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.

Is the radiation pattern on all of these bands acceptable/useful?

(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?

Study this before deciding: http://eznec.com/misc/ibalun.txt

Considering the capacitor in the Palstar isn't a balanced design, the
capacitive coupling from it to ground is asymetrical, so I would not
call it a balanced tuner. Also, I don't see anything that looks like
a 1500 W balun in there.

Ten Tec says, "Because there are only two variable components, there
is only one setting of each which will provide a perfect match to a
given load impedance. This unique setting automatically provides the
lowest Q network possible. Low Q means low circulating currents, hence
low loss, and it also provides the widest frequency bandwidth of
operation before retuning is necessary (very useful if you're moving
up and down the SSB portion of the band, for example)..."

They are correct when they say that there is only one setting for a
match, but the L-network Q is set by the load and source Z and is
likewise fixed and totally out of the control of the operator. This
may or may not give the largest operating BW and/or lowest loss.

For example, take a load Z of 5 -j10 at 7 MHz. With capacitor Q =1000
and inductor Q = 250 (good luck with a roller inductor), an L-network
of C = 1364 pF and L =0.568 uH will give SWR = 1.02. The network loss
will be 0.1 dB.

Using the same load Z and component Q, a high-pass-Tee network of Cin
= 1438 pF, L = 0.36 uH and Cout = 3912 pF will give SWR = 1.01 The
network loss will be 0.07 dB.

More parts, lower loss. So much for conventional wisdom. Now this is
a pretty wild load Z, but with certain antenna feedpoint Z and
transmission line lengths and Zo, it's possible. Admittedly, the
differences in insertion loss are negligble but they are different in
the -wrong- direction, thus proving the point.

Of course, try and find a tuner with capacitors of this high a value.

Also, there are some impedances that cannot be matched with either
configuration of a low-pass (series inductor) L-network. The same can
be said for any other topology, but you should be aware of this.

(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?

I wouldn't do this.

(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?

Maybe. In my opinion balun loss is no different from line
attenuation. Line attenuation is magnified by SWR and I see no reason
why balun loss wouldn't be too, particularly since most baluns are
constructed from a transmission line.

(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?

If you have plenty of room, why limit yourself to one compromise
antenna?