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A new Technician Class Operator has limitations on putting a 10m antenna anyplace but as a dipole over a paved surface. I do not have any practical experience there and googled around and found nothing specific to this. I'm ready to say no real problem but would like other opinions.
I only found on-line that a lossy earth on lower bands has a negative effect. The op does not have a tuner at the moment and by practical application a 10m center fed at .5wl should provide approx 72ohm and 1.4:1 SWR. The radiation pattern appears to be exclusively lobes at a 30degree elevation. Would the asphalt have a great impact here? Anyone?
73, Andy
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Andrew, If there is only one location for your dipole, then why do all this fretting? Get on the air and make contacts! Depending on your communication mode, you can make contacts with minimal antennas. If you have your rig and PC running FT8, you can track if the band is open by looking at decodes on ten meter FT8 frequency. Good luck... 73, Bill K2TNO On Mon, Oct 7, 2024, 8:36 AM Andrew Harman via groups.io <Nexus9d9= gmail.com@groups.io> wrote: A new Technician Class Operator has limitations on putting a 10m antenna
anyplace but as a dipole over a paved surface. I do not have any
practical experience there and googled around and found nothing specific to
this. I'm ready to say no real problem but would like other opinions.
I only found on-line that a lossy earth on lower bands has a negative
effect. The op does not have a tuner at the moment and by practical
application a 10m center fed at .5wl should provide approx 72ohm and 1.4:1
SWR. The radiation pattern appears to be exclusively lobes at a 30degree
elevation. Would the asphalt have a great impact here? Anyone?
73, Andy
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It's not going to have much of an effect that is different than being over soil. The effect would be slight enough that you'd never notice it. Someone spent quite a bit of time preparing this article. It is about a 40 meter dipole, but it gives you the idea of the effect of height. I've also attached a drawing of impedance vs. height of a dipole. https://www.qsl.net/aa3rl/ant2.htmlZack W9SZ < https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free.www.avast.com < https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Mon, Oct 7, 2024 at 7:36 AM Andrew Harman via groups.io <Nexus9d9= gmail.com@groups.io> wrote: A new Technician Class Operator has limitations on putting a 10m antenna
anyplace but as a dipole over a paved surface. I do not have any
practical experience there and googled around and found nothing specific to
this. I'm ready to say no real problem but would like other opinions.
I only found on-line that a lossy earth on lower bands has a negative
effect. The op does not have a tuner at the moment and by practical
application a 10m center fed at .5wl should provide approx 72ohm and 1.4:1
SWR. The radiation pattern appears to be exclusively lobes at a 30degree
elevation. Would the asphalt have a great impact here? Anyone?
73, Andy
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10m band is not NVIS so high emission angles wastes power into deep space. So, the correct heigh for a dipole in 10m band is K*0,5L k>=1. As higher k value lower and narrowed beam so larger hop distance.
Another matter is the impedance but in the worst case SWR is always below 2:1 and usually better than 1.5:1.
The ground environment is as is and nothing to do.
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Andy, The Asphalt should have little to no effect on the antenna.
Tell your friend to get on the air and have fun.
73 Greg WA1JXR
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I agree. I've been a ham now for over 65 years. When I was a kid we just put up a dipole and got on the air. After that, we realized what a marginal or bad antenna was and worked on improving it. But, we got on the air. My first V dipole for 80 meters was a disaster but I made contacts.
My point is that sometimes you have to start with a bad antenna before you realize what a good antenna is. Experience gives you something to compare improvement with. Today, with all the information on the internet and great inexpensive test equipment, new hams tend to fall into what some call "analysis paralysis". So. my suggestion is to pick a wire antenna that fits the space you have and put it as high as practical. Get some experience with how it works and go forward from there. Antenna experimentation is one of the popular areas of ham radio.
73 and good DX,
Joe, K1ike
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On 10/7/2024 10:22 AM, wa1jxr via groups.io wrote: Andy, The Asphalt should have little to no effect on the antenna.
Tell your friend to get on the air and have fun.
73 Greg WA1JXR
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Thank you all for your replies. My thoughts were that it shouldn't have much impact BUT this is not MY $ or rig. I couldn't find anything saying not to do it but wanted to just throw it out there in case I was missing something.
