Monday, June 29, 2020

Interviewed on ABC Sydney

A pleasure again to be a guest on ABC Sydney breakfast with Robbie Buck and Wendy Harmer. I was on to talk about the Apple World Wide Developer Conference announcements but the interview covered a wide range of topics in the end.

My bit is in the audio here but you'll need to spool right through to about 3 hours and 26 minutes.

My internet here hasn't been connected to cable yet so unfortunately I'm on the phone. Re-scheduling the NBN connection is a story in itself.

My thanks as always to the hard working producers Stephen and Yuske for thinking of me in relation to one of my pet topics.

Vinyl record stores in Thornbury

We are settling in to our new home in Thornbury, Victoria. We're out of the rental place in Alphington and happily new tenants were found to take over the lease.

Each day I walk around the area and one thing is striking - there are lots of vinyl record stores plus shops with record players and even loud speaker repair is available.

Wednesday, June 17, 2020

On ABC RN's Download This Show

I haven't done a Download This Show since social isolation and also moving to Melbourne so it was fun to see how the technology has changed.

The (full) radio version goes to air a few times on ABC RN and one of the stories is shown on ABC News24 TV. You can see it here:

Initially I set myself up on an office connected via Wifi but we had audio problems and so I had to quickly re-locate next to the cable router and connect with ethernet. Video was recorded locally with an iPhone SE 2020 set to 4K 24fps and it looks passable on a big screen. Amazing what a phone's selfie camera can do these days.

Always good to talk with Marc and great to meet Sarah Moran who is based in Melbourne, where I now live.

Saturday, June 13, 2020

Honest and dishonest reviews of the Spy Gear walkie talkie

Facebook's targeted advertising knows me too well and lately it's been repeatedly showing me ads for a pair of transceivers priced at just AU$15.

I wondered what frequency they are on and if they might be moved to a ham band just for fun.

When I was young my dad bought me a pair of 27Mhz transceivers and these were absolutely fascinating. All sorts of hide and seek games were devised where the hidden person could talk with the searchers and taunt them. CB was popular at the time and sometimes trucks could be heard and even remote stations in the evening.

Drilling in to the reviews on Target's web site soon reveals the truth...

But wait... there is one (incentivised) reviewer who really loves this product!

Peter, VK3YE, tests an even cheaper pair of transceivers that seem to operate better than the Spy Gear ones from Target.

Great work Peter. I would be interested to see the circuit traced out.

Currently preparing to move house here. All antennas are down and looking forward to the new QTH.

Saturday, June 06, 2020

Radio communication with friends in NSW

I'm now 709km away from my ham radio buddies in Sydney. Propagation is not great and my antenna, for the next few weeks, is a very poor end fed hanging out the window.

Stephen, VK2BLQ, is humouring me and we've been trying to establish digital radio communications via 40m.

We can hear each other on WSPR, best reception was -6dB. We tried Olivia 8/250, Stephen could decode me but alas, I can't decode him. Presumably the noise floor here is too high.

Now we're trying JS8call and we had two-way communication for a short time this afternoon. The software was already in the Ubuntu software library so installation was a breeze.

The software's user interface is rather mystifying at first but after filling in your call and grid square, the trick is to wait for a call to appear on the right, click on them, enter text in the middle box (it says "TYPE YOUR OUTGOING..." and then press the Send button.

There's also a bunch of common messages in the "Directed to..." popup button.

Also, of course, you can call CQ and happily there is some activity here (unlike PSK which seems to have died).

Thanks VK2BLQ for your help with this. JS8 is more interesting to me that FT8 as you can at least have a bit of a chat with it.

Monday, June 01, 2020

Settling in to Melbourne and Joining MERC

Moving back to Melbourne after 30 years in Sydney means that I was keen to make contact with ham radio people here much as the group from the ARNSW Radio Experimenters group has become a circle of good friends in recent years in Sydney.

I joined the Melbourne Electronics and Radio Club (MERC) and was quickly and kindly welcomed by President Stuart, VK3SH and treasurer John, VK3ZX.

The club has four regular nets each week and I've joined the Wednesday & Friday nets at 8pm which are FM via the VK3RML repeater on 146.700. That repeater was down and so the net moved to a repeater on 438.225. This is good as I have much better reception of this one anyhow.

Stuart kindly sent me five recent editions of the excellent "MERC Almost Regular News Letter" which has a good sprinkling of home brew radio construction including antennas, filters, audio amplifiers, antenna switches, and also some wonderful shack photos.

I look forward to pandemic restrictions being eased so we can meet in person.

For now, I have a minimal shack set up.

I look forward to the day when all transceivers have a single USB socket with both audio and control over USB. It will make computer connection much less messy.

Saturday, May 23, 2020

Virtual audio cable for macOS

Forgive me if this is old news but on Windows I've long used the excellent and free VB-Cable from VB-Audio Software for piping audio from SDR# into WSJT-X.

I mostly use macOS and Linux but for some reason SDR# seems to be the SDR software I like the most and it only runs on Windows.

A 2012 MacBook Pro is used to dual boot Windows for running this stuff as you see above right.

Today I noticed that there is a version for macOS and so far it looks good. (The software is free but "donation ware" and I've send them US$10 in appreciation of the macOS version).

A new device simply appears as an input and output device and settings are available in the Audio MIDI control panel.

I'm aware of Rogue Amoeba's Loopback but it is US$109 and seems more complex than is needed for this basic task. Their other software is excellent though.

Tuesday, May 19, 2020

What WSPR signal to noise ratio is needed for sideband to be intelligible?

The end-fed antenna is working pretty well on 40m and I'd love to have a contact with Sydney friends. John, VK2ASU, kindly agreed to run a WSPR beacon so I could find the best times to receive him.

Over a 24 hour period, with him transmitting just 10mW, the best SNR was -21dB here.

My question, to the brains trust hopefully reading, is what WSPR signal to noise ratio would be enough such that a higher power sideband call would be audible?

I have read that a signal to noise ratio of 6dB is needed to be able to copy SSB.

John is transmitting 10mW which is 10dBm but he could run 100W on sideband or 50dBm. An extra 40dB.

If the bandwidths were the same then -21dB + 40dB = 19dB of signal to noise but while SSB is about 2.5kHz wide, WSPR is much narrower, perhaps only a few Hz?

Here is the SNR between VK2ASU and VK2TPM (portable VK3).

Spots from all stations to me looks like this:

Any insights or pointers gratefully received.

Kevin, VK2KB, commented: "My understanding is the noise power doubles every time the bandwidth is doubled while the power level of the received signal stays constant. I've verified this on my SA by changing the bandwidth of the SA response and noting the noise floor, you can see the floor decrease by 3db every time I halve the  SA  window but the amplitude of the signal I'm watching stays the same.  With WSPR you need to know what the effective bandwidth is. I had a look at this site:

They say the effective bit rate is about 1.5 baud  and its possible to recover a wspr signal at -34 db  on a 2500Hz bandwith rx.

Say that you are using an effective bandwidth of 1.5 Hz to recover the digital signal the ratio of 1.5/2500 =  .0006 or -32db  Because the wspr signal is coherent I think they get a few more dbs in the demodulation process.

The difficulty with this is however the power bandwidth of the wspr signal vs the power bandwidth of the ssb signal.  Anyway something to spend time on."