Monday, September 30, 2019

Tiny KT0803K transmitter won't do ham bands

John, VK2ASU, tipped me off about these boards. It's a little FM broadcast transmitter that can be controlled via two wire interface from an Arduino (for example). The chip is a Monolithic, digital stereo FM Transmitter KT0803K.

I got mine for AU$4.87 via eBay.

Sample software to drive it comes from the manufacturer Elechouse, here.

The board will transmit from 58MHz to 134MHz. It seems to get a little unreliable at the edges, I guess a PLL isn't locking or something.

I had to slightly modify the library for it to compile on the latest Arduino IDE. It seems they'd defined some integer sizes that are already defined these days.

In the file FMTX.h, up the top add this line:

#define __TYPE_REDEFINE 1

This will stop the type defines from being processed. Here's my test code based on their example.

#include "FMTX.h"

float fm_freq = 134;  // Here set the frequency
void setup(void)
{
  fmtx_init(fm_freq, AUSTRALIA); 
}

Anyway, a bit of fun for $5 and it certainly puts out a decent signal on the FM broadcast band. Disappointed I couldn't have a QSO on a ham band with it.

Sunday, September 29, 2019

Amateur radio NSW meeting at Dural

A lovely day for a ham radio meetup. Great to see everyone and Dural is looking great with the amazing new antenna tower now in use.

Today was a trash and treasure and home brew group meeting.

The feature presentation from Gary was about microwave operation but we also had Bob showing an amazing ATTiny85 board, John on LoRa, Graham on a bus extender he made and then found on eBay (still great he made his own), and Colin showed his Clansman PRC320.

A NanoVNA was passed around and seems amazing for the money (as so many things do these days). I've ordered one for AU$60.

Here's a few pictures from the day.


Colin with a 10Kg radio:


Bob with a 10g computer



Graham with his extender cable:


Gary microwaving the audience.


John examines a microwave transverter from the Ukraine.






Monday, September 16, 2019

Antuino - first look at a "compact radio lab"

Ashhar Farhan, VU2ESE, creator of the low cost, excellent performance for the money uBitx and Bitx40, has a new gadget. A flexible test instrument in a single box called the Antuino. For US$99 plus optional US$10 courier shipping it turned up here in Sydney just five days after ordering.


It arrived well packed. A solid metal case, fully constructed (for some reason I thought there might be some work to do by me but that was just installing the big knob).

It can be powered either via a DC jack or it has long life running on 6 AA cells. I found that the cells were rather tight and power didn't come on due to some of the cells not being pushed by the springs to the positive contact.


The display is large and clear. One moves around the on-screen items by turning and pushing the knob.


Here's a plot of my 40m dipole. I found the low SWR being at the top a little unfamiliar but it makes sense.


Here's Stephen, VK2BLQ's excellent 40m loop plotted:



Rather than duplicate the creator's feature rundown, I'll just summarise here and say it's:
  • Frequency signal source from 10Khz to 150MHz (and harmonics can be used beyond that).
  • SWR meter with plot
  • Field strength meter with logarithmic response
  • Cable loss measurement
  • RF Cable velocity factor
  • Modulation meter
  • Frequency response - able to plot filters
Best of all the software is open source and, as you can see in the photo above, it's powered by a standard Arduino Nano board. The schematic here. The circuit has:

  • Arduino Nano as the brains
  • JHD128x64 LCD 128x64 display
  • Si5351A clock generator
  • ADE-1 mixer
  • AD8307 logarithmic amplifier
  • 6 crystal 25Mhz IF filters
  • 3 x 2N3904 gain stages in the IF
The main modes are:
  • SWR - antenna analyser (use the RF In port)
  • PWR - power measurement (Use the RF in port)
  • SNA - network analyser (device between RF out and RF in ports)
The RF out is straight from an Si5351 clock generator and looks like this:


Playing around with the user interface, I find it takes more turns that I'd like to move between menu options. There are already a few forks of the software and, like the uBitX, I'm sure we'll see some great improvements built on top of the open software.

This is a great piece of test equipment for a home brewing radio enthusiast.

Friday, September 13, 2019

My next iPhone is an older iPhone SE, but I'm happy

Last time I upgraded iPhones I decided to lease the iPhone X rather than buying outright. This spreads the expense out over two years. After watching the latest iPhone launch, none of the new models attracted me and I already find the X too big in my pocket.

Looking around eBay I saw some second hand iPhone SEs at decent prices and I was lucky enough to get a 64GB model for AU$180. The colour is ugly (to me) rose gold but it was in excellent condition and the battery health is 99%. I was lucky, but even at $250, these are a good buy.

The iPhone SE is compact in the hand and pocket. The A9 processor is decent and it seems quite snappy running iOS 13 GM. (I'm in the developer program so have early access).

Although I'll miss the extra screen realestate of the iPhone X, I don't miss the size of the body and I prefer TouchID to FaceID. I love that I can wake the device with my finger when it's lying flat on a table.

Battery life isn't as good as the X although it's a fresh install and the Photos app is hammering the CPU doing all sorts of analysis so I expect this to continue for a day or two. Interestingly, Siri is using 20% of battery so far, so I've turned that off for now.

I returned the iPhone X to Telstra today. My goodness that SEBEL system is a dog! Poor Telstra shop staff. I'm saving $30 a month on a "bring your own device" plan but I know I can do better, perhaps on Aldi Mobile but I'll leave it a month or two before making more changes.

The sales woman was puzzled that I thought that $50 for 15GB was too much and explained that I was getting "unlimited" data. Oh, I said, 10 Terabytes? She had to explain that mobile phone operators mean something different by the word "unlimited".

I'm not alone in my enthusiasm for the iPhone SE, check out BuzzFeed's "Tim Cook Will Have To Pry My iPhone SE From My Cold, Tiny Hands".

There are a few apps, including ones from Apple, that don't handle the small screen too well. Happily, my WSPR Watch app has always been tested on the iPhone SE size screen so I'm not embarrassed there.

iOS 13 seems solid despite a rocky beta period. I think they've wisely taken out the things that were causing trouble and deferred them to 13.1.

Apple should make a phone the physical size of the SE, but with the edge to edge screen. I'm waiting for in-screen TouchID to appear, or perhaps FaceID could be made to work at very high angles?