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    Together with a good directional antenna this high performance two-stage antenna amplifier for the VHF FM broadcast band will enable you to capture far removed (DX) stations. Alternatively, it will drastically improve reception of FM signals you’ve come to accept as marginal and noisy in your area.

    Together with a good directional antenna this high performance two-stage antenna amplifier for the VHF FM broadcast band will enable you to capture far removed (DX) stations. Alternatively, it will drastically improve reception of FM signals you’ve come to accept as marginal and noisy in your area.

    FM/VHF antenna amplifier circuit schematic

    vhf fm antenna booster circuit schematic

    For various reasons, an increasing number of people are not satisfied with the quality of radio signals that can be received via cable systems. Unfortunately, cross-modulation, and other nasty effects created in the head end station are in stark contrast with the superb quality of high-end FM tuners that can be bought commercially.

    Not surprisingly, owners of such tuners will often prefer to have their own antenna on the roof. Add to that a high-performance FM antena booster like the one described here and you can start DXing as well as enjoying high-quality stereo reception. The author employs the present amplifier in combination with a Sangean ATS-803 World band receiver, a Philips RR-571 tuner and a single-element cubical quad directional antenna at a height of just 15 feet. Using this setup he is able to receive FM stations as far off as 500 km.

    Antenna booster circuit description

    In the design we’re about to describe you’ll find the following important parameters coupled: low noise figure (approx. 1 dB); high gain (up to 40 dB) and low susceptibility to intermodulation products. Yet the amplifier is inexpensive and easy to build. The circuit diagram in Figure 1 reveals the secret: dual-gate MOSFETs in positions T1 and T2. The first of these, T1, is configured mainly for low noise and antenna matching and the second, T2, for high gain. Unusually, the antenna signal is applied to T1 via its source (S) terminal, which is convenient because unlike one of the gates (G1 and G2) it already represents a fairly low impedance. None the less, for impedance matching with the 50 Ω coax cable a tap needs to be used on tuned filter L1/C2.
    For VHF and UHF amplifiers, DG-MOSFETs represent a good alternative to cheap but noisy bipolar transistors and very expensive and difficult to get Ga-As FETs.

    The gain of the second DG-MOSFET in the circuit is adjustable using preset P1 which varies the bias voltage to T2’s G2 terminal — this is the classic way of controlling the gain of a DGMOSFET and it still works very well. Such a control is included in the design to allow you to get the exact amount of gain required for your particular application. For example, if you live near a powerful VHF FM or TV broadcast transmitter then you’ll find that a lot of gain produces cross-modulation and other unwanted effects like coupled oscillation and ‘birdies’ within the FM band.

    For stability the supply voltage is decoupled at several locations by electrolytic capacitors and ceramic capacitors for the low and high frequencies respectively. To enable it to be mounted as close as possible to the antenna, the amplifier is powered via the download coax cable, i.e., over coax connectors connected to K2 and K3. In the supply, the RF signal is taken off the coax core by capacitor C19.

    The supply voltage is adjustable to some extent with pot P2, which will also allow a degree of gain control. The current through ‘power on’ LED D2 should be about 10 mA. If a low-current LED is used, then R8 has to be increased accordingly. With electrical safety in mind we strongly suggest the use of a mains adapter with 12 VDC output. Depending on the gain set and the DG-MOSFETs used the circuit will consume about 50 mA so a 100-mA or slightly more powerful adapter will be fine in most cases.

    VHF FM antenna amplifier construction

    The amplifier is built on the singlesided printed circuit board shown in Figure 2. The inductors in the design are all very simple to make, see the parts list for construction details. L1, L2 and L3, are wound on a 4.5-mm dia. drill or pencil. L1 then needs to be stretched to a length of about 10 mm. You’ll find that a relatively large resistor is needed to wind choke L4 on — we used a 0.5-watt carbon-film resistor from the junkbox (metal film resistors seem to have taken over completely). The value 1 MΩ is uncritical, what we’re after is ‘a lot’ of carbon for the core so 820 k or 1.2 M will do just as well.

