Y is for... Your Own Radio Station.

copyright (c) 2008-2020 S Bluck.

OK, you would like to start your own FM radio station. and you want a transmitter.
You can buy transmitters already built on e-bay, although their quality is not always
good. (you may get a visit sooner rather than later from OFCOM and the police).
Or you may be able to find a commercial transmitter or exciter for sale.
Most of the little transmitters on the internet are very poor quality. They are really
only just suitable for a home radio station. definately not for broadcasts outside!
This is because they were designed using a simple single-chip radio transmitter, What's
wrong with that you ask... it a compromise and a very big one! Devices like the BH1415
andBH1418 were created for those tiny audio-sender things that you plug into your phone/MP3
and send to your car-radio. They are all-in-one devices that are dedigned
to do a very basic job, and do not have the critically tuned filtering and other circutry
on-board to make them usable as a full-on transmitter.

Here are the datasheets for the BH1415 the BH1414 and BH1418

You can buy kit or complete exciter boards from various sources. But first let's look at
what the bigger stations are or were using.

Here are a few commercial units. Usually they are quite expensive, but occasionally they
do turn up cheaply. Then, if you need more power, you can either buy, or build your own PA
if you need more power. (don't forget the filtering too). Although many commercial units
have enough power for our needs as they are....

(above). An Eddystone XE series synthesized exciter.
These are available with output powers up to 250W so you may not need a PA stage.
a 1.5KW version of this turned-up on fleabay in july 2019 for 3,500GBP so prices
are gradually coming down. price for these should be closer to a pound a watt...
so still a long way to go...

(above). A Continental Electronics 802B exciter.
Another synthesized unit, (10kHz steps), with 5 to 50 watts output.

(above). Norsk-Marconi exciter ( Marconi B6503 drive unit ).
This is my Norsk Marconi transmitter. it's a bi-crystalled exciter so not as frequency
agile as the synthesized units here. It has an added PA on the back to give an output
of 25 Watts. This can be used to drive a PA if required. It sounds lovely and warm!
With none of that synth-whine you can get from lesser units. I have used this with a
stereo encoder too and it sounds great.

These units are part of the UK's original FM network and were used to drive a 1000w
tetrode output stage. The crystal frequencies used in this exciter are Fo/3 +/- 500kHz
This unit dates from the mid 1970's and still sounds fantastic!

(above). CTE VL32-S.
This is my CTE VL32-S exciter. The S means that it has a built-in stereo-encoder. This
unit was made in about 1995, and still sounds very good in mono. The stereo encoder needs
setting-up properly to bring it upto the high standards that these exciters usually produce.
This exciter is internally of modular-construction making servicing easy, and all of the user
controls are on the front-panel under the cover-plate. it's a frequency-synthesized transmitter
so will cover the whole band and no tuning required. CTE are an Italian company who make.
great analogue and digital broadcast transmitters and link transmitters/receivers.
If you want a kit of parts to build your own exciter and PA, you can order the kits below
and put it all together yourself for a fraction of the price of a commercial unit. These
kits are from an outfit in the USA called "Free Radio Berkeley" see the internet for more
details. The designer Stephen Dunifer was one of the pioneers of low power radio stations
in the United States.

Above the one watt synthesized exciter kit before, and after building. All the parts you
will need are there, and the instructions are easy to follow.

Above. A 40 Watt PA kit. Free Radio Berkeley produce higher output PA units. I bought this
kit as the output I needed for this project was 25 Watts ERP. After the filter unit (below)
the output is cleaner, and still over 30 watts. The filter is well worth the extra few dollars.

All you will need to add will be a metal box to put it all in, a power supply to run it and
some tools. (solder, soldering iron, wire-cutters, pliers, screwdrivers, drill, drill-bits).

On pirate or restricted-service/special-events transmitters you may find it useful to add a
high-VSWR switch reduce the output or switch off the transmitter if an areial fault develops.

On The Air... The FRB exciter is a nice kit. It could do with a better Frequency/calibrate
trimmer. This one generally runs well but takes about 20 minutes to settle on frequency. The
sound is good BUT you'll need to use a good limiter with it or it will sound choppy on peaks.

