I have a TenTec 247 manual antenna tuner. I am thinking about
installing a roof-mount over the space between the driver and
passenger in the front of my mini-van and hanging my TT tuner below
it. I understand the combination with automatic tuners works well,
but I have been warned against using the TT to tune short antennas on
low frequencies. Of course, this was in reference to dipoles and base
antennas. The problem is reportedly that the loading coil will heat
up and be damaged and have to be re-wound.

I have about a 2 foot extension that I may also use to extend the
antenna a little.

I don't have the money to spend on auto-tuners and I have everything
but the whip and mount for the antenna configuration I just described.

comments?


--
73 for now
Buck
N4PGW

If there is a heating problem with a short dipole, there will be a
heating problem with a 102" whip.

Some automatic tuners may do OK with the short whip. I think SGC does
this, but if it works and is reasonably low-loss it is because the
tuner is designed to do well with a short whip.

One way to make the tuner match a short whip better on low frequencies
is to include a loading coil, in this case, at the base, to bring the
antenna into resonance. The impedance of the antenna will then be a low
resistive impedance, rather than a low resistive part and lots of
capacitative reactance. The tuner will handle this better than the
very short whip without a coil.

It seems to me that a short-whip automatic tuner should have an
inductance in series with the antenna input, maybe a LCL tee network.
I don't know what sort of topology the T-T 247 has but I don't think
anyone is building an LCL tee manual antenna tuner. It'd be easy to do
in an auto tuner though.

Anyone know the internals of the SGC short whip tuner (the one with the
whip mounted to it)?

Dan,
N3OX

In doing a bit of google searching for

short unloaded whip tuner

I've found some sources that say that the auto tuners tend to have a
wider efficient matching range than the typical manual tuner.

So it may have nothing to do with network topology, it's just that if
you can manage to match a very short unloaded whip with your typical
manual tuner, you're going to be out at the edge of the matching range
where it is quite inefficient.

What's the group experience with this? If it's true that the automatic
tuners tend to be more efficient for a given range of impedances, what
are likely reasons?

Can the typical auto tuner switch from LCL tee to CLC tee? Pi to Tee?

Is it always going to be better to use a binary switched inductor and
capacitor system as opposed to a variable capacitor/tapped inductor
system?

Maybe it's just that the latter usually gets shoved into a tiny box and
the inductor Q is ruined?

Dan,
N3OX

On 28 Apr 2006 08:52:31 -0700, "
wrote:

Hi Dan,

There are so many red lights going on, this was impossible to pass up.

I've found some sources that say that the auto tuners tend to have a
wider efficient matching range than the typical manual tuner.

Unless "they" can tie this to known antenna impedances, such claims
are worthless. And for another, what are the "typical" tuners that
are being compared to? Its easy enough to say what they are if it was
easy enough to measure them to support this claim.

So it may have nothing to do with network topology, it's just that if
you can manage to match a very short unloaded whip with your typical
manual tuner, you're going to be out at the edge of the matching range
where it is quite inefficient.

Matching and effeciency are only distantly related. Using padding
resistors could pull any antenna into a match - not much efficiency
there.

What's the group experience with this? If it's true that the automatic
tuners tend to be more efficient for a given range of impedances, what
are likely reasons?

There's a sucker born every minute?

Can the typical auto tuner switch from LCL tee to CLC tee? Pi to Tee?

That would have seem to have answered itself if your survey of
different auto-tuners was useful. Barring these results being
obvious, it would seem you simply discovered the font of Marketing
hype.

Is it always going to be better to use a binary switched inductor and
capacitor system as opposed to a variable capacitor/tapped inductor
system?

Depends on the granularity. Binary could mean one of two, or one of
1024.

Maybe it's just that the latter usually gets shoved into a tiny box and
the inductor Q is ruined?

For auto-tuners, that should be evident - and a marked counter to the
claim of greater efficiency.

