Anybody tried to build this trap antenna yet?

http://www.nerc.com/~jdegood/coaxtrap/
http://members.shaw.ca/ve6yp/
http://members.fortunecity.com/xe1bef/hf-antennas.htm

Need some help on where to tune the traps for the bands of operation, and
pruning the connection wiring. Can this be done with out a major test
equipment investment?

On Wed, 06 Aug 2003 21:59:37 GMT, "Bill"
wrote:

Anybody tried to build this trap antenna yet?

http://www.nerc.com/~jdegood/coaxtrap/
http://members.shaw.ca/ve6yp/
http://members.fortunecity.com/xe1bef/hf-antennas.htm

Need some help on where to tune the traps for the bands of operation, and
pruning the connection wiring. Can this be done with out a major test
equipment investment?

I love those coax traps. About 20 years ago, I spent several hours
with a sweep generator and scalar network analyzer building a set
of traps for 40/20/15/10 meters. Then, I spent almost all day putting
up the antenna. The process is basically "put up one section, check
swr, drop antenna, trim antenna, raise it back up, and repeat until
the SWR is acceptable" (typical dipole scenario). Then, however, you
add a set of traps and the next section, and repeat the entire process
for the next lower (in frequency) band. Keep repeating till you have
all bands covered. Got a nice sunburn and a decent antenna out of the
deal.

The traps can be fairly light weight and compact - I used RG-174 and
wound 'em on empty pill bottles. For test equipment, a plain signal
generator and oscilloscope will suffice, or maybe even just a grid-dip
meter.... Heck - I even got so involved with coax traps that I wrote
a computer program to characterize the things and tell me how many
turns of what kind of coax on what size form would be resonant at
my frequency of interest.

Since that time, I've discovered how pointless it was. Like WB3FUP
suggests, just put up as much wire as you can, as high as you can.
Right now, I'm using a 130 foot inverted L, and it works every bit
as good as the trap dipole did (if not better) from 160 through
10 meters - and it was a *lot* easier to put up. The only drawback
is that you gotta have a tuner.

-fb-

I've built a number of antennas with coax traps made from both RG-174
and RG-58. There are a couple of ways to connect the traps, with one
(sort of cross-connecting the ends) giving a more favorable L/C ratio
than the other. But after measuring the trap L, C, and Q and doing some
EZNEC modeling, I discovered that it's often hard, even with the RG-58
versions, to get low loss on all bands the antenna is intended for. The
loss might be low on the band the trap "traps", but relatively high
(typically a couple of dB) on a lower band. Or vice-versa, depending on
the combination of bands that the antenna is for. It depends on the
combination of bands that the antenna is for -- some are ok, some not so
good. The fact is that the effective inductor Q of coax traps made with
RG-58 or smaller coax is mediocre.

For a lot of applications, a couple of dB is an acceptable trade for the
simplicity of coax traps, but for some it's not. If it's not, I'd
recommend doing some modeling, or careful comparison to a non-trapped
antenna.

One other word of advice is to make sure you weatherproof the traps in a
way that prevents any water from getting between the turns. Water
between the turns can increase trap loss substantially.

Roy Lewallen, W7EL

funkbastler wrote:
On Wed, 06 Aug 2003 21:59:37 GMT, "Bill"
wrote:


Anybody tried to build this trap antenna yet?

http://www.nerc.com/~jdegood/coaxtrap/
http://members.shaw.ca/ve6yp/
http://members.fortunecity.com/xe1bef/hf-antennas.htm

Need some help on where to tune the traps for the bands of operation, and
pruning the connection wiring. Can this be done with out a major test
equipment investment?


I love those coax traps. About 20 years ago, I spent several hours
with a sweep generator and scalar network analyzer building a set
of traps for 40/20/15/10 meters. Then, I spent almost all day putting
up the antenna. The process is basically "put up one section, check
swr, drop antenna, trim antenna, raise it back up, and repeat until
the SWR is acceptable" (typical dipole scenario). Then, however, you
add a set of traps and the next section, and repeat the entire process
for the next lower (in frequency) band. Keep repeating till you have
all bands covered. Got a nice sunburn and a decent antenna out of the
deal.

