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RF wideband tv amplifier

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estenolotien

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Hello, i build this amplifier in Ltspice and i need to know if is good for tv pre amplifier. the .ams is inside .zip file.
Thanks you.
 

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Audioguru

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Why do you want to amplify TV signals 80dB (10,00 times)? Do you live on Mars?
If you have any local low frequency stations then the amplifier will be severely overloaded and you will have intermodulation distortion and interference on almost EVERY channel.
Doesn't your TV have an RF amplifier? Its RF amplifier is tuned and has AGC so it has no intermodulation.
 

estenolotien

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Thanks for your answers, the problem is that it is to amplify a signal from 90 miles that is why i designed it that way, I think it would be much better with GaAs FET, if someone could post a scheme i would be very happy.
Thank you.
 

SunnySkyguy

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TV sets already have this much gain in every stage ( but that includes Tuner , IF and Demod not direct RF gain so your design will not work), and when you add this much gain with Noise to a sensitive Tuner that already has a low noise figure your SNR does not improve. Although if your front end is lower NF by 1dB all you need is 15 dB gain to overcome the noise level of your TV plus loss of cable.

Your best option for OTA is a high gain bowtie antenna tuned within 1 degree. Which is what I use to get Channel 2.1 ~90 Miles away

Radar-All.png
www.tvfool.com/modeling/tmp/8e03/4a0/dd2a2bf/Radar-All.png

Or retrofit a Sat dish https://science.opposingviews.com/turn-old-satellite-dish-tv-antenna-14437.html
Or get TV/movies streaming ( but not live ) from web using KODI.tv and 1channel .. or some Bollywood server
 

biff44

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from a system point of view, simply amplifying the signal by 80 dB does not help that much. What you need to do is amplify ONLY the signal but not the background noise or other TV stations. I once tried to do a receiver for AM radio to pick up a unique station 120 miles away, and found that other stations leaking in were the biggest problem. You want to avoid jammer signals, but improve the signal-to-noise ratio as much as possible

So to start, you need the highest gain TV antenna you can get. and it will be directional, so you need it mounted on a mast with a motor to rotate it to the best position.

Then, right at the antenna, I would add a low noise amplifier. I am going to guess 30 dB would be sufficient, but more might be needed. If you start off with an 80 dB fixed gain, you might saturate the amplifier with other nearby noise, and corrupt the small signal you are trying to receive. Maybe a variable gain low noise amp? or a small gain low noise amp right at the antenna, and another switchable gain amp right at the tv set.

in the above channel power table, you can see that the propagation path for many of the long range tv signals is "tropo", meaning the tv signal is not line of sight, but instead bounces off the troposphere up in the sky. You might need to tilt your high gain antenna up to point more at the sky!
 

estenolotien

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Thank you very much for your help, the main thing is to have a good antenna and then a preamplifier with very low noise, so I was thinking of the choice to do it with GaAs fet me but has been difficult to find a scheme that covers this frequency band if someone could help would be grateful.
Thank you.
 

SunnySkyguy

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Unless you block strong signals by direction of antenna or if not possible with tuning stubs, and /or filters, you need to accurately define the Signal and Noise levels and frequency to properly design a front end to avoid compression from stronger signals and thus distortion and unviewable signal.

Mitsubishi GaAs Fet from the MGF 1200, 1300, or 1400 family. My favorite is the MGF-1402.

https://www.advancedreceiver.com/page12.html

- - - Updated - - -

I indicated 15dB gain minimum.

This product is 18dB gain ... Extensive testing of this preamplifier on existing communications systems indicate that a signal-to-noise improvement of 6 - 14 dB can be expected

https://www.advancedreceiver.com/page47.html

My Antenna also has Strip LEDs on that I installed.P1080755.JPGP1080768.JPG
 

estenolotien

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Very nice antenna....
Thanks for your help, i love also MGF1402.
I´m seaching in internet a schematic to build this preamp with mgf1402 or any other GaAsfet.
Thanks for all.
 

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