-------------------Let's look a little more at LINKS....---------------------

Now you are going to do it aren't you...? On the air with your own station!

Back in the "old days" we had these.. Free-Running exciters. Made-with copper-clad
and super-glue. They sounded ok-ish, but drifted like a total bitch....

A very long way from being ideal, but they were cheap to build.
The current exciters used these days look more like this, Synthesized, with FET PA and
a quite passable 9-pole filter

If you have somthing like this. Then carry on. If you have a fifty-quid 20 watt SanPan
sprog-box from the far east, Go back to the start of this page and read why you shouldn't
go on-the-air.

If you can find a friend with some test-kit then that's a total bonus! You will at least
need a meter, frequency-counter, power supplies, RF power-meter, 50-Ohm load. But if you can
save-up a few hundred quid, you may be able to find one of these....

The marconi 2955 and the later 2955B are the standard test-kit of the radio industry. The
companies I've worked for in the past used them, and now I am self-employed I use them too.

The main parts of a DIY Pirate radio station are.. YOU, a studio, and a transmitter.
If you would like to hang on to your studio, and stay out of a police cell you will need
to seperate your studio from your output transmitter.

When OFCOM track your station down they will first target the Band II output transmitter
and then try and trace the location of your studio. So making the system that sends your
programme-content to the main output site as tricky to trace as possible is the goal here.

LINKS. A link is simply a method of getting signals from one place to another, and a good
link will do this with very little noise or interferance. When I started transmitting back
in the mid 1980's we often ran the main transmitter from the studio. Later, when we started
using blocks of flats we had the transmitter on the roof, and simply dropped an audio-cable
down to the studio-flat. Sometimes with a "weak-link" so if the Radio Investigation Service
pulled the cable it would simply drop-away from the studio and would be an odd-length so as to
not give the game away and let them know where the studio was... They knew it was there but
didn't know what door to knock on first.

later experiments were made with infra-red LEDs, and even lasers were suggested as an alternative
(this was pre Laser-Diodes so lasers were real lasers!). Fuck it, we're radio people..
so we used radio. Band I and Band III television had closed down and we had some space to play
I built my first VHF links on Band I, and the station WNKR was working with links in Band III
still easy to track back, but not as obvious as a piece of cable running into a window.

Back in the times when things like Redifusion-Cable-Converters were being given away I used the
parts from them to make link recievers etc.. I've generally always been able to build stuff from
the electronic-junkbox. so just thrown-together links and other station kit rather than buying it.

Now people tend to use UHF or Microwave. This has been the case for the past 20+ years
There are other systems too. Intenet / IP-Links using point-to-point Wi-Fi kit. and of course
VHF is still there, but a bit too cluttered these days. Here is some of the link kit I have
kicking-about here...

A the bottom of the heap, a stereo-encoder, RDS unit. Above that an RDS / microwave-Gunn-TX
then Left-to Right a couple of microwave TX horns and oscillators, A complete microwave RX
with it's LNB taped to it. then on the right three microwave reciever units.

Using a horn for TX is OK, but even with a reasonably gainy horn, the beamwidth of your
transmitted signal will still be quite wide. I can DF microwave links so I know it can be
done if anyone wants to. For that reason I tend to use a dish at the TX end of my microwave
links. This narrows the beam-width and also increases the gain meaning you can throw your
signal further for any given input-power. Here is a self-contained microwave TX with RDS
and another spare dish. You can re-use sat-TV dishes if you prefer. I just use these because
I have them in my bits-box.

And this is what usually lives at the recieve end of the link.....

You can just leave it on the roof or wherever you choose to leave the Main/output TX. But a
better option is to have it in a flat a couple of floors down with your audio fed up the
building's wiring. This is a close-up of the three microwave RX units on the picture above.

There is one DC-tuned sat-can, and a pair of electronic tracking units. The DC tuned Sat-Can
is a good system, but there is no allowance for any drift in either the TX or RX side and you
may find theat the link flutters or drops-out as they settle, and due to temperature changes

There is a small preset on the pcb. You simply adjust this until the reciever locks-on and
hope for little drift. Below is a picture of the PIC-Controlled tracking unit.

