Wednesday, 5 June 2019

500kbps packet radio

Packet radio is pretty much all but dead here in the US but it seems not to be that way in France.

I recently saw a message on the AMPR mailing list about a 500kbps modem that someone in France had designed. The design files and software were put up on the Hackaday website. The design uses a handful of development boards cobbled together and has an Ethernet interface for the client computers to connect to. 

So I decided to have a go at this project. I ordered some PCB's from JCPL and searched the usual online suppliers for all the other parts. It took about 6 weeks to get everything together but for about $65 per modem I was able to build 2 and test them across my workbench.

One of the modems under test

I've been playing with them for a few weeks and am very impressed with them. I can sustain my MMDVM hotspot across them as well as attach a WiFi access point and make a WiFi Calling cellphone call through it too.

The downside for us here in the US is the bandwidth and speed. The FCC says that we can only use a symbol rate of 56kbaud and a maximum bandwidth of 100KHz for data modes on the UHF 70 centimeter ham band (where these modems operate). Currently the modem software will only allow links of 200kbps in 270KHz and so do not conform to the rules. 

Interestingly, this is not the only data mode to be found on the 70CMs band. Digital ATV has been around using the DVB-S standard for quite some time here. The ATV crowd erroneously reclassify their data (up to 2mbps!) as pictures/video rather than the data that it actually is. In this way they fool the FCC into allowing the mode without a rule change. So maybe that's how we do it for Packet Radio? Reclassify our data transfers as "image". After all, web pages have pictures in them. :)

Thanks to F4HDK for his design.

The network that supports the modems under test

Wednesday, 6 March 2019

Cheap "Geochron" clock

I've lusted after one of these clocks for quite some time now. But at almost $2000 I really cannot justify the cost. But it seems that the manufacturer has been listening to their customers and has produced a digital version for around $400 that you plug into a 4K TV which you also have to buy. Hmmm, I'm sure if I look hard enough I can do better than $400 and a TV set?

One can buy cheap 4K TV's these days for change of $200. The one above is a Hisense 43" with built in Roku that I got from Walmart in the January sale for $179. Below it is one of my work 37" wide screen monitors.

So basically the Geochron 4K clock is a bit of software running on an embedded device of some sort. I've not seen one up close but it looks like it might be some sort of AndroidTV Set Top Box? It's able to display the greyline, track satellites and do other things in that vein.

Looking around the Internet I found this piece of software by Simon Brown (of Ham Radio Deluxe fame). It displays a greyline graphic in real time onto your PC screen. It can also show you a handful of other details such as the Solar Indices and multiple clocks. The picture can also be changed for one of your choice.

In the junk pile I have an Intel Compute Stick. It's a 1.4GHz quad core PC that one shoves into the HDMI port of your monitor. It runs Windows 10 and has 2GB of RAM and 32GB of storage. It's also 4K capable.
Within minutes I had it up and running and displaying the greyline clock. I have configured the Compute Stick to automatically run the software upon power-up and so if I want to watch the clock I simply turn on the TV.

The total cost for this project (assuming everything was bought new) is as follows:

43" 4K TV = $180
Intel Compute Stick = $120
Software = FREE!!!
TOTAL = $300

Monday, 3 December 2018

$30 Low Power Echolink Node for the Shack

Over the years I've tried many different EchoLink setups. I have been dissatisfied with all of them. There were always too many wires or they consumed too much electricity or they were just too damned difficult to deploy.

For a while now I've been thinking about what I really want. What I really, really want. I came to the conclusion that I only need something that can be used in the shack to augment other activities there.  It has to be small, self contained, as few wires as possible and also portable.

I think I've achieved it! It's a complete EchoLink node (compute, RF, interface etc) in only 2 1/4 inches square (6cms). What's more it's entirely powered by a single USB connection.

I cannot claim that it's my design. I found it entirely by accident on Oshpark one day. Take a look at this web page by UR5TLZ. In turn he is using a software distribution called "Spotnik" which is based on SM0SVX's repeater software, SVXlink. I've used that software before.

The design is based on an Orange Pi Zero. With the addition of an RF addon board and some signalling transistors etc the OPi-zero can become a complete node. Unlike RPi-Zero the OPi-Zero has a built in bi-directional sound card that is presented to one of the many pins on the GPIO headers.

The addon board uses one of the Dorji DRA818 radio modules. This is a complete FM radio with built in CTCSS/PL facilites as well as audio in and out. It can operate at up to 1W but I have it set to 0.5W as otherwise the 5V supply fails. 0.5W is probably way too much for around the shack anyway. The rest of the components are SMD type soldered to the bottom of the addon board.

For my MMDVM project this summer I bought a load of surplus 433MHz spring style antennas. These would have gone into things like radio pagers, handheld radio's etc. I got 50 of them for $1.  So rather than add an SMA antenna connector and then install an external antenna I soldered one of the spring antennas in place of the SMA. The result is that I can now install the whole thing into the case without any extra holes being drilled.

