transmitters for radio applications.. (broadcasting voice, music, etc..) fm, and am http://www.reconnsworld.com/forum/list.php?18 Wed, 08 Sep 2010 23:31:20 -0700 Phorum 5.2.9a http://www.reconnsworld.com/forum/read.php?18,490,490#msg-490 http://www.reconnsworld.com/forum/read.php?18,490,490#msg-490 I am not an electronics expert, so may I ask your advice/ pick your brains, and maybe even get some "build it yourself" diagrams.

My problem is this:

In the UK, some railway lines are layed using steel sleepers (the bits the lines sit on) See: [www.pandrol.com]

The sleepers are insulated from the rails by insulating pads (approx. 10mm thick).
To detect the passage of trains, most use a small (2-6 Volts) DC voltage fed down one rail, through a relay coil and back down the other rail. The trains axles short out the rails, the relay coil loses voltage, and an indication is sent back to the signalling centre.
Some track circuts use a frequency to achieve this, common ones are, 1700Hz, 2000Hz, 2300Hz, and 2600Hz
Some track circuits use a tuned "reed" at the frequencies from 363Hz-423Hz, going up in 3Hz steps.
In all the different track circuits, the train axles short out the rails, dropping the relay.

When we've been on a relaying job, sometimes a steel sleeper(s) get the insulating pads left out, shorting out the rails. The signalling system thinks that there is a train sitting there, and those gallant chaps from the Signalling Dept. have to go and find the offending sleeper(s).

What I was thinking was, rather than use a voltage to find the location of the short circuit, as the voltage is too supceptable to the many of the variables, particularly the length of track circuits (from 20 to 1000 meters), I could use a frequency.

I would need a transmiter putting out enough power to go 1000 meters.
My idea would be to use both the rails as the arial, and send the transmitted signal down the whole length of the track circuit. The distance between the rails in the UK is 1432mm (4foot 8 inches), so I need the receiver to be sensative, but directional, as I will be pointing it at the sleepers, from a max. height of about six inches. My idea being that where the steel sleeper is in contact with the rail, it will become part of the transmitting arial, be detected by the receiver, and BINGO!, we've found the fault. A lot quicker than the current method of clearing every sleeper of stone and physicaly checking. (Sleeper spacing about 750mm, thats 1250 sleepers checked both sides for a 1000 metre relay!)

Limitations are that with the frequencies in use on the railways, and their harmonics, namely as mentioned above,the 50Hz traction current frequency, and the following TPWS frequencies (a train protection system), that uses:

64.25, 64.75, 65.25, 65.75, 66.25, 66.75 all kHz

It's also got to be small enough to be "one-person" portable (esp. the receiver!)

Thanks in advance for your thoughts ideas,

Chris]]> Chris Wink Radio Wed, 27 Sep 2006 12:59:02 -0700 http://www.reconnsworld.com/forum/read.php?18,413,413#msg-413 http://www.reconnsworld.com/forum/read.php?18,413,413#msg-413
I have a miniature, low-power FM transmitter (which can be used as a spy-tool). It transmits sound which have been received by little electret microphone included "on-board". Now i want to join this transmitter with e.g. computer or mp3-player, to transmit audio signal from line-in cable...

Here is the scheme: [rapidshare.de]

What do i have to change in this transmitter? How and where to plug the audio-signal from sound-card or mp3-player? Plz help me, i cannot find solution ANYWHERE in polish internet!!! Thx in advance ;)

