Graham,
Thanks, I picked up a box of the red ones at a hamfest and always wondered what they were called.They work well on my QRP EFHW antennas to add/subtract a 1/2 section of wire.
73 - Dave, N4ELM
|
On 6/18/19 2:18 AM, Vojtech Bubnik wrote: I wonder what would be the optimum UNUN (lowest losses) for 40m-20m end fed? That is the frequency range for a trail antenna nowadays due to solar minimum. Hi Vojtech, Good Question, and SimSmith to the rescue! Evaluating 4T FT114A 61 and 43 material for critical low frequency inductance and core loss: The first plot evaluates mismatched loss for evaluation where inductance causes a mismatch. Note SWR curve for 61 material, light blue trace, is below 1.5 at 7 MHz. Second plot evaluates core loss using a matched source. Note 61 material has significantly reduced loss from 43 material. John KN5L
|
I wonder what would be the optimum UNUN (lowest losses) for 40m-20m end fed? That is the frequency range for a trail antenna nowadays due to solar minimum.
|
Re: QRPGuys EFHW 40m-15m Mini Tuner
The comment on the critical frequency at the current solar minimum was quite enlightening to me. When I was simulating various in the field antenna typologies, I was taking into account the total far field radiated energy. While the total far field radiated energy takes into account the ground losses, it certainly does not take into account the critical frequency. Therefore it may be, that even though a T antenna strung between the tips of two 7m high crappie poles 7m far from each other with two elevated radials at 1m may have an integrated far field efficiency 3dB worse than a doublet with drooping ends strung between the same crappie poles, the vertical may actually produce more energy reflected back to Earth from ionosphere after sun set because of low critical frequency.
|
Re: QRPGuys EFHW 40m-15m Mini Tuner
Thanks Mike,
The critical frequency is also effectively the frequency where near straight up
the Ionosphere is for the most part transparent and non reflecting when at
lower angles like less than 20 degrees its usable for DX.
Water does the same thing, look straight down you see the bottom, look
at a shallow angle its a good reflector.
So to work close in on 40M NVIS is not the way but a good vertical
to get a good low angle ground wave is useful.
We have been below the critical frequency for many years and at it
peak it may reach 10mhz or slightly higher (solar maximum).
One of those things that shows how antennas and their composite
patterns interact with propagation to get signals out there.
Allison
|
Re: QRPGuys EFHW 40m-15m Mini Tuner
NVIS (Near Vertical Incidence Skywave) depends on the ionosphere reflecting
near vertical signals back to earth. However this happens primarily at low
frequencies and at a certain critical frequency the signals penetrate the
ionosphere and go out into space rather than being reflected. This critical
frequency varies depending on ionospheric conditions. What Allison is
saying is that over the last several years ionospheric conditions have been
such that the critical frequency has been below 7 mHz. except for rare
circumstances thus precluding NVIS communications on 40 meters.
Mike
K5ESS
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Alan Jones Sent: Monday, June 17, 2019 7:09 AM To: [email protected]Subject: Re: [qrp-tech] QRPGuys EFHW 40m-15m Mini Tuner Allison, can you explain what you mean by "critical frequency" ? N8WQ On Sun, 16 Jun 2019 22:56:03 -0400, ajparent1/kb1gmx <kb1gmx@...> wrote: Low antennas for 60M and down to 160 are useful for short range.
Unfortunately NVIS on 40M is way oversold as the critical frequency
hasn't been near 7mhz in years except on rare days.
I know as i have a low dipole for 40 and 75 also be default 160.
The 75M dipole is the antenna for ranges to about 400 miles and
occasionally further. That antenna is barely 12Ft up. Its also a
low noise antenna as its pattern is UP and houses with their noise
are not that direction. Same for the 160M even thought he center
is at 35ft (.25wave on 160 is on the order of 100-120 feet!).
However trying to use the 40M low dipole for close in work confirms
no NVIS. However on 40M a vertical was often god for close in
because of its low takeoff angle.
When I say higher we are definitely talking more than .25Wave and
more like .5 wave. On 40M getting 40-50ft up is not that hard for
most (note ,5wave is 66ft). But at 80M that's more than 60ft
for a .25wave up and .5 wave is 120ft.
HIgher is better but understanding what High means as a function
of wavelength (frequency) takes on dimensions, sometimes large.
