Thanks for the input, Bob. My problem (as a Novice) at the time, was
that tuning on low power and obtaining resonance, does nothing to
consider VSWR and heating effects.
The antenna impediance and antenna efficiency are key in radiating a
signal as opposed to an antenna merely being an electric heater.
Much has been written about matching and a dummy load is a pretty
good match; however, it's obviously about the entire set-up and
creating a good antenna system.
My intent was not to be critical of roller inductor tuners, but
rather to illustrate how easy it is for a newbie to go astray.
Thanks for reading ES 73,
de Phil - N8PS
-----
Quoting Bob McGraw - K4TAX <RMcGraw@Blomand.net>:
I agree Phil, most rollers just need cleaning and adjusting such
that the rolling contact doesn't loose contact with the roller coil.
Wiping them down with a clean lint free cloth and with a very small
amount of contact cleaner such as Cramolin or DeOxit seems to
restore them for years.
As to tuner ratings, keep in mind there are limits to the
impedances they will match. I've found that even though they may
match a wide range of impedances, this does not imply they will
handle the rated power over that range. See recent test reports
published by ARRL for some of the more popular tuners. Note the
loss factor too. That loss is directly converted to heat and it is
this heat which is dissipated by the tuner components. For example
at 1500 watts and a tuner having a loss of 25% the dissipated heat
would be about 375 watts to be dissipated by the components in the
tuner. This 25% figure is not out of bounds for some loads and
tuners but their ability to handle the power dissipated is
questionable.
Two recent tuners reviewed by ARRL, July 2013 QST, show loss figures
of 18% on 10M with a SWR of 16:1 or 800 ohms. One other tuner
shows a loss of 15% on 160M with a 2:1 SWR or 25 ohms and a 14% loss
on 10M with a 16:1 SWR or 800 ohms. Another test condition/tuner
data shows a 33% loss on 160M with a 2:1 SWR or 25 ohms and a 28%
loss on 10M with a SWR of 2:1 or 25 ohms. Also see test results
published in QST, March 2013.
My experience is that a 2KW PEP rated tuner is capable of handling
about 500 watts. Agreed, it will handle SSB PEP values at many but
not all impedance loads to 1500 watts or so. Put in a 1500 watt
carrier and watch for that tell tale odor of heating components and
the following smoke emissions!
While we may think antennas present a 50 ohm load, in fact based on
height above ground, they more typically present loads in the order
of 12 to 35 ohms. This impedance demands a higher current than a
load of say 100 to 500 ohms where the issue there is voltage.
A few noted values:
10 ohms @ 1500 watts = 122V @ 12.2A
12 ohms @ 1500 watts = 134V @ 11.2A
25 ohms @ 1500 watts = 193V @ 7.4 A
50 ohms @ 1500 watts = 273V @ 5.4 A
100 ohms @ 1500 watts = 387V @ 3.8 A
500 ohms @ 1500 watts = 866V @ 1.7 A
1000 ohms @ 1500 watts = 1224V @ 1.2 A
Add in reactive components of the typical nature and things get out
to bounds quickly. Based on ARRL test results it is clear that
tuners seem to handle higher impedance loads better and more
efficiently than low impedance loads.
73
Bob, K4TAX
----- Original Message ----- From: "Phil Sussman" <psussman@pactor.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>; "Wade
Staggs" <tvman1954@gmail.com>
Sent: Wednesday, June 19, 2013 10:14 AM
Subject: Re: [TenTec] 238A-C roller inductor
Ah, my first days with a roller inductor tuner. "Roller Inductors don't
wear out .. they just get dirty contacts."
Oh well, they do MELT as my MFJ did. All I did (after I tuned it on low
power) was apply 400w on 80m into a G5RV. Whoops. Smoke !! It was rated 2Kw.
Went out and bought a Nye-Viking M-B-V and still using it to this day.
Years later -- no problems.
73 de Phil - N8PS
PS. Golly your 'roller inductor' story brought back some old memories,
or rather I should say, foul smells of melted components. Whew - PU !!
----
Quoting Wade Staggs <tvman1954@gmail.com>:
I must agree with Bob/K4TAX ... My MFJ-989C Tuner is not built anywhere
close to the quality of your Tuner. I bought it new in 1995 and by never
tuning under high power, the only issue with it was from being not used for
a couple of years. When it came out of Moth Balls and returned to service.
After a good going over and cleaning with DeOxit, all is well. I also
checked all mechanical pieces for dried lubricants and used a light oil
where needed. Most Roller Inductors don't Wear Out .... they just get Dirty
Contacts and such.
73 from Wade/KJ4WS
On Tue, Jun 18, 2013 at 3:27 PM, denton sprague
<denton@oregontrail.net>wrote:
Got a nice used(again)238A TT tuner and the roller inductor is getting a
tad long in the tooth…
Priced a new one out of TT but can't justify it right now.
Has anyone installed an aftermarket inductor in their TT tuner…if so, can
you send me the details. Thanks...
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