The traps can be fairly light weight and compact - I used RG-174 and
wound 'em on empty pill bottles. For test equipment, a plain signal
generator and oscilloscope will suffice, or maybe even just a grid-dip
meter.... Heck - I even got so involved with coax traps that I wrote
a computer program to characterize the things and tell me how many
turns of what kind of coax on what size form would be resonant at
my frequency of interest.

Since that time, I've discovered how pointless it was. Like WB3FUP
suggests, just put up as much wire as you can, as high as you can.
Right now, I'm using a 130 foot inverted L, and it works every bit
as good as the trap dipole did (if not better) from 160 through
10 meters - and it was a *lot* easier to put up. The only drawback
is that you gotta have a tuner.

-fb-

Hi Bill -

I tried to find the specific antenna you are considering using your links,
but I wasn't able to do so with a reasonable amount of effort.

However, there is no doubt at all that a well-designed trap antenna
could do a good job for you.

I am rather bemused by the responses you got suggesting a one-size-fits-all
ladder-line doublet instead. I'm sure these can be good antennas; but
they usually seem to be presented by their advocates as having no draw-
backs at all. That would be an incorrect view, as those antennas have
their own tradeoffs--just like other antennas.

The biggest tradeoff is the tuner, of course. If you're planning on running
power, this is about a $600 +/- item (commercial models), and it takes
up space at your operating position. But you're not done when you buy
it and find a space for it... you also have to TUNE it every time you make
a significant QSY. (I won't mention tuner losses unless someone brings
up trap losses.)

I friend of mine took a look at my array of two W9INN trap/fan dipoles
(6-band coverage); but he decided that he wanted to go with the ubiquitous
135-foot doublet-plus-tuner. (He bought the tuner from me, which was
great... I don't need it!)

When I asked him how he was doing with his new setup, he reported
that it gets out fine on 80m and 40m, but is such a pain in the a*s to
tune on the higher bands that he doesn't bother with them. (That's just
his experience, other users seem to have less trouble.) Oh, and if he
ever decides to run power, he'll have to buy a BIGGER tuner, and
probably re-sell the low-power tuner he bought from me.

Meanwhile, I'm enjoying six bands, instant QSY, no tuner needed, and
I run power when I want to. Because of the loading effects of the traps,
my antennas fit in a very compact space... which is all the space I've got.
I hear well,and my reports are excellent. Not bad, not bad at all.
All I really want that I haven't got is the ability to get these antennas
straighter and HIGHER.

Good luck with your selection, and I hope whatever you choose works
great for you.

73,

Ed W6LOL

"Bill" wrote in message
...
Anybody tried to build this trap antenna yet?

http://www.nerc.com/~jdegood/coaxtrap/
http://members.shaw.ca/ve6yp/
http://members.fortunecity.com/xe1bef/hf-antennas.htm

Need some help on where to tune the traps for the bands of operation, and
pruning the connection wiring. Can this be done with out a major test
equipment investment?

Ed Senior wrote:
I am rather bemused by the responses you got suggesting a one-size-fits-all
ladder-line doublet instead. I'm sure these can be good antennas; but
they usually seem to be presented by their advocates as having no draw-
backs at all. That would be an incorrect view, as those antennas have
their own tradeoffs--just like other antennas.

The biggest tradeoff is the tuner, of course.

I use the transmission line to tune my 130 ft. dipole, no tuner needed.

Meanwhile, I'm enjoying six bands, instant QSY, no tuner needed, and
I run power when I want to.

I'm enjoying eight bands, throw a couple of knife switches to QSY,
no tuner needed, and I run power when I want to. Also no messing
with the interaction of multiple legs of dipoles.
--
73, Cecil http://www.qsl.net/w5dxp

Hi Cecil -

I'm glad your antenna is working well for you!
A few more comments below...

"W5DXP" wrote in message
...
Ed Senior wrote:
I am rather bemused by the responses you got suggesting a
one-size-fits-all
ladder-line doublet instead. I'm sure these can be good antennas; but
they usually seem to be presented by their advocates as having no draw-
backs at all. That would be an incorrect view, as those antennas have
their own tradeoffs--just like other antennas.

The biggest tradeoff is the tuner, of course.

I use the transmission line to tune my 130 ft. dipole, no tuner needed.

