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+--- Thread: Redesigning a Yagi (/thread-657.html)
Redesigning a Yagi - VK2CSW - 10-10-2018
I have been toying with the idea of building something like this 20m Yagi, only redesigning it for 15m.
https://www.nonstopsystems.com/radio/pdf-ant/frank_radio_mini-yagi.pdf
Can anyone suggest any references or calculators that might assist?
The idea is a for bit of practical learning and also a bit of 'shed time'.
TIA
RE: Redesigning a Yagi - VK4ADC - 10-10-2018
Consider each half element a loaded 1/4 wave whip and use something like this to determine your inductor when scaling :
https://m0ukd.com/calculators/loaded-quarter-wave-antenna-inductance-calculator/
It won't be exact but will provide a guide.
Remember to scale the spacing between REFlector / DIRector and Driven Element too. A DE plus DIR usually gives slightly better gain than a DE plus REF when dealing with 2 element arrays.
Typically tune the DE to desired frequency, a DIR to about 5-10% higher, a REF to 5-10% lower.
Final tip: don't actually cut the excess wire length (stage 8 step 2) when going through the tuning process - simply fold it back along the element length initially. Once the proper tuning point is found, only then do you trim the folded-back wire.
RE: Redesigning a Yagi - VK2CSW - 11-10-2018
(10-10-2018, 07:34 PM)VK4ADC Wrote: Consider each half element a loaded 1/4 wave whip and use something like this to determine your inductor when scaling :
https://m0ukd.com/calculators/loaded-quarter-wave-antenna-inductance-calculator/
It won't be exact but will provide a guide.
Remember to scale the spacing between REFlector / DIRector and Driven Element too. A DE plus DIR usually gives slightly better gain than a DE plus REF when dealing with 2 element arrays.
Typically tune the DE to desired frequency, a DIR to about 5-10% higher, a REF to 5-10% lower.
Final tip: don't actually cut the excess wire length (stage 8 step 2) when going through the tuning process - simply fold it back along the element length initially. Once the proper tuning point is found, only then do you trim the folded-back wire.
Thanks Doug.
Having a read now.
RE: Redesigning a Yagi - VK4WDM - 12-10-2018
When I started AR in the 1960's aluminum was very hard to come by (at least in ZL) and many HF and VHF beams were made of timber, usually Oregon pine (very hard to get now) or bamboo, with wire elements. Coax was also hard to get and costly so these beams were fed with open wire line and they worked very well.
Colin, this is an interesting design, but have you considered a Moxon? They have a small footprint and can be made with light timber and wire and you can nest the wire elements for several bands fed with a single feed line. I made one for 10 and 15m with an X shaped frame held together with a central bolt so it could be folded for portable use. It worked very well.
73
Wayne
RE: Redesigning a Yagi - VK2CSW - 12-10-2018
Decisions, decisions, decisions...
The yagi could be smaller, but the moxon could be collapsible.
Why do I always end up in analysis paralysis when thinking about antennas?
RE: Redesigning a Yagi - VK4WDM - 13-10-2018
(12-10-2018, 02:15 PM)VK2CSW Wrote: Decisions, decisions, decisions...
The yagi could be smaller, but the moxon could be collapsible.
Why do I always end up in analysis paralysis when thinking about antennas?
Just remember the old ham adage: Any antenna in the air is always much better than any antenna still inside your head
Just get something up there lad! 
Wayne VK4WDM
RE: Redesigning a Yagi - VK5TM - 13-10-2018
Quote:When I started AR in the 1960's aluminum was very hard to come by (at least in ZL) and many HF and VHF beams were made of timber, usually Oregon pine (very hard to get now) or bamboo, with wire elements.
Or copper pipe on a timber mast.
Don't remember where it came from but my first 3 el 2m Yagi in ZL (also in the 60's) was copper pipe with a coax feed.
RE: Redesigning a Yagi - VK5ZD - 14-10-2018
(12-10-2018, 02:15 PM)VK2CSW Wrote: Decisions, decisions, decisions...
The yagi could be smaller, but the moxon could be collapsible.
Why do I always end up in analysis paralysis when thinking about antennas?
Easy. Build both.
RE: Redesigning a Yagi - VK4WDM - 14-10-2018
(13-10-2018, 09:14 PM)VK5TM Wrote:Quote:When I started AR in the 1960's aluminum was very hard to come by (at least in ZL) and many HF and VHF beams were made of timber, usually Oregon pine (very hard to get now) or bamboo, with wire elements.
Or copper pipe on a timber mast.
Don't remember where it came from but my first 3 el 2m Yagi in ZL (also in the 60's) was copper pipe with a coax feed.
copper pipe with a coax feed! You must have come from a wealthy farm. My first antennas were made with fencing wire, held up with binder twine and fed with twin electric light cord
Wayne VK4WDM.