Ground gain - effect of antenna height...
Ground gain - effect of antenna height...
While understanding the principle of ground gain I am wondering what the effect is of significant antenna height. It seems from what information I can find is that something between a few wl and 10 wl is best.
Specifically I wonder what the effect would be for an antenna operating on the edge of a 70m cliff edge on 2M (35 wl) ?
Specifically I wonder what the effect would be for an antenna operating on the edge of a 70m cliff edge on 2M (35 wl) ?
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
hi Steve,
I have found on 6M antenna height makes a huge difference along with location.We did a test with KH7Y earlier this year and he has I think 2 x 7 el yagis at different heights.On the bottem yagi he was 56 he switched to the top yagi and the signal jumped to 20db over 9, he then ran the two antennas in phase which made little difference on the single top antenna. This was a great learning experience on the effects of antenna height. Also Paul VK4MA who lives about 7km from here generally hears 2 to 3 s points better than stations in Hervey Bay. Most of the guys here have antennas at 10M height where Paul has his antennas at about 19M high. This again shows the advantage of antenna height.
regards Wayne VK4WTN
I have found on 6M antenna height makes a huge difference along with location.We did a test with KH7Y earlier this year and he has I think 2 x 7 el yagis at different heights.On the bottem yagi he was 56 he switched to the top yagi and the signal jumped to 20db over 9, he then ran the two antennas in phase which made little difference on the single top antenna. This was a great learning experience on the effects of antenna height. Also Paul VK4MA who lives about 7km from here generally hears 2 to 3 s points better than stations in Hervey Bay. Most of the guys here have antennas at 10M height where Paul has his antennas at about 19M high. This again shows the advantage of antenna height.
regards Wayne VK4WTN
- VK3ZAZ
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Re: Ground gain - effect of antenna height...
K6STI DID SOM GRAPHS
but only for a dipole
http://www.ham-radio.com/k6sti/height.htm
So if that's what you are asking about a single yagi like I had at 25M agl it exhibited had best gain at 2-5 degrees for eme if you cant elevate.
But it was a 2.5WL yagi with a narrow aperture.
calculator for other antenna up 1 wl
https://www.rac.ca/tca/Antenna_Height_Calculator.html
I think ground gain vs height applies to EME as much as anything.
Does it not
is this what you were asking?
as for stacked heights using ionospheric prop as the signal yardstick too many variables to be conclusive especially the aperture.
better to try 2M stacks on a known path and even then the ref aerial has to be at same height..
But if you want the good oil on 6M arrays talk with W6BYA two stacks
K6QXY four stacks and dual polarity
or W6JKV 16 bay array
or Mike K6MYC four bay switch
but only for a dipole
http://www.ham-radio.com/k6sti/height.htm
So if that's what you are asking about a single yagi like I had at 25M agl it exhibited had best gain at 2-5 degrees for eme if you cant elevate.
But it was a 2.5WL yagi with a narrow aperture.
calculator for other antenna up 1 wl
https://www.rac.ca/tca/Antenna_Height_Calculator.html
I think ground gain vs height applies to EME as much as anything.
Does it not
is this what you were asking?
as for stacked heights using ionospheric prop as the signal yardstick too many variables to be conclusive especially the aperture.
better to try 2M stacks on a known path and even then the ref aerial has to be at same height..
But if you want the good oil on 6M arrays talk with W6BYA two stacks
K6QXY four stacks and dual polarity
or W6JKV 16 bay array
or Mike K6MYC four bay switch
Tread your own path
Re: Ground gain - effect of antenna height...
G'day Wayne and Steve - thanks for replying.
I am fairly well across the scenarios as mentioned (stacking and common heights).
What I am interested in is the specific case I mentioned:- a 2M antenna @ 70m.
As you might have gathered, from previous moans by me, the QTH here is not optimal for VHF-up operation because of the 100-odd trees on a 3/4 acre block.
I am interested in EME @ 2M and while the trees preclude operation near the house, there is a clear view for moonrise at the back of the block from a 70m high cliff.
It is this setup that I want to get information about.
