Dipoles and the rig's RF ground...
 

"Dave Oldridge" wrote in message

I swear OH8OS used to MAKE his own band openings or 15 back in 65 when
I
used to work him from VE8ML. He had a huge quad, 15 elements, I
think,
pointed right in my direction.

You just about can. Even with just two elements on 10, I worked several
contacts from Houston that couldn't hear anyone else in the US. I
really loved that antenna.

Dipoles and the rig's RF ground...
 

Tell me how to coax feed a dipole that works from 3.3 to 4.1 MHz and you
have my attention.

wrote in message
oups.com...
..
But...I am serious about what I say.. If you want the vurry
best 80m dipole, feed it with nuttin but coax.
MK

Dipoles and the rig's RF ground...
 

Where are the losses in a Ladder-
Line fed system? ....

The tuner that is usually used offsets the advantage
of the line itself. Sure, on paper you shouldn't really
be able to notice it. But I do when I test it. It's actually
measureable on an S meter when doing A/B comparisons.
Or at least it was for me when using a 989c tuner
and minimum inductance vs coax fed.
That tells me the tuner loss can often be a bit more
than it's cracked up to be. But I also found if you don't
use the minimum inductance when tuning the tuner,
you can lose quite a bit. I saw easy 20 % losses when
testing that one time. If I used the very least inductance,
I could get it down to an almost unmeasureable level.
If I get on 80m and want the very best efficiency I can get
feeding a dipole, I use coax.
Of course, the line is never more than 100 ft.
Usually more like 50 ft. I have a 50 ohm radio feeding a
low loss 50 ohm line, to a 50 ohm antenna feedpoint. You
have uncluttered perfection. :-) And in the real world
the most efficient that I've seen so far. If there was better,
I'd be using it. I could see using the ladder line on real
long distances. On the higher bands, it could be noticable.
But like I say, my run is about 50 ft. Considering efficiency
vs ease of use, wx resistance, ease of lightning protection,
coax is a no brainer for me. Of course, I ain't everyone.. :/
MK

Dipoles and the rig's RF ground...
 

Tell me how to coax feed a dipole that works from 3.3 to 4.1 MHz and you
have my attention.

Probably wouldn't be practical for you.. Just offhand, I can think
of a way, but you'd have to run at least two set of dipoles, and
maybe even three, tied together in parallel. You would stagger
tune them one low, one middle, one high, and the SWR
plot should look about like a \/\/\/ . I've never tried using
three dipoles, but I've done it with two and having a W SWR
plot. That is one way you could have that range and use
coax feed. But like I say, probably would be a PIA with
it needing at least one center support and six tie off
points.
MK

Dipoles and the rig's RF ground...
 

wrote:
Where are the losses in a Ladder-
Line fed system? ....

The tuner that is usually used offsets the advantage
of the line itself.

Fred and I don't use a tuner.
--
73, Cecil http://www.qsl.net/w5dxp

Dipoles and the rig's RF ground...
 

Fred and I don't use a tuner.

Then you and Fred aren't running the same G5RV that
most people buy and throw up. And then feed with a tuner. :/
That's why I say I'm not really talking about your antenna.
I know you will modify it to make it more usable. This is a
given. You are Cecil. But all those 1000's of users who don't
have the time or the clue to modify? Like Lurch would say
on the Addams Family...Gruggggghhhhhhhhhhhhhhh... :/
MK

Dipoles and the rig's RF ground...
 

On 11 Jan 2006 01:09:41 -0800, wrote:

Where are the losses in a Ladder-
Line fed system? ....

The tuner that is usually used offsets the advantage
of the line itself. Sure, on paper you shouldn't really
be able to notice it. But I do when I test it. It's actually
measureable on an S meter when doing A/B comparisons.
Or at least it was for me when using a 989c tuner
and minimum inductance vs coax fed.

You are telling us that you have evaluated the loss of a MFJ-989C
antenna tuner + open wire line vs coax by on air A/B tests using the
S-meter as your indicator.

Presumably you used exactly the same antenna, how are you sure that
the feedline wasn't an active part of the antenna, was the measurement
made over an ionospheric path, was the A/B comparison made at
different times when other things may have changed?

What would be your confidence limits on such a experiment?

If you recorded your results, the variance would be revealing.

I suggest that the noise in your experiment would probably swamp the
true difference between your A and B configuration, and therefore your
conclusion might not be sound.

Your observation is (as you note) different to "on paper"
expectations, that might be reason to re examine the experimental
setup in search of an explanation.

