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Old 27-Jan-2012, 2:28 AM   #1
ghz24
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Can you overload enough to hurt the tv tuner?

At what signal level is there a danger of damage to tuners.
Or what gain level for an antenna would it take to damage a tuner.
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Old 27-Jan-2012, 6:46 PM   #2
GroundUrMast
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That's not a published specification that I've ever seen.

The design of the tuner front-end would govern. If diode protected, voltage in excess of its forward bias voltage would result in the protection diode going into conduction, thereby limiting the peak voltage that can be seen by subsequent components in the tuner. The typical silicon diode has a Vf rating of 0.7V. Damage would occur if the current in the protection diode exceeded it's capability. If it failed in a short circuit condition, the rest of the tuner may survive, but with a short circuited input. If it failed open, then you would expect additional components to fail in the tuner.

To put some numbers around this, in a 75Ω system, a signal level of +6 dBm will have a voltage of about 0.773Vpeak or 0.546Vrms. This represents power of 4/1000 of a Watt.

I don't see how typical signal levels and antenna gain would be able to put a tuner at risk of damage.
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Old 27-Jan-2012, 7:41 PM   #3
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Quote:
Originally Posted by ghz24 View Post
At what signal level is there a danger of damage to tuners.
Or what gain level for an antenna would it take to damage a tuner.
It is inconceivable that a regular signal or combination of signals can damage a tuner. Immeasurably greater than the combined strengths of all broadcast signals in your area are the RF pulses from lightening discharges. Absent a direct hit, I have never heard of lightening damaging a tuner that was connected to a properly installed antenna. The signals from broadcast towers several miles away certainly can't do it.
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Old 28-Jan-2012, 10:28 AM   #4
ghz24
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So is this right ?

First thanks for your responses.
My strongest local station is -16 dBm (from my radar plot)
If I point a 23 dBi antenna at it that gives me a +7 dBm signal at the mast, so less than 2 dB of attenuation (coax) would possibly cause damage?
Is this right?
Quote:
I don't see how typical signal levels and antenna gain would be able to put a tuner at risk of damage.
That's what I thought but I didn't know about a-typical gains like 23 dBi.

Quote:
Immeasurably greater than the combined strengths of all broadcast signals in your area are the RF pulses from lightening discharges.
Will the extreme gain magnify these RF pulses more than a low gain antenna?

I'm immune direct lightning strikes, I'm in the "cone of protection" of a large lighting rod/tower that a local company thoughtfully erected nearby unfortunately they strung high voltage power lines over it.
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Old 28-Jan-2012, 3:15 PM   #5
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Quote:
Originally Posted by ghz24 View Post
...

Will the extreme gain magnify these RF pulses more than a low gain antenna?

...
There are two issues here. A broadcast signal is narrowband. Something like a lightening strike is wideband, but is completely unpredictable. Antenna gain depends on the frequency of the signal and the direction to which it is pointed.

Having said that, you are making this way to complicated. Your OP was about the potential damage of strong signals to tuners. The answer was that such damage is not possible. For whatever reason, you appear to be reluctant to accept this answer. Whether you accept it or not, that is the answer.

My advice to you is to worry about things that are more likely to happen--like running out of gravel.
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Old 28-Jan-2012, 4:15 PM   #6
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Originally Posted by MisterMe View Post
Whether you accept it or not, that is the answer.
I agree. I have even tried a CM 7777 here just to see what would happen with multiple blistering signals at close range when using high gain antennas. End result; only the weakest signals disappeared & no tuner damage.
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Old 28-Jan-2012, 8:36 PM   #7
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I'm very willing, but anything but typical

OK I'm sorry, I see I asked a very short question with very little background.

I'd be very happy to accept the answer of can't happen, don't give it a second thought.

But in the example I gave above the 23 dBi number was not chosen arbitrarily just to test GroundUrMast's numbers.

I have/am designing a true 23-24 dBi home brew E-Z build parabola (96 sq. feet) with slightly higher gain than the horizontal stack of two 8 foot parabolas seen here.
http://www.wade-antenna.com/Wade/uhfparabolic.pdf
I can show you the nec models.

and this is my plot/report I did round -15.9 to -16 dBm
http://www.tvfool.com/?option=com_wr...3e476ecbd7806e

I will be building a full scale prototype to take modeling measurements, and of course to play with.
I wouldn't be using it to provide local channels, just a test/DX-toy but it could get accidentally pointed at the local flamethrower or a very strong reflection of it.

So with signal levels ~8 times what any mass produced antenna produces does this change your opinion?

Because if my math above is not flawed it looks to me like I'm very close to producing a potentially damaging signal level.

If that is the case I may want to try and trade some of the massive gain for more beamwidth at least for my personal one.

My development efforts were kind of paused when I noticed references to needing better than consumer grade down stream equipment to handle the signal levels of the wade.

And if it matters the feed is a log periodic dipole array originally designed for 470-800 MHz. with a native impedance of 75 ohms

So don't mistake my questioning your answers as disrespect.
More a quest for a more complete understanding.

BTW klitz tech says their lowest priced amp (maybe all of them) overloads at -5 dBm and didn't know what signal level damage occurred.(it was the sales dept)
But use of an amp would just switch my concerns to the health of the amp. instead of the tuner.

Is that .7fv the point where damage potential exists or is it some higher (unknown) number based on the actual failure value of the actual diode in question?

Last edited by ghz24; 28-Jan-2012 at 8:48 PM. Reason: add last question
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Old 29-Jan-2012, 1:20 AM   #8
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Quote:
Originally Posted by ghz24 View Post
...

So with signal levels ~8 times what any mass produced antenna produces does this change your opinion?

...
How many different ways do I have to tell you? No.

Also, nowhere in your Wade Antenna documentation is there any mention of signal level. Wade publishes gain response in units of dBi. Gain response is the ratio of the signal strength collected by the antenna to signal strength collected by a reference dipole. To calculate the gain response in dBi, the logarithm-base-10 of this ratio is multiplied by the factor of 10.

I take note of the fact that Wade antennas are not optimal for North American broadcasts. Their peak gain is at RF Channel 80. The North American maximum is RF Channel 69 and is being reduced to RF Channel 51. For RF Channel 51, the antenna has a gain response of about 24 dBi. In linear terms, this means that the output power of the antenna is about 251 times the reference power at RF Channel 51.

The reference power is tiny. The output power is 251 times a tiny reference power. In terms of voltages, the output rms voltage is about 16 times the reference signal rms voltage. There is no way on Earth that either will damage your tuner.

If you ask this question again, then I will have to say something that you will not like.
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Old 29-Jan-2012, 4:04 AM   #9
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Perhaps another way to look at this is, "overload" of a tuner is usually a term used to describe a condition where non-linear operation occurs in circuit that is intended to operate in a linear fashion. In that context, overload is not expected to cause damage to any component.

To expand on protection diode operation, simply driving a diode into conduction is not harmful. Harm would result if the current was excessive and sustained. The diode rating would indicate how much current and power it's capable of handling without damage. numbers range from a few Milli-amps on up. So I would expect you would need a signal anywhere from 10 to 30 dB higher than the conduction threshold to begin expecting damage.

@everyone - Let's not be in a hurry to stifle honest questions, particularly those clearly motivated by a sincere desire to learn.
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Old 29-Jan-2012, 5:27 AM   #10
ghz24
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I've tried to be nice

so I will Thank you all for your input wow that is a big safety buffer I'll never even design an aracebo size dish so that is not a problem not even close to the edge thanks again.

Last edited by ghz24; 29-Jan-2012 at 7:16 AM.
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