Scheme here too:]]> Magz100 Radio Sun, 26 Mar 2006 18:14:58 -0800 http://www.reconnsworld.com/forum/read.php?18,376,376#msg-376 http://www.reconnsworld.com/forum/read.php?18,376,376#msg-376 guest Radio Mon, 12 Dec 2005 11:49:05 -0800 http://www.reconnsworld.com/forum/read.php?18,371,371#msg-371 http://www.reconnsworld.com/forum/read.php?18,371,371#msg-371 If somebody comes up with some schematic or anything, pls mail me at mailto:liverpooltilldeath@yahoo.co.uk]]> Jurgen Gerrard Radio Mon, 05 Dec 2005 13:49:09 -0800 http://www.reconnsworld.com/forum/read.php?18,356,356#msg-356 http://www.reconnsworld.com/forum/read.php?18,356,356#msg-356 what is the deal with am transmitting? is it legal and at what distance?
i need a schematic for the most powerful (legal) fm trans and a AM trans if possible
email me back at mailto:missrat@sbcglobal.net]]> colin Radio Thu, 13 Oct 2005 07:27:26 -0700 http://www.reconnsworld.com/forum/read.php?18,330,330#msg-330 http://www.reconnsworld.com/forum/read.php?18,330,330#msg-330 Jason Radio Thu, 04 Aug 2005 15:39:06 -0700 http://www.reconnsworld.com/forum/read.php?18,320,320#msg-320 http://www.reconnsworld.com/forum/read.php?18,320,320#msg-320 understanding of analog devices.

I'v built one of this miniature fm tranmitters, but i have no
idea about how they actually work!
I would realy appreciate it if someone would give me a link
that acctually explains it.(i mean in the engineer level...)

thanks.]]> endrew Radio Mon, 11 Jul 2005 18:16:13 -0700 http://www.reconnsworld.com/forum/read.php?18,257,257#msg-257 http://www.reconnsworld.com/forum/read.php?18,257,257#msg-257 miki Radio Fri, 11 Mar 2005 17:02:05 -0800 http://www.reconnsworld.com/forum/read.php?18,222,222#msg-222 http://www.reconnsworld.com/forum/read.php?18,222,222#msg-222 HafizMk Radio Tue, 31 Jan 2006 16:50:25 -0800 http://www.reconnsworld.com/forum/read.php?18,200,200#msg-200 http://www.reconnsworld.com/forum/read.php?18,200,200#msg-200 Ben Radio Wed, 05 Apr 2006 13:19:47 -0700 http://www.reconnsworld.com/forum/read.php?18,137,137#msg-137 http://www.reconnsworld.com/forum/read.php?18,137,137#msg-137
It would be legal here b/c i live in ZA (South Africa)
FM would be illegal thats why i would like AM]]> SpitFire Radio Wed, 05 Apr 2006 13:30:35 -0700 http://www.reconnsworld.com/forum/read.php?18,53,53#msg-53 http://www.reconnsworld.com/forum/read.php?18,53,53#msg-53 ]]> andrew Radio Tue, 01 Jul 2003 10:48:43 -0700 http://www.reconnsworld.com/forum/read.php?18,52,52#msg-52 http://www.reconnsworld.com/forum/read.php?18,52,52#msg-52

You'll find that this is a very easy project to build. It will transmit good quality sound in the FM band ( 88 - 108 mhz ). One inportant item is that the IC chip operates on 3 volts DC. The chip will get destroyed if it is operated on any voltage higher than 3.5 volts. The antenna can be a standard telescopic antenna or a 2 foot length of wire. The input is in the millivolt range and you may need to add additional pots for the inputs. I was able to use this circuit for a walkman and a portable CD player in my car. I used the headphone jack on both and varied the signal with the volume control.

To adjust the circuit tune your FM radio to a quite spot then adjust the trimmer capacitor C8 until you hear the signal that you are transmiting. When you have a strong signal adjust the resistor R4 until the stereo signal indicator lights. If the input is to high of a signal you may over drive the IC chip. Use two 15 turn pots on the input signals to bring the level down. You can balance the signal by using headphones. The inductor L1 is 3 turns of .5 mm wire on a 5 mm ferrite core.]]> andrew Radio Thu, 25 Nov 2004 21:23:43 -0800 http://www.reconnsworld.com/forum/read.php?18,51,51#msg-51 http://www.reconnsworld.com/forum/read.php?18,51,51#msg-51 ]]> andrew Radio Tue, 01 Jul 2003 10:37:15 -0700 http://www.reconnsworld.com/forum/read.php?18,50,50#msg-50 http://www.reconnsworld.com/forum/read.php?18,50,50#msg-50 ]]> andrew Radio Thu, 07 Jul 2005 05:21:30 -0700 http://www.reconnsworld.com/forum/read.php?18,49,49#msg-49 http://www.reconnsworld.com/forum/read.php?18,49,49#msg-49 ]]> andrew Radio Thu, 05 May 2005 12:40:49 -0700 http://www.reconnsworld.com/forum/read.php?18,45,45#msg-45 http://www.reconnsworld.com/forum/read.php?18,45,45#msg-45 www.reconnsworld.com]

