"Reg Edwards" wrote in message
...

"Cecil Moore" says -

There's no such thing as a 100% efficient tuner.
====================================

Cecil, not a very surprising statement.
There's nothing which is 100% efficient.

What is the typical efficiency of a typical tuner with a typical
antenna.
Does it differ significantly from 100% ?
Yes or no?
----
Reg.


I did some measurments on a MFJ tuner into a dummy load. While I am not
sure if the losses would be more or less than to an acutal antenna, I would
assume it should be the best case . The losses were around 5 to 10 watts
starting with 100 watts input depending on the band. I think 80 meters was
the worse from 80 to 10 meters. This is a small tumer rated around 200 or
300 watts and has a built in wattmeter. This may account for a small
aditional loss. I did not use this meter but did use 2 Bird meters , one on
the input and one on the output to keep the input power constant at 100
watts.

Can you give us a magnitude, for example for a g5rv on 3.8 MHz fed with 50
feet of 50 ohm coax. Is it .5 or 5 dB?

Or we can be more specific and say we want to match
a 50 Ohm source to R 5000 -J720 using an MFJ989C. What loss is to be
expected?

Granted there are cases of attempting to load a short (with respect to
frequency) antenna that has extremely low values of R can cause large
losses. I would think that a general statement could be made about antennas
that are 1/2 wavelength or longer at the operating frequency and the
magnitude of losses one could expect from the typical tuner.

Is there no way to quantify the losses, no rule of thumb, should we all
throw our tuners away because they may have unpredictable horrendous losses?
What steps should be taken by the average amateur to obviate these losses.

I am at a loss to understand how bad the losses are that you and Cecil refer
to. Can you lead me from the darkness Sir!.


"Roy Lewallen" wrote in message
...
Fred W4JLE wrote:
Can you give us a typical loss for a tuner matching a G5RV?

No, sorry, I can't, and I don't believe there is such a thing. It's
possible of course to find the input impedance of any wire antenna like
the G5RV at each of the frequencies of interest. But transmission line
lengths and impedances vary, which transforms the impedance seen by the
tuner. Those impedance changes can be dramatic, and can result in widely
varying tuner efficiency. On top of that, you have the variations in
tuner topology and construction which makes a "typical" tuner also an
elusive beast. I'd be very suspicious of any "typical" tuner loss
figure, and wouldn't expect to see it in practice unless the conditions
are spelled out really well and my setup was very similar.

You see, I'm not a true Guru. A real one wouldn't waffle like this, but
would give you a positive answer, and you'd very probably never have
reason to doubt it.

Roy Lewallen, W7EL

"Fred W4JLE" wrote in message
...
Can you give us a magnitude, for example for a g5rv on 3.8 MHz fed with 50
feet of 50 ohm coax. Is it .5 or 5 dB?
.................................................. .......
.................................
QST has on several occasions tested antenna tuners. The most recent one I
found was from last year. The worst case I saw was something like 40% loss
when matching an impedance of 6.25 Ohms on, I think, 40 meters. It is worth
noting that the 2KW tuners will have less loss than the 300W jobs. Also, the
loss depends on the impedance it sees, rather than the SWR. So, for an 8:1
SWR, the loss at 6.25 Ohms will be a lot worse than at 400 Ohms. Among other
things, the loss will then depend on the length of the feedline. The high
power tuners had a loss of less than 10% over most of the range.

Tam/WB2TT

Fred W4JLE wrote:
Can you give us a magnitude, for example for a g5rv on 3.8 MHz fed with 50
feet of 50 ohm coax. Is it .5 or 5 dB?

Sorry again, I can't help you much. There are a number of tuner
topologies in use (L, pi, high and lowpass tee, LCC, "ultimate
transmatch" to name a few), and the loss of one compared to another can
be quite different depending on the load impedance, even if all use the
same inductor(s).

The information you gave is enough to calculate the impedance seen by
the tuner, though, assuming your G5RV is 102 feet long and not one of
the countless variations. Assuming a height of 40 feet over average
ground, the impedance at 3.8 MHz seen at the input end of 50 feet of 50
ohm coax should be about 2.5 + j23 ohms (SWR ~ 27:1) if the coax is
RG-8, or about 4.1 + j22 ohms (SWR ~ 17:1) if the coax is RG-58. (The
SWR at the load will be greater than 60:1. You should maybe be worrying
more about feedline loss than tuner loss.) I didn't take into account
the effect of feedline radiation, which I'll assume is suppressed with a
balun.


Or we can be more specific and say we want to match
a 50 Ohm source to R 5000 -J720 using an MFJ989C. What loss is to be
expected?

Using the Z you specified or the Z I calculated, all that's necessary
then is to obtain a schematic of the tuner and information about the
physical construction of the inductor(s), calculate what settings will
achieve a match, and find out which of these settings you're using. Then
calculate the coil currents and from that the loss. I don't have a
schematic of the tuner nor a physical tuner -- I haven't used one for 30
years or more except for a small homebrew tuner for correcting small
mismatches to keep my QRP Field Day rig happy. So I don't have a clue.
Perhaps someone else who has the tuner, the math ability, the patience,
and the time will be willing to help you.

Granted there are cases of attempting to load a short (with respect to
frequency) antenna that has extremely low values of R can cause large
losses. I would think that a general statement could be made about antennas
that are 1/2 wavelength or longer at the operating frequency and the
magnitude of losses one could expect from the typical tuner.

