I believe in polarization now!

[NeoHam]

MIT Physics Demo -- Dipole Antenna - YouTube

 

[Mudfoot]

It's a cool video....

However, these students are repeating an demonstration that Bell labs did back in late 40's or 50's. They did basically the same thing. The video is on Youtube somewhere.

 

[KC9Q]

The published facts: Isolation value between polarization is 20 dB. What's that mean? If one station is vertical and the other is horizontal the received signals with be down 20 dB from each other. Thus, if a signal would be 20 dB over S9 if both stations were vertical, the cross polarization will be received at S9. Or if the stations were both S9 using the same polarization, the cross-polarized station will now be received at around S6. (Note each S-unit = 6 dB, thus 3 s-units are 3 x 6 dB = 18 dB).

Hard to see that will the light bulb, but easy to measure with a signal strength meter. (Note valid condition for direct ground wave only.)

 

[Moleculo]

(Note valid condition for direct ground wave only.)

I think you mean direct path, not ground wave, right? Ground wave propagation only occurs below about 3Mhz.

 

[KC9Q]

Correct, Direct Wave. It is meant to exclude any type of skywave transmissions.

 

[Captain Kilowatt]

Funny thing about cross polarization. It seems to matter more on VHF and above. I have noticed the typical 20 or 25 dB difference on HFbut on 2m SSB the difference is dramatic.An S-9 signal dissapears with cross polarization. Not sure why the difference but it is quite repeatable on my end regardless if it is me or the other station that switches polarity. Anyone else notice tht on VHF preferably SSB as on FM the alc action works differently.

 

[wavrider]

Funny thing about cross polarization. It seems to matter more on VHF and above. I have noticed the typical 20 or 25 dB difference on HFbut on 2m SSB the difference is dramatic.An S-9 signal dissapears with cross polarization. Not sure why the difference but it is quite repeatable on my end regardless if it is me or the other station that switches polarity. Anyone else notice tht on VHF preferably SSB as on FM the alc action works differently.

Yes.

At the QTH in FL a good many of us would rag chew on two meter SSB in the evenings.

Going from the yagi horizontal to the vertical used for repeater work some of the group would just drop off. Could not hear them yet on the yagi they would be strong, VHF is real sensitive to polarization IMO.

 

[KC9Q]

When I did microwave systems at 2 GHz and 6 GHz we would routinely get around 30 to 40 dB of isolation between vertical and horizontal signals on the same path. So yes the cross polarization values do increase at the higher frequencies.

I believe Avanti Antenna used this principal to get 20 to 25 dB of isolation between normal vertical polarized signals and horizontal polarized signals with their dual polarized PDL Quad antenna's. I also believe that man made electrical noise is generally considered vertically polarized, so going horizontal would reduce background noise a bit.

 

[hookedon6]

It's a cool video....

However, these students are repeating an demonstration that Bell labs did back in late 40's or 50's..

Dayum,................. some one else remembers BELL LABS, I used to work there (Columbus plant) back in the day.

now, it seems that I only work the annual special event station,........... do get some friendly comments about the "CB" prefix