These are better. You use the up-down buttons to search for your signal and that's it. If
if your Gunn-diode transmitter drifts a bit this will follow it.

If you are a little more serious about your microwave kit you can get a few bits of test
kit to help you out. Here below is my Microwave frequency meter and marconi power meter.
these are a fair way of getting your kit onto any given frequency and of measuring it's O/P

Strictly speaking you can get away without it. BUT if you need to lets-say tune a RX for a
certain frequency so it works with an existing Studio's TX. This is a good way to start.

Microwaves too quirky for you? All of those waveguides a little too much like taking a
course in plumbing? Test kit too expensive? You may prefer to use UHF.
UHF is a cool system too. Easier to trace back to the studio although you can make it
less obvious through careful choice of output site and studio.
Back in the late 90's I lived in a part of kent that had poor TV coverage, some houses
had thier aerials pointing to Crystal-Palace, Others to Bluebell Hill, and even one or two
towards the Anglia site north! The local block of flats had it's towards Crystal-Palace.
which was very handy as the studio TX yagi pointed to bluebell hill and straight at the
tower-block! The DC voltage tuned UHF tuner just plugged into the TV disribution kit on
the roof. Easy Peasy. Now analogue / DC-tuned units are thinner on the ground. Most of
the old TV-sets I strip have digitally tuned tuners. Mostly using the I2C protocol.
below is a picture of one I'm about to strip-out. You can see the little chip near the
tuner. That sends the data to the tuner to select the frequency and other functions too.

I tend to use Microchip PIC devices to drive these tuners. My favorites are the tiny 8-pin
16-series. I simply program them to "Bit-Bang" a stream of data and clock to the tuner.
these look almost the same as the tracking microwave kit above, and in some cases when I
have run out of vero board I solder then straight onto the tuner-lid! I program the
PIC chip with a normal USB programmer. I use a GQ-4X from MCU-Mall. as I also use it
for other programming jobs for other projects. Sometomes I make small PIC-boards with
18 pin PICs, LCD displays and buttons to drive radio kit. These work with I2C based pll chips,
and used to test data streams for tuners, or turn a dull taxi-radio into a free-tuning TX/RX.

This version is a little quirkier. I built it to drive the TX and RX PLLs in a duplex base
and gets it to frequency-hop or do Jam-Avoidance.

Here it is connected to the programmer via ICSP (in Circuit serial programming). Code can
be changed and uploaded during the development phases

Making your own UHF link-kit for band IV and band V is a good link method. If all else fails
and you have to. you can use Ex-Commercial talkback and link gear. This is NOT really advised
as it's often crystal-controlled and usually stuck on the programme-making/JF-MG channels.
BUT it can still be useful. I use Ex-commercial-station kit here for local links and talkback
and I also have a really old Marti unit that can still run. shown here with Dolby NR in line

Just in case you think it's easy....
There is no quick and easy way to just make it happen. You need to know what you are doing
and have the tools and kit to do the job. and be prepared to learn some new stuff.
I started building electronic gear when I was six, and built my first transmitter from scratch
when I was fifteen. By then I was already writing assembly language routines as I was working in
the computer industry at 15! I was also designing my own PCBs and having them made!
Have confidance in yourself and experiment! We have the internet as a research tool, Use it!
back in the 1980's you had to phone tech-support and persuade them to post you a book!

The easiest by far is a UHF analogue tuner can with a simple voltage regulator and a multi-turn
preset to tune it with. Some of these need a 30v supply as well as lower voltages. but it's
far easier than learning to program and getting into other life-sapping electronics..
For the transmitter side use whatever you've got. Or whatever you can get or build. My first
UHF link TX was a vintage burndept base-station transmitter. The crystal was multiplied by 96
if I remenber correctly, so it was replaced and modulated with a couple of vericap-diodes
I also used triplers on my early VHF transmitters to put them on about 520-550MHz
and after I stopped using my tiny television transmitter I used the amp-chain from that.