Wednesday 20 September 2017


I'm about to take a few weeks rest up in Bonnie M-Land. Since I always take the trusty FT817 on (domestic) holidays and am never far from an iPad or iPhone, I thought it might be fun to see if there is an iOS APP which could squirt WSPR signals out of my holiday antenna.

Sure enough, Federico, IW2MVI, has put together a terrific offering called iWSPR, which does the business. It is available for a reasonable fee on the App Store.

You can run iWSPR 'acoustically coupled' to your rig - but that is pretty much asking for trouble and it is so 1970s. I decided to look into lashing together a cable to connect the iPad to my '817.

Ordinarily, this wouldn't be a problem but for the fact that the '817 has no VOX on the DATA input and the iPad only offers an audio output. Consequently I had to derive a PTT signal from the audio output.

Federico offers such a circuit in notes supporting his software, using a FET to switch the PTT line. However, I wondered if a simpler solution would work.

I threw together this circuit, in which the audio output is rectified by a voltage doubler. The same idea is used by many other dabblers, including Alan Yates, vk2zay. I found there's plenty enough AF output from the iPad to generate sufficient d.c. voltage to allow the BJT to switch the FT817's PTT line reliably (in my case the transistor was a BC557).

The little circuit is designed to be used with my existing 'dead mice' interface, which is seen next to it here - there's an extra connection to the PTT line via the big ugly red 4mm plug (I was in a hurry).

The whole kit was tested here on the bench at home before we pile into the car for the drive north tomorrow.

Putting out a lazy 5 W on 20m I was easily able to get all over the place, before throttling back to a more conservative and appropriate 500mW.

I hope to contact you from Scotland, either on WSPR or (perhaps) on other modes.

...-.- de m(m)0xpd

1 comment:

  1. Have a good trip Paul. It was good to see another posting from Shack Nasties. 73 Bill N2CQR