Antenna-amplifier with BFT 12 for FM-range

The only way to improve the reception of FM-signals or particularly of stereo FM-signals under disadvantageous receiving conditions is to amplify the antenna signal. This should be made directly at the antenna, since the loss is increased meter by meter of any cable. In most cases higher line attenuations can be expected than usually calculated. Even receivers with an additional noise figure of zero do not show any improvements of the signal-to-noise ratio becomes too low because of a long transmission line. Therefore it is practically useless to require extremely low noise figures only for the receivers.

To avoid interferences of signals received from stations of other bands it is propitious to amplify the FM-band only. The band amplifier shown in Fig. 1.3 is connected directly to the 60 ohm output of the FM-antenna, i. e. it is placed at the top of the antenna pole. The matching is achieved by the input band-pass connected to the base of transistor BFT12, being a typically linear silicon transistor for broadband amplifiers. The output filter matched accordingly to a 60 ohm coaxial line is connected to the collector. The operating voltage of 15 V can be supplied by the coaxial line.

Fig. 1.3

Antenna-amplifier with BFT 12 for FM-range

Technical data:

  • Power gain Gp = 22 db
  • Noise figure F = 3.5-4.0 db or 2.2-2.5 KT0
  • Input and output reflexion coefficient |r1| and |r0| <= 0.3
  • dim(60db) at Vout = 680 mV
  • dim(50db) at Vout = 1000 mV

Optimum operating point of minimum intermodulation

Ic =~ 80 mA Vce =~ 7-7.5 V
Supply voltage 15 V

Coil data:

Vogt coil former, ordering code: Sp 3.5/16.6-2048C
Core: U17

  • L1 : 5 turns Cu 0.6 mm \o
  • L2 : 3 turns Cu 0.6 mm \o
  • L3 : 3+2 turns Cu 0.6 mm \o

Choke Ch1 = Ch2: 20 turns Cu L 0.3 mm \o, cross section of winding = 4 mm

Credits –

Antenna-amplifier with BFT 12 for FM-range
from Design Examples of Semiconductor Devices – Siemens

Treasure Hunting and Metal Detectors

Here are some Metal Detector Projects that are quite interesting for the purpose of education and experiments in the Art of electronics. This site may be as old as Y2K, but the url / domain may have changed.

Metal Detector Projects

If you are interested in the theory behind the mag I can highly recommend the book The Magnetics Measurement Handbook by J.M. Janicke. Besides a good coverage of magnetics theory, it contains much of what you need to build a useful fluxgate Magnetometer, plus other devices.

Traditional Geophysical instruments include ground-penetrating radar, earth resistivity meter, infrared, and sonar, to name a few. Currently, earth resistivity projects are the most practical for the do-it-yourselfer, although some people have been tinkering with side scan sonar.

Metal Detector Projects

Detection of Gold

Just the Jeohunter really works and directly detects Gold – see below screen. And even gold-worth 9-15cm diameter cannon-balls get detected as “Gold” (golden ring & cannonball analyses has identical values), but thats because of the huge metal mass and special shape – alot MDs have “problems” in such situation and perhaps only a magnetometer really works here. btw. there is no difference if you search with Ground Balance minus 200, zero or plus 200, the gold detection always remains the same.

Detection of Gold - Metal Detection

There are historical records of DIY Enthusiasts having created what is known as the “Donkey Kong Gold Hunter”. This Gold Detector uses a Nintendo Unit after many Mods.

Metal Detector Circuits Problem

With the best wishes for you. I found your address and browsed your website. I have a question and hope to take your help and answer.

I need to good metal detector’s circuit and I find several in the web, any of them worked ? what is a problem in them and where can I find one that works with best depth? Could you design or point the mistake in some circuits? Thank you for your answer beforehand.

delabs – See my Related Page at  Metal Detector Projects

Metal Detector Circuits Problem

Mail from AS


Thank you for your answer and sites. But some of them that are professional namely “twin loop” built but it has problem and didn’t work.

I think it may be a indicated, there is a problem with them. How can I make it correctly? could you proper design such circuits?

I am not professional and of you do, I will pay for your works.

Reply from AS

If you clearly specify what you want with a drawing, And indicate what you may be able to pay and your contact details too…….

Then, I will publish your request in my site. People visiting my pages may contact you. You can Try it out, I may not be able to help now.


(PS – You can offer a solution to AS’s Problem, post your design page details, All Comments are moderated, Commercial or Business comments will be deleted, designers can indicate homepage.)