Hi Gary,
I found time to come back in and continue addressing more of the points.
Nothing is wrong with the resonant antenna. It is what I have used quite a lot
over the years.
We are on the same page here. However it is wrong to believe that only resonant
antennas can be efficient. Maxwell clearly points that out, as does Cevik.
I was only saying that people often are forced to use non-resonant antennas due
to space limitations and that the JVM (in standard format) is not the best
matchbox for that.
I was in full concert with you on all points, except ... and maybe it wasn’t
even you who said it . . . it was claimed several times that the JVM was the
greatest matchbox ever. It was great in its days, but had weaknesses later as
we got more bands and people began to match funny things with them. At least
one company (Annecke) improved on the design and sold them. It was
distinctively better.
But wait, W6SAI published an article showing how to do that, something like 50
years ago. That's where I "borrowed" the idea, then applied it to the JVM and
improved it and published instructions on how to d-i-y.
I went to great length to explain and show people how to remedy this and many
people have applied my mod to their JVM. I continue to get thank you emails
for the work from people who have successfully done the mod.
I am a firm believer in link coupler matchboxes and have a couple of pages on
my web showing people how to build their own simple, dirt cheap link coupled
matchbox. But I have altogether 4 different circuits for 4 different
applications.
Each fits a different set of circumstances where it works, but it fails
everywhere else. It is difficult to put them all in one box and the high power
switch would cost a small fortune. So I make different proposals for people
confronted with different tough environmental situations . . . such as how to
get a relatively efficient power transfer into a short 20m (66 ft.) long (or
even shorter) dipole on 160m.
I love quads and loops much more than dipoles.
I began feeding them with open wire back in the 1970s, using the Annecke
Symmetrical Coupler, which was the matchbox that is an improvement over the
JVM. Except mine was home-brew using spare parts I purchased directly from
Annecke.
HOWEVER THE FACT REMAINS: THERE AREN'T ENOUGH JVM's to go around if everyone
wants one.
Even if you are lucky enough to find one, you often find them "melted" on the
inside.
Therefore some kind of alternative is required.
A much less quality but very practical solution is to use a good 1:1 Guanella
balun between a simple L-Network and the openwire. That's "1:1, not "4:1".
I often use the Model 238 like this.
Especially with low power (100w or less), this can be a good substitute.
In my 45 years of living on this side of the pond, I have never once seen a JVM
for sale on the used market. The ANNECKE I speak of was great, but Alfred
Annecke built and sold exactly 20 units. I built my own. So there are perhaps
21 units floating around somewhere in the world. Won't find one of those
either. So most people must seek or build something else.
Now to your two cats and the JVM.
I built something similar using two galvanized trash cans.
You can find a picture here:
http://www.dj0ip.de/antennas/
Pictured is one version which I fed with a short coax.
I'll put that up against your Siamese cats any day! (hi)
Cheers Gary!
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Gary J
FollettDukes HiFi
Sent: Monday, July 18, 2016 9:42 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] OT: Question to the group
>> Stating individual cases where something worked proves nothing.
Well, actually it does. As I pointed out, with a RESONANT cubical quad, driven
with 470 Ohm Dentron parallel line, I got a perfect match on 20, 15 and 10.
This was an efficient antenna with efficient feed lines and an efficient (in
this application) tuner. It was positioned quite a long distance from the
transmitter so the lower loss parallel feeling was of some advantage.
Better would have been the use low loss ceramic spacers and true parallel
ladder line. However, the Johnson matchbox would have worked equally well in
that application, whereas the autotuners and most of the T match tuners
wouldn’t have worked at all without an external BALUN.
Since my radio at the time, a Drake TR7, had pretty good low pass filters
within, I was not too concerned that the Matchbox offered no such lowpass
filtering.
Even more important than the match is the near-perfect balance of currents on
the line (as you mentioned). Two bad things happen when the currents on
“parallel” lines are not balanced. Your noise level on receive goes up since
the feedline begins to act as part of the antenna and your chances of getting
the Worked All Neighbors award in transmit also goes up dramatically as the
feed line begins to radiate where you do not want it to radiate.