As described elsewhere, there is up to 6dB of extra directivity over the free-space pattern obtainable by ground reflections, dependent on the conductivity of the ground and, of course, the coincidence of the interference lobe with the natural beam lobe of the antenna. Literature I have read generally only describes heights of up to about 5wl. Additionally, there are vague references to ground gain falling off at higher antenna heights - but no explanation as to why. My own theory about this is that at extreme heights the reflection points can be quite a distance away (orders of kilometres) and so the reflection is less specular and more diffuse. While this means there is a reduction in the depth of the nulls in the interference pattern, it must follow that the peaks will not be as strong.
It is important for operation where the link budget is tight that some estimation of antenna gain is made - therefore it is important to get good estimate of ground gain to determine the viability of a particular setup.
The question is - what effect does the operation of a 2M @ 70m height have on the nominal 6dB ground gain ?
I am fairly well across the scenarios as mentioned (stacking and common heights).
What I am interested in is the specific case I mentioned:- a 2M antenna @ 70m.
As you might have gathered, from previous moans by me, the QTH here is not optimal for VHF-up operation because of the 100-odd trees on a 3/4 acre block.
I am interested in EME @ 2M and while the trees preclude operation near the house, there is a clear view for moonrise at the back of the block from a 70m high cliff.
It is this setup that I want to get information about.
As described elsewhere, there is up to 6dB of extra directivity over the free-space pattern obtainable by ground reflections, dependent on the conductivity of the ground and, of course, the coincidence of the interference lobe with the natural beam lobe of the antenna. Literature I have read generally only describes heights of up to about 5wl. Additionally, there are vague references to ground gain falling off at higher antenna heights - but no explanation as to why. My own theory about this is that at extreme heights the reflection points can be quite a distance away (orders of kilometres) and so the reflection is less specular and more diffuse. While this means there is a reduction in the depth of the nulls in the interference pattern, it must follow that the peaks will not be as strong.
It is important for operation where the link budget is tight that some estimation of antenna gain is made - therefore it is important to get good estimate of ground gain to determine the viability of a particular setup.
The question is - what effect does the operation of a 2M @ 70m height have on the nominal 6dB ground gain ?
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
Steve
Google is your friend.
An extensive study and documents have been put together by ON4KHG
http://www.on4khg.be/EME_Gr_Gain.html
in particular
http://www.vk3um.com/Ground%20Gain_DUBU ... ON4KHG.pdf
http://www.on4khg.be/Ground%20Gain%20Me ... 20v2-0.pdf
Hope that helps you
VK5APN
Google is your friend.
An extensive study and documents have been put together by ON4KHG
http://www.on4khg.be/EME_Gr_Gain.html
in particular
http://www.vk3um.com/Ground%20Gain_DUBU ... ON4KHG.pdf
http://www.on4khg.be/Ground%20Gain%20Me ... 20v2-0.pdf
Hope that helps you
VK5APN
Re: Ground gain - effect of antenna height...
I have done some actual measurements on both 6 metres and 2 metres, On 6 Metres I measured around 5.5 db improvement at a take off angle of around 8 degrees with the antenna at a height of 8 metres. This was done using W7GJ off the moon with my 15 element yagi. This agreed fairly well with the EZNEC model. All extra gain was lost above about 15 degrees. It was then time to start tilting the antenna. I rana WSJT test with a station on the Isle of Mann where the moon was at around 8 degrees elevation at both ends. We certainly had a peak there but signals peaked at -27, but not quite long enough for a contact.
On 2 metres using the setting sun with a single 19 element DL6WU at a height of 12 metres I measured peaks at 3,9,15 and 21 degrees with quite deep nulls in between. This also agrees fairly well with the model. The second peak waas actually slightly better than the first in practice. The immediate foreground was a fairly flat grassy paddock.
The angle of radiation is an inverse function of the height of the centre of the antenna capture area above effective ground. Stacking does not lower the angle of radiation. If you want to compare antennas, you MUST have them at the same height.
One of the reasons why higher antennas work better is because of the lower angle of radiation and this generally corresponds with the low angle at which the incoming signal arrives. The station on the cliff top should get the whole 6 db plus something extra because of a greaater amount of incoming signal.
Ens of lesson.
David
On 2 metres using the setting sun with a single 19 element DL6WU at a height of 12 metres I measured peaks at 3,9,15 and 21 degrees with quite deep nulls in between. This also agrees fairly well with the model. The second peak waas actually slightly better than the first in practice. The immediate foreground was a fairly flat grassy paddock.
