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Old 25-Feb-2017, 2:41 PM   #1
rabbit73
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Join Date: Aug 2012
Location: S.E. VA
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powerline yagi hunting

Quote:
Originally Posted by nomorecomcast
hi rabbit73. primestar31 on satelliteguys.us forum recommended you for answering questions about tape measure power line hunting yagi. I cant post questions yet so i messaging you. hope that is ok. would you be willing to answer a few questions? thanks you. http://www.satelliteguys.us/xen/thre...erence.367781/
Quote:
I am trying to get kjwp but i think i have to much interference. i made a twin lead antenna if my math is right, the antenna is 98.46 inches long and in my attic about 22 feet off the ground. no reflector or director. i have tried aluminum screen about 40 inches back, but not covering the full length of the twin lead. that get the signal to 25%, without the screen its 5%. the percentages were taken around noon. i would like 40% for a "stable" signal. Also i have a twin lead antenna for WPVI, that is vertical and aluminum window screen as a reflector about 36 inches back, i get zero signal placed horizontal. my main question is for interference. How far can the electrical interference travel and still effect the tv signal? About 200 ft away, there is a utility pole that puts interference on AM radio across the whole band when is raining out. also i have residential power lines 30 feet from the antenna and at the same height. i have a 32 inch lcd up in the attice with me, the antenna is connected to the converter box " to get the signal meter" and then the tv. The RG6 is 25ft. cant post link to tvfool report. my zip is 08087.
Welcome, nomorecomcast

Here is an estimated tvfool report based on your zip code:
http://www.tvfool.com/?option=com_wr...e6a453aa51dd91

Some people have been waiting a long time to post; there is a shortage of moderators. I can't help with that, but I'll try to help you with your channel 2 KJWP problem.

The noise level from electrical interference is high on VHF-Low (channels 2-6), which makes reception of digital channels more difficult than analog channels were. That is why there are so few transmitters on VHF-Low. Some of the stations that stayed on VHF-Low after the transition from analog to digital, have had problems with reliable reception. Some have been allowed to increase their power, and some have had to move to VHF-High (real channels 7-13).

Now that the FCC is giving some of the UHF channels to cellular services, there will be more pressure to use VHF channels for TV broadcast.

I looked at your thread in the link that you gave, and also your first thread there:
http://www.satelliteguys.us/xen/thre...n-help.367751/

I can give you a design for a Fox Hunting 3 element yagi made with PVC and steel tape measure elements, but you would need a receiver connected to the antenna to measure the power line noise on VHF.

The best tool that I have found is a battery operated portable radio that tunes the AM broadcast band. Its built-in loop antenna can act as a direction finder. Tune it to a vacant frequency at the low 540 end or the high 1600 end and listen for noise. If the noise is loud on AM broadcast, it will usually be strong on VHF TV. An FM portable radio doesn't work as well, but a radio that tunes the aircraft band will work because it is AM.

MFJ makes several power line noise meters, but the quality control isn't very good. Read the eHam.net reviews for tips.
https://www.google.com/#q=mfj+power+line+noise&*
Quote:
About 200 ft away, there is a utility pole that puts interference on AM radio across the whole band when is raining out. also i have residential power lines 30 feet from the antenna and at the same height.
That doesn't sound like it will be easy to receive CH 2. You will need to improve the ratio between the signal and the noise (SNR).

If there is a defect in the power line, maybe the power company can fix it if they can find it. If the power line noise can't be reduced, then you will have to find a way to increase the signal relative to the noise.

An antenna with more gain will help. Grounding the coax with a grounding block might help, but the antenna itself will still pick up the noise. Moving the antenna to another location might help; having it behind a power line couldn't be good. You might have to do without KJWP.

I'll send another PM with antenna ideas.
__________________
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http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 25-Feb-2017 at 2:52 PM.
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Old 25-Feb-2017, 2:58 PM   #2
rabbit73
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Channel 2 is 54 to 60 MHz. I cut a folded dipole for mid channel.
5540/57 = 97.2 inches.







