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

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

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

Not counting the potential tuner problems you mention, my experience is
a 102” whip with no loading will work ok on 10-20m, but on 40m and below
it sucks.
Bob

Buck wrote:
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?

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 10:52:54 -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 Sat, 29 Apr 2006 02:06:48 GMT, Bob wrote:

Not counting the potential tuner problems you mention, my experience is
a 102” whip with no loading will work ok on 10-20m, but on 40m and below
it sucks.
Bob

with no tuning? you get acceptable match to your rig without a tuner,
would you explain more?

thanks
Buck
--
73 for now
Buck
N4PGW