    FM antenna booster PCB layout

    The DG-MOSFETs are not only sensitive to static discharges but also easy to fit the wrong way around. The non-SMD versions require 5-mm holes t be drilled in the PCB. Make absolutely sure you know each MOSFET’s final orientation on the board before soldering it in place — check, think hard and refer to the component drawing shown in Figure 1. You may find that the legs are a bit too long for the PCB but don’t use your cutters until the very last moment because without the stud marker (source terminal) you will be lost for device orientation.

    Several VHF/UHF DG-MOSFETs may be used in this circuit — see Table 1. With some dexterity it is also possible to use SMD devices. In general, you should aim to use a BF9xx with a low noise figure, although that may imply a slightly reduced overall gain. Remember, however, that the amplifier’s gain is secondary to the noise figure — in practice, any gain between 25 dB and 40 dB will be just fine.

    The power supply parts are not accommodated on a PCB but may be connected up using flying lead construction in a small case. The finished PC should be cleaned with isopropyl alcohol to remove solder residu.

    The amplifier must be housed in a metal case with proper coax connectors used for K1 and K2. The author used F-type sockets as customary with satellite TV rigs. They are cheap and easy to obtain. However, BNC sockets may be used equally well. The connections between the sockets and the amplifier input and output should be kept as short as possible using thin coax cable like RG174/U.

    VHF Antenna Setting up

    Give the PCB a final, thorough inspection for bad soldering, wrong components, etc., and resolve all problems before proceeding.
    Set all presets and trimmers to the centre of their travel. Apply power to the amplifier and check the various test voltages indicated in the circuit diagram. These voltages are typical and should not be taken to mean the ‘law’. Tune your VHF FM radio to a weak signal at around 98 MHz. Tune the amplifier back to front, that is, first C14, then C5 and then C2 for best reception — your ears and the tuner’s S meter will tell you what’s happening. If necessary reduce or increase the gain using P1. A good way to simulate a weak signal is to turn the antenna away from the transmitter direction.

    The amplifier’s 3-dB bandwidth will be about 10 MHz with all tuned elements at the centre frequency. By careful retuning of the three trimmer capacitors (‘staggering’), this may be widened to 20-25 MHz at the cost of some gain. Fine tuning may also be achieved by stretching or compressing the three air-spaced inductors. This method may be for specialists only, however.

    Other bands

    The amplifier may be modified for use at slightly higher frequencies like 120 MHz (VHF airband), 145 MHz (2-m radio amateur band or even 146- 174 MHz (PMR band). Some experience may be required in tweaking the inductors for resonance at their new frequency however. If you find that a particular trimmer no longer ‘peaks’ then the L/C combination is out of range. Lacking specialised test equipment like a grid dipper to see where it does resonate, go for trial and error by fitting an inductor with fewer turns and see what happens then. Whatever the frequency, the booster will not fail to give the kiss of life to a duff receiver.
    COMPONENTS LIST
    Resistors:
    R1 = 10kΩ
    R2 = 150kΩ
    R3 = 1MΩ
    R4 = 220Ω
    R5 = 100kΩ
    R6 = 3Ω3
    R7 = 1kΩ
    R8 = 1kΩ2*
    P1 = 47kΩ preset H
    P2 = 10kΩ linear potentiometer
    Capacitors:
    C1, C6 = 22pF ceramic
    C2, C5, C14 = 22pF trimmer
    C3, C7, C17, C18 = 1nF ceramic
    C4, C9, C13, C15 = 100nF ceramic
    C8, C10 = 10nF ceramic
    C11, C16 = 100μF 25V radial
    C12 = 3pF9 ceramic
    C19 = 12pF ceramic
    Semiconductors:
    D1,D3 = 1N4007
    D2 = LED
    T1,T2 = BF965 or BF966S
    Inductors:
    FB1,FB2,FB3 = 5 turns 0.15 mm (38SWG) enamelled copper wire on ferrite bead
    L1 = 7 turns 0.9 mm dia. (20SWG) enamelled copper wire; internal dia. 5mm; length 10mm; tap at 5 turns from ground
    L2,L3 = 7 turns 0.9 mm dia. (20SWG), internal dia. 5mm; closewound
    L4 = 30 turns 0.15mm dia (38SWG) enamelled copper wire on a 1MΩ 0.5W resistor
    Miscellaneous:
    K1-K4 = F socket, PCB mount
    S1 = on/off switch, 1 contact

