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dglen

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Posts: 4
Reply with quote  #1 
Hi,

I have assembled the K18V2 FM Transmitter - as far as I can tell all my solder joints are good.

I can't seem to find my transmission signal on my radio tuner - I've scanned up and down the entire dial several times and have found nothing. I'm new to this, so bear with me.

My question is, maybe, two-fold (three-fold?):

1. Is there a frequency region I should expect to find my signal? Or could it be transmitting anywhere in the 89-108MHz range? My antennae is about 80cm long, which suggests to me it should fall around 90MHz. 

2. How does the 0-30pF tuning capacitor work? Do I need to make adjustments there? 

3. IF the signal is falling in an already commercial radio-station utilized bandwidth, should I expect my transmission to be overshadowed? How might I adjust/move my transmission to an empty region of the dial?


Thanks much for all your help everyone!


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Frank

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Reply with quote  #2 
Please upload photos of both sides of the board ie. solder side and component side.

Would like to verify that soldering is indeed 'good' and that component placement and orientation is correct.
dglen

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Posts: 4
Reply with quote  #3 
hi,

thanks for the reply - here are images of the board: 2016-10-27 22.49.25.jpg  2016-10-27 22.49.48.jpg 


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Frank

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Reply with quote  #4 
I am suspicious of some of solder joints. There are 5 suspect joints - I have circled them on the attached photo. From what I can make out on the photo it looks like the solder is just attached to the component lead and not the PCB pad.

Also the red battery wire has a long 'tail' on it (also circled) which looks like it is contacting the antenna. You should snip that off.


K18v2 bottom.jpg

dglen

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Posts: 4
Reply with quote  #5 
Thanks for the tip -- I went through and cleaned up those points, as well as a couple of others -- I'm still not having any luck finding my signal though. I've had the transmitter across the room with an audio source, and scanned through my receiver a couple of times (with two different batteries) and still haven't been able to pick it out. 

I wonder if my signal is getting buried by a stronger signal on that same frequency? 

Is there a way to alter the transmission frequency? 

here are new pictures, also
2016-11-02 15.31.10.jpg  2016-11-02 15.31.27.jpg  2016-11-02 15.31.46.jpg 


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Frank

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Reply with quote  #6 
I cannot tell for sure if all your solder joints are good. There still seem to be some doubtful ones on those last photos you sent. Do you know someone with soldering experience who could take a look for you?
dglen

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Posts: 4
Reply with quote  #7 
Thanks for looking at it --

I've tested with a multimeter and as far as I can tell there don't appear to be any breaks in the circuit.

Assuming that the board itself is good, how do I go about "tuning" the transmitter? 

I have the antennae cut to about 84cm, which based on the documentation should put the frequency a little above 90MHz, right? 

I live in a somewhat urban area, is this a fool's errand because of too many competing commercial frequencies? Am I missing something when it comes to finding the broadcast?

Thanks for all your help and advice!



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Frank

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Reply with quote  #8 
Please realise that the board assembly needs to be right otherwise tuning will be impossible. Assuming that the assembly is OK then:

The operating frequency is set by components L1, C5 and C6. The antenna length should be set according to the operating frequency. The transmitter will still work if the antenna length is not 'optimum' - it will simply give reduced range.

Component L1 is etched into the PCB itself so no 'tuning' required there. C5 is a fixed capacitor and should be left as is. C6 is a variable capacitor - this is used to 'tune' the transmitter to the desired frequency.

For starters attach the antenna wire to tap B - this will give reduced range but is more stable and therefore should make it easier when tuning.

Set C6 to roughly midway. Power up the transmitter and leave it. Make sure it is not in contact with any metallic surfaces - sit it on some paper like a book or magazine.

Now move away from the transmitter by about 3 metres (10 feet) and start tuning the receiver at that distance. Tune the receiver slowly as it it easy to miss the frequency. With nothing feeding into the microphone look for a 'dead spot' on the receiver ie. silence. As I said tune slowly as it can be easy to miss.

Any competing commercial frequencies should not affect this tuning procedure. At that distance the transmitter should 'swamp'  any other competing frequency.

Make sure you are using a new 9V battery as well.
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