18-03-2019, 10:00 PM
Marcus
I am sure others will also provide suggestions but I will get in first, provide my impressions against your questions and also a couple of links for you to follow.
"I suspect that part of the issue I am having on 40m is that the centre feed on the dipole is too low." The height will affect the takeoff angle BUT it should still work ok. Something to try : assess the signals from within VK to those outside VK on receive. That may provide you with an idea as to whether it will work on transmit - i.e. reciprocity. Maybe your 1:1 balun is saturating on transmit, getting hot and lossy.
1) Given I have a fair bit of room to work with, should I stick with some sort of multiple band dipole arrangement?
Have a look at my article at https://www.vk4adc.com/web/hf-projects/4...d-v-dipole but contemplate it for 80 / 40 /20 in lieu. It's short enough to fit the distances you mention.
2) Is a end-fed type antenna through an ATU ever going to be as effective in this situation as a dipole?
End fed antennas will work if they are fed against an effective ground - and - there is a reasonable impedance match in place via an UN-UN device. The UN-UN is mandatory but might be one of 4:1, 9:1 or 16:1.
3) Can an ATU on a resonant long dipole also tune for lower bands? I've never used an ATU before so not sure what their capabilities are and whether this is a silly question!
A dipole is usually only efficient at its basic resonant frequency and any odd harmonics of that frequency. It is also where it will reflect a low impedance making it suitable for coaxial feed. An ATU (eg LDG Z100) will synthesise a match as far as the radio goes but will do so by consuming some of the RF (component losses) BUT the antenna efficiency drops if not at resonance. Lower bands - ATU-matchable ? probably. Efficient ? definitely not.
The other option might be a vertical but I am limited in room to run radials. Can the 50sqm colourbond roof of the shed be used as part of a counterpoise in this setup?
Have a read of post #4 in the topic at https://www.ahrdf.net/forum/showthread.p...50#pid3250
The 50SQM roof is big enough to act as a reasonable ground plane even on 80M, without adding extra radials.
I have successfully used the Z100 with a combination of Icom transceivers (718, 706..) over a number of years and it is amazing how well it will provide a match to the transmitter to enable it to produce maximum power output. It does not resonate the antenna and that relates back as actual efficiency- i.e. how well it actually works.
I have a set of ray dipoles up in the air at the moment, 160/80/40/30 with a second set for 80/40/30 at about 90 degrees to the first. The height is far less than desirable but I still worked most of VK and a ZL during the JMMFD over the weekend on 40M. I also have various homebrew trapped dipoles too that go portable eg 80/40/20/15/10/6 with a companion set that adds 30/17/12M (this was used for my VK9NU operation in 2016), then the one in the link provided earlier for 160/80/40. You can probably find more details in other articles on the VK4ADC web site.
I have done quite a bit of antenna experimentation over the last 5 years and have plenty still in operation today. I posted the count the other day : 17, and that counts the above multiband ray dipoles as one each ray dipole set. (One of the advantages of a 1.1 acre block - space.)
I am sure others will also provide suggestions but I will get in first, provide my impressions against your questions and also a couple of links for you to follow.
"I suspect that part of the issue I am having on 40m is that the centre feed on the dipole is too low." The height will affect the takeoff angle BUT it should still work ok. Something to try : assess the signals from within VK to those outside VK on receive. That may provide you with an idea as to whether it will work on transmit - i.e. reciprocity. Maybe your 1:1 balun is saturating on transmit, getting hot and lossy.
1) Given I have a fair bit of room to work with, should I stick with some sort of multiple band dipole arrangement?
Have a look at my article at https://www.vk4adc.com/web/hf-projects/4...d-v-dipole but contemplate it for 80 / 40 /20 in lieu. It's short enough to fit the distances you mention.
2) Is a end-fed type antenna through an ATU ever going to be as effective in this situation as a dipole?
End fed antennas will work if they are fed against an effective ground - and - there is a reasonable impedance match in place via an UN-UN device. The UN-UN is mandatory but might be one of 4:1, 9:1 or 16:1.
3) Can an ATU on a resonant long dipole also tune for lower bands? I've never used an ATU before so not sure what their capabilities are and whether this is a silly question!
A dipole is usually only efficient at its basic resonant frequency and any odd harmonics of that frequency. It is also where it will reflect a low impedance making it suitable for coaxial feed. An ATU (eg LDG Z100) will synthesise a match as far as the radio goes but will do so by consuming some of the RF (component losses) BUT the antenna efficiency drops if not at resonance. Lower bands - ATU-matchable ? probably. Efficient ? definitely not.
The other option might be a vertical but I am limited in room to run radials. Can the 50sqm colourbond roof of the shed be used as part of a counterpoise in this setup?
Have a read of post #4 in the topic at https://www.ahrdf.net/forum/showthread.p...50#pid3250
The 50SQM roof is big enough to act as a reasonable ground plane even on 80M, without adding extra radials.
I have successfully used the Z100 with a combination of Icom transceivers (718, 706..) over a number of years and it is amazing how well it will provide a match to the transmitter to enable it to produce maximum power output. It does not resonate the antenna and that relates back as actual efficiency- i.e. how well it actually works.
I have a set of ray dipoles up in the air at the moment, 160/80/40/30 with a second set for 80/40/30 at about 90 degrees to the first. The height is far less than desirable but I still worked most of VK and a ZL during the JMMFD over the weekend on 40M. I also have various homebrew trapped dipoles too that go portable eg 80/40/20/15/10/6 with a companion set that adds 30/17/12M (this was used for my VK9NU operation in 2016), then the one in the link provided earlier for 160/80/40. You can probably find more details in other articles on the VK4ADC web site.
I have done quite a bit of antenna experimentation over the last 5 years and have plenty still in operation today. I posted the count the other day : 17, and that counts the above multiband ray dipoles as one each ray dipole set. (One of the advantages of a 1.1 acre block - space.)
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.