SpectrumView app -137kHz QRSS3?

Many years ago I downloaded this free app on my Apple Touch. I see it is available for the iPhone too, so I have downloaded it. It is a spectrum analyser for audio frequencies and you can record up to about 150 seconds of audio on a spectrogram depending on the settings. 

I was thinking of trying this on QRSS3 with my 137kHz beacon locally. It would take the audio from the FT817 and produce an audio spectrogram. I am not quite sure how I shall do this yet.

 

The app is created by Oxford Wave Research Ltd. It is a most useful app and highly rated. I last used an earlier version in 2013, so I have to re-learn it and see any changes made. 

I was quite surprised to still find it, wondering if the company had long gone. The app is still free.

See the Apple app store for details.

It is not available as an Android app as far as I can tell.

Nanowave over the horizon tests - nearly ready

Original optical beacon

Just about ready now to restart my optical non line-of-sight tests again using my 481THz CW/QRSS beacon and a choice of 2 sensitive receivers. I'd intended to go out this evening but (a) the XYL needed the car to go to her choir and (b) the fog has descended!

Optical beacon capable of continuous subcarrier (choice of freqs) or QRSS/CW

SpectrumView in action - it's brilliant

The beacon design needs to change somewhat: currently I can TX either QRSS3, QRSS30 or CW at around 830Hz subcarrier, using the IRF640 fed directly from my K1EL keyer IC. However, I cannot actually send just a 830Hz tone continuously. This would actually be very useful when aligning TX and RX over a non-optical path e.g over a hill. So, when the grandchildren go home on Sunday I'll make a modified version of the beacon keyer so that I can choose a number of subcarrier frequencies, including some lower than 830Hz (detector sensitivity is greater at lower audio frequencies) and also add the option of a continuous subcarrier signal. This will involve adding a 4060 based oscillator and divider to be keyed by the K1EL keyer IC. So, it may be next Tuesday or Wednesday before I actually start testing again.

I also want to optimise the use of the iPod Touch 4g as a handheld audio spectrum analyser. I have used it for this sort of test before using an excellent package available free called SpectrumView (see screenshot) available from Oxford Wave Research. With a laptop PC, running Spectran, the problem is the brightness of the screen which emits an interfering optical signal. With a tiny iPod Touch it is much less bright and can be held in the hand. Unfortunately the bandwidth can't be screwed down as narrow as with Spectran on the PC, so there will be S/N limitations. One test will be to see how far away I can detect my beacon (about 0.5W into the LED) over the horizon using just the optical receiver and the iPod Touch.

The beauty of 481THz (red light) work is the kit is simple: everything that matters is at audio frequencies and can be built and tested with the simplest of test gear.

iPod Touch external audio - success!

Thanks to some input from Robin G7VKQ I have now managed to get an external mic to work with my iPod Touch 4g. He referred me to http://www.blackcatsystems.com/ipad/iPad_iPhone_iPod_Touch_Microphone_Wiring.html which shows that a resistor to ground is needed to make the device recognise the external mic is in place. In the end I found a couple of ways to make the connection work (shown below).

When used with the Spectrum View app from Oxford Wave Research I was able to connect my lightbeam receiver to my iPod Touch 4g and record QRSS3 and CW transmissions. This is 10wpm CW being received at home between rooms by scatter in broad daylight.

iPod Touch, SpectrumView and external mic input

A few days ago I mentioned SpectrumView as being a very useful package for the iPhone and iPod Touch 4g for audio measurements and spectrum analysis. Well, I've now got a 4 pin jack plug and wired it up (according to the best published data I can find) as an external mic input. To my great disappointment nothing happened and the internal mic was still being selected. I am wondering if something has to be asserted to select the external mic input? Anyone know please? What did I do wrong? The ring nearest the jack body is the mic input and the next ring down is supposed to be the ground. I checked the plug was correctly wired. Help!

SpectrumView for iPod/iPhone

SpectrumView 0-24kHz displays of waterfall and spectrum

Looking around for useful (free) software to help me with VLF and lightbeam tests I came across SpectrumView yesterday. This is a fabulous application for the iPhone, iPod Touch and iPad which provides a 0-24kHz spectrum analyser and a waterfall display.  The app is produced by Oxford Wave Research.

To make best use of this I need to connect an external audio input into my iPod Touch 4g.  A 4-pin jack plug when inserted, rather than a 3-pin one, allows an external audio input (or a mic) to be connected so I can feed my VLF receivers, used for both 8.7-9.1kHz earth-mode comms and for lightbeam baseband/sub-carrier detection, directly into the iPod.  Resolution will be down to around 2Hz at best, so this will be of somewhat limited use, but certainly easier than a laptop for quick field tests or quantitative measurements.

The mic input (on a 4-pin jack) is on pin 4 (nearest the plug cover) and the ground is the next one down the connector (pin 3). The tip (pin 1) and pin next to the tip (pin 2) are the two audio outputs for a headset.


UPDATE 16.3.12: to tell the iPod Touch 4g that an external mic is connected you seem to need to have a 4k7 resistor to ground across the terminals. See later post for details.