Series-tuned antenna tuner question

[JasonW]

Hello All,


I have a question regarding series-tuned antenna tuners for Part 15 AM use. Ham radio operators often use series-tuned antenna tuning units (as illustrated here: http://www.g4nsj.co.uk/atu.shtml ). The schematic goes like this:

transmitter---> tapped coil---> variable capacitor---> antenna

Ground radials and/or an Earth ground is/are connected to the transmitter chassis. The tapped coil along with the variable capacitor allows the transmitter to load a random-length antenna over a fairly wide range of frequencies.

For Part 15 AM use, I envision something simpler, like this:

transmitter---> variable capacitor---> un-tapped coil---> 3 meter antenna

It seems that if the coil had enough windings to make the 3 meter antenna + coil *electrically* longer than 1/4 wavelength, the variable capacitor could be used to electrically shorten the antenna + coil and bring the combination to resonance, as is commonly done with 3/8 wavelength wire antennas that use only a single variable capacitor for tuning.

What do you all think? -- JasonW

 

[radio8z]

> Hello All,
>
>
> I have a question regarding series-tuned antenna tuners for
> Part 15 AM use. Ham radio operators often use series-tuned
> antenna tuning units (as illustrated here:
> http://www.g4nsj.co.uk/atu.shtml ). The schematic goes like
> this:
>
> transmitter---> tapped coil---> variable capacitor--->
> antenna
>
> Ground radials and/or an Earth ground is/are connected to
> the transmitter chassis. The tapped coil along with the
> variable capacitor allows the transmitter to load a
> random-length antenna over a fairly wide range of
> frequencies.
>
> For Part 15 AM use, I envision something simpler, like this:
>
>
> transmitter---> variable capacitor---> un-tapped coil---> 3
> meter antenna
>
> It seems that if the coil had enough windings to make the 3
> meter antenna + coil *electrically* longer than 1/4
> wavelength, the variable capacitor could be used to
> electrically shorten the antenna + coil and bring the
> combination to resonance, as is commonly done with 3/8
> wavelength wire antennas that use only a single variable
> capacitor for tuning.
>
> What do you all think? -- JasonW
>
Hi Jason,

The only purpose of an antenna tuner such as is used in the amateur service is to achieve an acceptable impedance match from the antenna to the transmitter. They will make the antenna "look longer", etc. from the perspective of the transmitter but they will not change the antenna electrical characteristics. The antenna effective length will not change due to use of the tuner. For part 15 operation, the 3 meter rule sets a very low efficiency and a tuner will not change this. The tuner only presents an acceptable impedance to the transmitter.

The base loading coils which have been presented on this board do the same thing as an antenna tuner.

Hope this helps.

Neil

 

[JasonW]

Neil, that's what I'm after, a good impedance match to the transmitter. Will the "backwards" (xmitter---> VC---> coil---> 3 m aerial) series-tuned ATU do this? -- JasonW

> > Hello All,
> >
> >
> > I have a question regarding series-tuned antenna tuners
> for
> > Part 15 AM use. Ham radio operators often use
> series-tuned
> > antenna tuning units (as illustrated here:
> > http://www.g4nsj.co.uk/atu.shtml ). The schematic goes
> like
> > this:
> >
> > transmitter---> tapped coil---> variable capacitor--->
> > antenna
> >
> > Ground radials and/or an Earth ground is/are connected to
> > the transmitter chassis. The tapped coil along with the
> > variable capacitor allows the transmitter to load a
> > random-length antenna over a fairly wide range of
> > frequencies.
> >
> > For Part 15 AM use, I envision something simpler, like
> this:
> >
> >
> > transmitter---> variable capacitor---> un-tapped coil--->
> 3
> > meter antenna
> >
> > It seems that if the coil had enough windings to make the
> 3
> > meter antenna + coil *electrically* longer than 1/4
> > wavelength, the variable capacitor could be used to
> > electrically shorten the antenna + coil and bring the
> > combination to resonance, as is commonly done with 3/8
> > wavelength wire antennas that use only a single variable
> > capacitor for tuning.
> >
> > What do you all think? -- JasonW
> >
> Hi Jason,
>
> The only purpose of an antenna tuner such as is used in the
> amateur service is to achieve an acceptable impedance match
> from the antenna to the transmitter. They will make the
> antenna "look longer", etc. from the perspective of the
> transmitter but they will not change the antenna electrical
> characteristics. The antenna effective length will not
> change due to use of the tuner. For part 15 operation, the 3
> meter rule sets a very low efficiency and a tuner will not
> change this. The tuner only presents an acceptable
> impedance to the transmitter.
>
> The base loading coils which have been presented on this
> board do the same thing as an antenna tuner.
>
> Hope this helps.
>
> Neil
>

