[600MRG] A couple of crude Antenna Matching techniques - will either one work

[Frank Lotito]

A question - With certain transmitter designs the output can be quite rich in harmonics. Definitely when we opt for simple minimal output filter solid state designs, and simple single tuned and even double tuned link coupled OT and OOT designs.  Specifically, using no low-pass PI network. Is the simple ammeter technique really prudent to recommend?  Maybe not when the 630 meter second and third harmonis fall in the AM Broadcast Band.
..
In my mind, the simple "tune for max current" runs the risk of tuning up "on the wrong harmonic."  Using a nearby monitor receiver as a "poor man's spectrum analyzer" does not proove much w.r.t. tuning on the correct harmonic, e.g., the fundamental.  I think we should be careful with our advice unless we know for sure the transmitter has a more than adequate low-pass output filter. 
..
73 Frank K3DZ / starting to become a moot point WH2XHA
________________________________________
From: 600MRG <600mrg-bounces at w7ekb.com> on behalf of eric <kl7aj at acsalaska.net>
Sent: Friday, December 1, 2017 2:17 PM
To: 600mrg at w7ekb.com
Subject: Re: [600MRG] A couple of crude Antenna Matching techniques - will either one work

Check out my Feb. 2009 QST article, "Keeping Current with Antenna
Performance."   For the first half of ham radio history, the RF ammeter
was just about the only instrument any ham had at his disposal. :)

Eric the Old



On 12/1/2017 8:58 AM, Rudy Severns wrote:
> In the early days of radio Andy's problem had to be addressed by most
> everyone with nothing more than an RF ammeter.  The answer is simple: tune
> for maximum antenna current with the power available.  While that's very
> simple advice, sometimes it takes a good deal of fiddling to find the magic
> "maximum" but with some experience early hams and pro's for that matter,
> made it work.
>
> The first step is to make sure you have enough inductance to resonate.  That
> can be estimated pretty closely either from modeling or with the
> calculations shown in chapter 3 of my notes.  Assuming you have enough L the
> usual procedure is to have taps on the coil in two places, one set near the
> top which you adjust for resonance and one set for matching maybe 10-20% up
> from the bottom.  You the alternated taps, first the top taps for max
> current then the bottom taps again for max current, etc, etc, etc until
> there's no improvement.  As long as you have enough L to start with this
> procedure usually converges.  If you don't have enough L then the procedure
> should end with the tap at the top of the coil indicating more L is needed.
>
> The equation for inductance is also very simple: L=(D^2 N^2)/(18D+40l),
> where D= diameter in inches, l= winding length in inches, N=number of turns
> and L is in uH.
>
> GL and 73, Rudy N6LF
>
>
>
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