73's
Richard Clark, KB7QHC

Richard, first I'll say that I did NOT find a survey, I've seen
statements to this effect. (See http://www.eham.net/articles/4424) Of
course, I've found statements to the contrary.

I'd like to collect some data points if people have actually measured
the input and output power of their tuner into various loads, and I'll
keep looking for real data.

I'd also like to focus my question about matching range and efficiency
and retract all the other questions for now. I realize reading your
response that I asked a bunch of general questions that were at best
ill-defined an at worst trolly-sounding.

Pick a topology, let's say the shunt L tee (CLC) because it's so
common. Assume your tuner (the one who tunes), human or
microprocessor, is smart enough to select the most efficient values of
C1, L and C2 if there happens to be more than one solution for a
particular set of impedances.

Let's say I have a range of impedances within which I can get a 1:1 50
ohm SWR: How about the interior of the rectangle between 5 and 1000
ohms resistance, -500 to 500 ohms reactance.

Then take the subregion of that rectangle where efficiency of the tuner
is greater than some value, say, 79.4% (so you're losing no more than
1dB in the tuner)

Here's one question:

Is that subregion really complicated, with lots of small spots where
you can get an efficient match right next to spots where you're dumping
lots of power into the tuner, or is the variation more smooth?

I'll leave it at that for now. I've got more questions that would pend
knowing the answer to that one.

I may have to sit down with one of the CLC tuner simulators and make
myself a plot.

Dan
N3OX












Richard Clark wrote:
On 28 Apr 2006 08:52:31 -0700, "
wrote:

Hi Dan,

There are so many red lights going on, this was impossible to pass up.

I've found some sources that say that the auto tuners tend to have a
wider efficient matching range than the typical manual tuner.

Unless "they" can tie this to known antenna impedances, such claims
are worthless. And for another, what are the "typical" tuners that
are being compared to? Its easy enough to say what they are if it was
easy enough to measure them to support this claim.

So it may have nothing to do with network topology, it's just that if
you can manage to match a very short unloaded whip with your typical
manual tuner, you're going to be out at the edge of the matching range
where it is quite inefficient.

Matching and effeciency are only distantly related. Using padding
resistors could pull any antenna into a match - not much efficiency
there.

What's the group experience with this? If it's true that the automatic
tuners tend to be more efficient for a given range of impedances, what
are likely reasons?

There's a sucker born every minute?

Can the typical auto tuner switch from LCL tee to CLC tee? Pi to Tee?

That would have seem to have answered itself if your survey of
different auto-tuners was useful. Barring these results being
obvious, it would seem you simply discovered the font of Marketing
hype.

Is it always going to be better to use a binary switched inductor and
capacitor system as opposed to a variable capacitor/tapped inductor
system?

Depends on the granularity. Binary could mean one of two, or one of
1024.

Maybe it's just that the latter usually gets shoved into a tiny box and
the inductor Q is ruined?

For auto-tuners, that should be evident - and a marked counter to the
claim of greater efficiency.

73's
Richard Clark, KB7QHC

On 28 Apr 2006 08:29:58 -0700, "
wrote:

If there is a heating problem with a short dipole, there will be a
heating problem with a 102" whip.

Some automatic tuners may do OK with the short whip. I think SGC does
this, but if it works and is reasonably low-loss it is because the
tuner is designed to do well with a short whip.

One way to make the tuner match a short whip better on low frequencies
is to include a loading coil, in this case, at the base, to bring the
antenna into resonance. The impedance of the antenna will then be a low
resistive impedance, rather than a low resistive part and lots of
capacitative reactance. The tuner will handle this better than the
very short whip without a coil.

It seems to me that a short-whip automatic tuner should have an
inductance in series with the antenna input, maybe a LCL tee network.
I don't know what sort of topology the T-T 247 has but I don't think
anyone is building an LCL tee manual antenna tuner. It'd be easy to do
in an auto tuner though.

