RF Wideband AMP Broken?

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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:

http://www.southshore.com/~bposter/pins/RF_AMP.JPG
(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.

Barry


Re: RF Wideband AMP Broken?



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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?



Re: RF Wideband AMP Broken?


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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
compressed.

Thanks, Barry

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


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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.

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Pirate.
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.


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Of course, I meant to say:

Operating an FM transmitter in the FM Broadcast Band (88-108 MHz)
WITHOUT A LICENSE is
against the law.


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mpm,
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 :)

Barry



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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),
is:
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.  :)

-mpm



Re: RF Wideband AMP Broken?


"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...



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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!!

-mpm


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"mpm"

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 **  Only cos you are a hee hawing ass.




........   Phil



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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
stupid.

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Exactly, and axes aren't illegal in Florida now, are they?



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"Joel Kolstad"
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 ** A sig gen is simply not an FM transmitter.

     Your analogy is crap.



.....   Phil




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Oh yeah?  I'd got an HP 8648A signal generator here which is more than happy
to produce FM at base frequencies anywhere between 100kHz and 1GHz.  Output is
some decent fraction of a watt -- *far* more than enough to violate FCC part
15 regulations with any decent antenna connected to its output.



Re: RF Wideband AMP Broken?



"Joel Kolstad"
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**  Piss off  -   you autistic bloody  FOOL.




........  Phil








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Telling someone off when you've lost a debate is not considered good form, you
know. :-)



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Hey, what do you call the GNURadio USRP (http://www.ettus.com /)?  It's just a
pair of PCinterfaced DACs and ADCs after all.  I guess they were completely
off-base in suggesting it could somehow be used as "a radio."  You'd better
write them a message quick...

Note that there's software for it to make it an oscilloscope, signal
generator, FM transmitter, HDTV receiver... surely we ought to ban such
devices ASAP!



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<Grammar Nazi>
That phrase doesn't mean what you think it means.
It is NOT a *circular argument*.
http://www.google.com/search?q=define:beg+the+question

asks the question
poses the question
presents the question
raises the question
</Grammar Nazi>


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

I was going to crack a joke about the dummy load being "circularly
polarized"...
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.)


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"JeffM" <
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**  The term "to beg the question"  has an important meaning that is now
lost because of continual misuse in the media and elsewhere.

Likely not one person in 50 could say with any accuracy what " to beg the
question " really means.



........   Phil



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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
time.
Ever seen a more apt name for a town to be from?
http://www.dnsstuff.com/tools/whois.ch?email=on&ip12%.199.33.37


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