(30-06-2017, 10:00 PM)vk6tu Wrote: I am looking at making a light weight 20m Moxon antenna for the light house weekend.

Has anyone made a short Moxon by putting a coil in the element, I have some old traps that I have dismantled and plan on using the coil and insulated former to shorten the elements.

Got some good ideas from this site http://www.moxonantennaproject.com/IK0GDH/IK0GDH.htm


What I would like to know is there any tips on working out the correct length with the coil in the elements, or should I just put it together and adjust using a antenna analyser?

Any ideas options appreciated


73 from Michael
VK6TU

(01-07-2017, 08:28 AM)vk4adc Wrote:

(30-06-2017, 10:00 PM)vk6tu Wrote: I am looking at making a light weight 20m Moxon antenna for the light house weekend.

Has anyone made a short Moxon by putting a coil in the element, I have some old traps that I have dismantled and plan on using the coil and insulated former to shorten the elements.

Got some good ideas from this site http://www.moxonantennaproject.com/IK0GDH/IK0GDH.htm


What I would like to know is there any tips on working out the correct length with the coil in the elements, or should I just put it together and adjust using a antenna analyser?

Any ideas options appreciated


73 from Michael
VK6TU

Michael

Obviously the loaded Moxon works - the IK0GDH article says so - but his coil description is not completely correct:
"Both elements are insulated from boom. Each coil is abt 9.7 mH. with  a theoretical Q of more than 800. I used a 6 mm copper tube. Turns spaced 6 mm aparts. 16 turns wrapped on 90 mm diameter. "

My calcs indicate that the coil inductance is more like 9 uH (microHenries) not 9.7 mH (milliHenries), based on coils 90mm inside diameter (93mm mean diameter = 90mm + 1/2 of 6mm tube dia), 16 turns over a length of 200mm (6mm tube turns spaced 6mm apart = 192mm long).  If you wish to use his MMANA details to scale from to make it work on 20M, make sure you have that factor correct.

The traps idea probably will NOT work because they are actually a parallel resonant device using capacitance usually derived from overlapping metal sleeves with a dielectric in between plus the coil wound outside. You require just an inductor to load the lengths to make it shorter. 

Alternatively, see if you can pick up an old TH3-Jr tribander - small and light...

73 Doug VK4ADC

(01-07-2017, 08:55 AM)vk4adc Wrote:

(01-07-2017, 08:28 AM)vk4adc Wrote: Michael

Obviously the loaded Moxon works - the IK0GDH article says so - but his coil description is not completely correct:
"Both elements are insulated from boom. Each coil is abt 9.7 mH. with  a theoretical Q of more than 800. I used a 6 mm copper tube. Turns spaced 6 mm aparts. 16 turns wrapped on 90 mm diameter. "

My calcs indicate that the coil inductance is more like 9 uH (microHenries) not 9.7 mH (milliHenries), based on coils 90mm inside diameter (93mm mean diameter = 90mm + 1/2 of 6mm tube dia), 16 turns over a length of 200mm (6mm tube turns spaced 6mm apart = 192mm long).  If you wish to use his MMANA details to scale from to make it work on 20M, make sure you have that factor correct.

The traps idea probably will NOT work because they are actually a parallel resonant device using capacitance usually derived from overlapping metal sleeves with a dielectric in between plus the coil wound outside. You require just an inductor to load the lengths to make it shorter. 

Alternatively, see if you can pick up an old TH3-Jr tribander - small and light...

73 Doug VK4ADC

(01-07-2017, 03:47 PM)vk6tu Wrote:

(01-07-2017, 08:55 AM)vk4adc Wrote:

(01-07-2017, 08:28 AM)vk4adc Wrote: Michael

Obviously the loaded Moxon works - the IK0GDH article says so - but his coil description is not completely correct:
"Both elements are insulated from boom. Each coil is abt 9.7 mH. with  a theoretical Q of more than 800. I used a 6 mm copper tube. Turns spaced 6 mm aparts. 16 turns wrapped on 90 mm diameter. "

My calcs indicate that the coil inductance is more like 9 uH (microHenries) not 9.7 mH (milliHenries), based on coils 90mm inside diameter (93mm mean diameter = 90mm + 1/2 of 6mm tube dia), 16 turns over a length of 200mm (6mm tube turns spaced 6mm apart = 192mm long).  If you wish to use his MMANA details to scale from to make it work on 20M, make sure you have that factor correct.

The traps idea probably will NOT work because they are actually a parallel resonant device using capacitance usually derived from overlapping metal sleeves with a dielectric in between plus the coil wound outside. You require just an inductor to load the lengths to make it shorter. 

Alternatively, see if you can pick up an old TH3-Jr tribander - small and light...

73 Doug VK4ADC

Doug,
Thanks,
Will have to have a play, I plan on not using the outer sleeve of the traps I have, just the inductor which is on a nice insulated section which I hope will shorten the elements a bit.

I do have a 3 ele Tri bander I can use but is bigger than I want to use, may turn it into a 2 ele for the weekend, or even just make a 2 ele with the bits I plan to use for the Moxon, I guess it all depends on what time I get to make something.

73 from Michael
VK6TU