Corrected UHF antenna polarity and lost signal ???

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datigum

4 posts

Wannabe Geek

# 251620 3-Jul-2019 12:33

First a quick description of my setup...

A clear view of Mt Campbell transmitter across the width of Tasman Bay
- via UHF signal to
Phased array UHF antenna (https://www.jaycar.co.nz/heavy-duty-uhf-phased-array-tv-antenna/p/LT3154) with 24dB Masthead Amplifier (https://www.jaycar.co.nz/24db-masthead-amplifier-optimised-for-digital-tv/p/LT3254)
- connected with RG6 coax to
Panasonic DMR-XW380 DVD Recorder (twin tuner & HDD)
- connected from antenna passthru with generic coax cable to
Panasonic TH-L42E6Z LCD TV

I noticed that my antenna was mounted with Horizontal polarity, but Mt Campbell is Vertical (https://freeviewforum.co.nz/tip/rf). So I checked the signal levels on the TV, and all channels were Quality 10 Strength 10 except CH27 (mostly local Mainland TV programs), which was Q5 S10.

I rotated the antenna to Vertical, which improved CH27 to Q7 S10.

ISSUE: Sometime later I noticed ALL channels on the DVD Recorder had gone to Q0 S10 - No Signal! Running the auto-tune didn't detect any stations. But reception on the TV itself was still just fine.

It took me a while to make the connection, but when I returned the antenna to Horizontal, I could auto-tune the DVR, and all was well. I've repeated the antenna rotation a couple of times to confirm results.

The reason for correcting the polarity was an attempt to improve CH27 Mainland TV reception - in spite of good signal metrics, there is still quite frequent pixellation.

Can anyone offer a clue to what's going on?

cyril7

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# 2269208 3-Jul-2019 12:36

Hi, can you please post a photo of the current antenna showing us its orientation, polarity wise

Cyril

richms

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# 2269211 3-Jul-2019 12:41

Somethings broken in the antenna connection when you moved it?

Richard rich.ms

techricky

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Geek
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# 2269309 3-Jul-2019 13:46

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With those original high signal levels I'd guess it's quite likely overload of that masthead amplifier now..

The opposite pole was probably attenuating it enough for things to work ok before.

If you can try and get a direct connection to the antenna without the amp, it's always a better arrangement when there's sufficient signal level!

B1GGLZ

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# 2269371 3-Jul-2019 14:34

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Why use a masthead amp if you can see the Tx across the bay? Take out the masthead amp and try again.

skewt

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# 2269373 3-Jul-2019 14:39

I agree with removing the amp, probably way too much signal

DVB-T is a place about getting the right balance

datigum

4 posts

Wannabe Geek

# 2269380 3-Jul-2019 15:11

Thanks for your replies.

I installed the antenna Horizontal again without checking when I moved house, then added the pre-amp to get better signal levels. I thought maybe the distance was too much.

Will remove the pre-amp as soon as this weather improves, and let you know!

cyril7

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# 2269381 3-Jul-2019 15:14

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OK, so just confirming that your antenna as shown in the picture is infact vertical, I just needed to ask as some folk get a little confused with arrays as to which way is what.

As others have said I doubt you need that preamp, how far does google maps say you are from the tx.

Cyril

Hiamie

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Ultimate Geek
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# 2269400 3-Jul-2019 15:44

The picture you uploaded shows your antenna mounted vertically, (not horizontally). It is the driven elements that determine whether it's vertical or horizontal, not the antenna as a whole.

I also recommend removing the Masthead amplifier (and disconnect the power supply that feeds it) in case it is being overloaded with strong signal either from the TV station, or an unrelated nearby source.

Apsattv

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# 2269432 3-Jul-2019 17:46

You don't need the amp anywhere in Stoke, Richmond, Tahuna ,Atawhai etc

removing it should fix things.

datigum

4 posts

Wannabe Geek

# 2269438 3-Jul-2019 17:59

Well the weather didn't improve, but I went out & removed the pre-amp anyway.

Result? Magic Eye pictures on the TV's channels, and nothing on the DVR! I probably got some water in the connection :-(

Anyway, I grabbed the old rabbit's ears from the spare bedroom, and am running perfectly satisfactorily for now. So I'll get tonight's recordings done, and recheck connections in tomorrow's Nelson sunshine!

nitro

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# 2270296 5-Jul-2019 10:02

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looks like you got confused with the polarity.

also, if rabbit ears work, you definitely don't need the masthead amp.

datigum

4 posts

Wannabe Geek

# 2270405 5-Jul-2019 12:29

Strange, I thought I posted an update yesterday, but it's gone...

I rechecked reception yesterday when everything was dry outside, and was seeing Quality 10 Strength 10 on all channels except CH27, which is now Q10 S9 on the TV and Q10 S6 on the DVR. Everything's looking great.

The photo shows the new antenna position (Vertical), so you were right - signal overload from the pre-amp.

Thanks your your helps!

Apsattv

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# 2270667 5-Jul-2019 19:23

Mainland will always be lower as they are on Takaka Hill not MT campbell.