The other part is propagation, we have had a lot of solar and geomagnetic
activity where 20M and even 40M was dead and 75M had very high
absorption and people running 1KW 160 miles away were hard to hear
with any antenna. I have a fairly decent location. During conditions
like that I've had better results at 6 and 2M with only 100W to the
same stations. Often no one antenna is totally the solution for any
band and conditions.
Allison
|
Something nice to see for my brand new CWModem
Dear all,
My newest CWModem as partial kit available....
Please look at
for more information.
!n2YHGazC!fw2TXIHsowhLR5-BQ28PlAW5o9Chz2bI-0-eo1Q39Jk
73' PD0LEW
|
Graham,
Thank you, I had to go back to my aircraft maintenace logs to
find the part name and source I used. I are a pilot and aircraft
owner. And Aircraft Spruce has acquired many of my AMUs
(aircraft maintenance units, they come in increments of 1000$)
over the years. ;)
John,
What might help if you can find a ferrite with a Mu of 400ish
(lower than 43 and higher than 61) and that exists but
I haven't used it in toroid form (it was bars for the task).
Either way there is a trade for Ampere-turns, core loss
Vs working inductance and total turns on the core. The
range that works for a decade frequency range is fairly
narrow as you've shown.
Allison
|
Hi Allison, On 6/16/19 9:33 PM, ajparent1/kb1gmx wrote: I feel that's even more divergent from Johns work here as he is
working on Baluns and transformers that don't melt at 100 to
QRO power levels. A pair of FT240-43 are not light when put
in a Polycarbonate box. At QRP levels the problem is
manageable and the losses can be kept down. Its a big
part of the considerations that go into matching the radio
to whatever antenna.. Very correct. The design I've suggested is using two FT114-43 cores, not 2.4" cores. The Selection was a compromise between size and loss, attempting to keep core loss below 0.3 dB for a QRP 80M to 10M device. A single FT114A-43 could be used with just slightly greater loss. I had 114's in my inventory. Selecting a -43 core and turn count based on core loss can be performed using: Examples: FT82-43 4T primary 7.5uH @ mi -> ~0.7dB core loss FT82-43 3T primary 4.2uH @ mi -> ~1.1dB core loss FT82-43 2T primary 1.9uH @ mi -> ~2dB core loss John KN5L
|
Allison:
I think you are referring to "KNIFE DISCONNECTS" used in aviation.
They take a heavy pull load without disconnecting.
Quick and easy disconnect with a 90 degree rotation of the terminal.
If you slide a clear piece of spaghetti insulation over the connection,
there is no way it will come apart in the wind.
--- Graham / KE9H
toggle quoted message
Show quoted text
On Sun, Jun 16, 2019 at 9:33 PM ajparent1/kb1gmx <kb1gmx@...> wrote: Shirley.
I know Steve being a SB1/II builder and just about every one of his test
gear and digital dial bits over the last 15 or more years. He designs
really slick radios.
I have two of the PAR EF40/20/10s. I have them setup with stackable
wires for any band from 60M through 10M. I found some connectors
that are like spade lugs but they latch into each other in a hook like
way so the don't pull apart. I have to find more of them. Killer for
segmented wires. Usually used for 40 or 20M in my case so one
wire does it.
The idea of multiple antennas is not a killer for portable as often many
bands are unsuitable for the next few years or not a best choice.
The 10M antenna weighs in as fairly light (3.7 oz with the antenna
wire) but If I'd used a BNC connector and a QRP sized coil it would
be very light. I was thinking of FD and back yard use not packing it.
At the QRP power level I've gotten under 1oz for the box and the
wire can be very light as well (#26 Polystealth at .38 pounds per
1000ft ). After all I think in terms of .050 braided nylon cord
for hanging wires for temporary use as I often change and add
antennas here. Reality is often the antenna can be the lighter
part of the radio kit.
I also understand light weight. Usually the trail friendly radios are not
FT817 DC to daylight radios and typically 1 to 3 bands so a 80-10
antenna makes for much extra weight. I've watched people try and
get a 80M antenna up and mostly not succeed when the highest
thing around is maybe a 15ft high rock. Dense wooded areas
present challenges as well, its the branches in the way. Biggest
issue is an antenna that is viable on a hilltop with 25mpg gusts
and not a tree in sight.
I feel that's even more divergent from Johns work here as he is
working on Baluns and transformers that don't melt at 100 to
QRO power levels. A pair of FT240-43 are not light when put
in a Polycarbonate box. At QRP levels the problem is
manageable and the losses can be kept down. Its a big
part of the considerations that go into matching the radio
to whatever antenna..
