Advice Needed UHF antenna coupling

zorrin

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I know you already have the kit, but for a specific range of frequencies you could do worse than try a band dedicated yagi

Triax - Yagi 18 Channel 35-38 (108257)
Frequency Range582-614 MHz
Channels35-38
Elements18
Gain15.5 dBi
Front To Back Ratio>25 dB
Beam Width Hor+/- 17 Degrees
Windload64 N
Weight0.92 kg
Dimensions LxWxH1800x350 mm
EAN-number5702661082573
I want to keep full UHF spectrum.
I don't want to be limited even if I lose dB on the original project and be able to hit any other frequency.
 

zorrin

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the distance between the center and the end of the reflector is 30cm.
How much space do you think I should space then?

C841BCA1-DC22-499A-B74B-BDD4DB1785D3.jpeg
0c772c8f-e0df-415c-9670-28b42d2413df-jpeg.146316
 

Terryl

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If you have close in signals at the back then zip tie some aluminum window screen to the back side of the reflectors, works wonders.
 

Terryl

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And again, whats the lowest frequency your going to be looking at??
 

zorrin

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And again, whats the lowest frequency your going to be looking at??
I wish I could cover the full UHF spectrum.
If to start the goal is to capture Belgium on channel 56.
It seems that in 2023 the channels switch to 42.
I would like to test other directions so I would like to cover from 470 to 694 Mhz if I'm not mistaken.
To infinity and beyond ! :)
 

zorrin

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If I have to rely on 470Mhz.
The calculator gives 63.78cm
Can I use the full wavelength?
I would have a space of 3.78cm between the antennas.

1670581346000.png
 

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Nie, som si istý svojou pozíciou.
Som na jednom z najvyšších miest neďaleko Paríža.
Vychádzal som z vysielača bruselskej veže, nie z Wavre.
Ale verím, že na to máš pravdu.
Dnes budem prepočítavať:)
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Halfway between 470 and 694MHz would be 582MHz (bottom of channel E35) = 51.5107cm, 1/2 = 25.76cm, 1/4 = 12.88cm

Channel 56 = 754MHz (750-758 in 8MHz DVB-T/2 Channel width) = 39.7603cm, 1/2 = 19.88cm, 1/4 = 9.94cm

Channel 42 = 642MHz (638-646) = 46.6966cm, 1/2 = 23.35cm, 1/4 = 11.67cm

Halfway between 470 and 758MHz = 614MHz (bottom of channel E39) = 48.8261cm, 1/2 = 24.41cm, 1/4 = 12.21cm

So a gap of around 23.35-25.76cm would be optimised for the middle of the new UHF TV band with the lower end being exact for the new RTBF frequency of E42. You could optimise at 19.88cm for just channel E56 until the switch to E42 in a few months maybe?
 

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I would set them at 24.5 CM apart, (1/2 wavelength spacing) this from the bottom element of the top one to the top element of the bottom one, this would let you cover the entire UHF band without one affecting the other.
 

zorrin

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I would set them at 24.5 CM apart, (1/2 wavelength spacing) this from the bottom element of the top one to the top element of the bottom one, this would let you cover the entire UHF band without one affecting the other.
Do you mean arrow in red or green?

1670842981207.png

Either way, I'll have to cut the rear reflector.
 

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Maybe full wavelength spacing would work to avoid cutting them? Or double? I’m not totally sure how it works so I might be talking rubbish here though!

I think from what @Terryl has said the spacing should be for the red arrow in your picture (bottom element of top antenna to top element of bottom antenna).
 

zorrin

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Maybe full wavelength spacing would work to avoid cutting them? Or double? I’m not totally sure how it works so I might be talking rubbish here though!

I think from what @Terryl has said the spacing should be for the red arrow in your picture (bottom element of top antenna to top element of bottom antenna).
@Terryl We are waiting for your analysis :)
If it's red, I think it'll pass.
At worst by twisting a little... :cool:
Why is it ok for a half wave and not a full wave?
I can't find an explanation on the design of the "trinappe" antennas...
 

Terryl

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I'm talking about the biggest reflector or director, if your only going to use just the elements in your picture then its between the RED arrow, if your adding the back reflector and its bigger in height from the main mounting tube that hold the driven element, (I think you measured 30 CM in the one picture) then that's the one to set the spacing by.

