Hi
I have built/ assembled a little phono thing in a 60 watt mITX case.
The phono case is metal and now houses a soft latch switch, a moving magnet phono preamp, a headphone preamp with low wattage power amp and an FM transmitter. Happily, after a lot of fiddling (oh those ground loops) the whole setup is working surprisingly well.
When I first assembled the parts I tested the setup with a length of multi strand copper wire (trimmed to about 730mm), I have since found is about a 0.25 wave. It worked best when orientated vertically and compared to the rubber ducky I am now using it gave a much bigger range, close to 100 meters(ish) but wasn’t brilliant inside.
The rubber ducky antenna;
The antenna is supposedly good for 76 to 108 Mhz which I guess means it should work best at its midpoint of 92 Mhz. Unfortunately for me that area of the frequencies is rather cluttered so I had to go up to 107.3 Mhz for a clear frequency.
The rubber ducky works best vertically and FM reception within our house is good with some interference/static in one of the rooms which occurs whenever someone is moving near the (cheap) radio in that room. The general range outside the house isn’t huge, about 50 meters before static starts (using a mp3 radio as a receiver). The setup is roughly in the middle of a relatively small house which is constructed from concrete internal and external walls.
If it is at all possible, I would like to try and tune the FM transmission to be less about range and more about precision/accuracy within our house (alas, my skills are limited and I don’t know where to start).
So, I would appreciate input from anyone who has some thoughts, ideas and/or questions...
Regards.
If ayony wants/needs more info about the parts I used, here are the links
Case;
Phono preamp;
FM transmitter;
Switch;
http://www.electronics-lab.com/project/toggle-on-off-switch/
Antenna;
http://www.ebay.com/itm/321888374143?rmvSB=true
BNC connector;
Headphones / amp; http://www.ebay.de/sch/sis.html?_nkw=YAMAHA+YDA138+E+Digital+Stereo+Audio+Amplifier+Board+2+20W+headphone+AMP+12V&_itemId=291569626608&_trksid=p2047675.m4099
Well for those in Canada who use the RSS 123 law for event transmission could definitely use the BH 1415F chip and use a broadband amplifier circuit to amplify it. Just remember that you'll also need to worry about SWR ratios when you start using power above 200-300 mW. Again this is info for the Canada folks using RSS 123 but also beware that I've heart that spectrum management in Canada if they want to go strictly by the book will nab you for not using a certified transmitter.
For info purposes I did watch an interesting video titled Commercial FM VS Pirate FM in Canada and there was where I found info on the BH 1415F chip (made in Japan). The specs are very good against harmonics out of the chip because of its filtering. The problem only arises if the broadband amp used is not a clean linear amplifier and thus generating spurs.
It was interesting when they showed an expensive certified transmitter against a CZE 7C. Just something to ponder upon when you study what can be done with this amazing chip.
Best Regards.