audioguru2
- Apr 6, 2004
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radiopirate
- Mar 30, 2005
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More like the one on the right
components mounted on non metalic side
of board
Longish component leads esp T1 ?
Only difference compnents fairly close
components mounted on non metalic side
of board
Longish component leads esp T1 ?
Only difference compnents fairly close
audioguru2
- Apr 6, 2004
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The one on the left works fine. The one on the right doesn't work because its long wires have too much inductance and stray capacitance for it to work at the Very High Frequency of about 100MHz.
T1 is the main oscillator. It and its associated parts must have short wires. ;D
T1 is the main oscillator. It and its associated parts must have short wires. ;D
audioguru2
- Apr 6, 2004
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Hi Guys,
I measured the range of my mod4 FM transmitter: about 1km before it was drown by a real station on the same RF frequency. The signal faded when I walked or drove with houses in beween and might travel 5km or more line-of-sight if I had a clear station frequency.
It transmits with low distortion and wideband audio. For its range I had it transmitting the sound of my son's alarm clock beeping. Then I had it transmitting the sound it picked-up from my souped-up clock radio that was playing another FM station's music. Its reception on my Walkman, car radio and home stereo sounded exactly the same as the station directly! ;D Except it was in mono, not stereo. :'(
The range dropped sharply when I reduced the length of its 30" antenna.
It seems to eat batteries. After a couple of hours, its brand new alkaline 9V battery measures 8.25V and its current dropped to about 39mA.
I took it from my 21 degrees C home to 13 degrees C outside and didn't notice any drift in its RF frequency. I guess the tempco of the RF caps I used luckily reverse-matched the tempco of the oscillator transistor and my coils.
With its low-dropout voltage regulator powering its mic, preamp and RF oscillator nothing much changed when the battery voltage reduced. Its range probably reduced but I didn't re-measure it.
Google has 137,000 links for FM transmitters in my city (I wanted to find the weakest one the farthest from me, to use its RF frequency). Subtracting the 100 real FM stations, that leaves about 136,899 copies of my project here! ;D ;D
I measured the range of my mod4 FM transmitter: about 1km before it was drown by a real station on the same RF frequency. The signal faded when I walked or drove with houses in beween and might travel 5km or more line-of-sight if I had a clear station frequency.
It transmits with low distortion and wideband audio. For its range I had it transmitting the sound of my son's alarm clock beeping. Then I had it transmitting the sound it picked-up from my souped-up clock radio that was playing another FM station's music. Its reception on my Walkman, car radio and home stereo sounded exactly the same as the station directly! ;D Except it was in mono, not stereo. :'(
The range dropped sharply when I reduced the length of its 30" antenna.
It seems to eat batteries. After a couple of hours, its brand new alkaline 9V battery measures 8.25V and its current dropped to about 39mA.
I took it from my 21 degrees C home to 13 degrees C outside and didn't notice any drift in its RF frequency. I guess the tempco of the RF caps I used luckily reverse-matched the tempco of the oscillator transistor and my coils.
With its low-dropout voltage regulator powering its mic, preamp and RF oscillator nothing much changed when the battery voltage reduced. Its range probably reduced but I didn't re-measure it.
Google has 137,000 links for FM transmitters in my city (I wanted to find the weakest one the farthest from me, to use its RF frequency). Subtracting the 100 real FM stations, that leaves about 136,899 copies of my project here! ;D ;D
audioguru2
- Apr 6, 2004
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Hi Sasi,
Your very nice ground-plane antenna is strong enough to withstand a hurricane (monsoon?).
Are the lengths 1/4 wavelength?
I might be incorrect, but I figure that a dipole has 3dB gain over a whip antenna and your ground-plane has 3dB gain over a dipole and is omni-directional. Therefore yor ground-plane antenna has double the range of a whip. Correct?
Your very nice ground-plane antenna is strong enough to withstand a hurricane (monsoon?).
Are the lengths 1/4 wavelength?
I might be incorrect, but I figure that a dipole has 3dB gain over a whip antenna and your ground-plane has 3dB gain over a dipole and is omni-directional. Therefore yor ground-plane antenna has double the range of a whip. Correct?
Referring to my previous post. Yes Audioguru, you was right. I was reffering to a wrong schematic, I was talking about http://www.electronics-lab.com/projects/rf/001/index.html. I don't know how do I did such a reference mistake.
The transmitter you are talking about (4W with two transistors 2N2219) has certainly overheating problems and could never produce 4w of RF power, at least with those transistors.
By replacing T1 with 2N4427 and T2 with 2N4427, 2N3866, 2N3553, 2N3924, BFS23A, you can achieve a power increase compare to 2N2219 and a good heatsink would be sufficient for cooling them down. 2N2219 cannot dissipate such power levels. (easyly at least)
In case you increase R3 from 47 to anything between 51 to 100 Ohms, the transistor will run cooler but the power would be lower, still high for a good range. I suggest T2 be a real RF transistor like as suggested above. They have higher gain and efficiency at the desired frequencies.
Regards
P.
The transmitter you are talking about (4W with two transistors 2N2219) has certainly overheating problems and could never produce 4w of RF power, at least with those transistors.
By replacing T1 with 2N4427 and T2 with 2N4427, 2N3866, 2N3553, 2N3924, BFS23A, you can achieve a power increase compare to 2N2219 and a good heatsink would be sufficient for cooling them down. 2N2219 cannot dissipate such power levels. (easyly at least)
In case you increase R3 from 47 to anything between 51 to 100 Ohms, the transistor will run cooler but the power would be lower, still high for a good range. I suggest T2 be a real RF transistor like as suggested above. They have higher gain and efficiency at the desired frequencies.
Regards
P.
, now anyone wanting to contact aliens can build your groundplane antenna ;D ;D.radiopirate
- Mar 30, 2005
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Replaced T2 with another transistor Blw29
T2 gets hot but does not need a heatsink
getting 1- 1 1/2 watts out of it
I find this difficult to tune.
could the tuning capacitor be replaced with one of a smaller value
perhaps in parallel with another capicitor
I want to run this at 88Mhz. What values should I use?
T2 gets hot but does not need a heatsink
getting 1- 1 1/2 watts out of it
I find this difficult to tune.
could the tuning capacitor be replaced with one of a smaller value
perhaps in parallel with another capicitor
I want to run this at 88Mhz. What values should I use?
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