 

[radio8z]

> Neil, that's what I'm after, a good impedance match to the
> transmitter. Will the "backwards" (xmitter---> VC--->
> coil---> 3 m aerial) series-tuned ATU do this? -- JasonW
>
Jason,

If I understand what you are asking correctly, a series cap and coil and antenna string will allow you to achieve resonance but you will not have independent control of the resistive component. By definition, resonance means no reactive component.

Different configurations are used in these transmatches which allow control of the resistive component also. I have had the most success with the pi tuner on the ham bands but the antenna situation there is different than on part 15 AM due to the lower reactive component on the ham bands where the antennas are physically longer than 3 m. and the frequencies are higher.

Other types such as a tee, ell, tapped capacitor or inductor may be better suited. If you can borrow or buy the ARRL Amateur Radio Handbook or Antenna Handbook you will have a good reference. I don't know off hand which is best for part 15 AM but it is worth pursuing. Perhaps a match designed for 160 meters would work. Keep in mind that this will not change the radiation resistance of the antenna, it may just match the tx. better.

Also, in my last post I said "> The base loading coils which have been presented on this board do the same thing as an antenna tuner.". This comment is incomplete since a series coil just cancels the reactive component of the antenna impedance but does not transform the resistive component as the transmatch will.

Neil

 

[JasonW]

I'm partial to L-match antenna tuners:

antenna <---coil <---transmitter
+
+
vc
+
ground

(I had to draw it backwards for the ASCII art to look right--the variable capacitor-to-ground lead actually goes between the antenna and coil.) For use with a low-impedance antenna, you just reverse the transmitter and antenna positions.

If I understand you correctly, a series-tuned ATU will bring the antenna to resonance (no capacitive or inductive reactance), but its pure resistance still might not match the transmitter's 50 ohm or 75 ohm output? -- JasonW

> > Neil, that's what I'm after, a good impedance match to the
>
> > transmitter. Will the "backwards" (xmitter---> VC--->
> > coil---> 3 m aerial) series-tuned ATU do this? -- JasonW
>
> >
> Jason,
>
> If I understand what you are asking correctly, a series cap
> and coil and antenna string will allow you to achieve
> resonance but you will not have independent control of the
> resistive component. By definition, resonance means no
> reactive component.
>
> Different configurations are used in these transmatches
> which allow control of the resistive component also. I have
> had the most success with the pi tuner on the ham bands but
> the antenna situation there is different than on part 15 AM
> due to the lower reactive component on the ham bands where
> the antennas are physically longer than 3 m. and the
> frequencies are higher.
>
> Other types such as a tee, ell, tapped capacitor or inductor
> may be better suited. If you can borrow or buy the ARRL
> Amateur Radio Handbook or Antenna Handbook you will have a
> good reference. I don't know off hand which is best for
> part 15 AM but it is worth pursuing. Perhaps a match
> designed for 160 meters would work. Keep in mind that this
> will not change the radiation resistance of the antenna, it
> may just match the tx. better.
>
> Also, in my last post I said "> The base loading coils which
> have been presented on this board do the same thing as an
> antenna tuner.". This comment is incomplete since a series
> coil just cancels the reactive component of the antenna
> impedance but does not transform the resistive component as
> the transmatch will.
>
> Neil
>

 

[rfry]

JasonW wrote
>I'm partial to L-match antenna tuners:
>antenna Neil, that's what I'm after,
>a good impedance match to the transmitter.
>Will the "backwards" (xmitter---> VC--->
> > > coil---> 3 m aerial) series-tuned
>ATU do this?
___________________

Jason/Neil - If you can stand me butting into this thread, here is another view of this...

A tx can deliver power only into a resistance, not a reactance. The resistance term of the base impedance at the input terminal of the loading coil consists of...
1. The radiation resistance of the ~3-m vertical. This is a function of its electrical length at the operating frequency, and for Part 15 AM it is very small -- about 0.1 ohm more or less for a simple vertical structure, at its greatest.
2. The ohmic resistance of the radiator itself (very small, usually)
3. The resistance of the loading coil (ranges from maybe 2 to maybe 10 ohms)
4. The resistance to r-f current present in the r-f ground system returning those currents back to the tx ground terminal. Usually this resistance is the biggest of all, and can be 100 ohms or more, depending on the quality of the r-f ground structure you are using.

