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15th Oct 2007, 10:01 pm | #21 |
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Re: small FM transmitters
Err, hang on a tick!
Unless I'm having another 'senior moment' here, a 2N2646 is a UNIJUNCTION transistor! . In the cct. diag., TR1 is clearly drawn as a blocking oscillator using a bipolar (although the 'collector' and 'emitter' electrodes are not clearly identified . . . . Am I missing something subtle / obvious here? [Wouldn't be the first time ] Confused Al / Skywave Last edited by Skywave; 15th Oct 2007 at 10:07 pm. |
15th Oct 2007, 10:06 pm | #22 |
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Re: small FM transmitters
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15th Oct 2007, 10:16 pm | #23 |
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Re: small FM transmitters
Thank you, Paul.
Yes, I did read post #11 & I was a little confused about that as well - since Plaka did not explicitly state that there was an error in his earlier listing. Obviously, a 2N2369 is an appropriate device for TR1, unlike a 2N2646. However, it's all history now - and I suggest we now leave it at that. Regards, Al / Skywave. |
16th Oct 2007, 9:05 am | #24 |
Pentode
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Location: Salisbury, Wiltshire, UK.
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Re: small FM transmitters
I would have thought is there was any real problems with harmonics I would have seen some light pattering on my TV via the indoor aerial. I do not have the luxury of a spectrum analyser. The fact that it does not cause interference to the TV or Radio and that it is low powered I can’t see a problem with it. The results are excellent. I have used this cct with a different audio amp fitted in a small Fidelity
record player for playing 78s. The cct that I have built I have found to be very stable. Thanks to everyone that has put in there comment’s Low power Short wave transmitter coming soon that I have built prototype around two 10.7 IF coils. It’s very work well. |
16th Oct 2007, 1:45 pm | #25 |
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Re: small FM transmitters
I have played with such FM modulators in the past and drift has definitely been the main problem. One thing that your circuit seems to be missing is "pre-emphasis". Your high frequencies will be a little dull compared with what they should be.
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16th Oct 2007, 2:40 pm | #26 |
Pentode
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Re: small FM transmitters
pre-emphasis is about right and can de altered by changing the value of the audio input capacitor. The one I use sounds very good. As for drift it is very stable.
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16th Oct 2007, 5:57 pm | #27 |
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Re: small FM transmitters
Plaka78 -
What is the current that the final transistor is drawing and what is the power supply voltage to this transistor? I know we are talking (probably) milli-watts here. And what is the final frequency of the transmitter? Just curious Thanks Al / Skywave |
17th Oct 2007, 8:46 am | #28 |
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Re: small FM transmitters
Circuit runs on 9V. I will check the current later, although a PP3 seems to last for a very long time
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18th Oct 2007, 12:28 am | #29 |
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Re: small FM transmitters
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18th Oct 2007, 7:50 pm | #30 |
Pentode
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Re: small FM transmitters
The measured current was a constant 1.45ma (very low). As for frequency it should tune across the FM band. I took my cct around to a friend today and he was amazed at the sound quality hence he wants one now
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19th Oct 2007, 7:48 am | #31 |
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Re: small FM transmitters
Thank you, Plaka78.
In my main employment, a need has arisen to design and build a sweeping low-power osc. for 88 - 108 MHz - and now have the relevant info. to make a start. Al / Skywave |
19th Oct 2007, 11:26 am | #32 |
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Location: Farnham, Surrey
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Re: small FM transmitters
Have you looked at the new part from Silicon Labs ... single chip solution ... Si4713.
Neil |