I read the article you cited, looked at the QST article on the 238A (noting
the size of the 3.5 Kv peak capacitor), and looked at the Palstar webpage at
the "inside" shot of the Palstar BT1500BAL (huge capacitor by comparison,
rated at 4.5 KV; but noted it had a ferrite input balun) and also read
W8JI's comparison of balun loss that showed the difference between the
various baluns...with the DX Engineering, coiled coax (20 ft "scrambled"),
and 60-foot "solenoid", coming out the lowest loss, and with the DXE one
being the lowest...but that was at a LOW SWR!
If I had a low SWR on all bands why would I need a tuner? I know it will be
pretty high SWR on some bands, so what then?
I guess that is what MY REAL QUESTION boils down to...although I like the
"single resonant" L-type Ten Tec 238 unbalanced tuner (and it would work
great with my future inverted L), it needs a balun to match it to the open
wire feed. Will the balun, at HIGH SWRs, just burn up my watts in heat and
smoke? Versus, a balanced tuner (Johnson, Palstar), which doesn't need a
balun (just a small one at input, which is at low SWR and negligible loss),
and does not overheat. So what I am wrestling with is which configuration
AND WHY:
(1) 238B to DXE 1:1 current balun to open wire
versus
(2) Palstar BT1500BAL to open wire.
As I see it from all the answers I've received, there are people with strong
opinions on both sides, that have just given me their conclusion: do x or do
y. But what I am still missing is WHY do x or y, and how they bounce off
one another.
FOR INSTANCE, WHICH COMBO, (1) OR (2) WILL GIVE THE LOWEST LOSS WHEN FEEDING
A BALANCED ANTENNA AT AN 8:1 SWR? HOW MUCH LOWER...LOSS 100 WATTS FOR ONE
AND 125 FOR THE OTHER? That is what I don't understand yet.
One gentleman did address my question of whether I could feed an Inverted L
(like on 160) with a balanced tuner if I used a balun to change the
unbalanced feed from the antenna to a balanced feed connected the output of
the balanced tuner, saying don't, but why not? Does this mean that a
balanced tuner can NEVER be used for UNbalanced loads through use of a
balun?
Another gentleman pointed out that most people just go unbalanced and don't
worry about the heat/loss in the balun...or change the length of the feed
line slightly (per Cecil's method) until you get a "happy" length the balun
can handle, and then buy the most rugged balun you can get to handle the
mismatches.
CONCLUSIONS SO FAR: As I see it, the 238B has versatility in that it can do
both balanced and unbalanced (with a good external balun instead of its
internal voltage balun), but the external balun will heat up and could even
fail at 1200 watts to a feed line feeding some mismatched frequencies. But I
could lengthen/shorten the balanced feed line to adjust it I guess, looking
for its happy spot! On the other hand, the PALSTAR will work great with
unbalanced lines (no lossy balun), even at high SWR, but it doesn't do
unbalanced lines (although one person mentioned the capacitor might be too
small for some situations--but I compared it and it seems to be larger and
higher rated (4.5 KV) than the Ten Tec). From your comments I gather that
almost any tuner or tuner-balun combo will do great at LOW SWR...but I don't
need a tuner for those situations. It's when the SWR gets up higher, like
8:1 or 16:1 that I am concerned about with 1200 watts. In ARRL tests, the
Palstar handled that OK, but no such tests for a 238B handling balanced
lines (only unbalanced lines a few years back in QST). And what about the
DXE, which W8JI tests highly rated, but (if I read the tests right) the
tests were done at approx. 1.5 to 1 SWR...no where near the 8 to 1 that I am
envisioning. Some of you have said the balun will heat up or even burn up
(although I understand the DXE is supposed to be rugged enough to only heat
up), but doesn't that rob me of all my power--heat is not a good thing!
And, if both will work, to some degree (barring the burnout of the balun),
is the 238B the way to go because I can ALSO do unbalanced lines for other
antennas?
I guess if I never wanted to have any unbalanced antennas in the future, I'd
go the balanced tuner and be done with it. But if the loss through the 238B
and DXE Tuner Balun would not be substantially greater than the Balanced
Tuner, but will permit me to match unbalanced lines too for future antennas,
then that sure seems the way to go (and adjust the feed line length to best
match).
What do you all think?
And thanks for you many replies that have brought me this far so far!
73,
Greg N6GK
Greg, N6GK
"Bob Miller" wrote in message
...
On Sun, 24 Jul 2005 11:32:37 -0700, "greg knapp 5"
wrote:
I have decided to erect an 80 meter dipole at 70 feet fed with 450 or 600
ohm open wire, for use on ALL HF bands between 80 and 10 meters. Power
output will be 1000W CW and 1200W PEP.
(1) Which is the better setup and why: a Ten Tec 238B unbalanced tuner
with
a DX Engineering 1:1 balun on antenna side of tuner OR a Palstar BT1500BAL
balanced tuner?
(2) Also, if I later decide to erect an inverted L for 160/80, can I use a
balanced tuner with a DX Engineering 1:1 balun put on antenna side of
tuner,
but reversed in direction (converting unbalanced to balanced), or need I
get
a different tuner?
(3) In a perfect world, I'd buy both tuners (one for balanced and one for
unbalanced), but I can't afford it. Also, if I go with the unbalanced
tuner,
will the balun waste a ton of RF in heat and loss?
(4) I made a similar post on the Ten Tec List, and received lots of advice
on point designs, but not the COMPARISON data I was looking for that will
help me make the final decision to go with a balanced tuner vs an
unbalanced
(with balun) tuner.
(5) I have plenty of room, would it make any difference if I put a 160
meter
dipole instead?
Thanks & 73,
Greg, N6GK
Have not seen any published tests comparing balanced vs. unbalanced
tuners, so any comparisons will probably be theoretical in nature.
Also, instread of the dx engineering balun, you might look at a
w2du-style balun -- see his article at
http://www.w2du.com/Reflection2.html
bob
k5qwg