That and I'm likely one of the few that does things like run 10M
and do DX country hunting at the bottom of the solar cycle when
everyone else feels 20 is dead for DX. ;) I chalk it up to my
many years of VHF/uhf commercial work and my affinity to
VHF and UHF. That and I tend to favor phone(SSB) so
some bands like 30M are not my tea and digtial modes
means dragging a computer of some form.
However with that, going to the field with a portable radio
weight is a big factor, and the bands most likely to get contacts
typically have been 40 and 20. An 80M antenna is big and
daytime absorption is high and bands above 20 and likely to
be the level of sketchy most want to take on. So 60-20M
are the likely ones.
FYI: my favorite antenna for odd cases on the 160 and 80/75M
bands is the Grasswire, lossy and long at about 130ft but
universal rubber duck for HF and flat places. With the
transformer its under a half pound mostly for the ferrite.
Allison
|
Re: QRPGuys EFHW 40m-15m Mini Tuner
Allison, can you explain what you mean by "critical frequency" ?
N8WQ
toggle quoted message
Show quoted text
On Sun, 16 Jun 2019 22:56:03 -0400, ajparent1/kb1gmx <kb1gmx@...> wrote: Low antennas for 60M and down to 160 are useful for short range.
Unfortunately NVIS on 40M is way oversold as the critical frequency
hasn't been near 7mhz in years except on rare days.
I know as i have a low dipole for 40 and 75 also be default 160.
The 75M dipole is the antenna for ranges to about 400 miles and
occasionally further. That antenna is barely 12Ft up. Its also a
low noise antenna as its pattern is UP and houses with their noise
are not that direction. Same for the 160M even thought he center
is at 35ft (.25wave on 160 is on the order of 100-120 feet!).
However trying to use the 40M low dipole for close in work confirms
no NVIS. However on 40M a vertical was often god for close in
because of its low takeoff angle.
When I say higher we are definitely talking more than .25Wave and
more like .5 wave. On 40M getting 40-50ft up is not that hard for
most (note ,5wave is 66ft). But at 80M that's more than 60ft
for a .25wave up and .5 wave is 120ft.
HIgher is better but understanding what High means as a function
of wavelength (frequency) takes on dimensions, sometimes large.
The other part is propagation, we have had a lot of solar and geomagnetic
activity where 20M and even 40M was dead and 75M had very high
absorption and people running 1KW 160 miles away were hard to hear
with any antenna. I have a fairly decent location. During conditions
like that I've had better results at 6 and 2M with only 100W to the
same stations. Often no one antenna is totally the solution for any
band and conditions.
Allison
|
Re: QRPGuys EFHW 40m-15m Mini Tuner
Low antennas for 60M and down to 160 are useful for short range.
Unfortunately NVIS on 40M is way oversold as the critical frequency
hasn't been near 7mhz in years except on rare days.
I know as i have a low dipole for 40 and 75 also be default 160.
The 75M dipole is the antenna for ranges to about 400 miles and
occasionally further. That antenna is barely 12Ft up. Its also a
low noise antenna as its pattern is UP and houses with their noise
are not that direction. Same for the 160M even thought he center
is at 35ft (.25wave on 160 is on the order of 100-120 feet!).
However trying to use the 40M low dipole for close in work confirms
no NVIS. However on 40M a vertical was often god for close in
because of its low takeoff angle.
When I say higher we are definitely talking more than .25Wave and
more like .5 wave. On 40M getting 40-50ft up is not that hard for
most (note ,5wave is 66ft). But at 80M that's more than 60ft
for a .25wave up and .5 wave is 120ft.
HIgher is better but understanding what High means as a function
of wavelength (frequency) takes on dimensions, sometimes large.
The other part is propagation, we have had a lot of solar and geomagnetic
activity where 20M and even 40M was dead and 75M had very high
absorption and people running 1KW 160 miles away were hard to hear
with any antenna. I have a fairly decent location. During conditions
like that I've had better results at 6 and 2M with only 100W to the
same stations. Often no one antenna is totally the solution for any
band and conditions.
Allison
|
Shirley.
I know Steve being a SB1/II builder and just about every one of his test
gear and digital dial bits over the last 15 or more years. He designs
really slick radios.
