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Subject Topic: DSE USB FM Sender Post ReplyPost New Topic
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Spiker
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Posted: 22 May 2012 at 11:02pm | IP Logged Quote Spiker

Hi,
I have a question regarding the DSE USB FM Sender.

I recently bought one of these off TradeMe with the idea of using it to transmit interweb radio from my notebook to me while at work on my ride on mower. I mow lawns, mainly rural, around the place & wanted a change of listening selection.

I have it sitting above the sun visor & mainly it works reasonably ok, it just needs a few more legs to get the signal to me at the back of the bigger jobs..

At the moment I'm getting a good signal up to about 30-40 meters away depending on whats in the way after that it starts to break up..

On opening it up it has a coiled copper wire aerial, is it feasible to change that for something else that might make a little difference?

I see it's discontinued by DSE but is available overseas still. One picture I saw showed an external aerial hanging out of it, just a short bit of wire I guess. I'm wondering if it makes any sort of difference?

Any ideas?

My micro station



The guts of the sender..


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RadioTech
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Posted: 23 May 2012 at 5:07am | IP Logged Quote RadioTech

Hi Spiker,

Welcome to the forum :)

That's some good old kiwi ingenuity there!

Those USB senders are built around an IC made by a company called Rohm and it's the one that's uppermost in the photo - the black thing with all the legs on it near where the coil connects.

It's had the markings ground off (in an attempt to stop people cloning their design) but it will most likely be a BH series IC which is effectively a complete FM transmitter in a chip.

The RF output stage is built into the IC, and gives a few micro-watts output - which is why you don't get much range. 
As an 'audio sender' these things are made for very short distance operation.

They're designed to send audio from your USB device to your car radio or your home stereo etc - so 10 - 20 metres is about it.
(This is also done to comply with the Federal regulations in countries like the USA etc)

The coil is probably a quarter-wave helical (coiled up so it's compact and convenient).
You could try disconnecting it and attaching a piece of wire to the same point. The wire needs to be a quarter wave at whatever frequency you are using.
For example, if you are using 88.0 MHz, it needs to be 850 mm long. At 107 MHz it needs to be 700 mm long.

The other thing that may help is getting the antenna outside the car. Despite cars having glass all around, the metal body-work acts like a big Faraday cage and can severely attenuate RF signals.

If you try the external piece of wire experiment, and outside the car, you ideally need to get the wire vertical and away from the car's metalwork.

I can't guarantee that either of these will work but they are your best shot and there is nothing to lose by trying.

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Spiker
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Posted: 23 May 2012 at 2:57pm | IP Logged Quote Spiker

Hi RT,

Thanks for the welcome & reply. I'm surprised these forums aren't used much & appreciate you keeping an eye out for new posts.

I did a little research on the net last night & educated myself on how aerials & FM aerials in particular work & had come to the conclusion my best shot was to  attach a wire of the correct length as you've suggested.

If that helps, as a semi permanent solution would a standard car aerial adjusted out to the right length work as well? I could fit a female plug to the sender unit & corresponding male plug to the coax..

Thanks again for your help.
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Spiker
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Posted: 24 May 2012 at 5:01am | IP Logged Quote Spiker

OK that made a huge difference! Good solid signal for at least 100 metres. After that it starts to lose stereo & cuts in and out but can still pick it up over 200 metres away.

Next thing is to fit some sort of plug to the unit so that I can remove the aerial & connect a compact aerial of some sort to it so it can be used indoors as well. Some sort of bayonet fitting for quick easy changes would be good. I also need to somehow fit a semi permanent aerial to my ute. The bamboo pole is ok but may not be too durable..


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RadioTech
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Posted: 24 May 2012 at 5:49am | IP Logged Quote RadioTech

That's excellent news. I'm impressed with the photos you've provided too!
It makes a huge difference, and will help others who may come looking for answers on a similar situation.

You can certainly fit a socket to the case, and connect the centre pin of the socket to the point on the PCB where the coil used to connect.
Connect the body of the socket to the negative rail on the PCB.

There is also no reason why you can have a permanently mounted antenna on your car either, and connect it as per the above socket.
A standard car AM/FM antenna could be used - just extend it to the right length for the frequency you are using.

Good luck!
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Spiker
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Posted: 25 May 2012 at 3:50am | IP Logged Quote Spiker

Stopped in at Jaycar today to look at antennas. The magnetic mount ones seem like a good idea, pricey little buggers though..
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jamespoo
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Posted: 18 November 2012 at 8:19pm | IP Logged Quote jamespoo

i own this same fm broadcaster and in my tests i have done my one can reach about 310m to 400m this was done with a cheap mobile phone with built in fm radio and antenna

but if i go to my sister house witch is about 435m i can pick it up fine with her radio but she as a really good one

when her stereo is at the back of her house witch is 440m away it starts to cut out a bit

but i used to used the fm sender when i would cut our lawn and found the lawn mower would interfere with the signal
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