Monday, July 13, 2020

New antenna for 144/432Mhz now up on the garage

I'm very happy to report that my antenna drought is over. Today, Khan, The Antenna King mounted my 2m/70cm vertical on a pole on the roof of the garage.

Previously I had tried to get someone to put it on the roof of the house but it's a two level roof with very steep sides and, apart from being dangerous for the installer, it would have been impossible for me to get up there to do any maintenance.

Mounting the antenna on the flat roof of the garage means it's easy to work on. The drawback is a longer coax run. Tests so far show excellent signals from repeaters around Melbourne.

Currently I'm running WSPR and only hearing VK3DXE. I'm transmitting 10W and so far no one has spotted me.

The focus for now is 2m but I've also run two pieces of RG58U out to the back yard with the intention of adding a 20m dipole and whatever else I can come up with in very limited space.

Great book: "Radio Girl: The story of the extraordinary Mrs Mac"

I'm currently enjoying "Radio Girl: The story of the extraordinary Mrs Mac, pioneering engineer and wartime legend" by David Duffy. It's a terrific story of early radio in Australia and the remarkable career of Mrs Mac, the first, and at the time, only female electrical engineer in the country.

Mine is the Kindle edition but it's also available in Paperback.

Peter, VK3RV, (fellow FreeDV enthusiast) mentioned the book when we spoke recently. Thanks for the tip!

Saturday, July 11, 2020

macOS Big Sur is going to need larger screens

Apple has released an early version of the next macOS known as Big Sur. When I ran it on a Mac mini with my normal 4k screen my first thought was that I had the screen resolution wrong. Here's the current macOS "Catalina":


Here's the new "Big Sur":


As you can see, the dock is the same but the user interface elements in everything else is more spacious. I tried setting the screen resolution to the next sharp option and it was too small.

I like the new look. It is more consistent with iOS. I do like using small laptops though and I hope there's a way to scale back the size of elements a bit.

Both iOS 14 and macOS 11 betas seem much more stable than the versions released at this stage last year. Happily my apps work fine and even build for Apple Silicon without any obvious issues.

Update: my mistake, Catalina was scaled.



I didn't realise that I had my Catalina OS set for scaling to show more. When I tried scaled options under Big Sur they all look more blurry than what I see with Catalina. (You'll need to click on these to enlarge them).






Wednesday, July 08, 2020

Lots more VHF activity in Melbourne compared to Sydney

Since moving to the new home here in Melbourne I've been trying to get some antennas up. I've purchased a vertical for 2m and 70cm but so far two antenna installers have not been keen to climb on the roof here and put it up. One says he'll come back when the weather has been dry for enough time for the metal roof not to be slippery.

In the interim, I've mounted a painter's pole to the fence and put the vertical up in the back yard.

I sat outside last night (a Wednesday) and listened around on 2m. Amazing amount of activity compared to Sydney - perhaps it’s because Sydney is very hilly and not so good for VHF.

From 20:00 there was an active net on 147.250 FM. Peter, VK3RV could be heard direct! I heard the WIA news broadcast on 147.175 FM. At 20:20 I tuned to the MERC net on 146.700 FM.

I've read that there is an SSB net on 144.100 and I listened and called at 20:30 but heard nothing.

Tuning around I found an active net on 144.150 which VK3MQ referred to as the “150 net”. I could receive VK3MQ very well and when he moved his beam he came up to S9. No other stations were strong though.

It wasn’t freezing outside last night but not an ideal operating position as I have to bring the gear in after use in case of rain.

While out getting some permitted COVID exercise this morning I noticed this amazing antenna on Clarke Avenue, Northcote. I will try to figure out who it is.


Something to aspire to? I'll be happy if I can get coax from my radio room to the back yard for a small dipole.

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:
https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software)

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."

Saturday, May 16, 2020

Townhouse antennas

My first antenna in the rental townhouse was a dipole for 20m which has been working pretty well. The challenge here is that the windows seal tightly and it's not possible to run coax through them so I had the balun inside and the two legs of the dipole stuffed through the window seal.


One leg ran straight out and the other around the corner to the left. The KX3 tuner is excellent and could match this quite well.