R1 = 100 ohms           C1 = 1.5 pf NPO ONLY            Q1 = BF199, ECG 229,
R2, R4 = 10K ohms       C2 = 100 pF, NPO ONLY                2N5179 or eq.
R3 = 1K ohms            C3, C4 = 330 pF NPO             Q2 = BC183C, ECG123AP
R5, R7 = 47K ohms       C5, C9 = .1 uF                       2N4401 or eq.
R8 = 4.7K ohms          C6 = .001 uF NPO ONLY           L1 = approx. 1 uH
M1 = electret mike      C7 = 22 uF electrolytic         S1 = SPST switch
B1 = 9V battery         C8 = 6.8 uF electrolytic
C10 = 10 - 40 pF trimmer capacitor.

The coil L1 is so small that in the PC board version of this, it's just a coil
etched on the board with traces.  I think I breadboarded it with about four or
five turns of bell wire around a pencil and that made about the right value.
You tune the sucker with the adjustable cap C10.  If I remember, the
transistors are garden variety ones, though I think Q1 was reasonably high
frequency.  I was feeding in a signal other than an electret microphone.
This is neat to use with a cheapo FM walkman-type radio for cheap telemetry.
(We were actually going to build a device to transmit strain gauge signals
from someone's teeth over a whole day's time, and it was to be small enough
to be relatively unnoticed INSIDE THEIR MOUTH the whole time.  Never did
get the O.K. to proceed with that one.  Working for university research
gets pretty strange sometimes.)

Paul Marxhausen  University of Nebraska
                Engineering Electronics Shop



]]> andrew Radio Wed, 15 Jun 2005 04:21:15 -0700 http://www.reconnsworld.com/forum/read.php?18,44,44#msg-44 http://www.reconnsworld.com/forum/read.php?18,44,44#msg-44





Small Radio Transmitter
=======================


DESCRIPTION
-----------

This ZIP file contains information about building a small radio
transmitter, which has a PCB 1.75" x 2.5" (45mm x 68 mm) and
has a range of about 30 yards or so. The documentation with
the circuit says the freq range is 100-108 MHz, but I have found
it to be more like 85-100 MHz.

The circuit is (of course) only mono, and accepts an audio input
from either a microphone or other source. The input impedance is
1Mohm. The input sensitivity is 5mV and the max input signal is
10mV. The transmitted signal can be picked up on a FM radio. The
circuit can be used for short-range transmission, eg. for wireless
microphones.

The actual circuit comes from a 'Kit', available from Veleman
electronics (USA distributor is Tapto Corp., PO Box 1339,
CLAREMONT NH-03743-US. UK distributor is High-Q Electronics,
382 Edgware Road, London, W2 1EB). The kit number is K1771.
It is a very good transmitter.

I bought the kit, and made the circuit, which worked very well. I
wanted two transmitters, so I made my own 'copy' PCB and built the
circuit, and in fact my home-made version seems to work better than
the original!! So there is no need to buy the kit really, as it is
quite a simple circuit, and is the best 'home-made' transmitter I
have seen.

- CIRCUIT.GIF is the circuit diagram.

- PCBPLAN.GIF shows the PCB layout from above (components shown).
PCBPLAN.GIF is an accurate layout, scanned from the instruction
sheet. I have used * to mark one corner for reference.

- TRACKS.GIF shows the track layout on the soldering side of the
board. This is NOT a very accurate layout. This is because I didn't
actually have a plan of the track layout. To get TRACKS.GIF, I put a
bit of OHP film onto the bottom of the PCB, and traced the tracks
with an OHP pen. I then scanned this in. I have marked the component
leg holes (approximately) with white blobs.


