Fring area TV antennas (Hills CA 16)

[VK5PJ]

Hello to you all,
I live in what can be best described as "fringe area" location for TV coverage from the tranmitters at Mt Lofty in S.A. That on its own does not really constitute a good reason to rasie the subject here but over the last couple of years I have struggled to find a solution to our TV viewing difficulties. On a normal night / day we have acceptable coverage from the digital tranmitters but once any tropospheric influence start we tend to loose signal on selected frequencies.

So today I removed our old Hill CA16 that has been on the side of the house so I could give it a spring clean and move it away from the trees that have grown in front of it. This has not been our primary antenna for some time, so the other half has been reminding me I promised to remove it now its not in use.

Now down to the odd bit, the CA16 is essentially a phased array of four dipoles with what I had always thought were reflectors spaced behind the dipoles but today while giving the CA16 a spring clean I noticed the rear element halfs are not connected together. This made me wonder, was the antenna wrongly assembled and the bridging line between each reflector half left off? When I look at pictures of a Hills CA16, I can find no sign of any bridging strap on the 'reflectors' so how in the hell do they function as a reflector?[
attachment=0]ca_16_enlarged.jpg[/attachment]

I know TV antenna design is a black art but I would be interested in comments from others on the CA16's 'reflectors' as I had contemplated shortening up its elements to improve its 200MHz operation for ABC1 (digital). Any TV antenna guru's out there care to comment.

Still looking for a magic antenna to keep the partner happy on those nights when troppo is around.

Regards,

[VK3HY]

Hi Peter

There are no bridging straps. The CA16 has 8 end fed driven half wave elements arranged in pairs, fed in phase and backed up by 8 reflectors.

73 Gavin VK3HY

[VK7JG]

http://www.fracarro.com/international/d ... MA_6HD.pdf

Hi Peter .
If you want a good aerial these work very well .

In my past life I installed dozens of those phased arrays and there is an option reflector that was a continuous piece of pipe which was placed at the top and bottom of the array to increase their low frequency performance.

73
Joe

[VK5PJ]

Hello Gavin,

Hi Peter
There are no bridging straps. The CA16 has 8 end fed driven half wave elements arranged in pairs, fed in phase and backed up by 8 reflectors.
73 Gavin VK3HY

The reflectors on my CA16 and those I can find a photo of appear to have their reflectors as an open dipole (not bridged across to make a continuous element length in the middle) I even checked with an ohm meter to make sure there was nothing tricky done in the insulator block, so I am puzzled how it can behave as a reflector.

Regards,
Peter, vk5pj

[VK3HY]

Hi Peter

There are 8 reflectors on a CA16 behind 8 end fed driven half wave elements (not 4 reflectors 4 dipoles). That is why the elements are not 'bridged'.

Gavin, VK3HY

[VK5PJ]

Hi Peter
There are 8 reflectors on a CA16 - not 4 reflectors. That is why the elements are not 'bridged'.
Gavin, VK3HY

Oh, so in reality if I look back at the way you desribe it as having end fed DE's, if the driven elements are end fed, then there are 8 and not four driven elements and each of what I thought were broken reflectors are individual reflectors for each of these 8 end fed elements.

I think I will have to sleep on this one as I am not sure I see what they are trying to do, having 8 end fed driven elemets looks a lot like 4 centre fed dipoles to me. This might take a while to sink in and I should do some more reading to see if I can make sense of it.

Peter

[VK3ZAZ]

Even more puzzling was how they stacked them side by side and allowed them to receive CHANNEL 0 Melbourne.
The "Magic Mile" in Ballarat was the place to see these monsters up at 100 feet.
I was in Ballarat on Friday and marvelled at one array still clinging to the hills tower at 100 feet with bits falling off it everywhere.

The sad thing is this antenna was the standard for BTV CH6 and ABRV CH3 and
Western VIC and when aggregation came they all got ripped down in favour of combos.
Now wih VHF DTV in Mt Dundas we need the CA16HVs again.

I wonder if they still make them?

I have a fried who has a CA16 hanging from her rafters in a garage at Wickliffe still in mint if not dusty condition

2 cents worth.

