fm radio antenna amplifier

[artois]

Hi guys.
I need help pls, can anyone tell me how i can check to see if this antenne is working, i know obvious if it can pull in a far station, but actually how would i check and where measure with a scope if its working. what signal can be placed in to check. i could not get 2sc2570 but got replacement nte107(with this transister do i need to alter something). what do they mean by the ground? on a radio u dont have a ground (must i use neg of battery) also the input of the amp, just a long wire or what kind of antenna? if the antenna must be a large one, lets say outside would u place the amp by the antenna side or by the radio?
txs john

 

[RCinFLA]

You need some RF test equipment. You cannot do anything with a regular scope. Without at least an RF generator and RF detector it is not likely the tuning of the input and output tank circuits will be at the correct frequency.

Unless you live in a very rural area with few FM statiions it is not likely that this amp will improve your reception. It is much more likely that it will degrade your reception due to intermodulation overload by strong nearby stations.

Typical modern FM RF frontends yield a better then 4 db system noise figure. Adding an amp is not going to improve sensitivity much, but it will produce more intermodulation problems.

You will be better off improving your antenna then adding an amp. Your FM radio has an RF amp that has automatic gain control that reduces the RF amp gain to minimum needed for station tuned to. This reduces the amount of intermod created.

 

[roltex_rohit123]

search for FM Dixing on Google. there is a very good website for it. I just read it. he has also given a circuit for it

 

[JimB]

I am in general agreement with what RCinFLA said.

Adding a few details of my own:

how would i check and where measure with a scope if its working.
what signal can be placed in to check.

A scope is not a good tool to use for small signals (micro-volts) at 100Mhz.

In the absence of any good test equipment, the best you can do is to tune your radio to find a weak station "off air", connect the amplifier between the antenna and the radio and then tune the amplifier for best signal and lowest noise from that weak station.

I have done that myself many times before I became well endowed (with RF test equipment!).

i could not get 2sc2570 but got replacement nte107(with this transister do i need to alter something).

The NTE will probably be OK, it does not have a particularly low noise figure (4dB) but good enough for this application.
Just build it and see what happens.

what do they mean by the ground?
on a radio u dont have a ground (must i use neg of battery)

Ground, a very mis-used and mis-understood term.
In this case however, yes, it means the -ve supply.

also the input of the amp, just a long wire or what kind of antenna?

If you do not use a proper antenna designed for VHF, you are wasting your time with this amplifier!

if the antenna must be a large one, lets say outside would u place the amp by the antenna side or by the radio?

For best performance, the amplifier should be located at the antenna to overcome the effects of loss in the coax feeder cable from the antenna to the receiver.
Depending on the relative noise figures of the amplifier and the receiver, just try putting the amplifier at the receiver and see what happens.

At VHF, a proper outside antenna, connected to the receiver with low loss coax cable, will always outperform some odd bit of wire poked into the antenna socket of the receiver. Even if that odd bit of wire does connect through an amplifier such as we are discussing here.

JimB

 

[roltex_rohit123]

https://www.google.co.in/#hl=en&gs_...f.,cf.osb&fp=4ae52db3ae76062d&biw=784&bih=417

see these google options. hope this gives you a good picture.