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RF Wideband AMP Broken?

Discussion in 'Electronic Design' started by Les Ismore, Apr 17, 2007.

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  1. Les Ismore

    Les Ismore Guest

    I obviously am not astute in the field of RF circuits as I come from a
    digital background. I am unable to get advertised output from a RF
    wideband amp advertised as for the FM broadcast band. The amp is
    from Denmark and uses a single BLW76 transistor. I have isolated the
    low power circuit control with no improvement in power. I pulled
    resister R3 and lifted D1 to isolate the circuit. DC power input
    measures 23.5 Volts. RF power input measures 7.5 W at 92.5 MHz FM.
    RF output measures 18W. The output signal is clear and crisp. The
    BLW76 never gets very warm beyond room temp. I am using a ME82
    dummy load combo wattmeter - 52 ohm impedance (military). I only
    have DVM and Oscope and of course assorted logic probes. The
    adjustable caps were adjusted for max output on the wattmeter, input
    pair to outpair and repeated until no further gain could be eeked out
    on the wattmeter. The schematic looks like standard RF Amp stuff,
    and it matches the hardware. The schematic is located at:
    (the black-out marks were on the schematic when I got it)

    Is the BLW76 faulty? One of the trimmer caps has been replaced on the
    output side. It is a mica compression type not matching the other
    round trimmer caps.

    Thanks in advance for any guidance.

  2. Andrew Holme

    Andrew Holme Guest

    Are all the trimmers midway through their adjustment range? Make sure you
    don't have any fully meshed or fully unmeshed.

    What's the DC supply current?
  3. Barry

    Barry Guest

    Hi Andrew,

    The DC supply current = 1.58 amps. The power supply is rated for 12
    amps at 24 VDC.

    Trimmers: Input - 7/8 meshed and 3/4 meshed, Output 7/8 meshed and
    guessing more than 50% on the mica compression cap, but not fully

    Thanks, Barry

    Output power drops as frequency increases and is about 10 watts at 104
  4. mpm

    mpm Guest

    Before everyone is so quick to help "Barry", you should consider the
    fact that he is probably breaking the law.

    92.5 MHz in and around the Chicago area (in fact, Illinois & Indiana
    at large) is licensed to only a small handful of legitimate radio
    stations. None of these operate at such low power levels.
    Operating an FM transmitter in the FM Broadcast Band (88-108 MHz) is
    against the law.
    Violators typically risk confiscation of equipment and a $10,000 fine
    (1st offense).

    Note: This is not a first amendment right.
    It is not technically possible for everyone who wants a radio or TV
    station to physically operate one. What's more, it is quite likely
    that "Barry" will affect legal transmissions on adjacent stations, or
    even co-channel stations if he's close enough to their coverage areas.

    Sorry Barry.
    Give me a valid call sign, or some other legitimate reason to help you
    and I'll think about it.
    Otherwise, forget it. I would hope others here would have the sense
    not to offer suggestions.

    If you want to play FM part-time radio announcer / DJ, do it under
    Part-15 FCC Rules low power rules.
  5. mpm

    mpm Guest

    Of course, I meant to say:

    Operating an FM transmitter in the FM Broadcast Band (88-108 MHz)
    against the law.
  6. JeffM

    JeffM Guest

    It's a good thing then that he's not in Chicago.
    Out in the middle of nowhere, maybe he has a chance to avoid jail
    Ever seen a more apt name for a town to be from?
  7. Barry

    Barry Guest

    Jeff -- I am not in the middle of nowhere. That happens to be where I
    am connected.-- I am really just on the edge of nowhere. I am not
    even in the same county as my IP address indicates. But you got the
    state correct and you have demonstrated better research than mpm.

    P.S. FCC regulations are part of the civil code, not criminal code.
  8. Barry

    Barry Guest

    I once had a commercial radio license-- think spark gap. Now let me
    help you with your thinking. It is not illegal to operate a
    transmitter on VHF UHF, FM, AM at any power level as long as the power
    is shunted to a dummy load. Also, dummy load emissions must fall
    within FCC regulations, not laws. I meet all of these requirements.

    Please review your writings and accusations as they remain in the
    public domain for years and can be detrimental to you. Your spurious
    emissions can be a problem for you - legally.