Well, perhaps I should have said something like

"...no tuner needed, implemented either as the traditional box with
tunable L and C, OR implemented in distributed fashion as a switchable-
length transmission-line transformer, usually including a current balun."

But that would have been a heck of a mouthful; and most of the users
of this antenna type seem to advocate the traditional form of the tuner.

Actually, I rather LIKE the switchable-length transmission line idea.
Could you refresh me on many different lengths do you find you need to
be able to get the SWR below, say, 2:1 at every point in those 8 bands?
(I think we talked about this in an earlier thread, but I don't remember
all the details.) How do you stow the tuning lengths, and how many
physical switches (or plug-ins) are needed? When you do a typical
band change, does "a couple" of switch operations literally mean two,
or several? Any safety issues with the switches if you're running power?

Meanwhile, I'm enjoying six bands, instant QSY, no tuner needed, and
I run power when I want to.

I'm enjoying eight bands, throw a couple of knife switches to QSY,
no tuner needed, and I run power when I want to. Also no messing
with the interaction of multiple legs of dipoles.

I would only add that I found the W9INN dipoles to be extremely easy
to tune, with no troublesome interactions. Also, there is no "messing"
with either a traditional tuner, or switching a tunable transmission-line
transformer.

--
73, Cecil http://www.qsl.net/w5dxp

Ed Senior wrote:
Actually, I rather LIKE the switchable-length transmission line idea.
Could you refresh me on many different lengths do you find you need to
be able to get the SWR below, say, 2:1 at every point in those 8 bands?

I use 5 different lengths in a binary pattern. It's described on my
web page. 0-32 total feet is needed to cover all of 75m.

(I think we talked about this in an earlier thread, but I don't remember
all the details.) How do you stow the tuning lengths, and how many
physical switches (or plug-ins) are needed? When you do a typical
band change, does "a couple" of switch operations literally mean two,
or several? Any safety issues with the switches if you're running power?

The loops are about six inches apart on the outside of my window. I have
five 4PDT knife switches but I don't bother with the lower two on 75m.
I don't bother with the upper two on 10m. The knife switches handle 500
watts just fine.
--
73, Cecil http://www.qsl.net/w5dxp



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Gee I spent not more than 2 hours with my MFJ259, my MFJ Tuner (I think it
cost me 129.95 and is good for 300 watts, which is three times the power I
will ever need, and 600 times the power that I used most of the time), and
a pencil and paper. I am old fashioned and maintain a log. In the log I
have recorded tuner settings for each of the ham bands. (75 and 80 are
separate bands) QSY is a matter of referring to log, presetting dials, and
changing bands. If I feel the burning need a quick touch up of the
capacitor and I am matched. My transceiver, and the DIP unit sit side by
side on top of the tuner, so there is no significant footprint problem at
the operating position.

You failed to mention the only major drawback to the ladder line fed
doublet that I am aware of. It develops some strange lobes as it gets
longer. I have heard that the 44' length of the NorCal "Crappie" dipole
was chosen as a compromise between 80 meter efficiency and 10 meter lobes.
I have been scared of "fan" dipoles for years. I worry that given a
reasonable radiator I put enough 7.810 signal on the air to upset the FCC
when I was on 3.905. Of course the tuner you seem to refuse to run would
help with that somewhat, but I still do not like having the nearly resonate
antenna connected to the transmitter any way. I have found out just how
far I can talk with a couple of watts (halfway around the world, after that
it is shorter going the other way). I never have run an amplifier, there
was a time I put 225 plus watts out on 80, and 40 (TR4) but since I got my
first ICOM never more than 100, seldom that much. Still worried about
harmonics where I have no business radiating, and the FT817 has
dramatically demonstrated just how little power is required for a QSO.
Amplify the harmonic, and couple it to a nearly resonate antenna, no thank
you, I like my license to much, and do not have all that much money for
fines laying around the house.

--
73 es cul

wb3fup
a Salty Bear

"Ed Senior" wrote in message
nk.net...
Hi Bill -

I tried to find the specific antenna you are considering using your
links,
but I wasn't able to do so with a reasonable amount of effort.

However, there is no doubt at all that a well-designed trap antenna
could do a good job for you.