The radiation efficiency of a Part 15 AM antenna system is the ratio of its radiation resistance to the total resistance in the antenna system. So if the sum of all the resistances is, say, 25 ohms, and the radiation resistance part of that is 0.1 ohm, then system radiation efficiency is 0.1/25 = 0.4%.

An electrically short radiator has high capacitive reactance, and accepts very little power from a tx because its input VSWR is extremely high. The loading coil is used to ~cancel that reactance so as to present a load that a tx can deliver power into. BUT that low-reactance load still can have a wide range of resistance values depending on the resistances in the ground and coil.

A tx is designed to work into a known impedance value -- usually 50 +j0 ohms. So even if the loading coil has canceled the reactance of the short vertical, the R term of the load that the tx sees could vary from maybe 10 ohms for a really good system to several hundred ohms for a poor one.

So that is the function of the variable capacitor at the base of the antenna -- to transform the input match created by the loading coil and other resistances back to something near 50 +j0 ohms that the tx can deliver its rated power into.

The capacitor and loading coil haven't made the radiator either electrically longer, or more efficient. They have only allowed more power to flow into it from the source, due to matching their impedances.
//

 

[JasonW]

Not a problem--I welcome such "butting in."

The thing that got me thinking along these lines was the dual-band antenna described and illustrated in Orr's book on ham radio wire antennas. The 80 meter/160 meter antenna uses only a 250 pF variable capacitor (in series at the feedpoint) for tuning. On 80 meters, the variable capacitor is switched (shorted) out of the circuit and the antenna functions as a self-resonant 3/4 wavelength radiator. At 160 meters, the antenna is 3/8 wavelength and the variable capacitor is switched into the circuit to tune it to resonance.

My thought was to build a 3 meter antenna with a base loading coil having enough turns to make the coil/antenna combination *electrically* longer than a 1/4 wavelength antenna (and thus be inductively reactive), and then tune this out with a variable capacitor. I envisioned the system as xmitter---> VC---> coil---> antenna, although the more common xmitter---> coil---> VC---> antenna arrangement may work just as well. I know this wouldn't make the 3 meter antenna any better (3 meters is still 3 meters), but hopefully this would make the antenna better able to accept power and load up. -- Jason

> JasonW wrote
> >I'm partial to L-match antenna tuners:
> >antenna Neil, that's what I'm after,
> >a good impedance match to the transmitter.
> >Will the "backwards" (xmitter---> VC--->
> > > > coil---> 3 m aerial) series-tuned
> >ATU do this?
> ___________________
>
> Jason/Neil - If you can stand me butting into this thread,
> here is another view of this...
>
> A tx can deliver power only into a resistance, not a
> reactance. The resistance term of the base impedance at the
> input terminal of the loading coil consists of...
> 1. The radiation resistance of the ~3-m vertical. This is a
> function of its electrical length at the operating
> frequency, and for Part 15 AM it is very small -- about 0.1
> ohm more or less for a simple vertical structure, at its
> greatest.
> 2. The ohmic resistance of the radiator itself (very small,
> usually)
> 3. The resistance of the loading coil (ranges from maybe 2
> to maybe 10 ohms)
> 4. The resistance to r-f current present in the r-f ground
> system returning those currents back to the tx ground
> terminal. Usually this resistance is the biggest of all,
> and can be 100 ohms or more, depending on the quality of the
> r-f ground structure you are using.
>
> The radiation efficiency of a Part 15 AM antenna system is
> the ratio of its radiation resistance to the total
> resistance in the antenna system. So if the sum of all the
> resistances is, say, 25 ohms, and the radiation resistance
> part of that is 0.1 ohm, then system radiation efficiency is
> 0.1/25 = 0.4%.
>
> An electrically short radiator has high capacitive
> reactance, and accepts very little power from a tx because
> its input VSWR is extremely high. The loading coil is used
> to ~cancel that reactance so as to present a load that a tx
> can deliver power into. BUT that low-reactance load still
> can have a wide range of resistance values depending on the
> resistances in the ground and coil.
>
> A tx is designed to work into a known impedance value --
> usually 50 +j0 ohms. So even if the loading coil has
> canceled the reactance of the short vertical, the R term of
> the load that the tx sees could vary from maybe 10 ohms for
> a really good system to several hundred ohms for a poor one.
>
>
> So that is the function of the variable capacitor at the
> base of the antenna -- to transform the input match created
> by the loading coil and other resistances back to something
> near 50 +j0 ohms that the tx can deliver its rated power
> into.
>
> The capacitor and loading coil haven't made the radiator
> either electrically longer, or more efficient. They have
> only allowed more power to flow into it from the source, due
> to matching their impedances.
> //
>