My intention is to get her on the air quickly with a KISS antenna, even if not the most ideal before she loses interest all together. I appreciate the feedback.
/a
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There is material online about RF dielectric properties of asphalt, but my
reading of these is that it's just a ground material for ham radio
purposes. Grounds vary due to moisture (eg,water table) mainly. I'd say
don't worry about it and don't bother to try testing it.
Chuck K4TZO
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On Mon, Oct 7, 2024 at 8:36 AM Andrew Harman <Nexus9d9@...> wrote: A new Technician Class Operator has limitations on putting a 10m antenna
anyplace but as a dipole over a paved surface. I do not have any
practical experience there and googled around and found nothing specific to
this. I'm ready to say no real problem but would like other opinions.
I only found on-line that a lossy earth on lower bands has a negative
effect. The op does not have a tuner at the moment and by practical
application a 10m center fed at .5wl should provide approx 72ohm and 1.4:1
SWR. The radiation pattern appears to be exclusively lobes at a 30degree
elevation. Would the asphalt have a great impact here? Anyone?
73, Andy
--
Chuck Cole K4TZO
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On Mon, Oct 7, 2024 at 02:00 PM, Chuck Cole wrote:
Grounds vary due to moisture (eg,water table) mainly.
Apparently so does asphalt: "The moisture content of the asphalt mixture in asphalt pavement undergoes dynamic changes, affecting the pavement’s relative humidity (RH). This alteration in RH has a direct impact on the dielectric properties of the asphalt mixture, thus influencing the accuracy of GPR road detection. Therefore, it is essential to quantify the relationship between RH and the dielectric properties of asphalt mixtures." "Study on Dielectric Properties of Asphalt Mixtures Considering the Effects of Relative Humidity" Journal of Materials in Civil Engineering, Vol. 36, No. 8 If you have no choice, the decision has been made for you, proceed! 73, Don N2VGU
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Why bother with decodes? Just tune to the FT8 freq of interest and observe the signal strength of the mess. Dave - WØLEV On Mon, Oct 7, 2024 at 12:51 PM William Schrader via groups.io <wtschrader= gmail.com@groups.io> wrote: Andrew,
If there is only one location for your dipole, then why do all this
fretting? Get on the air and make contacts!
Depending on your communication mode, you can make contacts with minimal
antennas. If you have your rig and PC running FT8, you can track if the
band is open by looking at decodes on ten meter FT8 frequency.
Good luck...
73,
Bill K2TNO
On Mon, Oct 7, 2024, 8:36 AM Andrew Harman via groups.io <Nexus9d9=
gmail.com@groups.io> wrote:
A new Technician Class Operator has limitations on putting a 10m antenna
anyplace but as a dipole over a paved surface. I do not have any
practical experience there and googled around and found nothing specific to
this. I'm ready to say no real problem but would like other opinions.
I only found on-line that a lossy earth on lower bands has a negative
effect. The op does not have a tuner at the moment and by practical
application a 10m center fed at .5wl should provide approx 72ohm and 1.4:1
SWR. The radiation pattern appears to be exclusively lobes at a 30degree
elevation. Would the asphalt have a great impact here? Anyone?
73, Andy
-- *Dave - WØLEV* -- Dave - WØLEV
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so does just about everything..
But as a practical matter, the asphalt (and the underlying gravel/sand, and then soil) is WAY less than a skin depth at HF. At 1 MHz, you're looking at meters, unless the surface is highly conductive (like seawater conductive 3-4 S/m). So the effect you see is a combination of the asphalt and everything under it.
Just running some numbers for an epsilon of 10, and sigma of 0.005, I get 3.3 or 7.5 meters (depending on who's equation you use). go up to 50 mS/m (0.05 S/m) and it's 2 meters. 3.8 dB/meter attenuation
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-----Original Message----- From: <nanovna-users@groups.io> Sent: Oct 7, 2024 1:47 PM To: <nanovna-users@groups.io> Subject: Re: [nanovna-users] Effect of asphalt under a 10m 1/2w center fed dipole at 1/2 wave elevation On Mon, Oct 7, 2024 at 02:00 PM, Chuck Cole wrote:
Grounds vary due to moisture (eg,water table) mainly.
