cross polorisation isnt a real issue at hf though as far as im aware is it ?? with sloper dipoles i think you may get a slight directional gain in the direction of slope but i recon its a fairy tail with the vert . you should of done a poll rob and made it another teaser.. be interesting to hear steves take

billy

Rob,

It's very different if we are talking HF or VHF/UHF:

HF
The vagaries of the ionosphere mean that the polarization of a refracted signal is constantly changing, no matter what polarization antenna it was transmitted from. That's one of the reasons that when you receive it on say, a horizontal antenna, you get fading - sometimes the polarization lines up with your antenna, next second it doesn't. So there would be no advantage to any particular polarization on the transmit antenna.

As I explained in the horizontal vs vertical Puzzle, horizontally polarized signals suffer less loss at the first ground reflection, but I don't think that is what your Guru is talking about.

VHF/UHF
At these frequencies the transmitted polarization is typically maintained all the way through to the receive antenna - no ionosphere to muck things up Theoretically, if you have a Rx antenna which is 90 degrees orientated to the polarization of the incoming signal, you pick up nothing! In practice you don't get "zero", but you can easily be 20dB or more down compared with having the correct polarization.

If you don't know whether the signal you are trying to pick up is horizontally or vertically polarised, a 45 degree slant may be one solution but:

1) You sacrifice 3dB of signal compared with having the correct polarization.

2) Consider what happens if everyone adopts the idea and starts transmitting and receiving on 45 degree polarization - half the time your Rx antenna will be 90 degrees from the polarization of the received signal and you'll have 20dB attenuation or more.

Not sure that's answered it fully, but it's a start

Steve G3TXQ

Sorry - just re-read your posting more thoroughly and realised the "guru" must be talking about HF. In which case what he says is nonsense. As I (and Billy) said, cross-polaristaion is not a factor on an ionospheric path because the polarization direction is not maintained through the refraction process.

Here's a direct quote from the ARRL Antenna Book:



73,
Steve G3TXQ

I was going to post a comment but thought I would leave it to Steve first.

My comment:-
I assume here you are talking VHF/UHF.
If you think about this, and use a diagram, you will quickly see the problem.
Just think about two slant polarised beams pointed at each other and the options you have.

I'm afraid it's still vertical for FM and horizontal for SSB to avoid huge losses.
Going from a simple vertical to a horizontal dipole can give the equivalent of 20db, or more, gain.
We can all work out what that equates to in increased power output.

In reality horizontal is to be preferred whatever the mode as it is less prone to fading.
Natural objects are, predominantly, horizontal and therefore there is no Brewster angle cancellation.
Telephone poles, lamp posts, electricity pylons etc. cause less scattering effect to horizontally polarised signals.
Amateur, VHF, use of vertical polarisation is a relatively recent phenomenon as, back in the days of AM, everyone I knew used horizontal for mobile as well as fixed stations.
The VHF/UHF DX Book has useful information relating to this.

It was only with the advent of repeaters, and the need to use PMR standards on shared masts, that verticals became common place.
And, of course, verticals are the easy option when it comes to vehicle mounted antennas.

This all refers to direct, or tropo, signals.
With ES many say that the polarisation of the antenna does not matter as, by the time the signal arrives. the polarity could be anything.
Whilst there are elements of truth in this my understanding is that whereas the received signal polarisation may be unpredictable there are advantages if the signal reaching the E layer from the transmitter is parallel to the earths surface.
Additionally a good, horizontal, beam at the RX end is an advantage when peaking the required signals and nulling the unwanted ones from a different direction. Both of which could be well over S9.

Hope you don't mind me butting in Steve but this has been brought up a couple of times.

Cheers

Tony

Hi Tony,

Not at all! I'm still unclear whether the guru was talking about HF or VHF/UHF. The mention of trapped verticals and radials in the original posting made me think it was HF, but that's not necessarily the case.

Either way it's an ill-conceived idea

73,
Steve G3TXQ

One further thought - I wonder if the guru is expecting that a 45 degree slant might confer some advantage at HF in terms of "take-off" angle.

Here are the elevation responses of a 20m half-wave dipole with its centre at 35ft. Blue trace is with the dipole horizontal; then I rotated it 45 degrees about its centre and got the green trace; then another 45 degrees to get the red (vertical) trace:



Again there's no argument for a 45 degree slant.

Steve G3TXQ

When I read it I got the impression that the idea had been proposed for VHF but was being carried through to HF.
Maybe I'm wrong. I often am.
I was reading an old Radcom the other day.
I forget the date but it was probably the late 70s when repeaters were on the up.
A suggestion that all operations on VHF should be vertically polarised.
Needless to say that was also pointed out as being an extremely ill-conceived idea.

On another group some time ago one guy suggested that beams were mounted horizontally as that way they have less visual impact.

Where do people get these ideas.

Cheers

Tony

Without beating around the bush, the so called "expert" is talking Bollox !
73 de Dave. And A Happy & Healthy New Year To You All.

I am quite intrigued by the idea of a 'slanting' antenna. But can't see how it could ever work for everybody.

Consider this - which way do you lean your 45 degree antenna?

If everyone leaned any-which way then there will still be those who are 90 degrees different to others and thence have the same cross-polarisation losses. So no gain there then.

I seem to remember from my RAE days that, as Steve and Tony say, at HF it makes little difference. At VHF and higher then the convention is vertical for FM and always horizontal for SSB and CW.

I don't have beams any more, but did have an X-Y J-beam for 2m which was switchable between vertical and horizontal depending on mode being used.

Those who worked satellites used a phasing harness to give circular polarisation or used a helix beam.

is that vert or horiz bollox? unless one hasnt dropped then it would be slanted

As I've said before this has only become convention since the advent of repeaters.
It always used to be horizontal, even for mobile, through the days of AM and the transition to SSB.
The small amount of FM that was around was also horizontally polarised, until the advent of repeaters.
First FM mobiles became vertical for repeater operation and then FM in general became vertical with the band use changing.
FM DX seemed to dis-appear with even fixed stations operating through repeaters and using omnidirectional verticals and VHF FM being thought of as a short distance communications medium.
Meanwhile SSB carried on with beams, horizontal polarisation and 200km plus still being regarded as "local".
The exception is 4m where you often work, in the main DX, FM stations who are horizontally polarised.

The initial choice of horizontal polarisation was not a random , or accidental, choice but one based on technical merit.

Cheers

Tony

All encompassing !
As in Gatox & Bollaux

73 de Dave

i think theres a few hams on this forum that lean the other way

or
73 de Dave

's i think