I think you can say that if the SWR is no greater than 2:1 or maybe 3:1,
the loss in a properly designed tuner should be pretty low. Outside that
range, like your 17 - 27 SWR example, I wouldn't speculate.

Is there no way to quantify the losses, no rule of thumb, should we all
throw our tuners away because they may have unpredictable horrendous losses?

Hm, are those the only two options? Why not use the tuner, make
contacts, and be happy? And if the tuner has a horrendous loss, why will
throwing it away help? You'll still be better off with it than without it.

What steps should be taken by the average amateur to obviate these losses.

Adjust the feedline length for each band to present a moderate impedance
to the tuner. Cecil has posted quite a bit about this in the past. And
use a tuner with the largest coil(s) possible. You could set up jumpers
so you can change the topology of the tuner to pi, L, tee, etc. On each
band, try each configuration and, among those which effect a match,
choose the one that gives you the greatest field strength from your
antenna or the highest current to it.

Of course, you could do what I do -- I settle for other than all-band
operation, and make my antennas resonant or nearly resonant. When
matching is required, I do it at the feedpoint with components I've
characterized -- I know the antenna Z and the inductor Qs, so I can
calculate the loss. But most people don't want to do this, and happily
put up with whatever losses they get in exchange. Or you can get
something like the B&W terminated folded dipole, and put the losses at
the antenna instead of the tuner.

I am at a loss to understand how bad the losses are that you and Cecil refer
to. Can you lead me from the darkness Sir!.

Nope, sorry, I can't. What's the approximate value of resistors? I can't
answer that one, either.

Roy Lewallen, W7EL

For efficiency of the L-network tuner on different bands, and losses
in transmission lines and other data, download program DIPOLE3 from
website below.

The program covers dipole + balanced line + balun + coax line + tuner
L and C settings.

With one hit of a key the antenna system can be modelled as a G5RV.

Download program DIPOLE3 in a few seconds. It is also easy to find the
resonant frequencies of the G5RV.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

On Mon, 6 Jun 2005 15:06:13 -0400, "Fred W4JLE"
wrote:

Let's put this an easier way, how many of you have a low pass filter in
line. Most manufacturers claim a .25dB or less insertion loss. These filters
consist of a boat load of coils and caps.

A tuner normally has 2 varible caps and a single silver plated coil.

While any device indeed has loss, here we are picking fly crap out of
pepper.

Clearly you didn't read the links or you wouldn't be asking all of the
questions.

Is there no way to quantify the losses, no rule of thumb, should we
all
throw our tuners away because they may have unpredictable horrendous
losses?

In general I do....I don't use a tuner for any of my everyday
antennas...

What steps should be taken by the average amateur to obviate these
losses.

Quite simple really. Use the very minimum inductance needed to get
a usable match. I once did tests to determine the appx amount of
tuner loss when tuning properly vs improperly. When using an excess
of inductance to match, I saw tuner losses approach 20%. IE: 20w out
of 100w. When carefully tuning, using the very least inductance, this
loss could be reduced to a value nearly unreadable. BUT!!! This was
on a resonant 50 ohm system. You could expect the losses of an extreme
mismatch to be higher, even if you tuned very carefully. The losses
and
coil warming when feeding a 1/2 size dipole with a T net tuner are well
known.
Thats how I got a free MFJ 989c when a friend of mine couldn't keep
from
frying the plastic coil forms. He bought a nye viking, and gave me the
989c.
Which I've used since with no problems at all....It wasn't really the
tuners
fault...He was abusing it trying to feed a 1/2 size dipole, and then
running a
TL-922 flat out on top of that... MK

wrote:

Quite simple really. Use the very minimum inductance needed to get
a usable match. I once did tests to determine the appx amount of
tuner loss when tuning properly vs improperly. When using an excess
of inductance to match, I saw tuner losses approach 20%. IE: 20w out
of 100w. When carefully tuning, using the very least inductance, this
loss could be reduced to a value nearly unreadable. . . .

Why bother, unless you're having a problem with the heat? 20% loss is
just about exactly 1 dB.

Roy Lewallen, W7EL

My 2 cents on the subject of tuner loss.
A tuner will Always introduce more loss to the system.
If the total power output of the transmitter is not improved(ie, at
2:1 SWR), then using the tuner to reduce SWR to 1:1 is counter
productive, isn't it?
In other words, getting the SWR down to 1:1 from anything = 2:1, will
always cause a reduction in total power out.

Pat W0OPW

On 7 Jun 2005 04:35:50 -0700, wrote:

My 2 cents on the subject of tuner loss.
A tuner will Always introduce more loss to the system.
If the total power output of the transmitter is not improved(ie, at
2:1 SWR), then using the tuner to reduce SWR to 1:1 is counter
productive, isn't it?

For me, not so. The manual for my Icom 735 says it is designed to
handle 1:1.5 swr, but to try to get it as close to 1:1 as possible.

I just tried an experiment on 20 meters with my 80 meter dipole and an
MFJ 989c tuner. At 1:1 swr, the meter measures 110 watts out; raising
the swr to 2:1 lowers the metered output to 20 watts. So I'm not sure
what the advantage of running a higher swr is.

bob
k5qwg


In other words, getting the SWR down to 1:1 from anything = 2:1, will
always cause a reduction in total power out.

Pat W0OPW