Software Defined Radio talks

Today at the ARNSW Home Brew Group, we had two talks on Software Defined Radio, one dealing with VHF and up, the other on HF. First here's Gary, VK2KYP, who kindly gave me permission to post this video. Gary has previously purchased a FunCube dongle but finds a $20 DVB tuner works pretty well and is great value.



And here's Stephen, VK2BLQ, on HF SDR:

Feld Hellschreiber QRP beacon with arduino

I have been using a digital audio recorder to provide Hellschreiber test signals but this is clearly silly. So, thanks to Mark of the fabulous brainwagon blog I now generate test signals with an Arduino.

The Arduino sends port 13 (the one with the on-board LED) high and I use it to turn on a transistor to pull my final low. Off air locally it looks pretty good and the drift is quite mild.

I'm still running milliwatts with my big 2N2222a final transistor but Stephen, VK2BLQ can hear me 10km away fairly well over the noise. Here's how I look at his place:

On Sunday, November 25 2012, Stephen and I gave a little presentation about all this at the ARNSW Home Brew Group meeting at Dural NSW:

How to fix poor iPhone battery life

My iPhone 5 wasn't making it through the day. I was disappointed, but after a few simple changes it looks like it could even last two days.

My usage pattern is that I charge over night, get up at about 6am, listen to podcasts for an hour going to and an hour returning from work.

During the day I make a few calls, and use a lot of Wifi data. On the way home I use a bit of LTE cellular data to catch up with news feeds.

With the changes below, as you can see from the Usage screen to the right, after 11 hours without a charge my battery is still at 74%.

Long life suggestions

• Avoid polling for email. I was polling for GMail every 15 minutes, I switched to the GMail client (as I use Exchange for work email). So mail is pure push and it's instant.
• Turn off LTE unless you're in a good LTE reception area and actually plan to use it. LTE is very patchy here and I've noticed the phone running hot in my pocket trying to contact cell towers.
• Screen brightness under 50%.
• Choose a carrier with good strength at your home and office. Phones turn up transmit power is signal strength is low.
• Reset network settings: Settings>General>Reset Network Settings. I'm a little sceptical about this one but it forgets all those Wifi networks you've used once and stops the phone trying to join them again, unless you specifically want to.

Using Push instead of polling is the big one I think. Push is very efficient, it's a single TCP connection to Apple which all notifications come over (so I don't believe the number of apps that can push will make much difference).

Incidentally, all those tips you see about quitting applications that you aren't using are nonsense. iOS will only allow them to background for 10 minutes and then only for specific tasks like completing a download. The only exception is playing audio which you want anyhow.

Before the iPhone 5 I had a 4 (not the s). The battery was losing capacity after almost two years of daily cycles. The solution was to pay $9 for a replacement battery on eBay. It came with the tiny screwdriver and there are instructional videos on YouTube. It's easy and cheap to do.

I hope this clears up some mis-information I see around the place. Let me know how you go.

Update

Here's how my phone looks after 27 hours of not being plugged in and normal use for me. That includes quite a few hours of internet and podcast listening but no tethering. If you think you have a problem it would be useful to compare your usage with mine by the time you drop below 20% battery.

Feld Hellschreiber QRP beacon test

Stephen, VK2BLQ, and I continue to experiment with Feld Hellschreiber and I'm pleased to say that next Sunday, November 25th, we'll be presenting to the ARNSW Home Brew group meeting at Dural.

Today I did a test transmission with this little setup:

I've recorded "this is a test transmission from vk2tpm" on a digital recorder which is driving the simple audio keyer to key a two transistor QRP CW transmitter on 7027kHz.

Stephen is about 10km away as the crow flies:

He demodulated me like this:

Not great but amazing considering my transmitter. Come along next Sunday and we'll try to demonstrate across the room.

Red Blue 3D maps from Nokia

I'm a bit of a 3D fan. Nokia has a maps web app at here.net, somewhat like Google and Apple's and it has a unique feature of displaying in red/blue 3D. Here's a shot:

The view is somewhat similar to that which you get from Apple's map, clearly taken from a low flying plane. It's great to see some competition in the maps business.

Pixie 2 based Feld Hellschreiber transceiver

I've figured out that my keying of the CRK-10 CW transceiver is flawed and that I'm not shifting frequency so I've decided to start work on a dedicated Feld Hellschreiber transceiver based on the popular Pixie 2 design.

This clever little design uses the output transistor as a mixer during receive and my modification is to key it with rectified audio from the computer. It's putting out a very pleasing little signal (barely moves a power meter but thats fine for a mode like this) but my audio keying circuit needs work.

Digital QST now available via iPad app

I switched from a paper subscription to the ARRL's QST magazine some months back and have been distressed about the poor experience of having to read it through a terrible web based copy protection scheme.

Just noticed that there is now a QST app for iOS that makes it considerably more pleasant to read.

It's better but still pretty clunky. This feels like the output from some sort of cross platform publishing system. User interface buttons look alien. It surely should be in the Apple Newsstand and should use Apple's subscription system.

QST is laid out for print and it needs to embrace digital publishing by letting us read articles as tall scrollable streams rather than two or three columns of text.

It seems that it's published as images of the page, which makes it big and slow. While there are links, such as from the contents page, there is no text search. (In the end I'll want to search my whole collection for a phrase).

This is a good step in the right direction but it still needs work.

Tiny CW transceiver for Feld Hellschreiber

This morning I had a Feld Hellschreiber contact with Stephen, VK2BLQ on 40m. Here's how he looks to me:

And here's how I look to him:

Comparing the two waterfalls above I think I have too much RF gain which is leading to a noisy receive display.

My goal here is to be able to use a very simple, very small, CW transceiver with a digital mode. Next step is to get an audio driven keyer working.

Update

I've now got this working with the tiny CRK-10 CW transceiver via a simple audio keyer interface.

I'm using a little USB audio adapter and then you can see my simple audio transformer, full wave rectifier and 2N2222a transister to key the CRK-10. In the video below I test transmitting into a dummy load.


Stephen wrote "Good to work you on 40 Hell again.

The CRK10 has a very narrow filter, I was calling you back on 7030 several times, but not until I QSY to 7131.2KHZ that you heard me.

Your RST was about S3-5 but letters were good. Goes to show a microrig and pc  has possibilities.

The narrow filter kills the noise and makes the letters clearer.

I dug out  a couple of older T/R  boxes to mod for keying the tube TX directly. Don't think a relay is fast enough and is noisy. I'll use a powerfet rated for 100v and 1 amp as the Cathode current is 100mA and key up volts is quite high."

Here's how the QSO looked to me:

So aside from the fact that I'm off frequency, my reception is superior to my main rig.

Here is the simple keyer circuit. Small signal diodes, a 2N2222a and a few 0.1uF caps. The transformer is a little audio transformer, not sure what ratio.

I added a 3.5mm socket to the CRK-10 and connected it to the top of C22 where the transistor pulls low to key the carrier.

Thanks again to Stephen, VK2BLQ, for all his help at the other end but it looks to me that a truly minimal Feld Hell transceiver is quite practical.