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[IK1LBL]

Before all i have to apologize for my basic poor English, i hope to be clear enough to be understood on my message hi hi

I'm interested to build an inverted L for 80 meter, due to my post stamp lot i have no room for extensive radials etc.
So i have chosen the FCP folded radial https://k2av.com/  on this project seem to be mandatory the use of a specific isolation transformer. Here for me is hard to find most of the material to for his construction.
Then i have found the article of K9YC “Working 160 m from a Small Lot (and Larger Ones Too)” where he suggested using a choke and a coil, that inspire me pretty much, i have many toroids, i usually build chokes  etc.
The point is ? Maybe i miss something, and shame my self but i can't find the way to calculate the coil need on 80 (3.550 CW)
Can someone that know this project can help me ?
All the very best 73s and Merry Xmas
Mario IK1LBL

[KH6AQ]

The loading coil having reactance of 195 ohms comes from an analysis by W8JI. See page 77 of the paper you refer to, Working 160M From a Small Lot, by K9YC.

Paper  http://audiosystemsgroup.com/160MPacificon.pdf

Inductor
For 195 ohms at 3.55 MHz you need 8.74 uH. For this sort of inductor I wind common house wire on a piece of PVC pipe. Close winding (turns touching) works well and assembly is easy. What PVC and insulated wire have you got to work with? A wide range of pipe diameters will work and something around 4 cm diameter is good. The wire diameter can be 1-2 mm. This online solenoid inductance calculator can be used to design your coil.

http://electronbunker.ca/eb/InductanceCalc.html


Choke
A suitable common-mode choke impedance should probably be >1000 ohms and can be achieved with 12 to 17 turns of coax on one FT240-31 core. 17 turns on an FT240-43 core will also work.

http://www.karinya.net/g3txq/chokes/

[IK1LBL]

The feedline common-mode choke can be wound on a ferrite core. The common-mode impedance should probably be >1000 ohms and can be achieved with 12 to 17 turns of coax on one FT240-31 core. 17 turns on an FT240-43 core will also work.

http://www.karinya.net/g3txq/chokes/

Good morning, thanks !
My question is another, not about the choke but concern the FCP project Itself, where is pointed to use a particular isolation transformer and vice versa K9YC in his writhing suggest a choke and a coil, fcp side..   his article is about  a 160 meter antenna .. i need to find a way to scale the coil on 80 meter..
http://audiosystemsgroup.com/160MPacificon.pdf at page 73 he start to talk about the folded radial ..

[RFRY]

Before all i have to apologize for my basic poor English, i hope to be clear enough to be understood on my message hi hi.  I'm interested to build an inverted L for 80 meter, due to my post stamp lot i have no room for extensive radials etc.  So i have chosen the FCP folded radial ...

No apologies are needed for your command of the English language, Mario.

You also might be interested in some form of the 80m, inverted L antenna system concept outlined below — which needs/uses NO radials of any kind, might fit on a small lot, has high radiation efficiency, and useful radiation patterns.

73, and Happy Christmas to you.

Richard Fry, W9XMT

[KH6AQ]

The feedline common-mode choke can be wound on a ferrite core. The common-mode impedance should probably be >1000 ohms and can be achieved with 12 to 17 turns of coax on one FT240-31 core. 17 turns on an FT240-43 core will also work.

http://www.karinya.net/g3txq/chokes/

Good morning, thanks !
My question is another, not about the choke but concern the FCP project Itself, where is pointed to use a particular isolation transformer and vice versa K9YC in his writhing suggest a choke and a coil, fcp side..   his article is about  a 160 meter antenna .. i need to find a way to scale the coil on 80 meter..
http://audiosystemsgroup.com/160MPacificon.pdf at page 73 he start to talk about the folded radial ..

The FCP counterpoise loading coil inductive reactance is 195 ohms on 80 or 160 meters. 8.74 uH is the inductance for the 80 meter band.

I ran an EZNEC model of the 3.55 MHz FCP inverted-L and it does resonate at 3.55 MHz using an 8.74 uH FCP loading inductance. The FCP is one-half the size of the 160 meter version, or 33 ft across. In my model I used 2" spacing between FCP wires. If you'd like to use different spacing that should be no problem. Final tuning of the antenna can be accomplished by changing the length of the inverted-L wire.

To summarize, the common-mode choke and loading coil together take the place of the original FCP transformer.

