Portsdown - where do I begin?

From BATC Wiki
Redirect page
Jump to: navigation, search

Hopefully you've reached this page because you've read the Portsdown transmitter introduction and want to know more - if not, we suggest you do spend 5 minutes reading the system overview.

OK - now you've read that, you want to get started!

The next thing is really to read the hardware overview - sorry but there's load of useful information in there, such as where to buy the various bits that you need to send pictures across the shack.

2-2 GPIO Breakout.jpg

Once you've read (or decided not to read!) the Hardware overview, you can see there's not much to it!

Important note - the Portsdown transmitter has been designed to "work out of the box":

  • You do not need to do anything other than get a programmed SD card described here and then follow the initial set up guide
  • Do not connect a mouse, keyboard or monitor to the Rpi
  • Do not load any device drivers including the Waveshare screen drivers
  • Do not tinker with Linux commands

If you do, we don't have time to support you and will just advise you to reformat your SD card and start again!

So here's the shopping list - a full list of suppliers with links to their website is available on the Hardware overview page.

Shopping list

Raspberry Pi

Ideally you will buy a version 3, but if you have a version 2 or even a Model B lying in the cupboard, give it a try. Because, believe it or not, that's all you need to send pictures across the shack! But to do this you will have to read another section of the user manual and follow some instructions for "ugly mode" contained in the initial set up guide.

Waveshare touchscreen

If you do not want to always have a computer connected, you'll need to buy the touchscreen. But make sure you buy the right one from Amazon - other ones that look the same but they may not work and may even use pins on the Rpi GPIO that we already use for other connections.

Once you've bought the screen, you'll need to read initial set up again to learn how to configure it and make the Rpi boot straight to it so you never have to use the PC again.

By now, you're probably bored of the test sequences and bouncing balls so you want to add a camera input. You can have 2 types of camera:

The Raspberry camera

This produces very high quality images but is just the camera.

Easycap USB dongle

Readily available from eBay, these USB dongles have a yellow video phono connector and will enable you to connect your mixing desk, old camcorder or even your old VHS tape machine!

Guess what, once you've bought the camera or USB dongle, you'll need to read initial set up again to learn how to configure them and send live pictures from your Raspberry Pi.

Audio input

Presumably you want people to hear what you are saying so will also need a USB audio dongle - there's loads on ebay :-) Note: there's no audio in the MPEG-4 mode at the moment but we are working on it.

Modulator Filter PCB

So up until now, you've been sending pictures across the shack using Ugly mode (Serious note - Please don't connect it to an aerial unless you want a visit from Ofcom!).

To get your Portsdown on air properly with DATV on 146, 437 and 23cms you'll need a modulator / filter board - this is the only piece of custom hardware and you can buy blank PCBs or built units (from the end of February 2017) from the BATC shop.

ADF4351 Local Oscillator

As well as the Modulator Filter board you will need an ADF4351 chip to use as your local oscillator. Luckily, these are available from ebay ready assembled on a small PCB with an SMA connector so it really is "plug and play".

It is possible to buy ADF4351 modules with a 10 or 25 MHz reference oscillator - you must select which reference oscillator you have in the set up menu.

These are modules are available now and the Portsdown transmitter will definitely use one, so why not buy one and you'll be ready when the Modulator board is available.

Local Oscillator filters

Testing on the 3 prototype boards has shown that, due to the square wave output of the ADF4351, it will need band switched filtering on the output of the module when used on 146 and 437 MHz - no filtering is required on 23cms. The effect of running without a high pass filter on 146 and 437 is a reduced MER and RF performance.

GPIO extender board

In order to get at all 13 signals we need to and from the Rpi, we need to use a GPIO breakout board - you can use a standard Rpi board but the card must break out all 40 pins of the GPIO, and have another connector on top for the LCD display.

Because of this the Portsdown team have designed a board specifically for Portsdown and it is available from the BATC shop. For more details see the hardware overview.

Filters and drivers

That's all there is to the Portsdown transmitter - 6 simple parts, but of course, just like any other DATV transmitter, you will need filters and driver amplifiers - there's lot of designs around and anything you have built or bought for Digilite or DTX1 will work well with the Portsdown transmitter.

Take a look in the filters section of the wiki.

Where to buy the components?

Now you really do need to read the hardware overview as at the bottom of that page is a list of suppliers with links to their website where you can buy all the components needed or you could just leap to the hardware assembly instructions.