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fireflier
Joined: 24 Jun 2012
Posts: 58
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 Posted: Wed Jan 22, 2014 2:55 am Post subject: Tuning dipole aerial |
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Hi
I'm looking for some help with regards tuning in my dipole aerial as i seem to have a slight problem.
I Have everything connected up to my swr meter and got the following readings at the start
118.000 1.2
127.350 2.7
136.975 3.1
I have been trimming the copper tape of the dipole and the lower frequency swr reading has increased and the mid frequency has decreased however there has been no real effect on the hight frequency as this is still at a swr of 3.
I now have the copper tape legs cut to the lengths that were specified in my manual 480mm. I dont really want to cut much more off these as its not having any effect on the top frequency swr value therefore i feel there is an underlying issue that i need to sort out first?
With the 2 legs cut to 480mm i have the following swr readings
118.000 2.0
127.350 2.1
136.985 3.0
I would appreciated any help and advice that people have to offer to try and recrify this problem for me. Im now not sure how to proceed to sort this problem out.
I look forward to your replies.
Kind regards
Donald
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tim2542(at)sbcglobal.net
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| Posted: Wed Jan 22, 2014 7:26 am Post subject: Tuning dipole aerial |
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Plot it with more data points to find its center freq.
If you think of it in terms of the "higher the frequency the shorter the element", it was resonant at 118 MHz, and after cutting (how much?) it's moved higher.
Is you meter designed for VHF?
Also, nearby objects including you can affect it. Try to place it vertical and away from other objects. Both elements should be equal length, and you should measure from the crotch of the separated coax.
Tim
| Quote: | On Jan 22, 2014, at 2:55 AM, "fireflier" <fireflier(at)btinternet.com> wrote:
Hi
I'm looking for some help with regards tuning in my dipole aerial as i seem to have a slight problem.
I Have everything connected up to my swr meter and got the following readings at the start
118.000 1.2
127.350 2.7
136.975 3.1
I have been trimming the copper tape of the dipole and the lower frequency swr reading has increased and the mid frequency has decreased however there has been no real effect on the hight frequency as this is still at a swr of 3.
I now have the copper tape legs cut to the lengths that were specified in my manual 480mm. I dont really want to cut much more off these as its not having any effect on the top frequency swr value therefore i feel there is an underlying issue that i need to sort out first?
With the 2 legs cut to 480mm i have the following swr readings
118.000 2.0
127.350 2.1
136.985 3.0
I would appreciated any help and advice that people have to offer to try and recrify this problem for me. Im now not sure how to proceed to sort this problem out.
I look forward to your replies.
Kind regards
Donald
--------
Fireflier
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=417402#417402
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rv10pro(at)gmail.com
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| Posted: Wed Jan 22, 2014 12:09 pm Post subject: Tuning dipole aerial |
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Donald, you did not mention if the antenna was installed on Carbon Fibre, Fiberglass or Aluminum skin. Aren't the copper tapes used to establish an effective groundplane? Is it a concealed antenna? is it homemade or manufactured? Tesla's are having problems with quality FM reception due to dipole, concealed. Some owners thought the side mirrors were the concealed antenna, Turns out the location was selected for cosmetics not function along the rear window deck and use a two frequency combiner. Are you assuming the coax connections were both done on the shielding correctly?
John
On Wed, Jan 22, 2014 at 7:26 AM, Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)> wrote:
[quote]--> Avionics-List message posted by: Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)>
Plot it with more data points to find its center freq.
If you think of it in terms of the "higher the frequency the shorter the element", it was resonant at 118 MHz, and after cutting (how much?) it's moved higher.
Is you meter designed for VHF?
Also, nearby objects including you can affect it. Try to place it vertical and away from other objects. Both elements should be equal length, and you should measure from the crotch of the separated coax.
Tim
> On Jan 22, 2014, at 2:55 AM, "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)> wrote:
>
> --> Avionics-List message posted by: "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)>
>
> Hi
> I'm looking for some help with regards tuning in my dipole aerial as i seem to have a slight problem.