CONSTRUCTION
------------

Start off by scaling PCBPLAN.GIF and TRACKS.GIF by the same
amount so that they measure approximately the correct size
(1.75" x 2.5") when printed out.

Then make your PCB. As mentioned earlier, PCBPLAN.GIF gives the
accurate positioning of the holes, whereas TRACKS.GIF gives the
positions only approximately. So use PCBPLAN when drilling the
holes in your PCB board. Then draw on the tracks, using TRACKS.GIF
as a guide. The important thing is to make sure you draw the
'printed coil' correctly on the PCB - those lines are there for
a reason!

Then solder in all the parts. Here is the parts list:

D1 Varicap diode (eg. BB119)
D2 1N4148
R1 100K
R2 220K
R3 22R
R4 1K trimmer
R5 1K
R6 56K
R7 1M
R8 1K2
C1 5pF ceramic
C2 6pF ceramic
C3 15pF ceramic
C4 trimmer cap
C5 15pF ceramic
C6 1nF ceramic
C7 100uF electrolytic
C8 4.7uF electrolytic
C9 100pF ceramic
T1 BF244A or BF245A FET
T2 2N3819 FET
T3 BC307/8/9 or BC557/8/9 PNP

Bear in mind that in addition to the components, there is a jumper wire
which needs to be fitted (marked with a dashed line in PCBPLAN.GIF).

The power supply to use is 9-14 V DC, one of the little rectangular
9V batteries is fine. Connect this to the + and - points on the PCB.
The sound input goes to the points marked "MIKE".
The antenna should be connected to the point marked "ANT". The
emitter's output impedance is 50 ohms. You can make your own fancy
antenna if you like, but I have found that a foot or so of wire is
fine.

Good luck with the transmitter. If you have any improvements to the
circuit, I would be glad to hear from you.

--Dan Evans.
(email address: mailto:dan.evans@sjc.ox.ac.uk).
(WWW page: [sable.ox.ac.uk]).

5 April 1995.]]> andrew Radio Fri, 27 Jun 2003 09:37:25 -0700 http://www.reconnsworld.com/forum/read.php?18,22,22#msg-22 http://www.reconnsworld.com/forum/read.php?18,22,22#msg-22 ]]> andrew Radio Thu, 26 Jun 2003 18:50:10 -0700 http://www.reconnsworld.com/forum/read.php?18,20,20#msg-20 http://www.reconnsworld.com/forum/read.php?18,20,20#msg-20

similar to the "mini fm transmitter #1" but more sensitive supposedly...]]> andrew Radio Sun, 20 Nov 2005 17:17:31 -0800 http://www.reconnsworld.com/forum/read.php?18,19,19#msg-19 http://www.reconnsworld.com/forum/read.php?18,19,19#msg-19

parts:
Transmitter Parts:
R1, R4, R6 10K resistor
R2 1Meg resistor
R3 100K resistor
R5 100 ohm resistor
R7 1K resistor
C1, C2 0.1uf capacitor
C3 0.01uf capacitor
C4 4-40pf variable capacitor
C5 4.7pf capacitor
Q1, Q2 2N3904 transistor
L1 8-10 turns of 22gauge wire around non-conductive 1/4" diameter form
Elec Mike Electret Mic

This miniature transmitter is easy to construct and it's transmissions can be picked up on any standard FM receiver. It has a range of up to 1/4 of a mile or more. It is great for room monitoring, baby listening, nature research, etc. L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4 inch diameter form, such as a pencil. C4 is a small, screw-adjustable, trimmer capacitor. Set your FM receiver for a clear, blank space in the lower end of the band. Then, with a non-conductive tool, adjust this capacitor for the clearest reception. A little experimenting and patience may be in order. Most of the parts' values are not critical, so you can try adjusting them to see what happens.]]> andrew Radio Sat, 26 Aug 2006 07:24:56 -0700