I found that I needed to do a few mods to the design. Firstly, there is no RF decoupling capacitor in the PTT line. I found that the PTT would remain on when the software had something to say. Touching the antenna would make the PTT drop. The addition of a 100nF capacitor from the PTT to ground solved this issue.

The board set would not fit into the enclosure either. Upon further investigation I discovered that the issue was that the addon board aligned with the screw towers in the case thus preventing the set to slide in further. To overcome this issue I filed the corners from the addon board. Where they were square with a round hole in them as in the above picture, they are now a diagonal. The board set now fits into the case properly.

The sum total for this project was less than $50.

Orange Pi Zero  = $17
Dorji DRA818U = $8
Spring type antenna = $0.02
R's, C's, Q's etc = junkbox
PCB from Oshpark = $6 (you buy 3 units for $17 - use the spares to make one for your car?)
TOTAL = $31.02

You know you're in Virginia when ...

Even the menu is redacted. VA is the home of all those ABC agencies that may, or may not exist.

Monday, 5 November 2018

Stupid stuff you see at the Home Center

Yep, you guessed it. It's a toilet roll holder with a platform for your phone.

Add caption

Monday, 11 June 2018

More power!!!!!!!!

I own a 2018 Dodge Grand Caravan. It's the baseline model with absolutely no frills or addons whatsoever. And that included things like USB charging outlets. So I decided to add a few outlets of my own.

The USB outlets were purchased from amazon and are wired in parallel with the cigarette outlet so that they will follow the ignition. The Anderson Powerpoles are wired directly to my Ham Radio fuse box in the back of the van and are fused for 10 Amps. Again, the outlets were purchased from Amazon. I also purchased a set of large step-drill bits. The required holes for the outlets were 1-1/8" and you can see the remnants of the panel on the floor. I was able to source a replacement panel just in case I sell my van. I can then return it to factory condition.

Can you prove you have a brain?

Can you prove you have a brain? I can! Take a look at this. It's an MRI (one of MANY!!) of my brain. Clever bastards reading this will be able to spot my 1/2 ventricles, 3rd ventricle and 4th ventricle. Look really close you'll also see a Pineal Cyst right at the back of my 3rd ventricle.

According to my brain guy (he's my 3rd on this journey) my enlarged ventricles are suffering from something called Obstructive Hydrocephalus most likely cause by the Pineal Cyst. And whilst the ventricles are not "impressive" (thanks, Doc) my other symptoms were causing alarm. Alzheimer's like memory issues, incontinence, difficulty descending stairs, wide gait etc, etc, etc. So it was decided that we should "fix" the issue. The Ventricles are full of spinal fluid and because the fluid cannot drain as normal its like inflating a water balloon in my head.

I was scheduled for a procedure to install a VentriculoPeritoneal Shunt. Basically its a McDonald's straw connected to a valve that then dumps out into your stomach. After almost 9 months of chasing this issue down and a few wrong diagnosis and even being thrown out of a brain surgeon's office (thanks, Penn Med!!!), being told another surgeon did not have the tools for the job I ended up at Jefferson University Hospital in Philadelphia. These guys know what they are doing!!!

The night before surgery I had to shave my head.
Surgery day was June 1st 2018. As I write this I am 10 days post surgery. I'm still very sore but getting 500% stronger every day.

Erin and I share a laugh in the pre-op waiting room. My head is shaved but yet still I have to wear that ridiculous hat. 
So in a nutshell they put a hole in my skull. Into the hole they inserted a tube which was pushed through my brain into the right side Ventricle. This will allow the buildup of fluid to drain safely and thus deflate the balloon effect.

This is the hole they put in my head. You can clearly see the tube exiting under my skin to the right.

Here we can see the valve placed under my skin on the side of my skull. There's another tube that goes behind my ear, down my neck, across my collar bone and eventually to my abdomen in a single feed. That's the output with the waste spinal fluid.

Finally, the tube arrives in my abdomen where they cut me open, grab the end and secure it behind my muscle wall. Of all the wounds I got this is the one that hurts the most!!!

The tube from my ear to my abdomen is one complete section. The surgeon basically stabbed me from my ear to my stomach in one go. He used a sharp long steel tube with a wooden handle on the end and rammed it under my skin. I can actually feel the hose!

So that's pretty much it. I'll have to go for annual checkups on it and even though mine is an "MRI Safe" model I will still need x-rays taken before and after I get another ride through the MRI scanner. This would be so they can tell if the valve settings have changed. I'm good for up to 3 Tesla's - whatever they are? It also has a service life of about 5-7 years so I'll be back in there fairly shortly. Although, I'm told a replacement is not as bad as an initial installation. I'll let you know.