    All change to SMD

    Although the BF966 DG-MOSFET is no longer produced, it is still around in electronics retail and surplus circuits. Broadly speaking, DG-MOSFETs from the BF9xx series in the ‘traditional‘ SOT103 case are being superseded fast by their SMD (SOT143) counterparts.
    These are perfect electrical replacements but require short wires in order to be fitted on a board laid of for a SOT103 transistor. In many cases, the type number is that of the SOT103 parent device plus an offset. For example, a BF966S is electrically compatible with the BF996S, and the same applies to the BF981 and its successor the BF991.
    A further interesting point to note is that the –R suffix in the type code of SOT143 DG-MOSFETs indicates a ‘reflected’ pinout. The layout of the PCB designed for the antenna booster allows both SMD (SOT143) and ‘leaded’ (SOT103) DG-MOSFETs from the BF9xx series to be fitted, the latter being mounted recessed in a 5-mm hole allowing their terminals to be soldered flush with the PCB tracks. Unfortunately, ‘-R’ suffix SOT143 DG-MOSFETs cannot be used on this board.

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    57 Responses to "VHF FM Antenna Booster Circuit"

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    1. PRABHAT KUMAR SINGH says: on January 8, 2009 at 9:33 am

      I lived in india in a remote location the fm broadcasting station is 150 km from our residence can i receive the reception with the help of this booster

    2. Yes, I think it will improve the reception but you’ll need to take good care at the coils and the circuit construction. And ofcourse the antenna is very important.

    3. Guruthevan says: on February 9, 2009 at 12:33 pm

      I am an Electronics and communication engineer living in Tamilnadu India, this circuit may amplify the weak fm band signal but the receiver plays the main role, noise figure and sensitivity are very important, for superior reception I prefer NATIONAL(STEREO RADIO CASSETTE RECORDER WITH 4 BAND RADIO) model “RX-FM15F”…

      Regards,
      V.Guruthevan.

    4. donny ardalando says: on March 10, 2009 at 7:07 pm

      I am an Electronics, computer hardwares and wireless engineer living in Indonesia.

      What do you think when it redesign again and used for 2,4Ghz, does it need a minor changes or a totally new circuit??!!

    5. PRABHAT KUMAR SINGH says: on April 12, 2009 at 4:45 am

      PLEASE GIVE THE DETAIL OF COIL WINDING OF L1 AND L4 AND WHAT IS THE MEANING OF VOLTAGE 0V84 AND 14V66 ETC

      PLEASE HELP

    6. Vishwaeshakumaaran says: on April 30, 2009 at 1:37 pm

      I live in Vidyagiri Dharwad karnataka.Vidyagiri is the hillock region.I can catch the fm stations from Bangalore,Mangalore,andhra,tamil nadu and maharashtra without any amplifier.I regularly get signals from Bangalore and Mangalore only and the signals from the other areas are very rare.
      I wanted to construct the above dx-amplifier but the mosfets are very hard find in karnataka.Especially the BF966S is very rare.It is the bad news for dxers like us.Please help me where to get the mosfet bf966s in India and the mention the price in rupees.Thanks in advance.

      • PRABHAT KUMAR SINGH says: on December 12, 2009 at 9:49 am

        SAME CIRCUIT WITH BF966 READY MADE AVAILABLE TO ME IF INTERESTED TO BUY PLEASE CONTACT:09984797461

      • KALAIKUMAR /CHENNAI says: on March 1, 2012 at 6:54 pm

        Sir i have yamaha rx-v371 av receiver the fm reception in our area is poor and i cant here many channels can i use this circuit for my amplifier kindly help with ur suggestion

    7. very good but not exellent best of luck and take care………,

    8. hello
      i am searching a prototype

      with this prototype , i want to make a metal detector that it can detect metals into foods…you can thing it like food detector..
      but , while i make it, i dont use clsassical components. i want to it with MIR ( micropower impulse radar ) or anything UWB İmpulse radar kit.