Today I visited Jaycar and purchased some iron powder toroids, some wire and a soldering iron (all my electronics is still in storage). I constructed a QRP 9:1 Unun. (Three turns to 9 turns).


The end fed wire goes out through the window, around the corner, over a citrus tree and is held on the side of the clothes line. This now tunes up well on 20m, 30m and 40m.

Compared to the dipole WSPR reception has worse signal to noise but the addition of extra bands, particularly 40m, makes it a much better option. I'm receiving well and transmissions on 40m are getting out quite well.


I did notice that a ceiling fan turned itself on after I'd been transmitting and I'm worried about affecting TV reception so I'll be receiving mostly until I test that. Amazing what WSPR can do even in very challenging circumstances.


It's Sunday morning and I've been able to listen to the 40m broadcast from South Australia and also from Dural near Sydney. Here's a snippet. It does fade up and down but is mostly audible.


Saturday, May 09, 2020

Moved to Melbourne

We've now moved in to a townhouse in Alphington which is north east of Melbourne. It's much smaller than our home in Sydney and even though we still have stuff in storage it has been a bit of a struggle to downsize enough to fit in.

The area is nice and I've enjoyed walking along the river which is nearby and through some lovely park land.

In the photo above you might be able to make out the yellow wire which is one leg of a dipole for 20m. It's a bit of a challenge to run cable to the antenna as the sliding glass windows seal tightly. Currently I have a balun inside and run the two legs of the dipole out through the window. It tunes up quite well but I'm sure the trees absorb quite a bit of the transmitted signal. WSPR works ok and I'm hearing stations around the world to some extent.


Unfortunately the power lines for the block attach to the corner of the room I'm using for my office so there's quite a lot of noise.

There's lots of FT8 activity visible but so far no contacts. I called CQ on PSK31 but nothing heard just yet.

Internet

The unit has Telstra cable NBN connected and I've arranged a transfer from Sydney. Even though I can see that the cable is active they want to deliver a new wireless router before we can use it. It's been mobile data for a few days but I plugged our Sydney router in and it works! This is handy as yesterday we were informed that delivery of the new router has been delayed beyond the promised date of next Tuesday.

Vale Tim Mills VK2ZTM

Sad news that ARNSW volunteer Tim Mills died this week. He's been a dedicated part of the NSW amateur radio community who I've seen every time I've been at Dural and often heard on the Sunday broadcast. Many years ago he was one of my first contacts when I put up a new antenna at Killarney Heights in Sydney.

Tim was always cheerful and helpful. He worked behind the scenes to keep everything running smoothly. I didn't know him much beyond saying hello and chatting about the sausage sizzle and other trivia but I know he was a big part of the organisation.

It's my birthday today and it's a big one as I'm now eligible for a seniors card. Only a few of my friends have kicked on but I guess it's something that will become more frequent as the years pass.

Australian COVIDSafe app source code

The Australian Government has released the source code to the COVIDSafe app for both Android and iOS. I have downloaded the iOS code and have been reviewing it.

The source code in Swift looks modern and well written. There are few comments but names are well chosen. (I suspect many comments and attribution has been removed).

There has been some criticism about how the app needs to be running in the foreground on iOS to beacon and find other users but this is not a complaint about the app but rather a deliberate limitation that Apple enforces. iOS can respond to beacons without an app running but this is done at the operating system level and it looks like that capability will be added in the next update.

The app uses a CoreData database to store timestamped records of beacons it has detected along with their signal strength and transmit power which can be used to estimate distance.

Communication with the Amazon server API is protected with SSL and certificate pinning, so you shouldn't be able to intercept them.

I think it is great that the Australian Government and DTA have released the source. (Of course, there's no guarantee that the code in the app you install is the same as the source code we have seen but I feel more secure that it probably is).

If you haven't installed the app, please do, but note that when you are near a group of people you'll need to run the app and leave it in the foreground for the duration of your encounter.

Thursday, April 30, 2020

Moving house after 25 years

We've lived in Killarney Heights for about 25 years (with a few gaps including two years in Hong Kong). It's a quiet suburb north of Sydney and was a nice place for young kids. 

During that time, I've become very friendly with some people in our street and beyond. (That photo on the right was taken before social distancing).