The angle of radiation is an inverse function of the height of the centre of the antenna capture area above effective ground. Stacking does not lower the angle of radiation. If you want to compare antennas, you MUST have them at the same height.
One of the reasons why higher antennas work better is because of the lower angle of radiation and this generally corresponds with the low angle at which the incoming signal arrives. The station on the cliff top should get the whole 6 db plus something extra because of a greaater amount of incoming signal.
Ens of lesson.
David
Re: Ground gain - effect of antenna height...
G'day Wayne,
and again...
I guess there is no answer to my question unless I can google an EME-er with a 70m tower...
Yes - I know - I had already read the ON4KHG documents...VK5APN wrote:Google is your friend.
This a quote from that document...VK5APN wrote:http://www.on4khg.be/EME_Gr_Gain.html
...ON4KHG wrote:The antenna must not be too high up in the air. This, for two reasons, the first is that if it is too high, the ground gain lobes will be narrow, even too narrow to complete a JT65 QSO over a single lobe (with my antenna 17m agl, I can only make one QSO over one lobe, i.e. around 6 min). The second reason is that the higher the antenna, the furthest from the antenna the building of the ground gain lobes and hence, the higher the likelihood the ground not to be flat.
and again...
Soldiering on I downloaded the simulator file (http://www.on4khg.be/Ground%20Gain%20Ge ... 20File.zip), but found when loading into OpenOffice it locked up my computer requiring a reboot (Task Manager couldn't terminate it) - never had to reboot before for anything (we can argue whether this is the fault of the file or OO...). In any case it only theoretical and doesn't take into account the real effects of distant reflection points. It would only show very fine interference lobes - but as I have mentioned previously - I already know the theory.ON4KHG wrote:One outcome of this analysis is the conclusion that placing an antenna as high as possible up in the
air is not always an absolute requirement. Indeed, the higher an antenna, the further away from it
the Ground Gain lobes will build and, at some sites, the higher the likelihood that the ground is
cluttered with vegetation and/or buildings (attenuating the magnitude of the reflected wave). In this
case, is it worth losing 6 dB of Ground Gain by winning a few (tens) kilometres of short-range radio
horizon ? All is a matter of trade-off..
I guess there is no answer to my question unless I can google an EME-er with a 70m tower...
Last edited by VK2XV on Tue Dec 23, 2014 6:53 am, edited 1 time in total.
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
- VK3ZAZ
- Forum Diehard
- Posts: 785
- Joined: Sat Dec 18, 2010 1:46 pm
- Location: Hamilton Victoria Australia
Re: Ground gain - effect of antenna height...
Height is everything.
IMHO
As for 70 metres no experience except for work QTH which runs FM 3 el stacked yagis half horizontal zero and half with down tilt to cover near region.
EME
Most eme people I have seen have arrays close to the ground
including Mike K6MYC in Fresno the M2 Guru and Jimmy W6JKV the eme expert.
If u r going to 70M with LDF5/50 or 21/4 inch u r obviously filthy rich so should be able to research the knowledge u need.
we are but humble amateurs.
IMHO
As for 70 metres no experience except for work QTH which runs FM 3 el stacked yagis half horizontal zero and half with down tilt to cover near region.
EME
Most eme people I have seen have arrays close to the ground
including Mike K6MYC in Fresno the M2 Guru and Jimmy W6JKV the eme expert.
If u r going to 70M with LDF5/50 or 21/4 inch u r obviously filthy rich so should be able to research the knowledge u need.
we are but humble amateurs.
Last edited by VK3ZAZ on Tue Dec 23, 2014 6:20 am, edited 9 times in total.
Tread your own path
Re: Ground gain - effect of antenna height...
G'day David,VK3AUU wrote:I have done some actual measurements on both 6 metres and 2 metres...
Thanks.
Yes - I understand all this - but I am after an answer to a 70m high 2M antenna.
Could you repeat the experiments after cranking up your tower to 70m ?
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
- VK3ZAZ
- Forum Diehard
- Posts: 785
- Joined: Sat Dec 18, 2010 1:46 pm
- Location: Hamilton Victoria Australia
Re: Ground gain - effect of antenna height...