 

[radio8z]

"My thought was to build a 3 meter antenna with a base loading coil having enough turns to make the coil/antenna combination *electrically* longer than a 1/4 wavelength antenna (and thus be inductively reactive), and then tune this out with a variable capacitor. I envisioned the system as xmitter---> VC---> coil---> antenna, although the more common xmitter---> coil---> VC---> antenna arrangement may work just as well. I know this wouldn't make the 3 meter antenna any better (3 meters is still 3 meters), but hopefully this would make the antenna better able to accept power and load up. -- Jason"


Jason,

I think you understand what you are doing with antenna matching. Making the antenna look "long", in other words adding more inductance than is needed to resonate with the antenna is necessary if you intend to tune the system with a series cap. It seems to me that it is easier just to use a tapped inductor and leave out the cap since electrically this will be the same at the feedpoint.

rfry's comments expand on what I was saying earlier that you will gain by matching the remaining resistive component to the value that the tx. was designed to drive. This may or may not be 50 ohms. If your manual doesn't spec the output Z (neither of mine do) then you might want to contact the manufacturer. Actually, if the Z at the feedpoint of an antenna is around 20 ohms resistive, that is not a bad match for a 50 ohm transmitter.

I have designed VHF amplifiers in the 40 Watt range and have found an application note by Motorola (AN-267) to be very helpful when designing matching networks. For example, the output Z at the collector in one amp I designed was about .2 + j.1 ohms. It was necessary to transform this to 50 +j0 to match the antenna. A pi network worked very well and eliminated the j component of the output Z as well as transformed the R component to 50 ohms with only 2 caps and one inductor. Another nice feature of the pi network is it attenuates harmonics.

As you see, it can get complicated but if you know the Z that the tx. is designed to drive, the math is not that bad when designing the match. rfry's numbers, with his caveat about the effect of the grounding, for the 3 meter antenna would be a good launch point

As an aside, my low band rig for ham work has a built-in matching network which matches antenna Z's over a wide range. Since I was working 5 bands with an 40 meter inverted vee dipole with no traps, I used a transmatch to bring the antenna Z into the range of my tx. Z and it worked very well. Good SWR (1.4:1 at worst) and appropriate RF current between the tx. and the transmatch was the result.

Neil

 

[rfry]

> My thought was to build a 3 meter antenna with a base
> loading coil having enough turns to make the coil/antenna
> combination *electrically* longer than a 1/4 wavelength
> antenna (and thus be inductively reactive), and then tune
> this out with a variable capacitor.
______________

Unfortunately, that isn't possible. The loading coil doesn't change the electrical length of the radiator. It only adds inductive reactance (and resistance) to the antenna feedpoint. If you choose the right value for the coil, it can cancel the capacitive reactance of an electrically short radiator -- which makes it practical to deliver power into it.

If you add so much inductance in the coil that the input Z of the short antenna becomes inductive, that doesn't mean that the antenna is electrically longer. Its electrical length remains the same. But the inductive reactance at the input, then, makes it less possible for a tx to deliver power into the radiator. An input capacitor would be needed then to bring the input match to resonance. And if you need to do that, you might as well just use exactly enough coil inductance to get resonance that way, and avoid the extra part (the capacitor).

The electrical length, and radiation resistance of the same short radiator itself remain the same under any of these input conditions. NEW The loading coil used with a short radiator can give that short radiator the reactance value of an electrically longer radiator. But the coil won't change the radiation resistance of the antenna, and THAT is what determines its radiation efficiency in a given antenna system.

 

[JasonW]

Neil and rfry,

I thank you both very much for your comments on my idea. I know that a tapped coil is more efficient, but as my coil/antenna combination will be subject to detuning effects such as rain, snow, and deep cold frozen soil under it, an un-tapped coil (with a bit more inductance than I need) with a heavy-duty covered variable capacitor (tunable by a non-metallic extension shaft through the house wall) is mechanically more robust and easier to build.