It's a conservative electorate. Tony Abbott was our federal member but he was thrown out by a large swing at the last election. The suburb has a very active Facebook group which is both funny and useful. There's also a satirical blog that sends up observations about the area but hopefully with a warm heart.

Moving house is an eye opening experience.


I've accumulated too much stuff over the years and during packing I can see the folly of my ways. I've bought the same thing multiple times after losing sight of the previous ones. I've bought things and never used them. Getting rid of things takes work. A few things were sold on line and the local Facebook group is a good place to get people to take away things for free.

In recent years the rubbish bin has been replaced with a smaller bin and the local tip is quite selective about what they will take, so it's actually hard to get rid of stuff.

Our kids both live in Melbourne so we're moving there. I will miss this area and my friends throughout NSW but if COVID-19 has taught us anything it's that video conferencing is a great way to chat.

I'll particularly miss my 40m dipole over the large gum tree at the back of the block here. I'm sure the antenna situation in inner-city Melbourne will not be as low noise.

Saturday, April 25, 2020

ARNSW Radio Experimenters Group meeting again via video

Since the COVID-19 isolation came in to effect, we've been having meetings of the ARNSW Radio Experimenters (Home Brew) group via a Skype meeting. Today we held the second "normal" meeting. (We've also been holding a few lunch meetings which are less structured and more social in nature.

Today we had Ali, Gary, John, Stephen, Colin, Kevin and Peter.

Peter, VK2EMU, was mentioned in dispatches on the most recent edition of the Soldersmoke podcast. He had been mentioned in the last episode as the builder of a power amplifier with 6 meters. A misunderstanding! It turns out that it's an amplifier for 40m that has six meters on the front panel. See below.


We had a pleasant chat about what each of us is up to that went for about an hour. I recorded the audio and you can hear it here.

I talked about a few topics of interest to home brewers including:

* QSO today interviewed VK3HN, Paul Taylor where he talks about home brew radios for SOTA.
* A recent podcast from Hackaday drew my attention to the fact that you can buy surface mount components in the form of a book. For example, here's one from Little Bird.

Today, I had the final radio operation from the current QTH. I listened to the Sunday broadcast on 20m with a small dipole in the front yard and participated in the call-back. Next stop is a small unit in Alphington in Victoria. It looks like there's a bit of a yard with a tree so I hope to throw some wire up shortly after moving in.

Tuesday, March 31, 2020

Class E PA for WSPR with home brew variometer in the antenna coupler

Ross, VK1UN and EX0AA, is a frequent traveller and likes to get on air with WSPR under challenging conditions including using stealthy end fed antennas deployed from a window from hotels or flats. Currently he’s transmitting in Bishkek, Kyrgyzstan and getting amazing results even on 160m or lower.

His current configuration is interesting in several ways, he uses an Ultimate3 Beacon from QRP-Labs to drive a very efficient home brew class E PA that is coupled to an end fed wire antenna via a coupler with a home brew variometer.

The Class E PA is designed for 12V and 10.09W which, with an IRF530, gives a MOSFET R of exactly 4 Ohms and the PI output network of exactly 4 Ohms input and output as well. 

Why not 50 Ohms?

These PAs are designed for a single series C from PI out and shunt L (variometer) to match to a long wire. Also, he has a decent 4 Ohm load that can be used to test stage one of these PA's operation at 4 Ohms. The main strategy with these PAs is that, if the antenna changes such that the input |Z| is different, he can change the series C and L on variometer very easily.


L4 is the variometer and the secret to easily tuning different end fed antennas. When Ross had a good match direct from the PA via a series L (FET match) and then series LC match to the wire with a lumped inductor, a change the the wire's |Z| required a lot of work calculating and re-winding a new toroid. A variometer is a low cost and easily adjustable alternative to a roller inductor and can be home built.


The other advantage is, that in a 4 Ohm PI out can use 50V SMD caps without exceeding ratings and can get all values unlike those available as 500V caps.

Ross has built versions for several bands but most recently a 160m version which puts out 3W at 5.75V with good results and has a near perfect D-S waveform and good looking spectrum.


DC power input is very modest and efficiency is about 95%.


Here's the PA.


Ross is well received on WSPR from his remote location. Here's the display in the new WSPR Watch for macOS.


Thanks to Ross for sharing this project with us.