Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

question about VHF AERIAL AMPLIFIER

Status
Not open for further replies.

cocoloco

New Member
Hi!
Here is the link to the circuit: http://talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#69 .
I don't know what is twin feeder, I don't have it. Can anyone tell me in very simple words:
1) Is the "IN" of the circuit going to the back panel's "OUT" of TV (so "OUT" of the circuit is going to the antenna via simple short wire, or directly), or "OUT" of the circuit is going to the back panel's "OUT" of TV (so "IN" of the circuit is going to the antenna via simple short wire, or directly)?
2) Can I use SS8050C instead of these two recommended transistors in the circuit?

VHF-Amplifier.gif
 
Last edited:
Hi!
Here is the link to the circuit: http://talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#69 .
I don't know what is twin feeder, I don't have it. Can anyone tell me in very simple words:
1) Is the "IN" of the circuit going to the back panel's "OUT" of TV (so "OUT" of the circuit is going to the antenna via simple short wire, or directly), or "OUT" of the circuit is going to the back panel's "OUT" of TV (so "IN" of the circuit is going to the antenna via simple short wire, or directly)?
2) Can I use SS8050C instead of these two recommended transistors in the circuit?

View attachment 69601
IN is from the antenna - Out is to the TV

300 Ohm twin feeder is also referred to a 300 ohm twin lead - http://en.wikipedia.org/wiki/Twin-lead
Most modern Tv's use 75 ohm coax lead - http://en.wikipedia.org/wiki/Coaxial_cable
If you want to use 300 ohm twin lead with a newer TV, you would need a matching transmormer _Balun)
Try Google "75 to 300 Ohm UHF/VHF Matching Transformer"
 
Last edited:
That circuit is actually better used with 75Ω coax. If you really wanted to use it with 300Ω balanced twin-lead between the antenna and the preamp, you should put a balun at the input of the preamp. Use 75Ω coax between the preamp and the TV set coaxial F-connector input.
 
When we had VHF analog TV transmissions (now everything is digital high definition at UHF frequencies), that extremely simple circuit got overloaded by all the strong local TV stations. Its output is a high impedance that is attenuated by a low impedance coax cable and its load so it does not amplify.

An SS8050C is a high power little audio output transistor that is not suitable for VHF frequencies.
 
Even if you use a balun, the input and output impedances of the amplifier are terrible mismatches to 75Ω. Of course, a perfect termination on one end will forgive the mismatch on the other end, but what's the chance of that at VHF?
 
Last edited:
Even if you use a balun, the input and output impedances of the amplifier are terrible mismatches to 75Ω. Of course, a perfect termination on one end will forgive the mismatch on the other end, but what's the chance of that at VHF?
A 4:1 balun should be a pretty good match for the received signal when running 300 ohm twin lead from a TV antenna.
If you use 75 ohm cable to the TV, you are still using a Balun - but it is at the antenna instead of the TV.
 
Most TV stations are now channel 14 to 50 digital. Some stations have special permission to continue to transmit analog. Nashville TN is one station has both channel 5 analog and channel 5 digital. If you need an antenna amp buy a channel master CM7777 it works great if your receiving a weak signal. A channel master 4 bay antenna has a range of 30 miles. A channel master 8 bay antenna has a range of 60 miles. The pre amp does not always give you more range, it helps stops signal loss from things like a hard rain, hard snow, high wind, etc. Chain link fence top rails make great low cost antenna towers $8 each 30 ft tower = $24. If you have multipal TVs an antenna for each TV works best. Channel 14 is VHF analog but 14 digital could be any channel from 14 to 50 depending on your geographical location. Be sure to use a balum=antenna matching transformer at the antenna to connect the 75 ohm coax cable. Put your pre amp power supply at the TV and the amp on the antenna.

This in my antenna Nashville is 34 miles from my house at 308 degrees.

**broken link removed**
 
Last edited:
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top