Can you wind a vertical like a spring?

[svenmarbles]

I made a basic antenna this morning for around 255 MHz to listen in on the Brazilian sat pirates. It works well,.. It’s a simple measured and snipped vertical made from some solid core wire soldiered onto the center conductor of a tiny bit of coax that protrudes from the BNC connection that I snipped and repurposed. I also bunched up the shielding of the coax and soldiered that to a rat tail/radial length of stranded speaker wire that is also measured out to the formula...

I started the morning trying to monitor the pirates with my outdoor mounted discone. There were there but very quiet and buried in the noise floor. After making this antenna I had them loud and clear, so I know I got it spot on with the correct resonance.

My question is,... would it harm the properties of the antenna to wind the vertical into a coil/spring shape (around a pen or something)? Purely for aesthetic,...I’d just like to keep it more compact and not so “noodly”. Also, what is the polarization of the signal? I’ve heard helical?... Perhaps a coil shape would even be more appropriate?

 

[mmckenna]

Polarization would still be vertical.

And this is pretty much exactly what is used in VHF hand held antennas. If you take one apart, it's a coiled up wire.

It's not as efficient as a straight whip, but it will work. Question will be how poorly.
Aesthetics and Antennas don't always get along really well.

 

[prcguy]

Make the antenna shorter by winding it up as you describe and it will not work as well.

 

[Ubbe]

Perhaps a coil shape would even be more appropriate?

You will add inductance and probably also capacitance if the windings are done tight enough that will lower the tuned frequency. As you do not seem to have any tool, like a VNA, to check the resonance after a coiling some part of the antenna, or the whole one, it will be difficult to predict how well the antenna will work at a specific frequency.

But as mentioned the size of an antenna are important. The bigger the better, as more metal in the air will capture more of the energy from the radio waves. Even a badly tuned big antenna will often work better than a tuned but much smaller antenna. Making antennas smaller will always be a compromise in performance.

/Ubbe

 

[svenmarbles]

Ok

You will add inductance and probably also capacitance if the windings are done tight enough that will lower the tuned frequency. As you do not seem to have any tool, like a VNA, to check the resonance after a coiling some part of the antenna, or the whole one, it will be difficult to predict how well the antenna will work at a specific frequency.

But as mentioned the size of an antenna are important. The bigger the better, as more metal in the air will capture more of the energy from the radio waves. Even a badly tuned big antenna will often work better than a tuned but much smaller antenna. Making antennas smaller will always be a compromise in performance.

/Ubbe

First half - got it..

Second half - While admittedly I’m not the foremost expert on antenna science, what you describe goes against everything that I believed to understand. By that logic, can I use my 75’ longwire antenna that I use for shortwave reception on UHF? It wouldn’t be remotely resonant. In a more practical analogy,.. I began using my big outdoor high mounted discone made for VHF/UHF to monitor the activity on 255mhz. It’s not remotely even in the neighborhood of reception quality to my much smaller yet cut for perfect resonance on 255mhz home made antenna snipped for quarter wave...

 

[Ubbe]

I began using my big outdoor high mounted discone made for VHF/UHF to monitor the activity on 255mhz. It’s not remotely even in the neighborhood of reception quality to my much smaller yet cut for perfect resonance on 255mhz home made antenna snipped for quarter wave...

That could be because the satellites are up in the sky above you and a more badly designed vertical antenna might direct the lob up in the air more than a correctly designed antenna that focus more at the horizon.

To receive signals that transmits from a source above you'll need a more specialised antenna for that purpose.

/Ubbe