Apparently so does asphalt: "The moisture content of the asphalt mixture in asphalt pavement undergoes dynamic changes, affecting the pavement’s relative humidity (RH). This alteration in RH has a direct impact on the dielectric properties of the asphalt mixture, thus influencing the accuracy of GPR road detection. Therefore, it is essential to quantify the relationship between RH and the dielectric properties of asphalt mixtures." "Study on Dielectric Properties of Asphalt Mixtures Considering the Effects of Relative Humidity" Journal of Materials in Civil Engineering, Vol. 36, No. 8 If you have no choice, the decision has been made for you, proceed! 73, Don N2VGU
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All pretty much a moot point considering we're talking about a dipole for 10M which will likely be more than a half wave above ground, probably up to a full wave above ground which eliminates ground conductivity effects on the radiation of the antenna.
Near by objects will have a more significant impact than the material on or in the ground under a dipole at 10 meters.
Even so, it'll be fine. Especially since the op cannot change the conductivity of the ground under the antenna anyway.
Regards
Colin VA6GG
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On 2024-10-07 4:05 p.m., Jim Lux wrote: so does just about everything..
But as a practical matter, the asphalt (and the underlying gravel/sand, and then soil) is WAY less than a skin depth at HF. At 1 MHz, you're looking at meters, unless the surface is highly conductive (like seawater conductive 3-4 S/m). So the effect you see is a combination of the asphalt and everything under it.
Just running some numbers for an epsilon of 10, and sigma of 0.005, I get 3.3 or 7.5 meters (depending on who's equation you use). go up to 50 mS/m (0.05 S/m) and it's 2 meters. 3.8 dB/meter attenuation
-----Original Message-----
From: <nanovna-users@groups.io>
Sent: Oct 7, 2024 1:47 PM
To: <nanovna-users@groups.io>
Subject: Re: [nanovna-users] Effect of asphalt under a 10m 1/2w center fed dipole at 1/2 wave elevation
On Mon, Oct 7, 2024 at 02:00 PM, Chuck Cole wrote:
Grounds vary due to moisture (eg,water table) mainly.
Apparently so does asphalt:
"The moisture content of the asphalt mixture in asphalt pavement undergoes dynamic changes, affecting the pavement’s relative humidity (RH). This alteration in RH has a direct impact on the dielectric properties of the asphalt mixture, thus influencing the accuracy of GPR road detection. Therefore, it is essential to quantify the relationship between RH and the dielectric properties of asphalt mixtures."
"Study on Dielectric Properties of Asphalt Mixtures Considering the Effects of Relative Humidity" Journal of Materials in Civil Engineering, Vol. 36, No. 8
If you have no choice, the decision has been made for you, proceed!
73, Don N2VGU
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Exactly. I remember someone said in an article "While you've been worried
about having exactly +7 dBm of LO to a mixer, someone down the street has
20 new grids worked with an unknown mixer level to a mixer with unknown
specs." ..and that is why ham radio is going to the dogs. Not many seem interested in the technical side of the hobby any more. they just want multi band CB, buy a black box and exchange numbers and collect squares. 73 Jeff G8HUL
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On Mon, Oct 7, 2024 at 06:19 PM, Colin McDonald wrote:
All pretty much a moot point considering we're talking about a dipole for 10M
which will likely be more than a half wave above ground, probably up to a full
wave above ground which eliminates ground conductivity effects on the
radiation of the antenna.
Near by objects will have a more significant impact than the material on or in
the ground under a dipole at 10 meters.
Even so, it'll be fine. Especially since the op cannot change the conductivity
of the ground under the antenna anyway.