>
> I Have everything connected up to my swr meter and got the following readings at the start
>
> 118.000 1.2
> 127.350 2.7
> 136.975 3.1
>
> I have been trimming the copper tape of the dipole and the lower frequency swr reading has increased and the mid frequency has decreased however there has been no real effect on the hight frequency as this is still at a swr of 3.
>
> I now have the copper tape legs cut to the lengths that were specified in my manual 480mm. I dont really want to cut much more off these as its not having any effect on the top frequency swr value therefore i feel there is an underlying issue that i need to sort out first?
>
> With the 2 legs cut to 480mm i have the following swr readings
>
> 118.000 2.0
> 127.350 2.1
> 136.985 3.0
>
> I would appreciated any help and advice that people have to offer to try and recrify this problem for me. Im now not sure how to proceed to sort this problem out.
>
> I look forward to your replies.
>
> Kind regards
> Donald
>
> --------
> Fireflier
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=417402#417402
>
>
>
>
>
>
>
>
>
>
===========
t" target="_blank">http://www.matronics.com/Navigator?Avionics-List
===========
http://forums.matronics.com
===========
le, List Admin.
="_blank">http://www.matronics.com/contribution
===========
[b]
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tim2542(at)sbcglobal.net
Guest
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| Posted: Wed Jan 22, 2014 12:59 pm Post subject: Tuning dipole aerial |
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Copper foil dipoles are pretty common in glass airplanes. Jim Weir use to sell a kit and book, I don't think he's shipping them anymore but I'm assuming Donald's working from that recipe. He did mention it is a dipole.
Tim
On Jan 22, 2014, at 12:08 PM, John Cox <rv10pro(at)gmail.com (rv10pro(at)gmail.com)> wrote:
[quote]Donald, you did not mention if the antenna was installed on Carbon Fibre, Fiberglass or Aluminum skin. Aren't the copper tapes used to establish an effective groundplane? Is it a concealed antenna? is it homemade or manufactured? Tesla's are having problems with quality FM reception due to dipole, concealed. Some owners thought the side mirrors were the concealed antenna, Turns out the location was selected for cosmetics not function along the rear window deck and use a two frequency combiner. Are you assuming the coax connections were both done on the shielding correctly?
John
On Wed, Jan 22, 2014 at 7:26 AM, Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)> wrote:
| Quote: | --> Avionics-List message posted by: Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)>
Plot it with more data points to find its center freq.
If you think of it in terms of the "higher the frequency the shorter the element", it was resonant at 118 MHz, and after cutting (how much?) it's moved higher.
Is you meter designed for VHF?
Also, nearby objects including you can affect it. Try to place it vertical and away from other objects. Both elements should be equal length, and you should measure from the crotch of the separated coax.
Tim
> On Jan 22, 2014, at 2:55 AM, "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)> wrote:
>
> --> Avionics-List message posted by: "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)>
>
> Hi
> I'm looking for some help with regards tuning in my dipole aerial as i seem to have a slight problem.
>
> I Have everything connected up to my swr meter and got the following readings at the start
>
> 118.000 1.2
> 127.350 2.7
> 136.975 3.1
>
> I have been trimming the copper tape of the dipole and the lower frequency swr reading has increased and the mid frequency has decreased however there has been no real effect on the hight frequency as this is still at a swr of 3.
>
> I now have the copper tape legs cut to the lengths that were specified in my manual 480mm. I dont really want to cut much more off these as its not having any effect on the top frequency swr value therefore i feel there is an underlying issue that i need to sort out first?
>
> With the 2 legs cut to 480mm i have the following swr readings
>
> 118.000 2.0
> 127.350 2.1
> 136.985 3.0
>
> I would appreciated any help and advice that people have to offer to try and recrify this problem for me. Im now not sure how to proceed to sort this problem out.
>
> I look forward to your replies.
