Hi all
i am looking at puting together a 2 m yagi, what will work best for ssb and/or fm?. Do i need one for each? can i get one that is duel band?
ken
How Long Is Too Long for a Yagi?
Re: HOW LONG IS TO LONG FOR A YAGI
Hi Ken
Just for starters, horizontal polarization is used for SSB and vertical polarization for FM so, unless you can arrange to twist the antenna, you'll need two. An antenna for SSB would be optimized for 144.1MHz (or thereabouts) while for FM it would be optimized for around 147MHz. If you only want to build one I suggest making it for the SSB part of the band.
73
Iain
Just for starters, horizontal polarization is used for SSB and vertical polarization for FM so, unless you can arrange to twist the antenna, you'll need two. An antenna for SSB would be optimized for 144.1MHz (or thereabouts) while for FM it would be optimized for around 147MHz. If you only want to build one I suggest making it for the SSB part of the band.
73
Iain
73
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih
Re: How Long Is Too Long for a Yagi?
Ken
Iain is quite right in his comment about needing two yagis, one for each segment, however the actual answer to your question (How Long Is Too Long for a Yagi?) is when your construction technique is such that the boom cannot be supported. If you use boom bracing, it is easy to make up a yagi with a 6 to 6.5M long boom, on a single piece of aluminium (or material of better strength characteristics) tubing of a suitable dimension and wall thickness. For maximum strength, it is best to stay away from joining boom sections together. You will find it easier to work with square section tube rather than round - easier to line up the elements in the one plane and easier to attach to a masting /pipe.
That yagi could be on 2M, 70CM or any other band. If you use the VK5DJ Yagi calculator software ( http://www.vk5dj.com/yagi.html ), it will reveal how many elements on a given frequency can be fitted onto a given boom length. Keep in mind the total weight you want to swing around too.
Just remember that the more elements used, the narrower the beamwidth (and bandwidth) becomes, such that you need reasonable pointing methodology for it. A yagi consisting of only a few elements ( 4- 6) will be much easier to utilise unless you are looking at achieving comms over long distance paths.
Finally, you need to use a low loss feedline else your efforts to achieve gain will be for nothing. For example, a 20M length of RG58 will have around 3.5dB loss at 144, the same length of RG213 around 1.8dB and for CNT400/LMR400, around 1.0dB. Those loss numbers come straight off the anticipated gain of the yagi you put up in the sky. To obtain the most improvement due to your antenna, use a heliax cable run (eg LDF-450A) with CNT/LMR400 tails at each end for 2M, 70CM etc.
Happy building
Iain is quite right in his comment about needing two yagis, one for each segment, however the actual answer to your question (How Long Is Too Long for a Yagi?) is when your construction technique is such that the boom cannot be supported. If you use boom bracing, it is easy to make up a yagi with a 6 to 6.5M long boom, on a single piece of aluminium (or material of better strength characteristics) tubing of a suitable dimension and wall thickness. For maximum strength, it is best to stay away from joining boom sections together. You will find it easier to work with square section tube rather than round - easier to line up the elements in the one plane and easier to attach to a masting /pipe.
That yagi could be on 2M, 70CM or any other band. If you use the VK5DJ Yagi calculator software ( http://www.vk5dj.com/yagi.html ), it will reveal how many elements on a given frequency can be fitted onto a given boom length. Keep in mind the total weight you want to swing around too.
Just remember that the more elements used, the narrower the beamwidth (and bandwidth) becomes, such that you need reasonable pointing methodology for it. A yagi consisting of only a few elements ( 4- 6) will be much easier to utilise unless you are looking at achieving comms over long distance paths.
Finally, you need to use a low loss feedline else your efforts to achieve gain will be for nothing. For example, a 20M length of RG58 will have around 3.5dB loss at 144, the same length of RG213 around 1.8dB and for CNT400/LMR400, around 1.0dB. Those loss numbers come straight off the anticipated gain of the yagi you put up in the sky. To obtain the most improvement due to your antenna, use a heliax cable run (eg LDF-450A) with CNT/LMR400 tails at each end for 2M, 70CM etc.
Happy building
Last edited by VK4ADC on Fri Feb 15, 2013 9:15 am, edited 1 time in total.
Doug VK4ADC, QG62lg51
http://www.vk4adc.com
http://www.vk4adc.com
Re: How Long Is Too Long for a Yagi?
It all depends on how serious you want to get. I have been using the 19 element version of DL6WU for over 20 years. It nicely fits on a 12 metre boom. Mine has 40 mm tubing spliced in the middle with a short length of 1 3/4 inch water pipe. Use VK5DJ program. 3 db beam width is 25 degrees so dont be put off by those who say higher gain yagis are too sharp.
Happy building
David
Happy building
David
Re: How Long Is Too Long for a Yagi?
Till the neighbours object to it over there fence 
Re: How Long Is Too Long for a Yagi?
I run a 9element LFA horizontal for SSB and on the same boom a 7ele LFA vertical for FM
Have a coax relay to switch between Vert & Horizontal
The 9 ele LFA is cut for 144.1 and the 7ele cut for 147mhz interatction is minimal
height is 12mtrs pics on QRZ
Have a coax relay to switch between Vert & Horizontal
The 9 ele LFA is cut for 144.1 and the 7ele cut for 147mhz interatction is minimal
height is 12mtrs pics on QRZ
-
VK4WDM
Re: How Long Is Too Long for a Yagi?
Hi Ken
The setup that ZL3PX describes would be ideal and I will be putting up something similar when I replace my current yagi.
My current SSB antenna is 10 elements and I have worked from Townsville to VK2, 3 and 5.
Use the best feed line you can afford, and good quality N type connectors. If you are not certain of your ability to install the connectors absolutely correctly the cable suppliers will do it for a small fee. In my experience, the cause of a lot of signal loss and other problems is in connectors and "patch cables."
2m is a fascinating band and you don't need high power to achieve good results - have fun, hopefully I will work you during the next sporadic E season
73
Wayne VK4WDM
The setup that ZL3PX describes would be ideal and I will be putting up something similar when I replace my current yagi.
My current SSB antenna is 10 elements and I have worked from Townsville to VK2, 3 and 5.
Use the best feed line you can afford, and good quality N type connectors. If you are not certain of your ability to install the connectors absolutely correctly the cable suppliers will do it for a small fee. In my experience, the cause of a lot of signal loss and other problems is in connectors and "patch cables."
2m is a fascinating band and you don't need high power to achieve good results - have fun, hopefully I will work you during the next sporadic E season
73
Wayne VK4WDM
-
VK3FKRK
Re: How Long Is Too Long for a Yagi?
VK3AUU wrote:It all depends on how serious you want to get. I have been using the 19 element version of DL6WU for over 20 years. It nicely fits on a 12 metre boom. Mine has 40 mm tubing spliced in the middle with a short length of 1 3/4 inch water pipe. Use VK5DJ program. 3 db beam width is 25 degrees so dont be put off by those who say higher gain yagis are too sharp.
Happy building
David
Hi there David
had a look at your antenna the other day (from the road on the other side of the railway line) they may be a bit big for me, but plans are well on the way, i will be using the program that is linked to the vk3bez site when i get home
Ken