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

[Kenneth G. Gordon]

On 31 Mar 2016 at 7:32, Dennis Monticelli wrote:

> 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).

Yes.
   
> 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.

In fact, I would not call those "balanced-tuners" at all: they are a total compromise. To me, 
they are useless.

>   Of course you could roll 
> your own balanced tuner and do a good job if you pay attention to details.

...like making everything on both "sides" exacty equal. I also like to have some sort of RF 
ammeter in both sides to check on real balance.

>  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.

Yup. Which raises a concern I have for my proposed antenna: one leg will be high in the 
only antenna support I have on our much-too-small property, while the other leg will be very 
close to ground-level. I expect some imbalance from that situation. We'll see...

One possibly saving grace here is that our earth conductivity is, apparently, the absolute 
worst of any other place in all of North America.

> 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.

Yes. I used that trick many years ago, when I last used a balanced antenna.

There is also a very slight modification one can make to the Johnson Matchboxes to 
improve upper-band SWR and that is to add a good ceramic switch and some taps to the 
link coil. One size does not fit all in that part of the system. One should reduce turns on the 
link as one goes up in the bands. 10 meters seldom requires more than 1 turn, for instance, 
while 80 should have around 4 turns, and 160 around 5.

My home-brew coupler uses a switch from a BC-375 tuning unit (available NIB from Fair 
Radio for a few dollars) to switch link turns from a high of about 4 to a low of 1 turn in the 
link.

Also, my coupler does not include the double-split-stator cap that the Johnson's include. I 
couldn't fit that in the available space.

BTW, there are at least two places on the web which suggest removing that second 
split-stator cap from the Johnson couplers, but if one looks very carefully at Johnson's 
design, one eventually sees that the addition of that second cap provides a much better 
balance to GROUND than the "normal" balanced coupler like mine can provide.

Even without that cap, though, my coupler always managed to achieve a decent match.

I might also mention that the one single thing that so many folks leave out of the antenna 
feed equation is line-loss: line-loss in coax is, to my way of thinking, unacceptably high for 
any reasonable cost coax, over even a moderate run, while line-loss with open-wire-line 
(ladder-line) is almost non-existent. For instance, in one installation for a ham in Norway, 
one of his runs would result in over 50% signal loss if he used coax, while with his 600 ohm 
ladder-line feeder over the same distance (about 450 feet as I remember it) the loss was 
well under 1 dB.

I have a PowerPoint presentation here which I would be happy to share with anyone who 
would like to see it detailing some of these issues.

Ken W7EKB