[Test-Equipment] FS: Heath IM4180 FM deviation meter

Tue Apr 22 21:35:31 EDT 2008

If you really want to get into it, high quality AM can be generated by
properly phasing two FM transmitters together.

73
Gary  K4FMX

> -----Original Message-----
> From: test-equipment-bounces at mailman.qth.net [mailto:test-equipment-
> bounces at mailman.qth.net] On Behalf Of Mike Manes
> Sent: Tuesday, April 22, 2008 10:19 PM
> To: Discussion of Electronic Test Equipment
> Subject: Re: [Test-Equipment] FS: Heath IM4180 FM deviation meter
> 
> Yes.  I think some hams know about the Bessel function of FM mod index.
> In fact, one can modulate an FM xmtr effectively in CW by using a properly
> selected sine modulation freq and deviation.  If the mod freq is greater
> than the receiver bandwidth, then the carrier will disappear when the
> modulation signal is applied.  This has been used to generate CW with
> Gunn diode microwave oscillators equipped with tuning varactors.
> This lets a CW or SSB receiver copy a sig that it otherwise couldn't.
> 
> But despite that, the total output power of the oscillator remains
> constant over it's full output bandwidth. The power that appears one
> the carrier freq with no modulation gets spread out into the sidebands
> when the modulation is applied.
> 
> But again, that's an arcane aspect of FM that even goes beyond the
> scope of the Extra ham exam.
> 
> 73 de Mike W5VSI
> 
> Sheldon Daitch wrote:
> > Yes,
> >
> > the indicated power does remain constant, but if one is specifically
> > looking
> > at the power in the envelope at the carrier frequency, that power level
> > does
> > change.
> >
> > Take a look at:
> >
> > http://www.cliftonlaboratories.com/bessel_nulls.htm
> >
> > for one discussion on carrier null.
> >
> > Shamelessly llifted from the website:
> >
> > The principle behind Bessel Nulls is that in a phase or frequency
> > modulation system, the relationship of the carrier level, the modulating
> > frequency and the deviation is defined by a mathematical relationship
> > known as a Bessel function, named after their discoverer, the German
> > mathematician Friedrich Bessel. Bessel lived nearly 100 years before
> > FM was invented but his mathematical techniques have proven useful
> > in describing many physical phenomena.  For more details, see Agilent's
> > Application Note 1390. At the moment, it may be found at
> > http://cp.literature.agilent.com/litweb/pdf/5988-5677EN.pdf,
> > but Agilent periodically rearranges its web site so this address may
> > not last indefinitely.
> >
> > For our purpose, it is sufficient to understand that for certain values
> > of deviation and modulating frequencies, the carrier will reduce to
> zero.
> > More practically, a deep null, on the order of 30 or 40 dB can be seen
> > as these values are approached.
> >
> >
> > 73
> >
> > Sheldon
> >
> >
> >
> > Mike Manes wrote:
> >
> >> How arcane.  Yes, the math works, but try looking at it with just an
> >> RF power instrument: FM envelope amplitude is constant, and that's why
> >> one can use a non-linear PA, like Class C.
> >> 73 de Mike W5VSI
> >>
> >> James Duffer wrote:
> >>
> >>> While the provided answer to your question will suffice, actually
> >>> Frequency Modulation (FM), the carrier does not change in frequency,
> >>> the amplitude varies, this can be observed with a spectrum analyzer
> >>> and proven mathmematically.  The modulated wave has various side
> >>> frequencies that vary in both frequency and amplitude depending on
> >>> the modulating source.  AM (Amplitude Modulation) the carrier is
> >>> constant but the modulated composite varies in amplitude as a result
> >>> of the combination of the carrier and side frequencies.
> >>>
> >>> Keep asking questions about things that interest you, and follow up
> >>> with reference material.
> >>>
> >>> 73, Jim, wd4air> From: kc7hkp at comcast.net> To:
> >>> dickburk at ix.netcom.com; test-equipment at mailman.qth.net> Subject: Re:
> >>> [Test-Equipment] FS: Heath IM4180 FM deviation meter> Date: Tue, 22
> >>> Apr 2008 00:40:01 +0000> CC: > > Thanks You very Much Richard for
> >>> answering Me !, I did not know what it was, I can only learn from
> >>> books since elmer are not around much any more.> being handicapped in
> >>> a wheelchair and stuck in my bedroom, I only have books or the net to
> >>> learn> So Thanks again for taking the time to answer.> Instead of
> >>> degrading me because i did not know.> George> --> KC7HKP > George
> >>> Yazzolino > 14801 NE 20th Circle > Vancouver, Wa. USA ,98684 > Grid
> >>> CN-85 > kc7hkp at arrl.net> > -------------- Original message
> >>> -------------- > From: "Richard Knoppow" <dickburk at ix.netcom.com> > >
> >>> > > > ----- Original Message ----- > > From: > > To: "Discussion of
> >>> Electronic Test Equipment" > > > > Sent: Monday, April 21, 2008 1:25
> >>> PM > > Subject: Re: [Test-Equipment] FS: Heath IM4180 FM deviatio
> >>
> >> n > > meter > > > > > > > Hi Dick > > > What is FM Deviation ? > > > I
> >> have not heard this word before in ham radio . > > > Sorry to bother
> >> you > > > George > > > > > In case this is a serious question... > >
> >> Deviation is the measure of the amount of frequency > > modulation in
> >> an FM signal. It is superficially the amount > > the carrier is
> >> changed in frequency when modulated. There > > are several ways to
> >> measure the amount of FM but its > > possible to make a fairly simple
> >> device to indicate it on a > > meter although other methods are more
> >> accurate. > > FM transmission became popular for the ham bands after >
> >> > WW-2. It has pretty much disappeared on the HF bands but is > >
> >> quite widely used on 6 meters and above. > > The other reaction to the
> >> question is because FM should > > be elementary knowledge. OTOH, no
> >> one should be afraid to > > ask a question for fear of being
> >> humiliated. > > May I suggest that a Google search is a good place to
> >> > > start for definitions. > > > >
> >> --- > > Richard Knoppow > > Los Angeles, CA, USA > >
> >> dickburk at ix.netcom.com > > > >
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> --
> Mike Manes    mrmanes at gmail.com     Tel: 303-979-4899
> "Things should be made as simple as possible, but not more so."
> A. Einstein
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