Anyone know the internals of the SGC short whip tuner (the one with the
whip mounted to it)?

Dan,
N3OX

I believe my tuner is CLC, it has two caps and the inductor.


--
73 for now
Buck
N4PGW

On Fri, 28 Apr 2006 10:53:33 -0400, Buck wrote:

I have been warned against using the TT to tune short antennas on
low frequencies.

Hi Buck,

Such advice is worthless as it says nothing about frequency, nor
shortness.

Of course, this was in reference to dipoles and base antennas.

Of course, nothing! The tuner has no way of distinguishing any
antenna and the lead from it as anything but a load.

The problem is reportedly that the loading coil will heat
up and be damaged and have to be re-wound.

No doubt.

I have about a 2 foot extension that I may also use to extend the
antenna a little.

Try it with a "short" 160M antenna, and folks will be making coil
winding gestures next to their heads for you.

I don't have the money to spend on auto-tuners and I have everything
but the whip and mount for the antenna configuration I just described.

You must have some idea of what band you are going to use it on, what
is it?

73's
Richard Clark, KB7QHC

On Fri, 28 Apr 2006 10:52:54 -0700, Richard Clark
wrote:


You must have some idea of what band you are going to use it on, what
is it?

73's
Richard Clark, KB7QHC


Thanks, Richard for the comments. I would like to use it for 75-6
meters as I am not worried about 160 meters. I would like to use it
on 75 meters, as it is the band most likely to meet the coverage I am
interested in, but also to operate all bands as I would like not to
change antennas all the time. I have loaded the 20 meter and 40 meter
antennas with it to see how it works on other bands, but they really
suck!. I don't know if it is the way they are wound or what, but
tuning the 20 for six works well, but not with other bands. Going
lower doesn't help.

As for the mobile vs base antennas, there may be some difference. The
problem occurs when using a quarter wave or shorter dipole. However,
a quarter wave vertical is a match! This is part of my questioning.
Also, the fact that the tuner will be virtually at the antenna rather
than the coax, may make some difference, although, technically, I
think the coax would lower the reflected power to the tuner.

The theory i was hearing was that the loading coil takes all the
missing length of antenna and heats up. I can't imagine auto-tuners
having as large a coil as this manual tuner. (It uses a wire wrapped
around a toroid of some sort. ) I imagine an autotuner uses much
smaller inductors tied together thru relays.

I am trying to think of a type thurmometer that I could use that
wouldn't interact with the tuner to see if it heats up.

I will probably test the antenna this weekend if I can get the parts
and time....


--
73 for now
Buck
N4PGW

On Fri, 28 Apr 2006 22:57:40 -0400, Buck wrote:
I would like to use it for 75-6
meters as I am not worried about 160 meters. I would like to use it
on 75 meters, as it is the band most likely to meet the coverage I am
interested in,

Hi Buck,

All reports of short, mobile antennas on 80M generally cry crippled.
That is, unless, they are augmented by center loads under top hats a
dozen feet high or more. Even then, hardly remarkable unless you can
stand to be down 2 S-Units out the gate. For some, this knowledge is
a killer. For others who ignore it, they simply work those who can
hear them.

but also to operate all bands as I would like not to
change antennas all the time. I have loaded the 20 meter and 40 meter
antennas with it to see how it works on other bands, but they really
suck!.

Well, again, you are short on details. These two antennas (I presume
you have introduced two more to the discussion) may be air cooled
resistors for all their qualities you suggest. You might find an
object lesson here.

I don't know if it is the way they are wound or what, but
tuning the 20 for six works well, but not with other bands. Going
lower doesn't help.

Barring details....

As for the mobile vs base antennas, there may be some difference. The
problem occurs when using a quarter wave or shorter dipole.

Mobile quarterwave dipole?

However,
a quarter wave vertical is a match! This is part of my questioning.

Aside from this being natural, what could the question be?