I have two of the PAR EF40/20/10s. I have them setup with stackable
wires for any band from 60M through 10M. I found some connectors
that are like spade lugs but they latch into each other in a hook like
way so the don't pull apart. I have to find more of them. Killer for
segmented wires. Usually used for 40 or 20M in my case so one
wire does it.
The idea of multiple antennas is not a killer for portable as often many
bands are unsuitable for the next few years or not a best choice.
The 10M antenna weighs in as fairly light (3.7 oz with the antenna
wire) but If I'd used a BNC connector and a QRP sized coil it would
be very light. I was thinking of FD and back yard use not packing it.
At the QRP power level I've gotten under 1oz for the box and the
wire can be very light as well (#26 Polystealth at .38 pounds per
1000ft ). After all I think in terms of .050 braided nylon cord
for hanging wires for temporary use as I often change and add
antennas here. Reality is often the antenna can be the lighter
part of the radio kit.
I also understand light weight. Usually the trail friendly radios are not
FT817 DC to daylight radios and typically 1 to 3 bands so a 80-10
antenna makes for much extra weight. I've watched people try and
get a 80M antenna up and mostly not succeed when the highest
thing around is maybe a 15ft high rock. Dense wooded areas
present challenges as well, its the branches in the way. Biggest
issue is an antenna that is viable on a hilltop with 25mpg gusts
and not a tree in sight.
I feel that's even more divergent from Johns work here as he is
working on Baluns and transformers that don't melt at 100 to
QRO power levels. A pair of FT240-43 are not light when put
in a Polycarbonate box. At QRP levels the problem is
manageable and the losses can be kept down. Its a big
part of the considerations that go into matching the radio
to whatever antenna..
That and I'm likely one of the few that does things like run 10M
and do DX country hunting at the bottom of the solar cycle when
everyone else feels 20 is dead for DX. ;) I chalk it up to my
many years of VHF/uhf commercial work and my affinity to
VHF and UHF. That and I tend to favor phone(SSB) so
some bands like 30M are not my tea and digtial modes
means dragging a computer of some form.
However with that, going to the field with a portable radio
weight is a big factor, and the bands most likely to get contacts
typically have been 40 and 20. An 80M antenna is big and
daytime absorption is high and bands above 20 and likely to
be the level of sketchy most want to take on. So 60-20M
are the likely ones.
FYI: my favorite antenna for odd cases on the 160 and 80/75M
bands is the Grasswire, lossy and long at about 130ft but
universal rubber duck for HF and flat places. With the
transformer its under a half pound mostly for the ferrite.
Allison
|
Different operators have different goals. An operator who is trying to
minimize equipment weight, like KD1JV during his walks of the
Appalachian Trail, might prefer to carry just one antenna. (Steve also
designs ultra lightweight and ultra low power radios for that type of
operation to keep his pack weight down.) In that type of operation you
often have no choice in how to orient your antenna in any case because
the supply of suitable antenna supports such as trees is limited, so
antenna pattern is a secondary consideration. Low dipoles aren't very
directional in any case, and on the higher frequency bands you just
take what you get.
One wire trick I like is the removable jumper scheme used in PAR's
EFT-MTR multi-band antenna. It has a little stub with an SMA connector
on it that you can remove to shorten the wire. (The short coax stub
really just serves to make it a bit larger so you don't lose the
jumper, and give you something to grab.) So a 40m EFHW also serves on
20 using second harmonic operation, and on 30 by removing the jumper
to shorten the wire.
For the ham who is willing to carry a bit more gear, I like your idea
of separate antennas for the higher and lower bands.
toggle quoted message
Show quoted text
On Sun, Jun 16, 2019 at 6:45 PM ajparent1/kb1gmx <kb1gmx@...> wrote:
John,
I was aware of that. I have such an antenna, of good utility but for
trying to get an specific area on a given band I go to mono-band
antenna as the pattern is predictable even if the peak gain is lower.
The side effect is not transformer loss, it is that the direction I want to
work on 15 and 10 in my case is only broadside to the wire and that
is not a strong direction due to pattern. Hence the monobands.
Generally I always ask the person why 80-10 and often the answer is
"because I can't fit 160 -10" and often the user rarely uses more than
two maybe three bands. Its a curious thing to me.
The work your doing show how to optimize the transformer for all
band use is a good thing many do not understand where and why.
It also highlights one area of compromise that antennas for too
many bands may suffer. For those wishing to get optimal results
on a narrower set of bands a pair of transformers for 80 and 40
plus tricks to get 60 or 30 in the wire and a separate for 20 through
10 and maybe the intermediate bands as well.