[N2SR]

Hello Mario,

K2AV designed the FCP to be about 2 meters above the ground.  This makes the FCP a bit lossier than regular elevated radials which should be about 3-4 meters above the ground - for 80m.

A few years ago, I tried adding a FCP for 80m, based on K2AV's article, with a full size 1/4 wave wire.  In the article, he suggests the scaling dimensions for 80m.  I tried those dimensions, and found that the bandwidth was poor. 

NOTE that W8JI mentions the FCP as sort of a "gimmick" to get resonance.  He also describes it as narrow banded.

In the January QST, K3LC has a "part II" article with different radial configurations for an 80m 4 square.  In one of the configurations, he models a FCP for 80m and provides the dimensions, which are quite different than the K2AV scaled dimensions.

I do not feel that you need to use the isolation transformer with an FCP.  As long as you use a good choke from K9YC's cookbook, it should work.

-----

Another option is the Double L antenna for 80 and 160 by K2KQ.  It is a very popular antenna for those that have small lots.  It is very forgiving, and works well.  https://yccc.org/k2kq-double-l-antenna-for-80-160/

Good Luck,

Tom, N2SR

[IK1LBL]

David !! Thank you ! Just the answer I'm looking for !
For this kind of coil with ready available material ther is not problem at all.
The choke not problem, your suggestion is exactly what i already made, i just have one from and old project with two core 31 staked and 17 or 18 turns   
TNX also for the link of the calculator
Merry Christmas
73 Mario IK1LBL

The loading coil having reactance of 195 ohms comes from an analysis by W8JI. See page 77 of the paper you refer to, Working 160M From a Small Lot, by K9YC.

Paper  http://audiosystemsgroup.com/160MPacificon.pdf

Inductor
For 195 ohms at 3.55 MHz you need 8.74 uH. For this sort of inductor I wind common house wire on a piece of PVC pipe. Close winding (turns touching) works well and assembly is easy. What PVC and insulated wire have you got to work with? A wide range of pipe diameters will work and something around 4 cm diameter is good. The wire diameter can be 1-2 mm. This online solenoid inductance calculator can be used to design your coil.

http://electronbunker.ca/eb/InductanceCalc.html


Choke
A suitable common-mode choke impedance should probably be >1000 ohms and can be achieved with 12 to 17 turns of coax on one FT240-31 core. 17 turns on an FT240-43 core will also work.

http://www.karinya.net/g3txq/chokes/

[IK1LBL]

Thanks, Tom for the hints you give to me ! im going to read the article you suggest.
Maybe i have a local friend that he receive QST so i can read the article you mention !
Thank' you everybody here for the suggestion and help !

Hello Mario,

K2AV designed the FCP to be about 2 meters above the ground.  This makes the FCP a bit lossier than regular elevated radials which should be about 3-4 meters above the ground - for 80m.

A few years ago, I tried adding a FCP for 80m, based on K2AV's article, with a full size 1/4 wave wire.  In the article, he suggests the scaling dimensions for 80m.  I tried those dimensions, and found that the bandwidth was poor. 

NOTE that W8JI mentions the FCP as sort of a "gimmick" to get resonance.  He also describes it as narrow banded.

In the January QST, K3LC has a "part II" article with different radial configurations for an 80m 4 square.  In one of the configurations, he models a FCP for 80m and provides the dimensions, which are quite different than the K2AV scaled dimensions.

I do not feel that you need to use the isolation transformer with an FCP.  As long as you use a good choke from K9YC's cookbook, it should work.

-----

Another option is the Double L antenna for 80 and 160 by K2KQ.  It is a very popular antenna for those that have small lots.  It is very forgiving, and works well.  https://yccc.org/k2kq-double-l-antenna-for-80-160/

Good Luck,

Tom, N2SR

[KH6AQ]

To see if the FCP counterpoise compromises the SWR bandwidth I ran a model of it with the FCP and with four 1/4 wavelength elevated radials. Matched to 50 ohms the SWR at 3.500 and 3.600 MHz is 2.6:1 with the FCP and 2.3:1 with 1/4 wavelength radials. I do not consider this much of a bandwidth reduction.