Owen
--

Dipoles and the rig's RF ground...
 

You are telling us that you have evaluated the loss of a MFJ-989C
antenna tuner + open wire line vs coax by on air A/B tests using the
S-meter as your indicator.

Sure.

Presumably you used exactly the same antenna, how are you sure that
the feedline wasn't an active part of the antenna, was the measurement
made over an ionospheric path, was the A/B comparison made at
different times when other things may have changed?

The A/B testing is instant. All comparisons were done in the
usual up/down NVIS envionment. Mostly close in stations, and the
noise floor as another opinion. Just comparing any difference
in noise floor is a fairly accurate indication of efficiency in a
case like that. I didn't worry about the feedline being part
of the antenna, as I never would in the real world. I'm
running ladder line the whole way from the tuner to the antenna.
If the line is radiating, there would not be too much to do about
it at that point, without going to further measures. . I noticed
no obvious problems in tuning, or a "hot" line, rig, etc..

What would be your confidence limits on such a experiment?

Very high overall.

If you recorded your results, the variance would be revealing.

No. Not that time. It was just for my personal amusement.
In fact, I was out camping when I did that test.

I suggest that the noise in your experiment would probably swamp the
true difference between your A and B configuration, and therefore your
conclusion might not be sound.

What noise? I'm just using a switch to compare both antennas.
In that particular case, when switching to the coax fed, the noise
floor rose a bit, and strong signals that were way over S 9 rose
about 5 db worth on that particular meter. Easily repeatable
over and over. I'm not giving any numerical value to this
increase, I just know the coax fed system was the most
efficient. All signals increased when using coax. Noise floor,
desired signals, the whole deal. Switching to the tuner/LL fed
was like adding a small bit of attenuation. The way I see it,
the loss had to be at the tuner. And I was very careful in
tuning, using the least inductance to get a usable match.

Your observation is (as you note) different to "on paper"
expectations, that might be reason to re examine the experimental
setup in search of an explanation.

Why is it different? Actually, I found about what I was expecting.
I was expecting the coax fed to win. And it did.
Now, I realize this is a fairly sloppy test, and could be
improved greatly for accuracy, but there was no doubt
which system was better at that particular time.
The "on paper" expectations of the ladder line winning
would depend greatly on the losses of the tuner involved.
Sure, ladder line on it's own is very low loss, but add a
tuner, and things can change quite a bit as far as
system loss.
Now, granted the difference is small in general, but
I could see it. And if I can see it on a meter, it's not as
small as it's oft cracked up to be, or I wouldn't be able to
see it.
MK

Dipoles and the rig's RF ground...
 

ORIGINAL MESSAGE:


"Owen Duffy" wrote in message
...
snip

You are telling us that you have evaluated the loss of a MFJ-989C
antenna tuner + open wire line vs coax by on air A/B tests using the
S-meter as your indicator.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can do a pretty good evaluation of a tuner's loss by putting your hand
on the cabinet after running a few minutes. Just imagine a 25, 50 or
whatever watt resistor in there dissipating the same heat.

One needs to calibrate one's hand, of course. :-)

Bill, W6WRT

Dipoles and the rig's RF ground...
 

Bill Turner wrote:

You can do a pretty good evaluation of a tuner's loss by putting your hand
on the cabinet after running a few minutes. Just imagine a 25, 50 or
whatever watt resistor in there dissipating the same heat.

One needs to calibrate one's hand, of course. :-)

Bill, W6WRT


I disagree.

I'd venture to guess that the average output power of a 100 watt PEP
sideband rig is no more than about 10 watts unless heavy compression is
being used. And I think you'll find that a 10 watt resistor inside a
typical tuner cabinet -- representing loss of all the transmitted power
-- will make a barely noticeable difference in the cabinet temperature.

Add to that the fact that the thermal time constant of the tuner is
probably longer than the typical transmitting session, so the power
needs to be averaged over the receiving periods, too.

If you're running a kW, you're up to 100 watts or so during transmit
only. But can you tell the difference with your "calibrated" hand
between 1 dB loss in the tuner (25 watts), 3 dB loss in the tuner (50
watts), or 100% of the power lost in the tuner (100 watts)?

I'd love to see the results of a double-blind study where a measured
tuner loss is compared with an estimate made using Bill's method. But I
think the chances of that are about the same as finding a double-blind
study of the audio quality enhancement of $1000 speaker cables.

Roy Lewallen, W7EL