    I tried a variety of input frequencies and 92.5 provided the best
    output power. Higher resulted in lower power, and lower remained the
    same until 89 and dropped off.

    If you have some technical advise on my question please let me know.

    You are likely a "Sterling" 2219 gentlemen :)

  9. Phil Allison

    Phil Allison Guest


    ** Which simply means it is not a crime the police prosecute.

    But the FCC will if they catch you.

    Heavy fines and jail time are possible.

    ........ Phil
  10. Barry

    Barry Guest

    Hi Phil,
    Sorry, but you and other posters are making assumptions and
    accusations that are patently untrue and damaging . Do I have to
    engage a solicitor from OZ to help you keep your typing honest and
    legal through a court ordered C&D? That's the MO there isn't it? :)

    I repair computer software and hardware, I repair pinball machines SS
    and EM, video games, 8-liners, monitors, I set up networks, routers
    and I do this gratis - except the gaming equipment. I certainly
    invite you and the other falsely assuming posters to visit my shop,
    including representatives from the FCC to see nothing but parts,
    broken stuff and test setups. Please be prepared to fix something
    rather than talk about it.

    I am pleased to report the RF Amp problem has been resolved. Thank
    you Lazlo for the emails.
  11. Phil Allison

    Phil Allison Guest


    ** I made no such assumptions.

    You are suffering delusions of grandeur and persecution.

    Expect no honest person to offer help via a *public forum* for any
    apparently illegal activity.

    What you *claim* is the case is of zero consequence.

    ........ Phil
  12. Winfield

    Winfield Guest

    What was the solution?
  13. mpm

    mpm Guest

    Barry, with all due respect:
    Yes, the FCC is a regulatory agency, not a law enforcement agency.
    So guess what, all they do is contact the Justice Dept, and they
    enfoce the LAW.

    Did I say "Law"? Well yes I did!
    It goes like this: Congress passed the Communications Act of 1934 and
    it's been amended several times since.
    It's literally an Act of Congress so you call it what you want... but
    it doesn't change reality.
    The FCC has the delegated authority of the Congress to amend the Act.

    How is it amended you ask? Well, usually the FCC will develop and
    circulate a Notice of Proposed Rulemaking (NPRM), which, after the
    usual public comment period, FCC Commission Vote, (sometimes judicial
    review as in the recent case of Nextwave's bankruptcy), and finally a
    Report and Order (R&O). The R&O is then published in the Federal
    Register, after which time (typically 90 days), it becomes Public
    Law. Humm, there's that pesky word again..!

    I'm sure you can look all this up.

    If you are truly transmitting into a Dummy Load as you claim, and if
    your emissions meet Part-15 (which because you know everything, is a
    limit based on field strength and NOT on transmitter output power),
    then fine. But it does beg the question: Why do you need our help?
    Why 92.5?, which if I were I pirate, seems like the ideal candidate
    frequency for the area described in your profile. Otherwise, what
    possible good can come of this? Do you want to fix this thing so you
    can sell it to a real pirate??

    And just so you know: It's NOT called a "commercial radio license".
    Technically, the nomenclature is "FCC Station Authorization". (As
    long we're splitting hairs here.)
    Would you like me to explain the whole process of how to get one?
    And by the way, I'm pretty sure a Class-D (100W ERP) is the lowest
    power you can get these days, unless HAAT is so large as to
    effectively reduce this. Bonus Round: How much antenna gain would
    you need to reach 100W ERP with your rig?

    About the only thing (legally) this device can be used for (I guess),
    Antenna performance measurements on a turntable? (Note: Would require
    an experimental license, or waiver)
    Maybe use as an Exciter for a higher-power station (Note: Would still
    require a license)
    Use outside the country, perhaps requiring a license.(?)
    Maybe use as a toaster oven?, but at only 18 watts TPO I think you'd
    go hungry!!

    It's clearly not going to meet FCC Part-15 when connected to an
    antenna. Any antenna.

    I am also aware that some States have laws (there's that pesky word
    again) against POSSESSING (let alone opeating) an FM Broadcast
    Transmitter without a valid FCC Station Authorization, Construction
    Permit, or Program Test Authority.