[IK1LBL]

One more question to resolve a doubt.
The length of  the FCP is 5/16 Wl OK, but where? i mean, i have to cut 5/16 at my operating frequency, is that correct ?
On his project, he stated +-16,5 feet each side but 80 are a wideband... CW to Phone is large

To see if the FCP counterpoise compromises the SWR bandwidth I ran a model of it with the FCP and with four 1/4 wavelength elevated radials. Matched to 50 ohms the SWR at 3.500 and 3.600 MHz is 2.6:1 with the FCP and 2.3:1 with 1/4 wavelength radials. I do not consider this much of a bandwidth reduction.

[NO9E]

FCP radial is like 2 short radials tuned for equal radiation. The actual size of the radials is not critical for efficiency.

Almost any balun overheats with short radials. But a simple transformer does not. Wind 2 x 8 turns on a 43 or 61 toroid. A 1.4 inch (2.5 cm) toroid easily handles 500W.
Regarding inductance, buy an antenna analyzer. Then wind such a coil that you have resonance.

You can see my portable vertical matching unit at http://no9e.com/wp-content/uploads/2022/07/ST_GEORGE_STEW2017_NO9E_3.pdf
It is for 160m, but the rules for 80m are the same.

Ignacy NO9E

[IK1LBL]

Thank you Ignacy for the answer, i have read your article and is very inspirational.
I have a cheap chinese NanoVNA that is help my sometime, it's not the top of course..
Any way the more i dig in this project the more i feel the need of an alternate solutions hi hi
73s and Merry Xmas Mario IK1LBL

FCP radial is like 2 short radials tuned for equal radiation. The actual size of the radials is not critical for efficiency.

Almost any balun overheats with short radials. But a simple transformer does not. Wind 2 x 8 turns on a 43 or 61 toroid. A 1.4 inch (2.5 cm) toroid easily handles 500W.
Regarding inductance, buy an antenna analyzer. Then wind such a coil that you have resonance.

You can see my portable vertical matching unit at http://no9e.com/wp-content/uploads/2022/07/ST_GEORGE_STEW2017_NO9E_3.pdf
It is for 160m, but the rules for 80m are the same.

Ignacy NO9E

[KH6AQ]

Choke power dissipation
Choke dissipation should not be a problem as long as a suitable choke is used. EZNEC shows the G3TXQ 8k ohm resistive choke (17 turns on one FT240-43 core) at 300W key-down to dissipate 1 watt. This is not a problem. His 2k ohm, 12-turn, choke would dissipate 4 watts. Again, that should be no problem, although it will get warm in normal CW/SSB/FT8 operation. G3TXQ also shows two and four stacked core chokes which spread  core loss over more surface area. His 4 stacked core FT240-31 choke at 1500 watt key-down dissipates less than 4 watts spread over four ferrite cores.

No FCP loading coil
The FCP loading coil can be eliminated by lengthening the FCP by 23% for an end-to-end length of 12.4 meters.   

[N2SR]

Thanks, Tom for the hints you give to me ! im going to read the article you suggest.
Maybe i have a local friend that he receive QST so i can read the article you mention !
Thank' you everybody here for the suggestion and help !

Mario, I sent you an email direct to your gmail account. 

Tom, N2SR

[IK1LBL]

David ! Thank you !
I'm used to stacking always two cores, i don't usually run high power but sometime im using the PA,  and with the RG400 is pretty easy to reach 17 turns, on higher band I'm doing 12 turns but in cross mode.. i no idea how to describe better on English sorry, i make 6 turns then i invert the direction..  No better description, sorry...
I also i have thought at another way to get a small radial inspired from DJ0IP https://www.dj0ip.de/vertical-antennas/40m-minimum-space/   anyway i keep investigating any solution to be on the air on 80..    My low very low dipole is just a good NVIS antenna and i want to try something better for dxing

Choke power dissipation
Choke dissipation should not be a problem as long as a suitable choke is used. EZNEC shows the G3TXQ 8k ohm resistive choke (17 turns on one FT240-43 core) at 300W key-down to dissipate 1 watt. This is not a problem. His 2k ohm, 12-turn, choke would dissipate 4 watts. Again, that should be no problem, although it will get warm in normal CW/SSB/FT8 operation. G3TXQ also shows two and four stacked core chokes which spread  core loss over more surface area. His 4 stacked core FT240-31 choke at 1500 watt key-down dissipates less than 4 watts spread over four ferrite cores.

No FCP loading coil
The FCP loading coil can be eliminated by lengthening the FCP by 23% for an end-to-end length of 12.4 meters.