If you want to design your own yagi with aluminum tubing, you can do it here:
http://www.k7mem.com/Electronic_Note.../yagi_vhf.html
http://www.k7mem.com/Electronic_Note...vhf_quick.html
http://www.k7mem.com/Electronic_Note..._vhf_feed.html
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html
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Old 25-Feb-2017, 3:05 PM   #3
rabbit73
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Quote:
Originally Posted by nomorecomcast
]WOW your and artist. very nice diagram. i got may antenna from from http://users.wfu.edu/matthews/misc/dipole.html How do you get 5540? thank you again for you time.
Thank you for your kind words. I like to do a diagram; it's much better than words.

The 5540 is just to convert the feet formula for a half-wave dipole to inches.

468/57 = 8.21 feet = 98.5 inches

But I have found by experiment that is a little too long for VHF and UHF because of the end effect and length to diameter ratio of the conductor. "Fatter" conductors don't need to be as long for the same resonant frequency.
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 25-Feb-2017 at 3:23 PM.
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Old 25-Feb-2017, 3:32 PM   #4
rabbit73
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Location: S.E. VA
Posts: 2,516
nomorecomcast

I am not able to answer your last PM because it says your folder is full.

It is not worth your trouble to build a yagi for hunting power line noise if you don't have a receiver to connect it to. Here are some links about that:
http://www.homingin.com/equipment.html
http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm
http://www.arrl.org/files/file/Technology/HANDSON.pdf

But, I think it is worth the trouble to build a channel 2 or channel 6 yagi to see if they will make the signals stronger compared to the power line noise.
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 25-Feb-2017 at 6:43 PM.
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Old 25-Feb-2017, 5:58 PM   #5
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,516
Quote:
Originally Posted by nomorecomcast
what material/diameter is used for your antenna design? thanks
The design can use 300 ohm twin lead for the dipole driven element and 12 or 14 gauge insulated copper wire from Home Depot for the director and reflector, which is why it is called a wire yagi. Or, you can use the copper wire for all three elements.

You can use heavier gauge wire or tubing, but that would be more expensive.

Here are the calculations for the Channel 2 yagi:

Channel 2 Yagi, 57 MHz
5540/57 = 97.19
Reflector 97.19 x 105% = 102.1 inches
Director 97.19 x 95% = 92.3 inches
One wavelength in air is 11810/freq in MHz = 11810/57 = 207.19 inches
DE to Reflector spacing = 0.2 λ = 207.19 x 0.2 = 41.4 inches
DE to Director spacing = 0.15 λ = 207.19 x 0.15 = 31.1 inches

λ (Lambda, Greek) is the symbol for wavelength

Here is a channel 6 yagi for WPVI:



and the calculations for the channel 6 yagi for WPVI:

Channel 6, 82 to 88 MHz, center frequency 85 MHz.
5540/85 = 65.2 inches length for a folded dipole antenna
To convert the dipole antenna into a 3 element beam for more gain, add a reflector and a director:
Reflector is 105% of Driven Element = 65.2 x 1.05 = 68.5 inches
Director is 95% of DE = 65.2 x 0.95 = 61.9 inches
One wavelength in air is 11810/freq in MHz = 11810/85 = 138.9 inches
DE to Reflector spacing = 0.2 λ = 138.9 x 0.2 = 27.8 inches
DE to Director spacing = 0.15 λ = 138.9 x 0.15 = 20.8 inches

Here are some hourglass loops for VHF-Low designed by holl_ands who does antenna computer modeling:

http://imageevent.com/holl_ands/loop...673fd1.eagle_s

for very tall attics
Attached Images
File Type: jpg Channel 6 Yagi.jpg (79.7 KB, 864 views)
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 25-Feb-2017 at 7:56 PM.
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