Radio booster (I've Tried It)

Hi,

This is what I tried.

A coil and capacitor in parallel. One end was was connected to a long wire(antenna). The other end was grounded. I was trying to recieve 560 KHz.

The coil was 26 raps of 22 ga. wire, measuring 7/8" long. It was 3/4" diameter. Air core.

The capacitor was .01uF. So this should be tuned to about 560 KHz.

I took the coil and held it close to the base of the radio's antenna. When the radio was left alone, it's reception was fair, had some static. When the coil was in position, the signal became very staticy. :?

If it matters, my radio is a $25 Durabrand.

Does anyone know why it didn't work? Should the coil be larger?

Any help is appeciated

D.J.

Your capacitor is about 25 times too big. On the other post the link says to use a variable capacitor of about 365pF from an AM radio, but it was too small for the coil to tune down to 600kHz. They said either use a 400pF cap or add 1 extra turn on the coil.

Years ago I tried it and it worked very well. I was able to tune the big coil with the variable cap to the station whose reception was improved. The tuning was very sharp and had to be tuned to the same station as the radio.

Their coil and mine were much bigger than yours, about one foot in diameter and my AM radio was placed near it with my big coil's axis in line and in the same direction as the loopstick in my radio.

Hi

Thanks for the quick reply.

I am using a capacitor 25 times too big, oops.

I need to make sure, is the loopstick the antenna coil?

So nothing even touches the radio, it just set close and at the right angle?

Sorry if I seem to be a pest with these stupid question, I want to make sure I understand fully.

D.J.

I am a little confused :?

The resonance frequency of the coil and capacitor I am using is 560 KHz. So how is my capacitor too big? What am I missing(or doing wrong)?

Aren't we just using this as a filter? The coil/cap resonates at the frequency set, and since it's so close to the radio, it can recieve that signal. So the coil and capcitor can be any size as long as they are tuned correctly, shouldn't it?

Thanks

D.J.

how did you determine the inductance of your coil..?

I have a formula but I was lazy today so I found a calculator:
**broken link removed**

What, is my math wrong?

Funny thing, just after posting that last message I tried it again. The signal was so distorted that I couln't hear anything but static. So I did the same thing again except I ran a long anntenna from the Coil/ cap to our metal fram shade in back yard.
By the way, I am in my room so the wire was ran out my window, and the other end of the circuit is just laying on the floor. When I taped the coil to the base of my radio antenna and walked away, (just to make sure my body did not interfere) the reception became a little better so that I could hear some voices.

I tried just running an antenna from the porch frame to my radio and it really didn't help.

I need a varaible capacitor, I don't have any in my stuff. Right now I am just using a fixed capacitor and variable one would help so that I could tune that circuit as well as the radio. Mabey I can find one in my Dad's shop and try it.

So what do I need to do to make this work better?

Thanks

D.J.

Your coil is so small and close to the ferrite of the radio's loopstick that it is being very mistuned.

A huge value cap and a small coil like yours might tune to a certain frequency but not nearly as well as when the values are correct. Your 0.01uF cap is only 29 ohms at 560kHz, nearly a dead short.

So how do I correct the problem?

Could you give an example of the right coil and capacitor for 560 KHz.

Not sure If I understand how it's a dead short sorry.

Maybe if I knew the right values, it would become easier to understand.

Thanks very much for everyones time!

Regards,

D.J.

I made a coil about 1 foot square in size and connected an AM radio's 10pF to 365pF tuning capacitor across it and connected it to a long wire antenna and ground. When my radio was near it and they were tuned to the same station, the reception improved dramatically.

Google has many links to AM Loop Antennas and the best one describes what I've done and also says with a large 4 foot loop then it can be the antenna without external connections:
https://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=3191

There are some places on the internet where you can find the actual inductance value of a custom made coil.

Find the inductance and convert it to henry's, and do the same with the capacitance for the equation below:

1 /(2 * pi * sqr(L * C))

the sqr means square root, L = inductance in henry's, C = capacitance in Farads, and pi = 3.14159..... (the funny t with two legs on your calculator).

the 1/ is needed to convert time to frequency.

The answer from the equation will be frequency in Hertz.

As for the capacitor, If you go over 400pF, then you will be transmitting(?) at around 200 or so Khz.

Hi everyone,

Thanks for the help.

Audioguru, your coil is much larger than mine. I going to try this again using those values. Thanks

Thanks for the formula Mstechca.
"and pi = 3.14159..... (the funny t with two legs on your calculator). "
Yes I know what pi is, learned that a long time ago. Do you know what phi is? :lol:

This is the formula that I have been using: Fr(KHz)=159155/SQR(LC)
Fr is frequency, L is inducatance in uH, C is capacitance in pF.

Thanks for everyones help and time, I really appreciate it.

D.J.

Hi everyone,

I just wanted to let you guys know that your time in answering my questions payed off . I built a crude version that works pretty good.

The coil is 412 uH, it's about two inches long and is about two and a half inches in diameter.

I wanted it to be tuned to 560 KHz, so I would need a 190 pF capacitor. I didn't have one so I used two 100 pFs in parellel. I know I need a variable capcitor so that I can tune it better but I don't have any.

Well it worked before I had my coil/cap, I couldn't hear a think except for static. Now the reception is alright, hints is still not tuned quite right, I think it's about 555 KHz.

Right now I listening to Coast To Coast AM

Thanks for all the help!

D.J.