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-   -   build a tuned antenna for one VHF Channel (http://forum.tvfool.com/showthread.php?t=14599)

timotb 30-Jun-2014 7:03 PM

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.

Stereocraig 30-Jun-2014 8:07 PM

Quote:

Originally Posted by timotb (Post 44680)
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.

GroundUrMast 30-Jun-2014 10:59 PM

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.

timotb 1-Jul-2014 12:21 AM

Quote:

Originally Posted by GroundUrMast (Post 44684)
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.

ADTech 1-Jul-2014 1:07 PM

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.

timotb 1-Jul-2014 4:35 PM

Quote:

Originally Posted by ADTech (Post 44691)
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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