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Post by Admin on Fri Feb 01, 2019 5:10 pm

That looks fantastic  Very Happy Smile Surprised
Lovely job.

This is one of the things I like about the radio hobby. You can be serious, frivolous, inventive, whatever you like.

BR Harry - EA/SM0VPO

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Post by zsolt on Fri Feb 01, 2019 10:30 am

Meantime 
Tadaaaammm 
loop antenna Radio10
I built a radio around the loop antenna  lol!
It's a joke of a radio , but it was fun to build it from scrap and believe it or not i works. I get to hear 2 stations loud and clear.

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Post by Admin on Thu Jan 31, 2019 12:07 am

Hi Pirx,
That was interesting information.

> So the size of the antenna can by reduced, possibly hundreds times
I think that is according to the area of the antenna. If so then that agrees very closely with the experiments I did in my younger days.

The ferrite rod antenna cannot handle any power without the ferrite saturating. Ivan's post with the pictures of the receiver show what can be achieved if the loop can be hidden, or made more acceptable.

I once tried to stuff about 8 Watts into a loop-stick antenna at 1.4MHz. The ferrite got hot and the VSWR was way out. When it cooled down the antenna would not tune.

But thank you for the information. Surprising how much one can do with so many different antenna designs.

Best regards from harry - SM0VPO

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Post by pirx on Wed Jan 30, 2019 10:08 pm

Hi,
My feeling about loops says: the ferrite rod gives approx mu times the effective area compared to air loop. So the size of the antenna can by reduced, possibly hundreds times
Thats god, but ferrites has losses. And losses go upp and mu goes down att high frequencies.
Pirx

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Post by Admin on Sun Jan 20, 2019 10:59 pm

Ivan wrote:Please excuse the typos, I lie on a hospital bed with spondylitis. I know better companuons to lie with hi

Hi Ivan,
I am sorry to hear that you are in "dry-dock" and I hope that you will get better soon.
BR Harry - SM0VPO

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Post by Admin on Sun Jan 20, 2019 10:57 pm

Hi again,
Regarding the loop versus "loopstick" (ferrite rod) antennas.

The ferrite rod antennas main advantage is it's small size and easy to tune (by sliding the coil along the rod). It is also surprisingly efficient for the size.

The wire loop antenna that used to be in the lid of many tube radios required an extra preset capacitor in the radio circuit to set the low-frequency end of the band. It was more efficient than the ferrite antenna but the price was a greater physical size.

I did some experiments in the late 60's using the ferrite and loop antennas as a transmitting antennas for 1.2MHz. The loop antenna robbed from a battery-tube radio radiated a much stronger signal (more efficient) and I had about 3x the range using my fathers transistor radio in a distance test.

BR Harry - SM0VPO

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Post by zsolt on Sat Jan 19, 2019 7:55 pm

HI,
get well
If i have some time i will start to build a spider web looking antenna , and maybe a radio next to it .

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Post by Ivan on Sat Jan 19, 2019 2:01 pm


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Post by Ivan on Sat Jan 19, 2019 12:17 pm

Hi zsolt,
I know Such radios as well. They attempted to eliminate the necessity of an external wire antenna before invention of carbonyl and ferrite cores.They were surely tuBe ones and probably not superhets.
Please excuse the typos, I lie on a hospital bed with spondylitis. I know better companuons to lie with hi

BR Ivan

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Post by zsolt on Fri Jan 18, 2019 10:22 pm

HI,
Is a loop antenna better than a ferrite rod with a coil on it? on AM band ? I know that both are somewhat directional ...
I saw a picture with a radio with loop antenna . Probably it had lamps . Beside of looking interesting i found it a real artwork , the wood frame and the antenna on top looking like a spiderweb on four wooden sticks. I would like to build something like that sometime .
Can those big ancient variable condensators be built in other interesting ways ? 
Can anyone post some schematic of such radio , maybe with lamps ? It would look pretty cool to have the lamps at sight out of the box....I can find lamps but i  think i don't know how to use them so a working schematic would really help.
Can those radios be superheterodyne ? i found some schematics in regenerative configuration with (old)transistors .

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