I am rather bemused by the responses you got suggesting a
one-size-fits-all
ladder-line doublet instead. I'm sure these can be good antennas; but
they usually seem to be presented by their advocates as having no draw-
backs at all. That would be an incorrect view, as those antennas have
their own tradeoffs--just like other antennas.

The biggest tradeoff is the tuner, of course. If you're planning on
running
power, this is about a $600 +/- item (commercial models), and it takes
up space at your operating position. But you're not done when you buy
it and find a space for it... you also have to TUNE it every time you
make
a significant QSY. (I won't mention tuner losses unless someone brings
up trap losses.)

I friend of mine took a look at my array of two W9INN trap/fan dipoles
(6-band coverage); but he decided that he wanted to go with the
ubiquitous
135-foot doublet-plus-tuner. (He bought the tuner from me, which was
great... I don't need it!)

When I asked him how he was doing with his new setup, he reported
that it gets out fine on 80m and 40m, but is such a pain in the a*s to
tune on the higher bands that he doesn't bother with them. (That's just
his experience, other users seem to have less trouble.) Oh, and if he
ever decides to run power, he'll have to buy a BIGGER tuner, and
probably re-sell the low-power tuner he bought from me.

Meanwhile, I'm enjoying six bands, instant QSY, no tuner needed, and
I run power when I want to. Because of the loading effects of the traps,
my antennas fit in a very compact space... which is all the space I've
got.
I hear well,and my reports are excellent. Not bad, not bad at all.
All I really want that I haven't got is the ability to get these antennas
straighter and HIGHER.

Good luck with your selection, and I hope whatever you choose works
great for you.

73,

Ed W6LOL

"Bill" wrote in message
...
Anybody tried to build this trap antenna yet?

http://www.nerc.com/~jdegood/coaxtrap/
http://members.shaw.ca/ve6yp/
http://members.fortunecity.com/xe1bef/hf-antennas.htm

Need some help on where to tune the traps for the bands of operation,
and
pruning the connection wiring. Can this be done with out a major test
equipment investment?

I tried to find the specific antenna you are considering using
your links, but I wasn't able to do so with a reasonable amount
of effort.

Sorry, my ISP recently ceased operation. You can find the page
originally referenced, at least in the near term, at:

http://users.tellurian.com/jdegood/coaxtrap/

It's simply a six-band trap dipole. The 5 pairs of coaxial-cable traps
provide significant physical shortening, although to fit in an attic
some or all of the outermost (80 meter) portion will probably have to be
run at right angles to the main dipole. The advantages of such a
resonant antenna include a decent match to a coax feedline and no-tune
operation (but over limited bandwidth, a side-effect of the reduced size.)

Another alternative for multi-band operation in a restricted space
situation such as an attic is a physically shortened dipole in
conjunction with a tuner and open wire feedline. For details, see:

http://www.arrl.org/tis/info/HTML/li.../limited1.html

73,

John NU3E

Hi John -

I checked your link... It worked, and the article is excellent!

The antenna described looks very neat, and would be a
fun project for someone who enjoys home-brewing.

For someone preferring a minimum of home-brewing, W9INN
has about eight similar models (SSD series and MDX series),
ranging in length from 46 to 71 feet. I haven't tried them all,
but my experience with his MBD-847 and SSD-021-5 antennas
has been excellent.

73, Ed W6LOL

"John DeGood" wrote in message
...
I tried to find the specific antenna you are considering using
your links, but I wasn't able to do so with a reasonable amount
of effort.

Sorry, my ISP recently ceased operation. You can find the page
originally referenced, at least in the near term, at:

http://users.tellurian.com/jdegood/coaxtrap/

It's simply a six-band trap dipole. The 5 pairs of coaxial-cable traps
provide significant physical shortening, although to fit in an attic
some or all of the outermost (80 meter) portion will probably have to be
run at right angles to the main dipole. The advantages of such a
resonant antenna include a decent match to a coax feedline and no-tune
operation (but over limited bandwidth, a side-effect of the reduced size.)

Another alternative for multi-band operation in a restricted space
situation such as an attic is a physically shortened dipole in
conjunction with a tuner and open wire feedline. For details, see:

http://www.arrl.org/tis/info/HTML/li.../limited1.html

73,

John NU3E