That's understood. But this will be @ .5wl elevation to center, higher is not possible. I wasn't sure if the asphalt would compromise it in some way, and although it might on lower bands, 10m should be less susceptible. The understanding was that the antenna would be cut for 28.4 to achieve best SWR in the phone segment, to include FT8 was not an objective but maybe should be discussed with her. Good point "if" bandwidth were there using #12awg wire and without a tuner. (I have to work on her to buy a tuner when she has some extra $$) I think at this point the original question is somewhat resolved over just saying throw it up and see. Regards, Andy
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Any wire will do. Band width on 10M with a wire dipole antenna at a half wave above ground should give you several hundred KHz of band width with a 2 to 1 or less SWR.
If there is no tuner, even a 3 to 1 SWR isn't a big deal for FT8. You should see much less than that at the FT8 frequencies if you tune the dipole for 28.4MHZ.
Make a coaxial balun near the feed point to reduce common mode current back down the coax and the band width should be sufficient between 28 and 28.7MHZ.
Might be a little harder to extend that out to the FM repeater frequencies which are absolutely hopping right now.
But with a basic tuner, that is doable too.
Mono band dipoles are easy and exhibit good wide band width especially on 10M.
Regards
Colin, VA6GG
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On 2024-10-08 6:14 a.m., Andrew Harman wrote: On Mon, Oct 7, 2024 at 06:19 PM, Colin McDonald wrote:
All pretty much a moot point considering we're talking about a dipole for 10M
which will likely be more than a half wave above ground, probably up to a full
wave above ground which eliminates ground conductivity effects on the
radiation of the antenna.
Near by objects will have a more significant impact than the material on or in
the ground under a dipole at 10 meters.
Even so, it'll be fine. Especially since the op cannot change the conductivity
of the ground under the antenna anyway.
That's understood. But this will be @ .5wl elevation to center, higher is not possible. I wasn't sure if the asphalt would compromise it in some way, and although it might on lower bands, 10m should be less susceptible. The understanding was that the antenna would be cut for 28.4 to achieve best SWR in the phone segment, to include FT8 was not an objective but maybe should be discussed with her. Good point "if" bandwidth were there using #12awg wire and without a tuner. (I have to work on her to buy a tuner when she has some extra $$) I think at this point the original question is somewhat resolved over just saying throw it up and see.
Regards, Andy
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I use 10 ga RW-90 power cable for wire ants, sloper's, etc. With 10 ga, it will be plenty strong enough.....and also have loads of BW.
BW increases a bunch when using bigger ga wire.
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It's definitely possible to over think this as few antenna installations are in the perfect world scenarios modelling software works with.
I experimented with a 10metre band antenna (tuned to 28.1 MHz ) that was a horizontal 5.3m wire horizontal out of a house window at 4m over a large concrete patio, built on cement, gravel, hardcore and sand.
(For convenience the wire is end fed and runs South to North from feedpoint but the pattern of a half wave will be much the same wherever it's fed) .
I'm in a valley and large 10 - 15m trees totally overhang the antenna where its not obstructed by the house. Hopeless right ?
Using a WSPR beacon, QRP power and good 10m conditions (Image is last 5 weeks, but terrible the last few days) and from the UK it reaches Europe, W USA, Asia, S Africa, Arctic, Antarctic and Australia with lots in between
Moral Just try it . . .
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Now, the idea of 10AWG IS something I already considered. Strong as hell and lots of BW. Although there were no considerations for FT8 at all, if she wants to go that route later the BW may be adequate. (I've suggested her next major purchase be a tuner.) So the 10awg, that's going to be the way we go thanks. Stranded, black, THHN, I'll initially cut it 5% shorter for capacitance (aka velocity) factor - gtg.
73 /Andy
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On Wed, Oct 9, 2024 at 01:11 PM, Andrew Harman wrote:
Now, the idea of 10AWG IS something I already considered. Strong as hell and
lots of BW. Although there were no considerations for FT8 at all, if she wants
to go that route later the BW may be adequate. (I've suggested her next major
purchase be a tuner.) So the 10awg, that's going to be the way we go thanks.
Stranded, black, THHN, I'll initially cut it 5% shorter for capacitance (aka
velocity) factor - gtg.
73 /Andy
## I cut it initially on the longer side. It's easier to trim it..... vs mucking about trying to add wire at each end.
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Juan Pablo EA4CIV
Chuck Cole
Donald S Brant Jr
Bruce Akhurst
