22-03-2019, 01:07 PM
Marcus
Back before I moved semi-rural I used copper wire for my HF wire antennas, mostly insulated and of varying wire gauges. One of the things that became apparent over many HF antennas over the last 40+ years has been wire stretch - particularly during storms and high winds.
I used to keep a page with the SWR minimum frequencies and I would update it from time to time and note the frequencies slowly dropping - except after a storm, when the drop was more noticeable. None of the copper wire was hard-drawn and varied from hookup wire to building wire. The stretch factor applies to all of them.
Every so often I would either shorten to re-tune or replace the wire completely figuring that it was likely to snap eventually.
I put up the existing sets (160/80/40/30 and 80/40/30) about 5 years ago now and have not noticed any frequency shift. I was using my East-West mounted set when you heard me on Saturday so it must work.
I can't quote minimum SWR values but I typically aim for 1835, 3610, 7110, 14190, 18135, 21190, 24920 and 28470 when I am tuning my HF antennas and try for minimums at those frequencies.
The final SWR is not critical as when you analyse the height above ground scenario, your antennas are usually lower than optimum to get the 50 ohm centre-feed impedance that results in a 1:1 SWR. Different bands = different optimum heights so SWR is usually never perfect on every band. One maybe, others will be variable. Unless, of course, you can get the whole array more than 10 wavelengths above ground at the lowest frequency.... ( let's see : 800 metres above ground at 3.5MHz
)
Stainless may not be optimal as a conductor but it does have the other physical advantages as mentioned. The 3mm as a 7x7 is what I use most now.
A postscript about using s/s wire: make sure you include a "weak link" in the supporting arrangements. The wire won't break if a large branch flies through the air and lands on it (or a tree falls over !) but you don't want the antenna supports to be damaged, particularly if one (or more) end(s) or centres are at a house or tower. I use a length of 3mm 'handycord' on my dipole-set centre-support halyards as a mechanical 'fuse' and it becomes the purposeful weak link.
Back before I moved semi-rural I used copper wire for my HF wire antennas, mostly insulated and of varying wire gauges. One of the things that became apparent over many HF antennas over the last 40+ years has been wire stretch - particularly during storms and high winds.
I used to keep a page with the SWR minimum frequencies and I would update it from time to time and note the frequencies slowly dropping - except after a storm, when the drop was more noticeable. None of the copper wire was hard-drawn and varied from hookup wire to building wire. The stretch factor applies to all of them.
Every so often I would either shorten to re-tune or replace the wire completely figuring that it was likely to snap eventually.
I put up the existing sets (160/80/40/30 and 80/40/30) about 5 years ago now and have not noticed any frequency shift. I was using my East-West mounted set when you heard me on Saturday so it must work.
I can't quote minimum SWR values but I typically aim for 1835, 3610, 7110, 14190, 18135, 21190, 24920 and 28470 when I am tuning my HF antennas and try for minimums at those frequencies.
The final SWR is not critical as when you analyse the height above ground scenario, your antennas are usually lower than optimum to get the 50 ohm centre-feed impedance that results in a 1:1 SWR. Different bands = different optimum heights so SWR is usually never perfect on every band. One maybe, others will be variable. Unless, of course, you can get the whole array more than 10 wavelengths above ground at the lowest frequency.... ( let's see : 800 metres above ground at 3.5MHz
)Stainless may not be optimal as a conductor but it does have the other physical advantages as mentioned. The 3mm as a 7x7 is what I use most now.
A postscript about using s/s wire: make sure you include a "weak link" in the supporting arrangements. The wire won't break if a large branch flies through the air and lands on it (or a tree falls over !) but you don't want the antenna supports to be damaged, particularly if one (or more) end(s) or centres are at a house or tower. I use a length of 3mm 'handycord' on my dipole-set centre-support halyards as a mechanical 'fuse' and it becomes the purposeful weak link.
Doug VK4ADC @ QG62LG51
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.
http://www.vk4adc.com
This Forum is only going to be as interesting as the posts it contains.
If you have a comment or question, post it as it may trigger or answer the query in someone else's mind.