Does the component arrangement (xmitter-vc-coil-aerial or xmitter-coil-vc-antenna) make a difference in performance? The latter arrangement is what I've always seen in series-tuned ATUs. -- JasonW

 

[radio8z]

> Neil and rfry,
>
> I thank you both very much for your comments on my idea. I
> know that a tapped coil is more efficient, but as my
> coil/antenna combination will be subject to detuning effects
> such as rain, snow, and deep cold frozen soil under it, an
> un-tapped coil (with a bit more inductance than I need) with
> a heavy-duty covered variable capacitor (tunable by a
> non-metallic extension shaft through the house wall) is
> mechanically more robust and easier to build.
>
> Does the component arrangement (xmitter-vc-coil-aerial or
> xmitter-coil-vc-antenna) make a difference in performance?
> The latter arrangement is what I've always seen in
> series-tuned ATUs. -- JasonW
>

Jason,

Interesting tuning idea. I don't know if the order matters. In theory it does not but in practice it may. Since you intend to tune it with an insulated rod, I would say not.

Maybe you could motorize the cap. Another thing to consider is to build a varometer and eliminate the cap. You probably know this site, but in case you don't here is the link:

http://lpam.info/index.php?page=antennas#loadingcoil

Neil

 

[JasonW]

Thank you for the link. I just got that book, but hadn't looked through it in detail yet. I may try a variometer. -- Jason

> Interesting tuning idea. I don't know if the order matters.
> In theory it does not but in practice it may. Since you
> intend to tune it with an insulated rod, I would say not.
>
> Maybe you could motorize the cap. Another thing to consider
> is to build a varometer and eliminate the cap. You probably
> know this site, but in case you don't here is the link:
>
> http://lpam.info/index.php?page=antennas#loadingcoil
>
> Neil

 

[jammerdave]

I've had a wild hair of late, and will be attempting to build a center loaded part 15 compliant AM antenna. My experience with the 1.8 and 3.5 mhz ham bands while mobile gave me this nutty idea. Mobile HF antenna theory shows that a center loaded antenna is more efficient than a base loaded antenna. There was a book out by Don Johnson, W6AAQ, who is the "godfather" of efficient mobile antenna design, when you are dealing with low frequencies and electrically very short antennas. I learned a lot by reading this (the book is "40 years of HF mobileering"), and by speaking to him (he lives nearby) We typically use mobile antennas on 1.8 and 3.5 mhz that are only 7 to 9 feet in length or so. Valor/Pro-AM and Lakeview/Hamstick make antennas for 1.8 mhz already. I thought I'd expand on that idea by building one that resonates at say, 1600 khz, and then matching the very low base impedance. Maybe a series cap after the impedance matching network will allow me to "slide" it up band a bit, up to 1700 khz. Bandwidth on these types of antennas is very narrow, unless there are too many resistive losses, so it may be a challenge to get one wide enough for an AM signal, who knows? Anyway, the whole idea is to see if we can make the absolute most of a legal part 15 system, so why not? I have a commercial AM field strength meter, so it will be easy to make real comparisons of different designs. I hope to pick up a SSTRAN tx pretty soon to help me figure it all out. I'll let ya'll know what I find...

fmnostatic...




> Hello All,
>
>
> I have a question regarding series-tuned antenna tuners for
> Part 15 AM use. Ham radio operators often use series-tuned
> antenna tuning units (as illustrated here:
> http://www.g4nsj.co.uk/atu.shtml ). The schematic goes like
> this:
>
> transmitter---> tapped coil---> variable capacitor--->
> antenna
>
> Ground radials and/or an Earth ground is/are connected to
> the transmitter chassis. The tapped coil along with the
> variable capacitor allows the transmitter to load a
> random-length antenna over a fairly wide range of
> frequencies.
>
> For Part 15 AM use, I envision something simpler, like this:
>
>
> transmitter---> variable capacitor---> un-tapped coil---> 3
> meter antenna
>
> It seems that if the coil had enough windings to make the 3
> meter antenna + coil *electrically* longer than 1/4
> wavelength, the variable capacitor could be used to
> electrically shorten the antenna + coil and bring the
> combination to resonance, as is commonly done with 3/8
> wavelength wire antennas that use only a single variable
> capacitor for tuning.
>
> What do you all think? -- JasonW
>

 

[JasonW]

That's interesting. Valor doesn't seem to be in business (or at least have a web site), and I couldn't find a 1.8 MHz Hamstick on the Hamstick web site.

