Follow up

So… this arrived in my email this morning

Participation certificate - Trans Tasman

What a nice surprise, well done to the organisers. If their plan was to get people thinking about the next contest in July, it’s working. I’m not a dedicated contester by any means, but the Trans-Tasman was relaxed fun last time, so I’m keen to sort out the problems with my dipole and have another shot. I’m pretty much a 40m only operator for this due to the difficulty of squeezing in enough wire on the block. I have looked at plans for some loading coils but I’m finding it difficult to find the time to get to that and a number of other projects.

Another contest I’ll have a shot at if I can make the time is the VK Shires. Since I’m out in the bush, but in easy 40m range from Perth I should be able to give some points away to the VK6 operators.

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More Space APRS

psat__2NO84

Using space based digipeaters this weekend I had a couple of firsts. One was successfully having a packet digipeated by PSAT (Parkinson Sat – NO84). This is a 1.5U CubeSat launched in 2015 carrying a APRS transponder and a PS31 experiment.

I’ve heard this satellite before, but yesterday I had a shot at sending it a packet, I heard it digipeated, but didn’t receive it back well enough to decode it. I waited 30 seconds or so and had another shot with the same result.

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Terrestrial APRS

I took my first road trip within range of some earthbound digipeaters and iGates tonight. The D72 was secured on the dash of the ute, but using the dual band whip on the roof. I decoded one packet just out of Narrogin, I assume via VK6-RAW (I haven’t read enough of the manual to work out how to sort the list by time yet) but didn’t get any of my own packets digipeated back to me until I got much closer to Perth.

APRS map showing track

I had the beaconing mode set to Auto, but also sent through some manual packets when I could hear good signals from other packets being repeated. Next on the list is to re-read the manual in much more detail to get my head around all the settings.

Accessing the ISS Digipeater

image_product01With a long weekend, and a major project at work behind me, I had a tiny bit of breathing space to play radio this weekend. What I should have been doing is putting in a couple of hours on the AllStarLink for my club (currently at about 30% finished). What prevented this was a new toy scored second-hand from eBay that arrived this week – a Kenwood TH-D72A handheld.

 

qslI grabbed this off eBay, the main attraction being it’s APRS capability, including: built in GPS, stand alone digipeating, and the ability to plug it into a PC and use it as a TNC. My first big plan for this, since I’m miles from anywhere, was to use it to get my staion on the ARISS map by having it digipeated by the International Space Station

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FM320 Nominated Channel Modification

manual coverThe Phillips FM320 UHF CB has the facility to be locked to a particular channel. This is controlled by the existence or absence of a number of diodes on the circuit board. I’ve been looking into this for a telecommand project I’m working on. I wasn’t able to find the information of how to do this anywhere else, but it was pretty straight forward to figure out.

This post describes how modify the FM320 radio to set the nominated “NOM” channel.

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Phillips FM320

Phillips FM320 UHF CB radio

Here’s a blast from my radio past, the Phillips FM320 UHF CB radio. I’ve dusted one off from the slowly collapsing box of radios left over from my farming days. My plan is to use one as the receiver for my DTMF pump switch.

As a kid I had always been encouraging Dad to consider radios for the farm. I was a regular reader of CB Action and it seemed like the perfect excuse. He never succumbed to this until the advent of UHF CB. We had seen them at one of the field days, and organised for a Phillips representative (a German guy called Hans) to come out to the farm and do a demonstration. Hans arrived with a wind up mast that he set up at the house and wound up to the same height as our TV antenna. Then we drove around the farm to see what the coverage was.

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DTMF Tone Control

I’m in the process of replacing a windmill on the farm with a solar pump. The windmill, carefully adjusted, can keep up with the water consumption at the house and troughs a couple of kilometers away. It isn’t perfect; sometimes the house tank overflows and we either water the garden or go down and turn the windmill off for a few days. Sometimes the tank sounds a bit empty and I drive down to the windmill and adjust it for a bit more flow.

The solar pump is not so analogue. In order to lift the water the height needed, the centrifugal pump is oversized in relation to the actual flow required. The pump controller can be turned down to some extent, not not enough to avoid overflowing the tank and wasting water. Some system is needed to turn it off an on remotely. My current plan for this is to use DTMF tones over UHF CB radio.

DTFM Keypad layout.Dual-tone multi-frequency signalling (DTMF) tones are used widely in telephone systems. The frequencies are chosen to be easily transmitted in the narrow voice bandwidths and using two tones  for each key allows for a small amount of frequency drift as well as good rejection of noise.

The frequencies were originally chosen far enough apart to use analogue bandpass filters for detection, so it’s possible that someone smarter than me could implement a simplified Fourier transform that would run on the Arduino. As I need this to be robust, I rejected that idea and decided to use an MT8870 Integrated DTMF Receiver. Continue reading