Also, the fact that the tuner will be virtually at the antenna rather
than the coax, may make some difference, although, technically, I
think the coax would lower the reflected power to the tuner.

Many antennas are designed with a match external to them, but quite
close by. Why would this be detrimental? Even more, many antennas
are built with the match as part of them. They go by many names,
Gamma being one. Certainly nothing is lost in their use.

The theory i was hearing was that the loading coil takes all the
missing length of antenna and heats up.

Dare I say you can't trust everything you hear (read here)?

Myself, I taught RF communications in the Navy and had no trouble
whatever with the concept that a coil replaces the electrical length
missing in a short antenna. However, the Navy was never a slave to
fashion nor strict interpretation in this matter, and it was enough to
observe this quid-pro-quo as symbolic, and not literal.

I can't imagine auto-tuners
having as large a coil as this manual tuner. (It uses a wire wrapped
around a toroid of some sort. ) I imagine an autotuner uses much
smaller inductors tied together thru relays.

Indeed.

I am trying to think of a type thurmometer that I could use that
wouldn't interact with the tuner to see if it heats up.

Yuri might suggest aquarium thermometers (Liquid Crystal) - but you
would have to make sure the entire surface fit the entire strip (or
versa vice). If you have a very old digital camera, then they were
sensitive to IR. You could take a picture in the dark and resolve hot
spots.

I will probably test the antenna this weekend if I can get the parts
and time....

Further reports would be interesting.

73's
Richard Clark, KB7QHC

On Fri, 28 Apr 2006 22:07:00 -0700, Richard Clark
wrote:

On Fri, 28 Apr 2006 22:57:40 -0400, Buck wrote:
I would like to use it for 75-6
meters as I am not worried about 160 meters. I would like to use it
on 75 meters, as it is the band most likely to meet the coverage I am
interested in,

Hi Buck,

All reports of short, mobile antennas on 80M generally cry crippled.
That is, unless, they are augmented by center loads under top hats a
dozen feet high or more. Even then, hardly remarkable unless you can
stand to be down 2 S-Units out the gate. For some, this knowledge is
a killer. For others who ignore it, they simply work those who can
hear them.

I realize this. I have used a Hustler on 75 before. I was definitely
a weak signal station. I can only imagine that a tuned whip would
generate similar results, or more likely, poorer results.

but also to operate all bands as I would like not to
change antennas all the time. I have loaded the 20 meter and 40 meter
antennas with it to see how it works on other bands, but they really
suck!.

Well, again, you are short on details. These two antennas (I presume
you have introduced two more to the discussion) may be air cooled
resistors for all their qualities you suggest. You might find an
object lesson here.

There are a total of four antennas I have mentioned in here for
comparison sake. The Hustler, just mentioned above, the 102 whip with
a possible 2 foot extension, and two Antenna Specialists (AS) (look
exactly like HamSticks). I haven't had the Hustler for over a decade.
I will introduce another antenna in this message later.

The AS antennas are thin fiberglass poles with long stingers on the
top. The fiberglass poles, of course, have copper wound around them
from bottom to top, above which is a whip (stinger) about the same
length as the pole. The hustler was a center loaded trap that was
several inches in diameter and about 10-12 inches tall (the trap part)
with a stinger on top. (You are probably familiar with the Hustler.)
I also have a Volvo brand CB whip. It is a thin fiberglass whip
similar to the bottom portions of the AS antennas, but it does not
have a stinger. Like the AS antennas, the fiberglass has copper wire
wound from bottom to top with the top tightly wound and the bottom
section loosely wound. There is no stinger on top of the CB antenna.

