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problem with AM transmitter

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problem with AM transmitter
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New registered user
New registered user

Joined: 20 Nov 2004
Posts: 14

Post problem with AM transmitter Reply with quote
I have a transmitter that is about 2.5 watts, and the range completely sucks, and its only about 300 feet before its burried in static.

I took the WPRDJ schematic thats floating around, because I had a similar toy with the same exact transmitter, and hooked an IRF510 transistor in place of the final, and i used a modulation transformer instead of the lm386 design.

I have a copy of the schematic I made in pspice, I need a way to upload it, and maybe you can figure out what is wrong.

the irf510 is running off of 19 volts, and the CMOS ocillator is using 9.6 volts. any lower than that, i get a weaker carrier, and distorted audio.

the CMOS circuit is a divide by 4 system, and I have a 6.44 mhz crystal.

i know its at 1610khz, and it cannot be tuned in on any part of the dial, except that freq. it cant be picked up in shortwave, FM, or nothing. It has a harmonic supressor, and a variable capacitor loading cap after the harmonic network, and before the antenna.

according to my power meter, im putting out 2 to 2.5watts.

Ive got a big ground poll hammered into the ground, and im using a long CB antenaa, thats the only thing I had lying around. the antenna is bolted to the roof of the garage which houses the transmitter.

here is the problem: if i try to ground the transmitter to that poll, or the power line ground, it doesnt matter, the signal becomes distorted, and weak, and the distance is reduced to about 5 feet.

If i leave the transmitter ungrounded, it works alot better, about 300 feet, and if the radio is too close to the coax, it becomes distorted because the tx is overloading the reciever.

but if im not too close, or not too far away, the transmitter modulation sounds very nice, no distortion, or anything, so I must be doing something right.

i think its radiating out of the coax is why.
Sun Nov 21, 2004 8:22 pm View user's profile Send private message
Regular poster
Regular poster

Joined: 08 Jun 2009
Posts: 29


Post Reply with quote
im no expert but if your using a CB antenna then it sounds like SWR problems to me. A CB antenna is ment for 27MHZ not 1000 and somthing KHZ
Fri Jun 19, 2009 2:47 am View user's profile Send private message Visit poster's website
Site master
Site master

Joined: 18 Jan 2002
Posts: 3099
Location: Radio Land

Post Reply with quote
Crappy antenna and crappy transmitter.

Best regards,
Marko - PCS Electronics
Turn your PC into a FM radio station!
fax +386 4 2316 128
Fri Jun 19, 2009 8:44 am View user's profile Send private message Visit poster's website
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