With my full licence issued recently I have started preparations, the radio has undergone a basic transmit test (though not at APRS duty cycle yet) into a dummy load and is running output at 10 watts as measured at the antenna socket (losses will reduced ERP to below this)
The radio is a Leixen VV898, programmed solely with the APRS frequency of 144.800MHz and all the front keys disabled and the key lock activated so frequency cannot be changed, at time of writing it is currently on the bench receiving APRS packets though no device is connected to decode them
The shelf positions in the shed have been measured out and will be fabricated after my next payday all being well, the TNC-Pi kit will be used in this setup, this has to be shipped from the United States so I may get hit with a customs charge, so may be a bit later on before I can get this, it requires a suitable Raspberry Pi as well and as the new Pi 4 is a bit too power hungry a 3B+ is the best solution as this whole setup will be grid indepedent (no mains power is available in my shed)
I have learned in the last day or two that Coastal Chipworks, manufacturer of the TNC-Pi kit, has ceased trading and as such the kit is no longer available, this comes as a massive blow because it now means I will have to find an alternative way to get the Pi to key the radio for packets to be gated out of the APRS-IS and of course the requirement that the station transmit its callsign at the specified interval on the NoV.
The Pi header pins do give access to serial lines but only TXD and RXD, no DCD or RTS lines, I do have a USB to serial adaptor for this and schematics to make up a suitable interface that may work, but more research is needed first into what both direwolf and Xastir can do
at the time of this post the world is in the grip of a coronavirus pandemic, this will obviously slow down NoVs and hardware may be a little harder to obtain should supplies be disrupted and lockdowns potentially enforced by governments worldwide to stem the spread of the virus
I will of course keep you updated in due course
With the UK currently under a government mandated lockdown I can't go very far so have took the time to rearrange the shed a little, this involved moving of things at the back of the shed and removal of an old CRT TV which is now in my shack until I can test it, access is improved and all I need to do now is fit some shelves and start obtaining and bench testing hardware
I also have a video on YouTube and I have included it here
The UK's COVID-19 lockdown has since eased though I've had to go through a change of employent due to insufficient hours, and today, after working out how much pay I will get from the new job, the old job's final salary has yet to come, I have put a Raspberry Pi 3B+ on order as well as a case for it and a USB sound card as this is the only way I can now realistically get the RX side working, the TX side requires I order components which I cannot do now as I have to be off to work soon. I should have the bench tests for RX underway in the next few days and this will be put onto YouTube as well, receive should be mainly into a dummy load from a local transmitter, my Yaesu FT2D, and on the odd occasion a scanner antenna as and when I can
With a quick turn around by both Amazon (where I found the USB audio adaptor I will need to take audio from the radio to the computer and vice-versa, and The Pi Hut (my preferred Raspberry Pi supplier) everything for the foundation of the igate is now here, I have yet to get hold of an SD card to boot the Pi and install direwolf to (as this is what I will need) and components to do the TX switching (a document on the direwolf website says this can be done with the Pi GPIO header, a version of the 555 timer IC that can be run off 3.3 volts a transistor and some other components so I will get these ordered in as soon as I can
I hope to get the receive side of the igate working in a couple of days
Testing has now begun on the receive side of the igate at a local, off antenna, level, simply me sending a beacon from my Yaesu FT2D to the setup, the radio is connected to the Raspberry Pi by way of the USB audio adaptor, this has both the audio and mic bias voltage on the tip of the mic connector, so a cable had to be made up that had a capacitor inline on the audio side, the capacitor removed the bias voltage near enough completely and kept audio, as reported by Direwolf, at the correct levels once all adjustments were made on both radio and in alsamixer on the Raspberry Pi, next will be tidying up of the audio cable and heatshrink over the joins and capacitor
I have been testing the igate setup on an antenna, a telescopic antenna on a magmount on top of my steel breadbin in the kitchen window and it has been receiving fine, I also added a DCD light using an LED from a string of garden lights and two resistors in parallel to give around 280 Ohms, this connects to the Pi's ground and GPIO24 and is pulled negative to light up if direwolf detects a data carrier, which is far more informative than the green receive light on the front of the VV-898
The components needed to make the transmit side up have arrived after I ordered those from CPC (at a fraction of the cost to what I would have paid had Maplin still been trading) which means I am now in a position to build and test the transmit side of the igate into a dummy load (with my Yaesu FT2D acting as the receiver)
I also include my YouTube video showing the receive side so far filmed on Wedesday (before the DCD light was fitted)
I have built the circuit required for transmit and that side of the igate now works, it is currently into a dummy load because I do not have the NoV, final antenna and feeder or power to the shed, or even shelves in there for that matter, the circuit to transmit is based on a version of the 555 timer IC that runs as low as 2 volts to work with the 3.3 volts the Pi can safely tolerate on its GPIO, I have a video being rendered at time of writing this showing the circuit, and another short one showing the transmissions being received on my Yaesu FT2D
I include the short video below
I have taken the igate hardware off the soak test and it seems to be working fine, the next job is getting it all set up in place once I have built the shelves to mount it on
I decided a few days ago having not had the hardware powered since August that I should power it back up to make sure everything is working fine, doing this involved me setting the radio up in the kitchen with a dummy load and power meter on the antenna socket, the pi is running fine and the radio transmits and receives fine, in fact it seems to be receiving better than expected because even though it is on a dummy load it was able to receive my APRS beacons from my car last night 3 miles away, which I was not expecting.
I plan to apply for the NoV in the new year, and to get it going I plan to use an idea by Gil of YouTube channel 'Radio Prepper', that is to build a dipole out of the copper tape used normally to stop slugs and snails eating plants as I can stick this outside a window, just temporary until I can get the shed better arranged, of course I will test this under my own callsign and also put this antenna onto a VNA in order to see if it works fine on 144.800MHz, the frequency used for APRS in this country.
Once the APRS igate has its associated NoV I will do a walkabout test with the FT2D beaconing both automatically and manually to see just how good it is covering, there may still be some blackspots however this is to be expected
I applied for the NoV last week, this week, yesterday in fact, Ofcom issued the NoV for the igate, with the callsign MB7UCG, the igate is running from a magmount antenna on a Fray Bentos pie tin, however I need to give Ofcom notice of 7 days before powering up the station, so I hope to have it up by the end of next week, if not this may be the week after, and videos on the subject will be up not too long after this on my YouTube channel
On the day I received the NoV for MB7UCG I emailed a response to Ofcom with Thursday at approximately 12pm, today they confirmed at Spectrum Licencing that I can go ahead with this so Thurdsay the 18th February is the first switch-on date, at about 12pm, I have also made some tweaks to the configuration file to put a shortened URL into the 'position' beacon that is periodically transmitted (about every 10 minutes) to identify the station that comes back to this website as the normal URL is far too large for transmission in an APRS packet in my opinion
As I am working overtime that day I won't be able to go out with the HT to do a walkabout test, however I will film a quick video as I turn on the igate for the first time and the walkabout tests will be done the following week