      please write me , if you have any idea

      thanks so much

      best regard

    9. harun mail address: habu_58@hotmail.com

      please help me

    10. I am an Electronics, computer hardwares and wireless engineer living in mongolia.

    11. Om Prakash Johari says: on December 5, 2009 at 9:27 am

      Thanks for a nice circuit.Can it be convert into an easy to make one MOSFET design as there are many technical complications with this circuit. I am looking for a single MOSFET/FET/Transistor circuit having a gain around 10 db. Can somebody help ?

    12. I have a marine radio on my boat but it doesn’t seem to have a very clear signal. Even when I transmit a message, no one can hear me unless I’m right on top of them. How can I boost my signal on the boat VHF radio?

      Thanks

    13. Iam a supercomputer photonics protonics hardwhere engineyaaarrr!!!!!!!!!!! I want to make the mosfet for the boooooooooooooostaaaaaaaaaaaar

      • rene constantin says: on March 14, 2012 at 1:49 am

        Dear R(ridiculus)T (Totally) G(ga)G(ga)G(GI) Did I got this right ?

        Making a MOSFET is for grownth up poeple something that will never happen to you, why don’t you just leave us alone ?
        Don’t waste your time answering, nothing will affect me

    14. i am live in sagar .i am recives manglore fm stations but signal is very week how to impro the signals have any antena plz help r give contct no plz my no is 08105278777

      • harish T says: on August 11, 2011 at 7:16 pm

        hello,
        i am working in INDIAN ARMY(SIGNALS)i am now attending a course equavallent of BE in ARMY. My project is same of “VHF FM ANTENNA BOOSTER RECEIVER” but i cannot have any guidance, you may please help me some guidance of the above project.

      • Muzammal Baig says: on January 28, 2012 at 7:42 am

        Dear Harish T,
        Booster is nothing but a wide band RF amplifier whereas RF amplifier (the first stage of a TV / Radio) is normally a tuned single frequency amplifier. other than that there is not much difference so one idea is that you may use a TV Channel selector as a booster.
        other than that you may be interested in using wide band Op Amps to boost (amplify)the received radio signal. the coils and capacitors are only there to tune the amplifier to the band of interest. This way you increase selectivity of the band of interest.

        best of luck for your projetc

        Muzammal Baig

    15. nice and perfect these cct….
      thanks
      YD0LOG

    16. i made a single mosfet (BF966S) based pre amplifier circuit for receiving far away FM stations. I am from central kerala (India) where my nearest FM station is more than 85 kms away. With the help of this circuit along with a home made 4 element cubical quad antenna i could get almost all stations from Kerala,Tamilnadu & some Karnataka stations & FM stations from SriLanka. You may wonder its more than 500Kms away from me.

      • Dear Jinson. Interesting result.

        Will you be able to share more info on which are the stations you are able to receive and any other issues if any.

        Thanks and Regards

      • off course i am glad to provide the details of the circuit i made. It contains only a handful of components easily available except that BF966F MOSFET. I managed to get one from the online store of “element14″.

      • Thanks Jinson for your reply. Sorry for the late response from me. In fact I noticed your reply now only. Very sorry about it. Can you please contact me on my email ID habib,h123@yahoo.com

        Thanks and Regards,

        Habib

    17. P.K.SINGH says: on April 14, 2012 at 1:11 pm

      this circuit ready made available can contact 09984797461

    18. I am an beggar and homeless and I want to built this good stuff.

      Maybe someday I find the mosfets in the trash bin. hope..

    19. P.K.SINGH says: on June 11, 2012 at 11:35 am

      BF 966 DG MOSFET AVAILABLE PRICE Rs.200/- each
      09984797461

    20. I think coil part and trimmer part are very important in this rf. Please explain about making 5 turn 0. 15 mm (38 swg ) enamelled copper wire on ferrite bead It is very important part and L1, L2,L4. Also . Please please explain it .

