RSSI measurement as well as carrier detection function". Maybe that is enabled by so coding.

I love good old analogue. No nasty bits to lose.

[rperkins]

It isnt sound but if you wanted to show the frequency hopping and the amplitude of 2.4 ghz signals

http://www.ubnt.com/airview
http://www.youtube.com/watch?v=-LX-Hk9vAzg

additionally if you fire up the java based software that comes with the dongle it makes a connection to a serial port. by monitoring that port it appears to be sending some rssi values for a range of frequencies. pick your freq, average them together or whatever then pipe that number to a program that plays a sound based on the number. Yea I know. It's sorta out there

Code: Select all

rperkins@zotac:~$ cat /dev/ttyACM0 
-100 102 -96 -99 -101 100 -100 51 -103 98 -100 99 -86 99 -99 102 -80 -69 -100 -87 -99 -100 -100 -100 -101 -99 -100 -99 -102 -103 -98 -99 -101 -100 -100 -69 -99 -100 -101 -102 -70 -95 -100 -101 -80 -98 -93 -98 -101 -101 -98 -96 -100 -100 100 -95 100 -98 98 -101 -99 -98 94 -99 -96 94 -97 100 -100 94 -98 96 -98 99 -98 -97 100 -99 97 -89 96 -99 -98 -98 -95 -100 -89 -98 -97 -98 -83 -100 -99 -102 -100 -99 -84 -100 -99 -98 96 -83 -93 -94 -97 -94 -98 -99 -99 -100 -96 -99 -98 -83 -98 -98 -97 -100 -98 -99 -98 -101 -99 -99 -98 -100 -98 -98 -101 -99 -100 -97 -99 -100 -99 -99 -97 -100 -98 -101 97 -100 99 -84 99 -100 100 -99 98 -102 -100 
scan|0,100 -101 -99 -99 -99 -99 -101 -91 100 -103 -101 -103 -104 -102 -61 -102 -100 100 -90 100 -99 100 -100 -101 -100 -103 -94 -101 -101 -101 -47 -100 -102 -103 -99 -73 -99 -100 -101 -99 -101 100 -87 79 -100 -101 -71 -99 -70 -101 -99 100 -98 -101 100 -102 -101 99 -101 96 -104 83 -100 99 -102 -99 98 -100 98 -99 -84 -98 -95 -99 -98 -101 -100 100 -98 97 -98 -99 -84 -97 -97 -99 -100 -99 -100 -99 -101 -82 -100 -82 -100 -99 -89 -97 -100 -84 -99 -100 -99 -98 -100 -98 -97 -102 -99 -90 -99 -98 -99 -101 -96 -84 -94 -101 -101 -103 -93 -98 -99 -101 -100 -98 -95 -97 -76 -79 101 -100 -83 -82 -97 -99 -100 -93 -98 -99 100 -99 -99 -100 96 -99 98 -101 99 -99 101 -99 98 -99 -100 -100 97 -98 -102 -100 -101 -99 -102 -101 -99 -101 -85 -96 -98 -99

[Bill]

Wouldn't the RSSI detector on the receiver, even if you could get it out, only give the computed signal strength as a single output with no indication of the spectrum spread of the 2.4, surely that would be the point to show how the signals are distributed over the band? Hopping vs DSM2 etc how DSM2 can't actually avoid other signals like 2.4 video that's a good demo!

[Flaps 30]

Thanks rperkins and all... The talk is all about antennas and what not to do with them and how to spot a Lemon. All this hopping stuff and related items are outside the scope of the talk.

Having looked at the RSSI side of the RX it seems that it isn't much use when working close in. So now I'm waiting for a few items to arrive before I start building up something that can be used for this event. I may try it for fun later on.

In the good old days of 27 Mhz it was all so simple with amplitude modulation and (in my case) high power levels to drown out the American CB stuff way back when we had real highs in the Solar cycle. Knocking up a meter to measure the RF field and produce an audio output was easy. Mind you it may be just as easy with a nice forward biased microwave diode and a few magic bits.

[kaos]

flaps30:
here is a video showing what not to in placing your rx. in the video the satellite rx was close to the ESC (not the main rx) which created all kinds of havoc.
https://www.youtube.com/watch?v=tEnC8MNbbqE

[rperkins]

Good luck with your talk.
I'll be looking forward to the utube video