For the 1.8 MHz Hamstick, maybe a small loading coil connected to the base (or a small top-loading capacitance hat added to the tip) would drop its resonance point down to 1.6 MHz - 1.7 MHz without narrowing its bandwidth too much. -- JasonW

> I've had a wild hair of late, and will be attempting to
> build a center loaded part 15 compliant AM antenna. My
> experience with the 1.8 and 3.5 mhz ham bands while mobile
> gave me this nutty idea. Mobile HF antenna theory shows that
> a center loaded antenna is more efficient than a base loaded
> antenna. There was a book out by Don Johnson, W6AAQ, who is
> the "godfather" of efficient mobile antenna design, when you
> are dealing with low frequencies and electrically very short
> antennas. I learned a lot by reading this (the book is "40
> years of HF mobileering"), and by speaking to him (he lives
> nearby) We typically use mobile antennas on 1.8 and 3.5 mhz
> that are only 7 to 9 feet in length or so. Valor/Pro-AM and
> Lakeview/Hamstick make antennas for 1.8 mhz already. I
> thought I'd expand on that idea by building one that
> resonates at say, 1600 khz, and then matching the very low
> base impedance. Maybe a series cap after the impedance
> matching network will allow me to "slide" it up band a bit,
> up to 1700 khz. Bandwidth on these types of antennas is very
> narrow, unless there are too many resistive losses, so it
> may be a challenge to get one wide enough for an AM signal,
> who knows? Anyway, the whole idea is to see if we can make
> the absolute most of a legal part 15 system, so why not? I
> have a commercial AM field strength meter, so it will be
> easy to make real comparisons of different designs. I hope
> to pick up a SSTRAN tx pretty soon to help me figure it all
> out. I'll let ya'll know what I find...
>
> fmnostatic...

 

[jammerdave]

I've never actually found the valor site, but have seen the antenna at AES in las vegas:

VAL PHF160 VALOR 160M 8'3/8-24WHP/PHF160B $89.99

Maybe i was dreaming on the lakeview product.. hmm..

I know I've seen another one somewhere. At any rate, tehre isn't enough wire in the valor, not sure if there is room to add. At that price, i might as well start from scratch anyway. I've built a bunch of mobile HF antennas before, this would be similar...




> That's interesting. Valor doesn't seem to be in business
> (or at least have a web site), and I couldn't find a 1.8 MHz
> Hamstick on the Hamstick web site.
>
> For the 1.8 MHz Hamstick, maybe a small loading coil
> connected to the base (or a small top-loading capacitance
> hat added to the tip) would drop its resonance point down to
> 1.6 MHz - 1.7 MHz without narrowing its bandwidth too much.
> -- JasonW
>
> > I've had a wild hair of late, and will be attempting to
> > build a center loaded part 15 compliant AM antenna. My
> > experience with the 1.8 and 3.5 mhz ham bands while mobile
>
> > gave me this nutty idea. Mobile HF antenna theory shows
> that
> > a center loaded antenna is more efficient than a base
> loaded
> > antenna. There was a book out by Don Johnson, W6AAQ, who
> is
> > the "godfather" of efficient mobile antenna design, when
> you
> > are dealing with low frequencies and electrically very
> short
> > antennas. I learned a lot by reading this (the book is "40
>
> > years of HF mobileering"), and by speaking to him (he
> lives
> > nearby) We typically use mobile antennas on 1.8 and 3.5
> mhz
> > that are only 7 to 9 feet in length or so. Valor/Pro-AM
> and
> > Lakeview/Hamstick make antennas for 1.8 mhz already. I
> > thought I'd expand on that idea by building one that
> > resonates at say, 1600 khz, and then matching the very low
>
> > base impedance. Maybe a series cap after the impedance
> > matching network will allow me to "slide" it up band a
> bit,
> > up to 1700 khz. Bandwidth on these types of antennas is
> very
> > narrow, unless there are too many resistive losses, so it
> > may be a challenge to get one wide enough for an AM
> signal,
> > who knows? Anyway, the whole idea is to see if we can make
>
> > the absolute most of a legal part 15 system, so why not? I
>
> > have a commercial AM field strength meter, so it will be
> > easy to make real comparisons of different designs. I hope
>
> > to pick up a SSTRAN tx pretty soon to help me figure it
> all
> > out. I'll let ya'll know what I find...
> >
> > fmnostatic...
>