I previously did a little experimenting with the two AS antennas and
the Volvo CB antenna (I don't have the 102 whip yet.) I used the tuner
to compare receive signals on various active bands. the results
weren't very good. Basically, each antenna performed best on the
frequencies for which they were designed (no big surprise here) but
they performed terribly on any other band. In fact, they were not
even acceptable for use on other bands. The signal strength on 20
meters, for example went from s-9 on the 20 AS antenna to less than
s-2 on the other antennas. I know others who have used the 102 steel
whip/auto-tuner combination that I have talked to never complained
that they only received s-2 signals with the system. Therefore, my
theory is that the winding of the coil on the fiberglass poles is
adversely affecting the radiation on out-of-band operation. I am
hoping that the steel whip, with or without the extension, will
perform better on all bands than any of these antennas tested. I
realize it is a compromise but the loss of an s-unit or two in
exchange for all band coverage for my mobile without having to switch
antennas or get out of the car and change taps is an acceptable
trade-off.

Remember, too, that in the original post, money is a big issue. The
purchase of a screwdriver (the best known mobile antenna design for
all band coverage) is not an option at this time. My theory is that I
should be able to mimic the 102 whip/auto-tuner results using a manual
tuner. My question is whether or not the tuner itself can hold up to
the task without being damaged.





I don't know if it is the way they are wound or what, but
tuning the 20 for six works well, but not with other bands. Going
lower doesn't help.

Barring details....

I think I addressed that above, the fiberglass poles are wrapped
tightly at the top and then loosely to the bottom, a stinger extends
from the tops of the AS antennas, and the Volvo antenna doesn't have a
stinger.


As for the mobile vs base antennas, there may be some difference. The
problem occurs when using a quarter wave or shorter dipole.

Mobile quarterwave dipole?
base. The suggestion I was given was not to use the antenna tuner on
a 20 meter dipole to tune a 40 meter frequency. This would be a 1/4
wave dipole on 40 meters. I don't know what the impedance of such an
antenna would be, but I do know that a 1/4 wave vertical is a
reasonable match. We never discussed the use of the tuner in the
mobile.



However,
a quarter wave vertical is a match! This is part of my questioning.

Aside from this being natural, what could the question be?

Also, the fact that the tuner will be virtually at the antenna rather
than the coax, may make some difference, although, technically, I
think the coax would lower the reflected power to the tuner.

Many antennas are designed with a match external to them, but quite
close by. Why would this be detrimental? Even more, many antennas
are built with the match as part of them. They go by many names,
Gamma being one. Certainly nothing is lost in their use.

The theory i was hearing was that the loading coil takes all the
missing length of antenna and heats up.

I should have clarified that this statement. The internal inductor of
the tuner makes up the missing length of the antenna and heats up
which can cause damage to the antenna tuner's inductor. This is how
it was presented to me, or how I understood it. Again, the discussion
was using the tuner to tune short dipoles to transmit on lower
frequencies.


Dare I say you can't trust everything you hear (read here)?

Myself, I taught RF communications in the Navy and had no trouble
whatever with the concept that a coil replaces the electrical length
missing in a short antenna. However, the Navy was never a slave to
fashion nor strict interpretation in this matter, and it was enough to
observe this quid-pro-quo as symbolic, and not literal.

I can't imagine auto-tuners
having as large a coil as this manual tuner. (It uses a wire wrapped
around a toroid of some sort. ) I imagine an autotuner uses much
smaller inductors tied together thru relays.

Indeed.

I am trying to think of a type thurmometer that I could use that
wouldn't interact with the tuner to see if it heats up.

Yuri might suggest aquarium thermometers (Liquid Crystal) - but you
would have to make sure the entire surface fit the entire strip (or
versa vice). If you have a very old digital camera, then they were
sensitive to IR. You could take a picture in the dark and resolve hot
spots.

I will probably test the antenna this weekend if I can get the parts
and time....

Further reports would be interesting.



I have been scheduled to work this weekend. I hope to be off Sunday,
If I can, I will try testing the whip idea using the side mount on the
van and if it appears to be promising, I will drill the holes in the
roof to mount the whip there near the radio and tuner.


73's
Richard Clark, KB7QHC
73 for now

--
73 for now
Buck
N4PGW