Hi folks,
Currently i have a 6 element rfi yagi yb6-61 (uhf) attached to our t.v. mast. The swr is very low and it keys channel 7 brisbane even with 2 watts from about 80 kays away. I'm happy with recieve but when transmitting with more than 2 watts there is interference with the television. There is only about 1.5 meters separation between the tv and uhf yagi. I cant really go much lower with the yagi without hitting the roof. I'm wondering if earthing the tv mast would help things? Or perhaps moving the yagi to the top of the mast and dropping the uhf tv lower might do the trick?
Any thoughts welcome
Thanks Ziggybyrne
antenna earthing necessary?
Forum rules
Aussiescanners takes no responsibility for any modification undertaken, these are to be done at your own risk and should only be performed by those with good knowledge of radio and soldering.
Aussiescanners takes no responsibility for any modification undertaken, these are to be done at your own risk and should only be performed by those with good knowledge of radio and soldering.
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ziggybyrne
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Comint
- Senior Member
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Re: antenna earthing necessary?
I would suggest you put it on a totally different mast, as far from the TV antenna as possible.ziggybyrne wrote:Hi folks,
Currently i have a 6 element rfi yagi yb6-61 (uhf) attached to our t.v. mast. The swr is very low and it keys channel 7 brisbane even with 2 watts from about 80 kays away. I'm happy with recieve but when transmitting with more than 2 watts there is interference with the television. There is only about 1.5 meters separation between the tv and uhf yagi. I cant really go much lower with the yagi without hitting the roof. I'm wondering if earthing the tv mast would help things? Or perhaps moving the yagi to the top of the mast and dropping the uhf tv lower might do the trick?
Any thoughts welcome
Thanks Ziggybyrne
In simple terms, your TV is designed to receive microvolts, and you are basically shoving millions of microvolts down its throat (1 Watt = 1 million microvolts).
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Comint
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Azoic
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- Location: Underwater in the Clarence River
Re: antenna earthing necessary?
Without wanting to step on any toes...and not offending Comint.
The problem that you have is known as RFI ( Reflected Frequency Interference ) .
Most often this is due to poor rejection on the affected device. Older TV's and AM/FM Radio
receivers were prone to it. The 455Hz filter was usually to blame, as the received signals were
boosted beyond what the filter could cope with. The most common solution 20 years ago was
to tell the affected person buy a new TV or Radio, but this wont work nowadays.
You could try an RFI filter, these come in various shapes and sizes, or you could try
carbon rodding the feedline, this is VERY affective, but isnt cosmetically neat.
Your issue is most likely RFI from proximity. Your using a UHF radio with a concentrator
antenna attached to a mast with a PULL IN ALL SIGNALS antenna on it....of course its going to
SWAMP the TV when your transmitting. Best option, mount the TRANSMITTING Antenna at least
1.7 m ABOVE the TV antenna. Run the coax feedline to it as far from the TV antenna as possible,
if you can, run it inside some electrical conduit, and run an earthline from the mounting mast to
the waterpipes on the house
The problem that you have is known as RFI ( Reflected Frequency Interference ) .
Most often this is due to poor rejection on the affected device. Older TV's and AM/FM Radio
receivers were prone to it. The 455Hz filter was usually to blame, as the received signals were
boosted beyond what the filter could cope with. The most common solution 20 years ago was
to tell the affected person buy a new TV or Radio, but this wont work nowadays.
You could try an RFI filter, these come in various shapes and sizes, or you could try
carbon rodding the feedline, this is VERY affective, but isnt cosmetically neat.
Your issue is most likely RFI from proximity. Your using a UHF radio with a concentrator
antenna attached to a mast with a PULL IN ALL SIGNALS antenna on it....of course its going to
SWAMP the TV when your transmitting. Best option, mount the TRANSMITTING Antenna at least
1.7 m ABOVE the TV antenna. Run the coax feedline to it as far from the TV antenna as possible,
if you can, run it inside some electrical conduit, and run an earthline from the mounting mast to
the waterpipes on the house
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Comint
- Senior Member
- Posts: 1621
- Joined: Sat Mar 22, 2008 5:17 pm
Re: antenna earthing necessary?
RFI is the abbreviation for Radio Frequency Interference.Azoic wrote:The problem that you have is known as RFI ( Reflected Frequency Interference ) .
Most often this is due to poor rejection on the affected device. Older TV's and AM/FM Radio receivers were prone to it. The 455Hz filter was usually to blame,
Actually, the problem is usually with the Radio Frequency stages of the equipment, ie., the Front-end, and NOT with the Intermediate Frequency stages, ie, the 455 kHz and 10.7 MHz sections.
? ? ?Your issue is most likely RFI from proximity. Your using a UHF radio with a concentrator
antenna attached to a mast with a PULL IN ALL SIGNALS antenna on it....of course its going to
SWAMP the TV when your transmitting. Best option, mount the TRANSMITTING Antenna at least
1.7 m ABOVE the TV antenna. Run the coax feedline to it as far from the TV antenna as possible,
if you can, run it inside some electrical conduit, and run an earthline from the mounting mast to
the waterpipes on the house
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Comint
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Vkfour
- Senior Member
- Posts: 376
- Joined: Tue Oct 05, 2010 11:27 am
Re: antenna earthing necessary?
Agreed, the "R" stands for RADIO, not reflected, and agreed, the front end of the TV is being overloaded by the transmitter, which shouldn't happen if only 5 watts is being used, and I'm NOT saying 5 watts only in not being used. RF is funny stuff and it can be difficult to isolate a cause.
I once eliminated RFI, that RADIO frequency interferance by replacing a splitter I had on the TV antennas. On another occasion, whilst cleaning the gutters, I found a piece of rusty metal, and when that was removed, no more TVI. Turns out that rusting or otherwise corroding metal can cause a diode effect.
Because only 5 watts is being used, it could be a problem in the TV coax. Try cleaning attachments to the antenna. Have a look at any connections, no, don't just look at them, re-do them. How good is the coax on the transmitter? Is there any TVI anywhere else? The ACMA have a brochure on TVI and it may well be worth a look at.
I agree with Comint, the last paragraph makes absolutely no sense at all. Are we to imply from the comments that merely the location of a receiving antenna can overload another radio? Wow, over 40 years in radio and I never knew that! Certainly, the proximity of one antenna compared to another can affect performance, but it can't transmit signals received.
I once eliminated RFI, that RADIO frequency interferance by replacing a splitter I had on the TV antennas. On another occasion, whilst cleaning the gutters, I found a piece of rusty metal, and when that was removed, no more TVI. Turns out that rusting or otherwise corroding metal can cause a diode effect.
Because only 5 watts is being used, it could be a problem in the TV coax. Try cleaning attachments to the antenna. Have a look at any connections, no, don't just look at them, re-do them. How good is the coax on the transmitter? Is there any TVI anywhere else? The ACMA have a brochure on TVI and it may well be worth a look at.
I agree with Comint, the last paragraph makes absolutely no sense at all. Are we to imply from the comments that merely the location of a receiving antenna can overload another radio? Wow, over 40 years in radio and I never knew that! Certainly, the proximity of one antenna compared to another can affect performance, but it can't transmit signals received.