Allison
|
John,
I was aware of that. I have such an antenna, of good utility but for
trying to get an specific area on a given band I go to mono-band
antenna as the pattern is predictable even if the peak gain is lower.
The side effect is not transformer loss, it is that the direction I want to
work on 15 and 10 in my case is only broadside to the wire and that
is not a strong direction due to pattern. Hence the monobands.
Generally I always ask the person why 80-10 and often the answer is
"because I can't fit 160 -10" and often the user rarely uses more than
two maybe three bands. Its a curious thing to me.
The work your doing show how to optimize the transformer for all
band use is a good thing many do not understand where and why.
It also highlights one area of compromise that antennas for too
many bands may suffer. For those wishing to get optimal results
on a narrower set of bands a pair of transformers for 80 and 40
plus tricks to get 60 or 30 in the wire and a separate for 20 through
10 and maybe the intermediate bands as well.
Allison
|
Hi Allison,
The quest was an 80 to 10 Meter Unun. Correct, for 20M and higher
frequency, 61 material can be used with reduced loss. Similar stack of
two FT114-61 with four turn primary, about 2.4uH, will result with
approximately 0.04 dB loss at 14 MHz, as shown in:
John KN5L
toggle quoted message
Show quoted text
On 6/16/19 12:55 PM, ajparent1/kb1gmx wrote: For the 14mhz model, try using mu 125 material (FT240-61)
as you getting near the point with hard ferrites (31 and 43)
where their absorption properties are becoming significant.
|
John,
For the 14mhz model, try using mu 125 material (FT240-61)
as you getting near the point with hard ferrites (31 and 43)
where their absorption properties are becoming significant.
An image borrowed from wa7ark, Mike is something I find more
important. The antenna is a 80-10 End fed in harmonic modes.
The transformer losses are less relevant when you look at the
patterns as its not whats the loss in the transformer but where
is the RF going? The broadside 80m pattern is an end fire
20m pattern with broadside nulls.
Allison
|
In line with the end fed theme, but done differently...
Mono band 10M EFHW about 16.3ft long (4.98m) fed with a L network.
L network 2uh air wound for power handling and the cap is a roughly
6" of PTFE coax (RG316). Wire for the element #22 stranded insulated.
Tune up was with 2500 ohm resistor on the bench and MFJ269B
to get the cap (rg316 coax) to the right capacitance (1:1 match).
then the resistor is removed and wire installed and outdoors the
wire is then adjusted for 1:1 match at 28.4mhz.
It will be used as a vertical (hanging) 2:1 bandwidth is below 28 to
above 29mhz. Since it is short it can also be suspended using a
single 20Ft z(6M) Breem/Crappy pole.
Testing concluded with FT817 and a few SSB contacts on 10M in 4 land
(Florida, Georga).
Monoband as its important to have a clean pattern for RF on the horizon
when suspended vertically. An air core inductor was chosen as lower loss
and adequate power handling at 100W. At 2uh it is a relatively small coil
with low weight. The end result is a small 4x2x1 inch plastic box with
SO239 connector and a #8 stud to connect the antenna. The finished
antenna gets the wire coiled up around the box for storage. The #22
PVC insulated hookup wire works well for two reasons I had it and it is
not being subject to any great weight.
Use will be for the 10M station at Field Day and to generally have handy.
Allison
|
Hi Vojtech, An EFHW antenna with high impedance, fixed ratio, Ferrite transformer Unun is but one antenna solution. As you mentioned, deploying portable antennas may result with varying antenna resonant solutions. A fixed ration Unun EFHW antenna can be tuned by adjusting length of the antenna. Length can be adjusted by looping free end over to shorten antenna wire. Should be a two step process, measure resonant frequency, compute length ratio for desired frequency, adjust length. A tuned Unun is handy if the Unun is located at a convenient location for tuning. Down side is that tuned Unun convenient height suggests lower antenna resulting with possible antenna pattern or gain compromises. Powdered Iron core tuned transformer Unun will have lower loss than Ferrite core transformer Unun. On 6/16/19 2:44 AM, Vojtech Bubnik wrote: I wonder what are the losses of such EFHW UNUN if faced with real world conditions. Ferrite transformer Unun loss is dominated by Ferrite core loss and can be represented with parallel resistance. SimSmith plot under title "2 X FT114-43 4T:30T 3300¦¸ Load SimSmith Approximation With Fair-Rite Complex Permeability Model" R1, 677.9 Ohm at 14 MHz, represents ferrite core loss. If match impedance is reduced, ferrite core loss will decrease, if match loss is increased, Unun core loss will increase. The assumption though is antenna being deployed as a resonant match EFHW, not an End Fed Random Wire antenna. John KN5L
|
I wonder what are the losses of such EFHW UNUN if faced with real world conditions.