75 feet
50 watts +47dbm
2014-12-22 04:38 VK3ZAZ 144.490504 SNR +0 0 QF12ag +47 50.119 VK2KRR QF34mr 524 km
and 1 watt +30 dbm
2014-12-22 04:42 VK3ZAZ 144.490505 SNR -16 0 QF12ag +30 1.000 VK2KRR QF34mr 524 km
17 db drop in power produced 16 db drop in snr
Free space for sure I imagine going from 25M to 75M would prove nothing except cost me about $500 in cable and increase attenuation even then.
dropping it down to 10 and 5m would be terminal
Correct me if I am wrong?
50 watts +47dbm
2014-12-22 04:38 VK3ZAZ 144.490504 SNR +0 0 QF12ag +47 50.119 VK2KRR QF34mr 524 km
and 1 watt +30 dbm
2014-12-22 04:42 VK3ZAZ 144.490505 SNR -16 0 QF12ag +30 1.000 VK2KRR QF34mr 524 km
17 db drop in power produced 16 db drop in snr
Free space for sure I imagine going from 25M to 75M would prove nothing except cost me about $500 in cable and increase attenuation even then.
dropping it down to 10 and 5m would be terminal
Correct me if I am wrong?
Tread your own path
Re: Ground gain - effect of antenna height...
G'day Steve - can't answer this as I struggle to see how this is related to the topic...VK3ZAZ wrote:Correct me if I am wrong?
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
G'day Steve - as it is on a 70m cliff why do I need to be rich...VK3ZAZ wrote:If u r going to 70M with LDF5/50 or 21/4 inch u r obviously filthy rich so should be able to research the knowledge u need.
we are but humble amateurs.
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
Found this interesting exchange of opinions and practical experience...
http://www.dxmaps.com/discuss/polarization.html
...it's about polarisation - but feeds into ground gain effects...
http://www.dxmaps.com/discuss/polarization.html
...it's about polarisation - but feeds into ground gain effects...
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
An article I wrote for NZART Break-In magazine in 2010 combines theory and practical results of 2m antennas at various heights ... including at 50m above the ocean.
http://www.qsl.net/z/zl1rs//images/groundgain.pdf (1.3MB)
While specific measurements of signal level vs. moon elevation angle were not done, the theory and the practice seemed to generally follow each other (e.g. a mass of sharp 'interference' lobes at the 50m ASL site). A similar effect was noticed while operating 2m EME from KH8 earlier this year from a site well elevated over the ocean (from memory, 60mH). No doubt there will be differences at 70m above 'ground' at your site, and there is only one way to find out ...
73,
http://www.qsl.net/z/zl1rs//images/groundgain.pdf (1.3MB)
While specific measurements of signal level vs. moon elevation angle were not done, the theory and the practice seemed to generally follow each other (e.g. a mass of sharp 'interference' lobes at the 50m ASL site). A similar effect was noticed while operating 2m EME from KH8 earlier this year from a site well elevated over the ocean (from memory, 60mH). No doubt there will be differences at 70m above 'ground' at your site, and there is only one way to find out ...
73,
Bob, ZL1RS in the Bay of Islands at RF64vs
Re: Ground gain - effect of antenna height...
Hi all....
Yes it is an interesting question Steve.
a question, you say you have a 70m cliff , how near is it.....and are we talking the side of mountain situation were it just continues on at 70m below your QTH, maybe some low rolling hills ? I would think all these issues would mess up ground gain.......also...is it just rock...or is there plenty of bushes, trees and the like...would not think vegetation will play nice with any ground reflections
Yes it is an interesting question Steve.
a question, you say you have a 70m cliff , how near is it.....and are we talking the side of mountain situation were it just continues on at 70m below your QTH, maybe some low rolling hills ? I would think all these issues would mess up ground gain.......also...is it just rock...or is there plenty of bushes, trees and the like...would not think vegetation will play nice with any ground reflections
Re: Ground gain - effect of antenna height...
Thanks Bob - most interesting. I wonder - can you remember if the observed effect at Cape Reinga went down to the 2 deg mark as shown on the theoretical graph ?ZL1RS wrote:An article I wrote for NZART Break-In magazine in 2010 combines theory and practical results of 2m antennas at various heights ... including at 50m above the ocean.
Another reference I have found for high antenna heights is this...
http://www.sydneyobservatory.com.au/201 ... ron-ekers/
...where they used a "Cliff Interferometer".
But as you say - over ground ????
