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alanh

Antenna Design Basics + Amplification

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Thanks for the thoughts, questions and suggestions everyone.

Digital penetration

I tried severing the cable braid close too (but not in) the plugs. Sorry it made no difference

M'bozo

Both antennas are outdoor. The buzz antenna is an Hills but the model sticker is illegible. It has a blue anodised "spine" and gold bars. The no buzz is Hills too with more bars and all silver but I can't see a model number.

The TV is a Kogan LED 3D KALED553D1ZP and is a 2 wire power cord

Magnum72

Tried buzzy antenna to receiver FM input. Still get buzz with TV on standby or on or fully off and receiver selecting TV or FM Tuner

alanH

no antenna amplifier

I wondered if the buzzy antenna was picking up a nastie but I have tried rotating it for any polarity effect and also pointing it in every direction and there is no change to the buzz

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The TV is a Kogan LED 3D KALED553D1ZP and is a 2 wire power cord

When the home theatre is buzzing, does unplugging the TV from the power point make the buzz go away?

If yes, you need to ensure the TV is somehow connected to the building earth. This won't be happening, in & of itself, if the TV has a 2 wire power cord.

The easiest way I have found to overcome this, is to get a protected power board, with an antenna input/output connection, that has the antenna outer (shield) connection tied to building earth.

Then, when feeding the antenna lead through the board, it ties the TV chassis (in most cases) to earth, and the hum/buzz/interference goes.

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A bit more detail please Marc.

OK.

Power board with FTA antenna in/out connection.

Multimeter on continuity setting.

On the power board, is there continuity (very low Ωs) between earth pin on power plug, and outer connection of the out FTA connection that goes to TV, etc?

Yes - done. (Assuming active/earth/neutral are connected correctly to the GPO, & the building doesn't have an O/C neutral*)

No - find another power board.

*I've come across faults like these. I'm not a sparky (should have been - had the option, passed on it.)

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Unplugging the TV does not make the buzz go away.

I have tried connecting a wire from earth to the antenna coax clamp (which clamps to the shielding). That had no effect on the buzz.

The soldering on the antennas' printed circuit board looks ok but I can't see the underside without busting attachments. Is there something there that may be the problem?

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The buzz will sound too if the TV is only on standby and there is no antenna connected.

In this state, does unplugging the TV stop the buzz?

Is there something there that may be the problem?

In the balun? Unlikely. My next step would be to try an antenna isolator on the wallplate to see if this stops the buzz, when it is happening under these conditions.

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This may be unrelated, but I've seen numerous audio noises generated by poorly-shielded flyleads and HDMI cables.

Worth checking.

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Agreed MTV but why would the buzz stop when connecting to a different antenna?

Different coax used on the two antennas.

The 'buzzy' one has poorer shielding, some corrosion or moisture ingress perhaps.

Faulty connection on a wall outlet.

Difficult to determine without being there with a speccy to 'see' what's happening.

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but why would the buzz stop when connecting to a different antenna?

I'm presuming an earth loop type issue here, since I'm not on the ground at the problem, and can't otherwise get a handle on it.

Antenna mast not earthed, earthed, parasitic earth through some other method, antenna has coaxial connection isolated from boom/not isolated from boom etc.

I sometimes use an analogue multimeter to assist when looking at these sorts of issues.

As Col mentions, the interconnecting leads could also be faulty.

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Cheers fellas-makes sence,

just another one to throw in the mix-mice/rats-yum yum cables!

Yep.... even tradies etc walking through the ceiling standing on and crushing poorly installed coax cables.

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Thankyou all for your attempts to help. I diligently tried all suggestions.

Frustratingly I have to fess up that under pressure from "the dreaded" I got an antenna guy in today.

The erratic reception of SBS was fixed by replacing a poor coax extension so that antenna continues to be used.

The antenna guy could not quickly work out why the buzz was occuring with the other antenna so on a service-cost basis we opted to ignore.

I regret that we could not learn anything from the exercise. Thankyou again.

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Phased Array design question - These have been around commercially for a long time and the design seems to unchanged as we enter the digital age (ie channels 6 -12) Whether 2 or 4 driven elements (which on there own are just simple dipoles) are all the same length. For example on the Hills models are these half or full wave and what is the optimum frequency? As they are not fold dipoles (300ohms) why are baluns used?

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Leike

Phased arrays and Yagi-Udas have been around a very long time.

The typical phased array TV antenna has its dipoles a half wave length long in total length for each one. Reflectors are usually 10 % longer. This also applies to the Yagi-Uda Vertically the dipoles are connected with a quarter wavelength long harness, with the dipole/reflector a half wavelength spacing to the one above. At the junction of the quarter wavelength harness, the signal is available. Putting the dipoles in parallel reduces the impedance. The folded dipole acts as if it is a pair of dipoles. The quarter wavelength connection increases the impedance. Now the result is a 300 Ω output. In the latest Hills catalogue they are including a balun to go from 300 Ω balanced to 75 Ω.

The old Hills CA16 4 bay phased array was designed for channels 6 - 11 ie 174 - 222 MHz. The current use is from channels 6 - 12 which is 174 - 230 MHz.

The centre frequency for the old requirements is 198 MHz giving a half wavelength of 755 mm. The new requirements 202 MHz, 740 mm.

Alanh

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