    21. Robertas says: on August 7, 2013 at 10:47 am

      Could You describe the making of bandwidth to 88-108MHz?In other words,how to turn trimmers to receive all FM range? Thanks.

    22. Velmurugan says: on September 3, 2013 at 12:58 pm

      Hi ,

      I am planning to build an High gain FM antenna with VHF FM booster circuit to recieve signals in my home . In this regard will you be able to help me in sending a VHF FM booster to my place , I can transfer the required money
      Thanks
      Velmurugan
      09840522599

    23. hi,can i replace bf966 mosfet with 3n200 mosfet? cause it is really hard to find bf series mosfet . or could i find it inside a old tv set?

    24. how do u specify a 36 db pre amp in the market . can u let me know where we can get this in chennai and how is it specified.

      • Mr. Velmurugan,
        Its available in cart2india.com its available with the name’TV ANTENNA SIGNAL BOOSTER AMP AMPLIFIER HDTV UHF VHF DTV CABLE INDOOR OR OUTDOOR’. The making of above circuit may be difficult as the availability of MOSFET BF966S is unsure.

    25. Mr. Jinson,I’m new to these kind of stuffs. So, what do 2 and 9 mean in R8 = 1kΩ2* and C12 = 3pF9 ceramic
      respectively?

    26. Sir, are there any easily available and good substitutes for BF966S mosfet?

    27. I want to buy BF966S or its substitute from Indian websites only because I don’t have a credit card.
      Therefore, please tell me the BF966S MOSFET’s easily available and reliable substitute.

    28. Mr. Jinson, please I need your help ASAP.
      Bf966S MOSFET’s easily available Substitutes???

      • Sorry man i failed to get this MOSFET for a second time. So i bought a new ready made booster from an online market. My earlier circuit elements were obtained from kitsnspares.com. I think BF966S is no more available in indian market.

    29. Also my circuit was not the above one. I think the circuit image cannot be posted here. Its posted in facebook.com/Jinson.FMDxing

    30. what about bf998?

    31. Robertas says: on October 2, 2013 at 4:41 pm

      BF998 is the best choice among MOSFETs.But it comes in SMD case.Noise figure at 200MHz is 0.6dB,at 800MHz – 1.0dB

    32. Hello
      I’m from Czech. Bf966S there is little available. You can get bf966. May be replaced bf966S for Bf966? Thank you

    33. Machrus says: on March 16, 2014 at 7:11 am

      It’s good Thank you sir. godblessyou

    34. PrashanthSuvarna says: on June 27, 2014 at 3:52 pm

      Hey,Hey,Hey! Every1 esp those who are having reasonable dexterity and knowledge in putting/modifying electronic equipment, I have a very good solution2this problem. with a little effort you can do what I had done some time back. look for old(But working& not used anymore)Catv(Cable Tv)amplifiers that most Catv Operators would we glad2handout freely2u.There are many types.Just look out4old&simple Broadband units,(These are usually rated 4 operation @300Mhz or so&r ideal4the job)Now don’t rush2the Catv suppliers shop&ask them4the latest model.Although these are indeed much,much better than the 1 that I asked u2use, the extra wide bandwidth is surely not in our intrest4a variety of reasons.Now open it up carefully and do away with the built in pwr supply. Now isolate the pwr leads that pwr the unit as well as pass the external pwr from input 2 output,(or you may get the pwr coming out from the input terminal.)Now make a small A.C power supply unit(if u are curious then u can use the transformer that I had asked u2 take out earlier. remember2use the output tap of 18V if its is a transitorised unit which I recommend,or use the 27V winding if u wind up with a hybrid IC unit(Bit more than what we’d recc& a lot heavier and larger also.Even the pwr pass coil used inside the amp near the input stage can be taken out2b used in the pwr unit 4 supplying the amplifier)Do it properly and connect an antenna2the input.u should get a significant improvement in the reception of your signals. the best part is that you can mount the amp really far away as it was designed 4 that purpose.Low lying areas can benefit immensely from this tip.Happy foraging and execution…

    35. @PrashanthSuvarna….ok good.. plz send me some pics of modified Catv amp

    36. @PrashanthSuvarna….. R u busy?

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