Antenna stacking

[gordon_s1942]

This array was built I believe soon after Aggregation occured in the Orange (NSW) area, Circa 1989/1990?.
This array faces Mt Canobolas some 130kms away.
I believe the MHA is a Hills type that was very popular at the time and predates todays Kingray.
Note the both the connection between the coax and the antenna and the Phasing bars joining it all together.

I belive the reason it was located in the front yard rather than at the rear of the house was to use the house for some protection from the severe West/SouWesterly winds we can experience in the Mountains during late winter.
Even today there was just a breeze I noticed that the array moved.
Even though it looks rather skeletal, it must present some loading against the wind.
Today most in this village use multi element Yagis with the odd phased array.
I have a friend who lives down in the gully behind this house and with a single Phased array and a MHA, he gets a faily reliable digital signal but Storms/Frosts and extreme heat do cause short periods of no signals.

[ol' boy]

Nice gordon, is that your gear???

I have seen some good UHF DX set ups lately.....

never seen a 4 stack though?

[gordon_s1942]

Oceanboy, I wish it was but NO, afraid not.

If you think thats good, you should have seen the VHF version using CA16 Hills phased arrays of some years past.
Rarely though did they use more than a 30 foot mast because of the sheer size and wind drag.

I am sure the Guru's will tell you that the phasing assembly is the most critical part of these installations, also they become VERY directional and not recomended for broadband reception.

[networkD]

This is a remarkable installation, I have always wondered how they actually match the impedance of the antennas when stacking/co-phasing two or even four antennas.

Over the years I have seen many stacking/co-phasing installations in the Gippsland region usually with two or even four Hills CA 16 Vhf antennas that look very complicated and interesting!

I have wondered how to make a co-phased installation for myself? I live in the northern suburbs of Melbourne and can get snowy reception of WIN/Prime/Southern Cross from MT Tassie near Traralgon in Gippsland. (Using a Hills Ultimax 36 - 15db gain and no mast head amp.)
I recently came into possession of another Hills Ultimax 36 and wondered if I could co-phase them to get a better signal and combine them with a UHF only mast head amplifier to receive the digital channels.
Do you think this could be possible?

Some time ago I set up a friends house with a Hills Ultimax about 10 kms away and he can sometimes get the Gippsland channels on the odd day depending on the weather.

Regards

networkD

[ol' boy]

Have a read through these boys.

[networkD]

oceanboy,

Have you had experience stacking antennas? or experimented with UHF/VHF DX?
Those sites are very interesting! What is most effective way to combine the antennas though?

Regards

networkD

[ol' boy]

I haven't stack any VHF or UHF antennas.
But i have seen plenty of them around here.

From what i read in those links, there is a bit of gear you use to combine them..... Not really sure, some just plug them straight into a mast head amp.
Not to mention thier distance apart is critical and the use on nonconductive material to suspend them.



Sorry, this next one is probably the best.

[gordon_s1942]

networkd, all the phasing is done on multiples of the frequency you want to receive.
Each antenna has to be a 1/2 wave apart, so the phasing harness is a 1/4 wave each, taking into account the 5% ? velocity ??? factor of the cable.
Phasing horizontals is easier as you use the mast as the 'seperator' but you need to stand verticals off because the metal of the mast becomes part of the antenna.
All vericals unless mounted behind the last element or 'Reflector' of the antenna, are usually on a standoff bracket.
This 'phasing' is a pain to understand and deal with.
One long deceased installer told me of the problems he had with 300 ohm ribbon on tall masts as the local channel was Vertically polarised.
He used to try in every case to have as much ribbon 'behind' the mast to minimise its picking up the local channel and cause ghosting and other problems.
Little or no coax in those early years.

[networkD]

gordon_s1942,

Thanks for your assistance, the antennas I'm trying to combine are both phased array UHF antennas.

I found this site very helpfull :



Regards

networkD

[JK200SX]

My experience with antennas stacking...

1. Around 1986 I designed and built an antenna to receive BTV6 in Ararat from Melbourne. I had a fair bit of success, then I heard about stacking and built a second antenna. After much experimentation I found that an antenna separationof 1/2 wavelength gave the optimum signal. The antennas were stacked vertically (ie on top of each other). The antennas were connected to each other using a length of 300 ohm ribbon cable, and this was spliced into exactly at the centre with another ribbon cable and ran to the TV. I tried to use coax and a balun instead instead of ribbon at the splice to feed the TV, but could not figure out why it wasn't as good as the ribbon cable.

2. A few years ago I setup 2 stacked Yagis (Fracarro 20/4046 i think?) to pickup reception from MT Tassie in St Leonards. The horizontally polarised antennas where stacked vertically. I found that the optimum spacing between the 2 antennas to be 5/8 wavelength of the centre channel I was trying to pickup. As for a combiner, I looked at the combiners available from laceys, but wher not suitable as I was trying to pickup channels ranging 33-46, but they only had dedicated conbiners for band for or band 5. The only band 4/5 combiner they had was to connect 4 antennas and this was not suitable with 2 antennas. Once again I found that the best way I was able to combine these 2 inputs was with the 2 way F-type splitter from Jaycar (ie the one that does NOT pass power on either port), and of course, equal lengths of coax from each antenna to combiner is of paramount importance.

[gordon_s1942]

when I said that everything was based on a 1/4 wavelength was misleading but correct for VHF because a 1/2 wavelength at between 55 and 88 mhz is physically big, even 108 to 210 isnt overly small either and would be major job to erect as compared to a 1/4 wave.
As jk200sx did at UHF, he used 1/2 wavelengths which is managable.
As for 300 ohm ribbon, it has a fantasticly low loss compared to coax BUT when it gets wet, the loss is astronomical.
There were several types of 300 ohm available, a solid, one with slots, one was a solid conductor plastic coated and separated with plastic pegs and a white and a brown, the others being black.
The brown was so-so but the white was useless as the UV rays literaly destroyed it in a few months outside.
I was using ribbon right up to the 70's and really didnt start using coax untill around the start of Colour.
There was a trick to enclose the ribbon is a soft plastic sheath to minimise water or salt coatings, this was used extensively in coastal or around industrial cities.
My old stacked phased arrays have that open wire 300 ohm lead as the stacking harness. I bought it ready cut from Hills when I bought the antennas.