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Old 30-Jun-2014, 7:03 PM   #1
timotb
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build a tuned antenna for one VHF Channel

I would like to pick up a Channel 8 (real) that is 40.6 miles from me with a signal NM of 17.5dB and power -73.3dBm.

As an amature I read this channel is 180-186 mHz. Would a simple dipole antenna roof mounted pick this up reliably? I also read the dipole needs to be 31" to tune to this frequency. I assume 31" each side and positioned as a "T"

If this would work, what matching transformer would be needed 75 or 300 Ohm?

Thanks.
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Old 30-Jun-2014, 8:07 PM   #2
Stereocraig
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Originally Posted by timotb View Post
I would like to pick up a Channel 8 (real) that is 40.6 miles from me with a signal NM of 17.5dB and power -73.3dBm.

As an amature I read this channel is 180-186 mHz. Would a simple dipole antenna roof mounted pick this up reliably? I also read the dipole needs to be 31" to tune to this frequency. I assume 31" each side and positioned as a "T"

If this would work, what matching transformer would be needed 75 or 300 Ohm?

Thanks.
I believe your calculations are correct, I'm just not sure if that's 1/4, 1/2, or full wave. You may also need a reflector.

I'm sure it would be a standard 300/75 balun.
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Old 30-Jun-2014, 10:59 PM   #3
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I have built successful antennas based on the design generated by this software... http://forum.tvfool.com/showthread.php?t=1106

I opted to use a folded dipole as the driven element, and used an off-the-shelf 75/300Ω transformer to couple to the down-lead.
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Old 1-Jul-2014, 12:21 AM   #4
timotb
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Originally Posted by GroundUrMast View Post
I have built successful antennas based on the design generated by this software... http://forum.tvfool.com/showthread.php?t=1106

I opted to use a folded dipole as the driven element, and used an off-the-shelf 75/300Ω transformer to couple to the down-lead.
I seen one of these antennas made from a 2x4 and scrap wire on Youtube. Looks easy. My concern, as an amateur, is tuning it correctly for this single channel 8. Someone above raised the concern that a reflector might be needed.

Even if I construct my simple 31" dipole, I'm not sure of the distance between the two poles.

I can build if I can work from a well thought out design like what I saw on a PDF file here for the 195Mhz, but instead for the 180-186 range.

If I am reading correctly, this program VK5DJ is exactly for that. Just getting a bit over my head.

Last edited by timotb; 1-Jul-2014 at 12:42 AM.
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Old 1-Jul-2014, 1:07 PM   #5
ADTech
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Ignore the Youtube UHF antennas, your requirements are completely different since you're looking for VHF, not UHF. You'd have to rescale the coat hanger antennas by a factor of 2.5 to 4X for VHF.

Our simple VHF Retro Fit Kit may well do the job. It's a dipole that's tuned to 195 MHz (ch 10) and there's very, very little drop off in performance on channel 8. If not, you will need to step up to a more directional array of elements to get better reception of a single VHF channel. An additional resource for designing your own is at http://www.k7mem.com/Electronic_Note.../yagi_vhf.html Otherwise, there are commercially available high-VHF antennas such as our ClearStream 5 that would be expected to do the job.
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Old 1-Jul-2014, 4:35 PM   #6
timotb
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Ignore the Youtube UHF antennas, your requirements are completely different since you're looking for VHF, not UHF. You'd have to rescale the coat hanger antennas by a factor of 2.5 to 4X for VHF.

Our simple VHF Retro Fit Kit may well do the job. It's a dipole that's tuned to 195 MHz (ch 10) and there's very, very little drop off in performance on channel 8. If not, you will need to step up to a more directional array of elements to get better reception of a single VHF channel. An additional resource for designing your own is at http://www.k7mem.com/Electronic_Note.../yagi_vhf.html Otherwise, there are commercially available high-VHF antennas such as our ClearStream 5 that would be expected to do the job.
Thanks, that might work for me, ...if they would only just provide me a simple drawing that I can interpret and build from. I'm a builder not an engineer.
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