Hi,

I am looking for a something that will help my radio recieve better stations.

I've heard that using a passive antenna set at the frequency you desire will improve reception. Does anyone have a schematics for one?

Hears how I think a passive antenna works:
By using a big coil to get more power, the passive antenna circuit resonated at the same frequency as your radio is set. Now by recieving the signal with device, the radio will have better reception.
Is that explanation anywhere's close to what a passive antenna does?

I don't have the know how to build one myself. So I wanted a schematic from someone here who has the expertise to biuld a good one.

Any help is appreciated.

D.J.

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Almost all aerials are passive - in fact even those that aren't passive are passive really, just with added electronics.

Making an aerial bigger is more likely to reduce the signal, aerials should be specific sizes for the frequency in use - there are ways to make them 'better', but this is basically by making them directional (either horizontally or vertically).

You really need to give far more details of what you are wanting to do, including the type of radio, what aerial socket it has, and what bands you are wanting.

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Hi,

Thanks for the reply!

The passive antenna I want is a devise that goes on an antenna. All I know is that it has a big coil and a variable capacitor that resonate at the frequency set. Do you have a schematic for one.

The bands shouldn't be important should they. I just want the circuit, and I assume, by changing the capacitors I could recieve wahtever band(or station) I want.

I don't have the radio right now, I'm actually doing this for someone else. But the radio cost somewheres around fourty, fifty dollars. I think its just the area we are in.

Thanks

D.J.

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This sounds like an ATU (Aerial/Antenna Tuning Unit), it usually goes between a long wire aerial and a shortwave receiver - it's to match the too short long wire to the radio.

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Hi Nigel,

I think that might be what I'm after.

Someone told me about it a while back, what I told you was really All I got out of him.

Do you have the schematic for the thing you where talking about?

All I know is that it consists of a coil and capacitor in parallel, that resonates at a certain frequency, that is supposed to recieve the signal for the radio.

I did hear the guy say, that the passive antenna was supposed to be beside the radio, not touching it.

Thanks

D.J.

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An ATU connects between an aerial and the aerial socket on the receiver, the sort of device you're talking about isn't likely to do very much.

One 'similar' sort of thing is a frame aerial, which is often active, and the radio can sit inside it, but it still needs a connection to the aerial socket.

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Hi,

IS the attachment a good ATU? I found the schematic on the internet.

"One 'similar' sort of thing is a frame aerial, which is often active, and the radio can sit inside it, but it still needs a connection to the aerial socket."

This seems pretty neat, How does it work?

Thanks for your help,

D.J.

Attached Images

atu.jpeg (9.7 KB, 572 views)

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It's a large coil of wire, with the windings usually spaced apart, so you can tap on different windings - they usually have a tuning capacitor on them as well - and quite often have an active amplifier to improve performance.

It's a very old idea, in fact it was the predecessor of ferrite rod aerials, and gives a similar (directional) performance.

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Hi Nigel,

Thanks for your help!

Regards,

D.J.

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A loop antenna might be suitable - typically used for frequencies below 10 mHz. A ferrite rod is a small version of a loop antenna.

The loop antenna that I have is a coil of wire supported by a wood frame- 24 inches square with about 20 turns of wire and a 365 pf variable capacitor in parallel. The capacitor is adjusted to the frequency of interest. The energy from the loop can be connected to a radio via a coupling loop or the radio (usually a portable) can be set close to the loop. The loop must be rotated to the optimum position. This one is set up for the AM broadcast band here in the US. Less turns would work for higher frequencies (up to 10 mHz).

Dipoles can be excellent antennas at higher frequencies. At 1500 kHz a dipole would have to be 312 ft long to be resonant - not always practical. Inductors could be added to get a shorter dipole to resonate. at 10 mHz a dipole would be 47 ft long- more practical. At 100 mHz the dipole would be 4.7 ft long. The elements of many directional beams are similar in length to those of a dipole.

Inductors and capacitors can be used to improve the match between the antenna system and receiver (or transmitter). This will often improve the reception.

Anyway, just trying to supplement prior responses. What is the frequency or band of interest?

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stevez

 

Hi

Thanks for the reply it seems helpful.

So all I have to do is have a varaible capcitor and coil in parallel, and hook that up the the antenna on my radio. Will it look like the schematic below?

Am and Fm bands is all I'm after.

Thanks for the help.

D.J.

Attached Files

radio_amplifier_antenna.sch (1.6 KB, 138 views)

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DJ - I can't see the schematic.

AM broadcast band here in US is 550-1700 kHz. FM is 88-108 mHz. The antennas would be quite different though one could argue that adding any length of wire might improve either situation. Still - the demands of each band are different.

Describe what you have now and where you live. Note that adding an antenna in an RF rich environment can cause as many problems as it solves. A stronger signal at the input can overload your receiver -some being more sensitive than others.

Do you want the antennas to be directional? If directional, you'll need the means to rotate it - mechanically or electronically.

Typically the loop or ferrite loop is good for the AM broadcast band. A length of wire can work but isn't ideal. A log periodic yagi is a good directional choice for the FM band. The loop and the yagi require some means to rotate them. A discone could work well for the FM band and is omni-directional.

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stevez

 

Hi Steve,

Sorry my computor is acting up again, can't get the schematic to post right.

Lets work on the Am band first, that's what I want mostly. My radio was only twenty dollars. Dosen't play CD's right and obviously doesn't get good radio stations. So I don't care if this one gets broke experimenting.

The radio station is located on top of a mountain about thirty miles away, it is a clear path to our house.

So a capacitor and inductor placed parallel, one end of the inductor is antenna and the other goes to my radio antenna. Is that what you are talking about?

Not sure about the antenna. My antenna is just a straight wire, so if it could be positions straight up I would be happy.

Thanks for your help, I appreciate it.

D.J.

__________________
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http://www.coasttocoastam.com/

 

Are you interested in the AM broadcast band - 550 to 1700 kHz?

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stevez

 

This looks like an excellent description of the loop antenna -

http://www.vk2zay.net/article.php/47

Sorry I don't have time to read it - but if you have questions let me know.

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stevez