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
G'day John,
As mentioned in previous posts it is at the back of the block here (3/4 acre) - so antenna will be at the edge. The edge drops away almost vertically (60 degree slope) 70m down to farmland with almost no trees for about 3km.VK2FAK wrote:a question, you say you have a 70m cliff , how near is it.....
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
Re: Ground gain - effect of antenna height...
According to the times logged, the 2m EME stations were worked at the Cape with the moon at 12 degrees ... 11 degrees ... 8 ... 5.6 ... 4.6 ... 3.3 ... and 1.1 degrees. I normally log the end time of the contact, so the moon would be a degree or so higher 4 minutes earlier at the beginning. I also remember that during one or more contacts the moon 'went through a null' and the contact was completed on the 'upswing' of the next peak.VK2XV wrote: ... I wonder - can you remember if the observed effect at Cape Reinga went down to the 2 deg mark as shown on the theoretical graph ?
... and as I said "there is only one way to find out" ...VK2XV wrote: ...But as you say - over ground ????
Portable EME is a lot of fun, take the Nike advert hint and 'just do it'. If you have not been on 2m EME, with a little "advertising" prior to the event you will have plenty of takers for a "new initial" ... and even more if the site is a "new square".
73,
Bob, ZL1RS in the Bay of Islands at RF64vs
Re: Ground gain - effect of antenna height...
Steve
My QTH is on a 70m asl terrace about 1km from ocean. The antenna is about 10m high at about 20m from the edge of the terrace which drops away at about 45deg. I get great results over the sea on terrestrial and EME. On EME frequently decodes at down to -1deg.
Your picture looks pretty good to me, maybe a bigger antenna would help...
Bob ZL3TY
My QTH is on a 70m asl terrace about 1km from ocean. The antenna is about 10m high at about 20m from the edge of the terrace which drops away at about 45deg. I get great results over the sea on terrestrial and EME. On EME frequently decodes at down to -1deg.
Your picture looks pretty good to me, maybe a bigger antenna would help...
Bob ZL3TY
Bob
Greymouth RE57om
Greymouth RE57om
Re: Ground gain - effect of antenna height...
Hi All,
Thanks for all the responses. I think I have an answer - there is no theoretical answer.
As Bob says - I just have to do it.
As a final comment I reckon that for 70m height on 2M the angle between peaks is (from RA interferometry) is ~0.8 degrees. Therefore the first peak is ~0.4 above the horizon (first null is at horizon). The second peak is at ~1.2 degrees and so on in ~0.8 increments. The higher elevated peaks will come via ground reflections closer in, while the lower elevated peaks will come via reflections further out. My feeling about this is that the reflections further out over earth will be more diffuse and ground gain will drop (ground only comes from coherent constructive interference) for the lower elevated lobes. I would not be surprised that over earth the lowest couple of lobes (say 1st, 2nd, 3rd..) will actually have lower ground gain than for lobes a little higher (say 4th, 5th 6th). That is, I would say there is a peak in ground gain which occurs not in the first lobe but a lobe further up - followed by a decline again in higher elevated lobes.
Please note: the above comment is for 2M at a height of 70m.
Thanks & 73
Thanks for all the responses. I think I have an answer - there is no theoretical answer.
As Bob says - I just have to do it.
As a final comment I reckon that for 70m height on 2M the angle between peaks is (from RA interferometry) is ~0.8 degrees. Therefore the first peak is ~0.4 above the horizon (first null is at horizon). The second peak is at ~1.2 degrees and so on in ~0.8 increments. The higher elevated peaks will come via ground reflections closer in, while the lower elevated peaks will come via reflections further out. My feeling about this is that the reflections further out over earth will be more diffuse and ground gain will drop (ground only comes from coherent constructive interference) for the lower elevated lobes. I would not be surprised that over earth the lowest couple of lobes (say 1st, 2nd, 3rd..) will actually have lower ground gain than for lobes a little higher (say 4th, 5th 6th). That is, I would say there is a peak in ground gain which occurs not in the first lobe but a lobe further up - followed by a decline again in higher elevated lobes.
Please note: the above comment is for 2M at a height of 70m.
Thanks & 73
Steve VK2XV/VK2ZTO
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...
North Richmond, NSW QF56ik
http://www.joataman.net
You are truly knowledgeable when you know what you don't know...