Log Periodic help please.....

[fires999]

Good Morning from a wet UK !!
Quick question please as I keep getting conflicting answers !!
I have replaced a couple of antennas at home for a log periodic designed for a wideband 200 - 1300mhz.
It's on my telescopic mast with a rotator.
Tend to listen to UHF Military Airband and Satcom ( 250mhz) and also stuff found in 400-480 mhz UHF.
So, does the antenna need to be mounted vertically so it looks like a directional arrow or horizontal meaning flat ?
Had lots of answers, to be fair, 50/50 split and in honesty , will it really matter ?
Thanks so much in advance.
Keep safe everyone,
Kevin
(US Airforce Mildenhall Fire Department, Suffolk, England - UK Firefighter attached to USAF here in East of England)

 

[AB5ID]

It can make a big difference. You want the antenna polarity to match whatever you are listening to. I'm not sure about satellites at 250 MHz; circular polarization maybe the best option?

 

[prcguy]

For terrestrial stuff go vertical. UHF satcom downlink is RHCP so the linear pol of your log periodic will not matter.

 

[Ubbe]

Receive antennas for cellular sites use crosspolarisation where half of the elements are in one polarisation and the other half are turned 180 to the first and have one receiver connected to each polarisation and use diversity to receive from the best one. RF Signals bounce around and shift polarity and cellular phones are held in different positions. But for 2-way radio they use antennas in vertical positions even for portable radios, so vertical antennas will be preferred and will receive most of the signal compared to horisontal.

I know that they did experiments with horisontal and vertical antennas for 2-way radio sites in a diversity configuration but the horisontal didn't receive much and it was more efficient to have two vertical antennas spaced apart as much as possible.

/Ubbe

 

[fires999]

Good morning,
Sorry for the reply delay..unfortunately my big boss Mr Biden insists the Fire Dept has some sort of roster for its firefighters..basically I was on duty !!!
Thanks so much for the replies, really appreciate it.
Realistically I'm able to easily access the telescopic mast so think I will try 1 month vertically and then one month horizontally, back to back months so conditions should be similar and then see what works.
As mentioned I do have a rotator so that can help with reception, just wish I had similar device that could move the log periodic from horizontal to vertical in a similar fashion...is there such a device ?
Speak soon, be safe
Kev ( US Airforce in Uk)

 

[mmckenna]

just wish I had similar device that could move the log periodic from horizontal to vertical in a similar fashion...is there such a device ?

Azimuth/Elevation rotor. It's designed to rotate and aim antennas upwards, like for satellite/EME work, but you could mount the log periodic on there to rotate it from horizontal to vertical.

Not cheap, but it'll do what you want:

Welcome to Yaesu.com

 

[Ubbe]

A log period antenna use a dual boom design, so there will be all kinds of installation issues, balancing with counter weights, trying to use a $700 azimut rotator. Just the rotator alone are the same cost as a second log period antenna installed in a different polarisation.

I wish more scanners would use dual diversity receivers. Icom's $600 conventional analog R2500 are the only one I know of and works fantastic to switch unnoticeable between different antennas. In a vehicle while driving, or monitoring a mobile unit from home, it gets rid of all that picket fencing sound when the signal rapidly change in signal level.

I guess one could get one of those $50 TV antennas of dipole or logperiod type of elements, not the butterfly x-wing models, and connect to a portable scanner and stand on the roof and tilt it in different angles to see what the result would be.

/Ubbe