    Don't know if Illinois is one, I'd have to look it up. I believe
    Florida is one, though, so you can look that up too since you're so
    smart. (Personally, I'm against local law enforcment in this area -
    but that's a whole other discussion.)

    And just how OLD are you anyway??. Spark-gap transmitters? Please!!
    You must be like 100.
    My advice: forget repairing it. Your hands are probably shaking so
    bad from the Parkinson's medication, and obviously demensia has
    already kicked in. You want to fix something - fix your understanding
    of this issue.

    OK, that was bitchy and probably uncalled for, but I don't appreciate
    your response to me either.

    Especially since you seem to have glossed over that fact that I
    originally gave you the benefit of the doubt when I said you SEEMED to
    be a Pirate - not that you were, in fact, a Pirate. But obviously
    that comment touched a nerve with you...

    And by the way, I could fix that transmitter (exciter) with my eyes
    closed and no tools but a set of nine-irons and some garlic bread. :)

  14. Joel Kolstad

    Joel Kolstad Guest

    "I am also aware that some States have laws (there's that pesky word
    again) against POSSESSING (let alone opeating) an FM Broadcast
    Transmitter without a valid FCC Station Authorization, Construction
    Permit, or Program Test Authority."

    That seems a little silly... any electronics design facility and many home
    hobbyists are going to have a frequency generator around that could be used
    as a (crude) FM transmitter... and such facilities are also going to have
    general-purpose wideband gain "blocks" available...
  15. Phil Allison

    Phil Allison Guest

    "Joel Kolstad Fucking Imbecile "

    ** So fucking what ?

    Any rusty axe can be used to murder the wife, neighbour or the next JW to
    knock on the door.

    What a brainless ****.

    ........ Phil
  16. mpm

    mpm Guest

    I agree completely and that is just one of the many reasons I think
    local law enforcement should stay out of it. They typically don't
    understand issues such as the very one you mention.

    But you can see why it happens. Citizens complain about the crude
    language and trash "hip-Hop" invading the dial & their favorite
    programs - many of which can be found in the non-commercial portion of
    the band, 88-92 MHz - (and that's exactly where a lot of pirates hang
    out because the spectrum is usually less occupied). ..And sadly,
    (except for some high-profile abusers) the FCC has clearly proven
    itself to be next to useless in cracking down on violators.

    But the FCC is quite clear: Without a license, emissions can be no
    greater than 250uV/m @ 3m (using an average detector, not peak), for
    the 88-108 MHz band.

    I just get annoyed by folks, who claim to be doing one thing, (and in
    fairness, maybe they are), but then refuse a reasonable request to
    offer any good reasons for wanting to know how an FM doo-hickey works,
    or how to fix it, etc... (What are we to believe??)

    I would rather they just review Part-15, and stop spouting out all
    this nonsense.!!
    ....or at the very least - play some Steely Dan, or Moody Blues, or
    Journey once in a while.

    Maybe even some Disco?. Gasp!!

  17. Joel Kolstad

    Joel Kolstad Guest

    So it effectively becomes impossible to write a law that somehow makes it
    illegal to have "an FM transmitter" but not "a signal generator with frequency
    modulation abilities and significant power output." Hence, such laws are
    Exactly, and axes aren't illegal in Florida now, are they?
  18. JeffM

    JeffM Guest

    <Grammar Nazi>
    That phrase doesn't mean what you think it means.
    It is NOT a *circular argument*.

    asks the question
    poses the question
    presents the question
    raises the question
    </Grammar Nazi>
  19. mpm

    mpm Guest

    That's fantastic!!! Where do you dig up this stuff!!

    I was going to crack a joke about the dummy load being "circularly
    But I'll stand by my original usage...

    If he can only (legally) dump this RF power into a dummy load, and
    he's already doing so by his own statements, then why does he need us
    to help him fix it so he can dump the RF power into a dummy load.??

    That's as circular as it gets.

    --- And with that, we finally get some intelligence in this thread!
    (Thanks for the link, GN.)
  20. Phil Allison

    Phil Allison Guest

    "Joel Kolstad"

    ** A sig gen is simply not an FM transmitter.

    Your analogy is crap.

    ...... Phil
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