[ARC5] Tuning up BC-230 and ARC-5

[Dennis Monticelli]

I too was hesitant to mess with a virgin Matchbox Jr and went external with
a couple of small series coils that mechanically attach to the antenna
posts whenever I want to get on 6M.  Yes, with a little help the Matchbox
will actally do 6M.

Dennis AE6C

On Thu, Mar 31, 2016 at 11:44 AM, <mstangelo at comcast.net> wrote:

> I use a Matchbox Jr. tuner to match a 100 foot inverted V feed with
> ladderline.
>
> I use this as an all band antenna 80 through 10 meter antenna.
>
> It does a good job on most bands, including the WARC bands but I could not
> get a decent SWR on 10 and 40 meters.
>
> I wanted a quick way to increase the matching range without modifying the
> tuner. I fabricated L brackets to mount 5-way binding posts on the the
> balanced feed studs. I made 1 inch diameter coils from heavy gauge enameled
> wire I had an hand. I found I could get a good match on 10 with a single
> turn while the 40 band required 30 turns. I then mounted the coils on a
> bracket with banana plugs so that I could easily swap coils to change bands.
>
> You need a symmetrical antenna with feedline perpendicular to the antenna
> to get a balanced feed. I was worried about common mode currents on the
> feedline so I but some Fair Rite 31 toroids around the feedline where it
> enters the basement.
>
> I have another Matchbox Jr, which was hacked. I am intend to modify this
> by switching the number of turns on the input link coil, similar to the
> "Annicke Mods".
>
> Mike N2MS
>
>
> ----- Original Message -----
> From: Dennis Monticelli <dennis.monticelli at gmail.com>
> To: Kenneth G. Gordon <kgordon2006 at frontier.com>
> Cc: ARC-5 List <arc5 at mailman.qth.net>, AKLDGUY . <neilb0627 at gmail.com>
> Sent: Thu, 31 Mar 2016 14:32:37 -0000 (UTC)
> Subject: Re: [ARC5] Tuning up BC-230 and ARC-5
>
> All my antennas are balanced and so are the feedlines and so is the tuner.
> It's important to maintain balance throughout the system if one wishes to
> keep the feedline from either radiating or picking up signal (including
> noise).
>
> The most overlooked part of this fully balanced system is the tuner.  Many
> of the so-called balanced input tuners are not well balanced at all.  QST a
> while back ran a collection of tuners (both modern and vintage) through
> their paces with various loads and on all bands.  They also measured the
> degree of balance.  The hands down winner for balance was the Johnson
> Matchbox (both KW and Jr).  I use a Matchbox Jr.   The ferrite balun based
> balanced input tuners did not fare well and were particularly bad on the
> upper bands.   Of course you could roll your own balanced tuner and do a
> good job if you pay attention to details.  Remember even if you do a great
> job installing a balanced feedline should the "terminations" of the
> feedline (i.e. antenna and tuner) not also be well balanced, then unequal
> currents are going to flow on that feedline and it will become part of the
> antenna whether you like it or not.
>
> As an aside, many hams turn away from a tuner like the Matchbox because
> they cannot get a perfect SWR on all bands.  Even after playing with
> antenna length or feedline length there always seems to be one band or two
> that doesn't want to play along.  So they turn to a more modern tuner that
> has a wider tuning range.....that is also lossy and not well balanced. Well
> there is a better solution.  You can use the unbalanced ATU in your rig to
> clean up residual SWR or you could use a good quality unbalanced external
> tuner in series with the Matchbox.  On the bands where the SWR is already
> good via the Matchbox, just run the other tuner on bypass.  On the problem
> bands as long as the SWR is "dipping" with the Matchbox, there is a
> resonance going on within the Matchbox so it's doing its job acting as a
> wonderful balun.  It just can't transform the impedance all the way to 50
> ohms.
>
> Dennis AE6C
>
>
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