Let's say, I cut the end fed wire to length at my back yard, where the center of the wire is fixed to the top of a crappie pole. Then I go to the fields, where the ground has different conductivity, and I do not take the crappie pole with me, but I use the trees (lower or higher than the crappie pole). I may decide to hang the center of the end fed higher than the top of the crappie pole if there are such trees available to lower losses. I may hang not just the center, but also the far end of the wire as high as possible to lower ground losses. Certainly the complex impedance at the end of the EFHW will change and I would bet my shoes that it will be out of the 1:2 SWR range of my back yard setup the wire has been cut to and the transformation rate of the UNUN was tuned to.
I may decide to use your end fed UNUN design to precondition the antenna to an Elecraft T1 auto tuner or similar. What will be the losses in your UNUN then? I may model couple of EFHW installations with NEC2 to get the end fed impedances to match.
Wouldn't be wiser to use a resonated EFHW transformer tuner with a tuning capacitor and taps? This way the tank could be tuned slightly off resonance to provide the required inductance or capacitance.
Or wouldn't be more efficient to just use a high Q LC tuner? Even just providing a high Q coil external to an Elecraft T1 auto tuner should lower the losses of the LC circuit significantly.
By the way, I spent quite some time toying with 4nec2. What I found out (and I just hope I got it right) when modeling a 40m antenna using 7m crappie poles as support is following:
1) Using two 7m crappie poles for an 40m antenna is always better than one. Two crappie poles allow one to bring more wire further from the ground, thus minimizing ground losses. The modeling shows that one can achieve roughly half the losses with an antenna over two poles than over a single pole. The losses below contain the ground losses, as the efficiency numbers are derived from the radiated power accumulated at the far field. Most of the losses of an inverted V antenna are due to the close proximity of the ends of the wire towards the ground.
2) A full size dipole between two 7m crappie poles reaches radiated efficiency above 60% over an average ground, but the full size dipole may be too long and it may be too heavy for two 7m crappie poles, as the tips of the crappie poles are very thin and they will bend. Bringing the two 7m poles to just a 7m distance (quite a difference compared to 20m distance for the full scale dipole) and hanging the ends of the dipole along the crappie poles leads to a radiated efficiency of around 40%. The trick here is to keep the ends of the dipole around 2 meters above the ground to minimize ground losses. The hanging ends act as capacitive hats, thus increasing antenna standing wave current between the two poles high and keeping the dipole impedance reasonable, so it could be matched with an ATU.
3) Very similar wire topology (a dipole over two 7m crappie poles at 7m distance, with one end hanging down along one crappie pole as in the previous case up to 2m above the ground, while the other end going to the ground and end fed offers a radiated efficiency of around 37%, very close to the center dipole in the previous case. Now contrary to the popular belief I think the key to the end fed efficiency without very dense ground system is not the high end fed impedance, but the horizontal polarization of the antenna, which minimizes ground losses. The more of the end fed antenna wire is vertical, the more vertical polarized the radiated signal will be and the more the antenna will be sensitive to a good ground, making it not much different from any other vertical.
3) A T antenna strung between the two crappie poles (wire between the two pole tips, a vertical strung from the center of the horizontal wire) and with two radials strung at the height of 1 meter between the two crappie poles, makes quite a nice 40m vertical with around 20% radiated efficiency and reasonable impedance to be tuned with an ATU. Again the two crappie poles are cheap and they will make a much better vertical antenna than any other single crappie pole exercise with loading coils or top hats.
I am looking forward to a fruitful discussion. The 7m crappie poles here in Prague are around $17 at the Decathlon sports equipment chain. They are not very rigid at the tip, so it does not really make much difference whether they are guyed 1m, 2m or 5m above the ground, 1m above the ground is just fine. I have seen a lot of discussion on EFHW antennas on a single pole, but not much on field antennas on multiple crappie poles.
73, Vojtech OK1IAK, AB2ZA
|
Alan N8WQ
Shirley Dulcey KE1L