And you can use full wave spacing if you have room on the mast, full, half or quarter wave spacing between antenna elements helps to keep things in phase for the lowest desired receive frequency.

And after looking at your last photo did you move the mast mount? I think those antennas utillized a rear type mount for the mast, this to keep from affecting the incoming signals.
 

zorrin

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I'm talking about the biggest reflector or director, if your only going to use just the elements in your picture then its between the RED arrow, if your adding the back reflector and its bigger in height from the main mounting tube that hold the driven element, (I think you measured 30 CM in the one picture) then that's the one to set the spacing by.

And you can use full wave spacing if you have room on the mast, full, half or quarter wave spacing between antenna elements helps to keep things in phase for the lowest desired receive frequency.

And after looking at your last photo did you move the mast mount? I think those antennas utillized a rear type mount for the mast, this to keep from affecting the incoming signals.

Yes I will put the rear reflectors.
Ok if I understand correctly the space must be measured from one refector to the other (in red on the photo below)
A full wave, a half wave or a 1/4 wave.

Yes I moved the attachment point from the back to the center of the antennas to better distribute the weight for the rotor.

The result should look like this.


1670923100576.png
 

Terryl

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Yes the red arrow would be the correct spacing location...

And the mounting mast at the location you have it now will affect the signals to the receiving elements, it will affect the bottom antenna more then the top one, as it is now the biggest reflector/director element in the system, if this setup was horizontal it would not affect anything, but in a vertical polarized system it will.

Those antennas were designed with the mast mounts on the back, this to keep the directed signals from bouncing off a large metal mast in the way, if your worried about an offset load on the rotor then use a counter balance.
 

zorrin

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Yes the red arrow would be the correct spacing location...

And the mounting mast at the location you have it now will affect the signals to the receiving elements, it will affect the bottom antenna more then the top one, as it is now the biggest reflector/director element in the system, if this setup was horizontal it would not affect anything, but in a vertical polarized system it will.

Those antennas were designed with the mast mounts on the back, this to keep the directed signals from bouncing off a large metal mast in the way, if your worried about an offset load on the rotor then use a counter balance.
Did you see @ozumo's post with this link ?

Aerial positioning tests : polarity of obstructions - A.T.V. Poles, Brackets, Clamps & Aerials

I know that I lose with this modification but according to the tests it seems that the loss is slight and I protect my rotor a little.
The gain is not great with two antennas coupled but it is more fun :)
We'll see in the spring if we have anything.:)
 

Terryl

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All well and good for that type of antenna,(single inline yagi) I would like to see a test like that run on the type your using, all antennas are not the same.

I would like to see the "Smith Chart"*(if there is one) for the antenna your using, this to see where the reflection lobes would be.

I use to design and test microwave antennas for a living (yagi types).....Many Many Many Moons ago.

*Smith chart...https://en.wikipedia.org/wiki/Smith_chart
 

zorrin

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All well and good for that type of antenna,(single inline yagi) I would like to see a test like that run on the type your using, all antennas are not the same.

I would like to see the "Smith Chart"*(if there is one) for the antenna your using, this to see where the reflection lobes would be.

I use to design and test microwave antennas for a living (yagi types).....Many Many Many Moons ago.

*Smith chart...https://en.wikipedia.org/wiki/Smith_chart
I can't find any clear information on the "trinappe" antenna...
I even wonder if it is not a design evolution solely for marketing purposes to sell TNT antennas which, for some, seemed obsolete...

At my level it is also a story of budget.
both antennas = 20 euros
The Programmable terrestrial filter amplifier = 45 euros
The rotor = 15 euros
I only have the tubes left something like 20 euros
the coupler / mat preamp probably 20 euros
I already have the cables and the mount was installed at the same time as the mount for my first antennas.
Total = 120 euro

if I have an interesting result I might invest in more professional antennas but for the moment it's for fun.
It allows me to learn stuff with you and that's the main thing for me :)
 

ozumo

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zorrin

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Seems likely, found this test of a smaller tri-boom antenna:
I'm not a professional but I suspected...
at the same time my little low cost antenna at 16 euros picked up Belgium in Paris...
those if are bigger and they will be two.
Already by adding the Programmable terrestrial filter amplifier, the trace of another channel has arrived in addition to those of the Belgian channels and radios : BFM Grand Lille from Wattignies transmitter close Lille.

I believe we can have a good surprise :)
 
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