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Need directional antenna design for AM

 
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Need directional antenna design for AM
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mbates14
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Joined: 20 Nov 2004
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Post Need directional antenna design for AM Reply with quote
I have an IRF510 1watt, it might be 2watt 1610khz AM transmitter.

the range completely sucks, so I want to make a directional antenna for it.

is this possible? if so, how?

(current range with omnidirectional antenna is about 300 feet before it burries in static with 2W)
Sat Nov 20, 2004 11:27 pm View user's profile Send private message
DrSandi
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Location: Olympia, WA USA

Post AM Antenna hints Reply with quote
First, a directional AM antenna would take a LOT of space.

Second, if you're not getting more than 300 feet with 2 Watts, you need to redesign the antenna you've got now.

What is it? Where is it? What kind of ground do you have. How long is it. Is it horizontal or vertical. Do you have any kind of matching network between the TX and the antenna?

Unlike FM, AM frequencies really need a good ground or the signal goes nowhere.

An outdoor antenna is better than an indoor antenna. Buildings and trees block AM signals too, just not as badly as FM.

Is it away from solid objects. Metal is the worst, but even being close to non-conductive material sucks away power before it can travel through the neighborhood.

A little more information would help diagnose what's wrong.


Dr. Sandi
Sun Nov 21, 2004 4:12 am View user's profile Send private message Visit poster's website
erobertg
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Post What is it? Reply with quote
Is IRF510 that the name of your transmitter or the output MOSFET transistor? The IRF510 MOSFET is good for 5-15 watts.

At 1610 kHz, are you picking up the right frequency, or a stray harmonic or a hetrodyne? It seems you should be getting out better than that. Just what are you using for an anteena

I agree with Dr Sandi, a directional antenna is impractical for your frequency. They dont use yagis or log perodic antennas for that frequency. You would need at least 2 large towers or more in a phased array. I think you need simply an efficient antenna.
Sun Nov 21, 2004 4:26 pm View user's profile Send private message
mbates14
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Post Reply with quote
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.

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.

i think its radiating out of the coax is why.


Last edited by mbates14 on Sun Nov 21, 2004 8:14 pm; edited 1 time in total
Sun Nov 21, 2004 6:36 pm View user's profile Send private message
mbates14
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Post Reply with quote
ill make a schematic, and show you what I have done, to build my transmitter.

its very very clean sound. if i get too close to the coax, or antenna, the dio overloads, and distorts.
Sun Nov 21, 2004 6:44 pm View user's profile Send private message
mbates14
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Post Reply with quote
i have the schematic of my transmitter done in pspice, as soon as I figure out how to use attachments, i will post it.
Sun Nov 21, 2004 8:07 pm View user's profile Send private message
mbates14
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Post Reply with quote
i think ill start a new thread, because im running off topic

i started it into a new topic, since it isnt dealing with directional antennas anymore, so you can kindly delete this thread.
Sun Nov 21, 2004 8:20 pm View user's profile Send private message
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