>
> Kind regards
> Donald
>
> --------
> Fireflier
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=417402#417402
>
>
>
>
>
>
>
>
>
>
===========
t" target="_blank">http://www.matronics.com/Navigator?Avionics-List
===========
http://forums.matronics.com
===========
le, List Admin.
="_blank">http://www.matronics.com/contribution
===========
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rv10pro(at)gmail.com
Guest
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| Posted: Wed Jan 22, 2014 2:07 pm Post subject: Tuning dipole aerial |
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Dave hasn't answered up, but the math does not look right. Assuming a concealed dipole, the starting measurement for a 1/4 wave in the mid band of the frequencies desired might have been 564.1 mm or 22.2". Trimming it to 488 moves that SWR towards the higher end frequency giving rise to the loss of 118mHz for SWR = 1.2 and then heading south to the more undesirable 2.0. Just a perspective. Maybe he is going 1/8 wave, no ground plane and properly matched BALUN for the coax to the transceiver??
John
On Wed, Jan 22, 2014 at 12:58 PM, Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)> wrote:
[quote]Copper foil dipoles are pretty common in glass airplanes. Jim Weir use to sell a kit and book, I don't think he's shipping them anymore but I'm assuming Donald's working from that recipe. He did mention it is a dipole.
Tim
On Jan 22, 2014, at 12:08 PM, John Cox <rv10pro(at)gmail.com (rv10pro(at)gmail.com)> wrote:
| Quote: | Donald, you did not mention if the antenna was installed on Carbon Fibre, Fiberglass or Aluminum skin. Aren't the copper tapes used to establish an effective groundplane? Is it a concealed antenna? is it homemade or manufactured? Tesla's are having problems with quality FM reception due to dipole, concealed. Some owners thought the side mirrors were the concealed antenna, Turns out the location was selected for cosmetics not function along the rear window deck and use a two frequency combiner. Are you assuming the coax connections were both done on the shielding correctly?
John
On Wed, Jan 22, 2014 at 7:26 AM, Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)> wrote:
| Quote: | --> Avionics-List message posted by: Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)>
Plot it with more data points to find its center freq.
If you think of it in terms of the "higher the frequency the shorter the element", it was resonant at 118 MHz, and after cutting (how much?) it's moved higher.
Is you meter designed for VHF?
Also, nearby objects including you can affect it. Try to place it vertical and away from other objects. Both elements should be equal length, and you should measure from the crotch of the separated coax.
Tim
> On Jan 22, 2014, at 2:55 AM, "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)> wrote:
>
> --> Avionics-List message posted by: "fireflier" <fireflier(at)btinternet.com (fireflier(at)btinternet.com)>
>
> Hi
> I'm looking for some help with regards tuning in my dipole aerial as i seem to have a slight problem.
>
> I Have everything connected up to my swr meter and got the following readings at the start
>
> 118.000 1.2
> 127.350 2.7
> 136.975 3.1
>
> I have been trimming the copper tape of the dipole and the lower frequency swr reading has increased and the mid frequency has decreased however there has been no real effect on the hight frequency as this is still at a swr of 3.
>
> I now have the copper tape legs cut to the lengths that were specified in my manual 480mm. I dont really want to cut much more off these as its not having any effect on the top frequency swr value therefore i feel there is an underlying issue that i need to sort out first?
>
> With the 2 legs cut to 480mm i have the following swr readings
>
> 118.000 2.0
> 127.350 2.1
> 136.985 3.0
>
> I would appreciated any help and advice that people have to offer to try and recrify this problem for me. Im now not sure how to proceed to sort this problem out.
>
> I look forward to your replies.
>
> Kind regards
> Donald
>
> --------
> Fireflier
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=417402#417402
>
>
>
>
>
>
>
>
>
>
===========
t" target="_blank">http://www.matronics.com/Navigator?Avionics-List
===========
http://forums.matronics.com
===========
le, List Admin.
="_blank">http://www.matronics.com/contribution
===========
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