CA16 with Gain Lifter

VHF Bands 1 to 3
Fringe Signal Antenna
Forward gain 12.5-15dB
Front to back ratio
11-19dB

[VK5PJ]

Hello Steve,

Even more puzzling was how they stacked them side by side and allowed them to receive CHANNEL 0 Melbourne.
I wonder if they still make them?
CA16 with Gain Lifter
VHF Bands 1 to 3
Fringe Signal Antenna
Forward gain 12.5-15dB
Front to back ratio
11-19dB

They fill the country side over here in many locations, (just as you described, many are in a very poor state of repair) especially where they had any ghosting problems. The CA16 is still listed on the Hills site as a current item. I have removed the "Gain lifter" from mine here as it was apparently only to help with low freq response, some thing I no longer need as only interested in Ch6-12 on VHF. So it would seem the legend of the CA16 lives on... if only I could get a handle on its design as I would like to improve its top end frequency response for Digital, until then its one of the COMBO antennas is operation from a pole on the house. I probably just need more height so a tower for the TV antenna may have to appear.

Peter

[VK6XLR]

Hello to you all,
I live in what can be best described as "fringe area" location for TV coverage from the tranmitters at Mt Lofty in S.A. That on its own does not really constitute a good reason to rasie the subject here but over the last couple of years I have struggled to find a solution to our TV viewing difficulties. On a normal night / day we have acceptable coverage from the digital tranmitters but once any tropospheric influence start we tend to loose signal on selected frequencies.
Regards,

Why not just so the satellite route and get a VAST system. Info here http://mysattv.com.au/
Much simpler than and easier than fringe area antennas, etc.
73,

[VK5PJ]

Hi Rick

Why not just so the satellite route and get a VAST system. Info here http://mysattv.com.au/
Much simpler than and easier than fringe area antennas, etc.
73,

I had thought of going satelite but we wanted to be able to record a program from a different channel to what we are watching with our hard disk recorder, something that would be pretty hard via a sat link unless it has all changed how they do it. No idea how the Foxtel people do it with their IQ recorder so I guess I need to get upto date with the current satelite decoders available for the VAST system.

The CA16 still intriuges me as I had thought of trying to cut one down in size to be a phased array on 144, some thing that would make a good club project with all of the old CA16's around the country side.

Peter

[VK5ZD]

Hi

The Foxtel IQ box has effectively got two receiver/decoders (and a dual LNB up at the dish) so you can watch one channel while recording another.

73
Iain

[VK5GR]

While not on VHF, I have had similar battles with UHF DTV reception at Tickera on SA's eastern Spencer Gulf area about 25km north of Wallaroo. We have seen problems with tropo, and also with ground reflections causing frequency selective fading. The DTV channels for the upper Spencer gulf are between 590-640MHz (ch38-45) and we regularly were seeing one DTV channel set at a time fade out and break up. With the demise of Ch4 analogue, interrupted TV reception was not going down well with the in laws

The solution for me was one high and one low antenna - roughly spaced so that when the low one was in a null at a given frequency that the high one would be in good signal (basic space diversity theory). As the fade moved through the band, which antenna was doing all the work changed with it. These were only roughly coupled together with a 3dB splitter - very crude indeed. I cant complain about the result, however, as reliability has gone from loosing at least one set of channels for 3-4 hours a day during low tide/high tropo times to near continuous reception.

Now, depending on your path you may see the same occurring at your place.

The other thing to be aware of with DTV is that if you see a ghost that is enhanced by the tropo ducting to a level higher than about 16dB below the main signal, via a path that is delayed greater than the guard time of the signal, then problems can also arise. I remember one of the broadcast engineers I spoke to about DTV when it first started explaining problems they were seeing at the top of St Vincent's gulf with ghosts coming from the Balacklava silos I think it was rendering the signal un-watch-able because of this. You had signal, but it was being corrupted by ghosts outside of the delay window. I don't have handy the actual delays and levels involved - this is all from memory from about 10 years ago, but it might be worth while analogue is still transmitting, to see what ghosting you are seeing and see what you can do to remove it (e.g. pan the antenna off beam to put the ghost further into a null, or maybe a second antenna aimed at the ghost and fed out of phase into your main RF feed perhaps?).

Hopefully this has given you another angle and some ideas to consider.

Regards,
Grant

[VK3AIF]

I had thought of trying to cut one down in size to be a phased array on 144.

Peter

The elements would need to be lengthened for 2M use by about 11inches each but the phasing would still be incorrect. They are factory set to around 200MHz so increasing each dimension by 200/146 or by about 1.37 would put you squarely in the ball park. I have one waiting for modification to 2M and I think they should prove to be a formidable antenna though pound for pound a yagi will give slightly better gain but the phased array is much broader in tuning and could be rotated vertical or horizontal for either end of the band and beyond with out any loss of performance. Another advantage would be a small rotational radius compared with a yagi of similar gain.