Nothing matches everything. Nothing even works well for everything. Devices
like this need to be matched to the application. I only sang the praises of the
Johnson because it did indeed work with every application in which I used it.
Nothing else did as well…
As I said before, improvement is always welcome and what you discuss in terms
of such improvements is great. Why does this become contentious?
A little humor, if that’s allowed:
I once got a perfect match with a Johnson Matchbox using two cats as an
antenna, with alternately polarized mice as spacers for feed line made of old
violin strings (catgut).
Of course, they were Siamese cats… It was, after all, a balanced dipole…
April fools...
Beyond that, what is wrong with resonant antennas? Where is the advantage of a
non-resonant antenna? Nikola Tesla clearly showed the inherent advantages of
resonant loads 120 years ago… They are pretty easy to match too!
> On Jul 18, 2016, at 1:09 AM, Gary J FollettDukes HiFi <dukeshifi@comcast.net>
> wrote:
>
> I’ll just stay with resonant antennas…
>
> Gary
>
>
>> On Jul 18, 2016, at 12:48 AM, rick@dj0ip.de <Rick@dj0ip.de> wrote:
>>
>> Stating individual cases where something worked proves nothing.
>> I've had half a dozen cases where it did not work and other matchboxes did.
>>
>> In order to gain clarity on this, you must try it with all kinds of
>> antennas; resonant antennas, long antennas, short antennas, odd sized
>> loops, etc.
>>
>> What the Johnson does well is push equal amounts of current into both
>> wires of the feedline with relatively high efficience, if and only if
>> it finds a match.
>> What it does poor is match over a very broad matching range.
>>
>> You don't have to trust me; try it as I have and compare it to an
>> MFJ-974 or MHF-976.
>>
>> OR... simply read the ARRL test report where the ARRL shows several
>> balanced matchboxes and their matching ranges, including the JVM.
>>
>> Now I guess I have to go research the issue it was printed in because
>> it's probably too much work for some of the readers.
>>> "A New Generation of Balanced Antenna Tuners", by Joel Hallas, W1ZR,
>>> QST
>> September 2004.
>>
>> OR, simply do what I have said her MANY TIMES, go to my web site,
>> find the page on MATCHBOX-SHOOTOUT And read the page, plus download
>> the file at the bottom of the page.
>> THERE you will find a nice colorful Excel spreadsheet comparing the
>> matching range of the various matchboxes.
>> THERE you will see that the JVM was indeed limited in matching range.
>>
>> THEN go read my web page on how to fix it.
>>
>> AND THEN YOU WILL HAVE THE BEST MATCHBOX EVER! ;-)
>>
>> 73
>> Rick, DJ0IP
>>
>>
>> -----Original Message-----
>> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of
>> Carter
>> Sent: Saturday, July 16, 2016 9:32 PM
>> To: tentec@contesting.com
>> Subject: Re: [TenTec] OT: Question to the group
>>
>> On 7/16/2016 10:13 AM, Carter wrote:
>>> On 7/15/2016 6:59 PM, Jim Allen wrote:
>>>
>>>> I had one of those [135 foot dipole fed with ladder line], not at
>>>> > 60', about half that. CC&Rs and all that.
>>>
>>> The exact setup I've got, also at 30 feet.
>>>
>>>> What is a "well designed truly balanced antenna tuner?" From what
>>>> > I've read, there aren't many.
>>>
>>> Johnson Matchbox, kW or 275 watt version, not "perfection" but
>>> certainly very good -- and readily available at a fairly modest price.
>>>
>>> Just my 2 cents...
>>>
>>> Carter K8VT
>>>
>>
>> Sorry, forgot to mention it earlier...
>>
>> Not to say my Johnson kW matchbox is the "best ever"; however, it
>> works flawlessly with my FT1000MP and 135 foot ladder line fed
>> dipole on ALL (including WARC) bands. Worst case is 2.1:1 on 30
>> meters, all other bands 1:1.
>>
>> Carter K8VT
>>
>> ---
>> This email has been checked for viruses by Avast antivirus software.
>> https://www.avast.com/antivirus
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|