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Old 4-Apr-2016, 3:46 PM   #1
chris1379
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Help with one VHF Channel

I have a second-hand Radio Shack VU-75XR about 20 feet up. HERE is my report. I first tried it at 15 feet and barely received WCHS and WOWK. I added 10 feet of mast and lost those 2 completely. I lowered it to 20 ft. and still no joy. I'm using an RCA matching transformer. Could that could be hurting a little? If it proves impossible to receive WCHS, is there a way to optimize the VHF portion for one channel? WOWK is VHF 13.

Last edited by chris1379; 5-Apr-2016 at 6:37 AM.
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Old 4-Apr-2016, 6:00 PM   #2
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Welcome, Chris:

Please post the link to your tvfool report. I see "HERE" but nothing happens if I try to click on it.

I see a report on your previous thread. Is that still accurate, or have you moved? It would have been better to add your new question to that thread for background information, instead of starting a new thread.

previous thread
Why can't I receive this station?
http://forum.tvfool.com/showthread.php?t=15444

old report:
http://www.tvfool.com/?option=com_wr...f1f05778a90214

Quote:
I'm using an RCA matching transformer.
Matching transformer or preamp? If it is a preamp, what model is it?
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Last edited by rabbit73; 4-Apr-2016 at 7:24 PM.
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Old 5-Apr-2016, 6:41 AM   #3
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It's just a matching transformer. I fixed the link to my report,
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Old 6-Apr-2016, 4:45 AM   #4
chris1379
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I did some testing today. I tried an indoor matching transformer that I believe is good and got the same results. I swapped coax also. While I was out there, I took a picture looking the direction of most of the stations. The antenna is higher than the huge bush by the sidewalk. The hill is probably my biggest issue. I believe the tower across the street is the college TV station uplink. Another possible concern is the local FM station. It's not very powerful but a cheap radio will pick it up all the way across the dial.

As for the antenna, is there a way to modify the VHF section so it works better on channel 13? I believe 13 inch elements would be a half-wave dipole. The live elements on the antenna are 6, 26, 38, and 48 inches. That's not exact because its cold and dark out but close. It seems to me that with 13 being the lowest channel, I don't need any elements longer than 13 inches.
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File Type: jpg 20160405_144901a.jpg (229.1 KB, 406 views)

Last edited by chris1379; 6-Apr-2016 at 4:52 AM. Reason: add picture
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Old 6-Apr-2016, 3:33 PM   #5
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To pick up channel 13 I'd get a HLSJ to filter out the FM stations. The local college station is 50 KW from .8 miles away which will cause fundamental overload. Yet there is a second FM station at on 107.1 at .9 miles that will also overload the tuner in the TV set which creates an internal second harmonic within channel 13.
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Old 6-Apr-2016, 11:34 PM   #6
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Tower Guy is correct. You have some very strong FM stations that most likely are causing interference to TV reception. The HLSJ can be used as an effective FM filter. It will block signals below TV channel 7, including the FM band. Use the High and common ports and insert it in the coax line from the antenna.
http://www.solidsignal.com/pview.asp?p=zhlsj

http://www.atvresearch.com/hlsjvhfba...-combiner.aspx

http://www.nsccom.com/hlsj.aspx

Here is an FM signal report based on your short coordinates as showing on your tvfool report:
http://www.fmfool.com/modeling/tmp/a...7/Radar-FM.png

Here is a report based on where I think you were standing when you took the photo:
http://www.fmfool.com/modeling/tmp/2...f/Radar-FM.png
Quote:
Another possible concern is the local FM station. It's not very powerful but a cheap radio will pick it up all the way across the dial.
To keep the strong signals from causing interference, you should ground the coax with a grounding block connected to the house electrical system ground.



If the antenna is outside, the coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge, but the system will not survive a direct strike.
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Last edited by rabbit73; 7-Apr-2016 at 12:16 AM.
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Old 7-Apr-2016, 12:20 AM   #7
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Quote:
As for the antenna, is there a way to modify the VHF section so it works better on channel 13? I believe 13 inch elements would be a half-wave dipole. The live elements on the antenna are 6, 26, 38, and 48 inches. That's not exact because its cold and dark out but close. It seems to me that with 13 being the lowest channel, I don't need any elements longer than 13 inches.
You don't need to modify the antenna for channel 13. It's as good as it will ever be for 13. If you need more gain for channel 13, you should use an antenna with more gain.

Channel 13 is 210 to 216 MHz; center frequency 213 MHz. A half wave dipole is 5540/freq in MHz, with the answer in inches.
5540/213 = 26 inches for a half wave dipole

VU-75XR VHF/UHF/FM Antenna (150-2151)
Specifications Faxback Doc. # 38046
Average Gain
Low Band VHF 2-6: ...................... 2.8 dB
High Band VHF: 7-13..................... 5.8 dB
UHF Band: .................................... 5.6 dB
FM Band: 88-108 MHz................... -0.8 dB
Median Av. F/B Ratio
VHF Low Band: .................. 8.0
VHF High Band: ................. 9.0
UHF: ............................... 15.0
FM: ................................... 6.0
Average Half-Power Beam Width
Chan. 2 - 6: ................. 69 degrees
Chan. 7 - 13: ............... 49 degrees
UHF*: ......................... 54 degrees
FM: ............................. 72 degrees
* At Chan. 30 (566 MHz)

Attached Images
File Type: jpg Radio Shack VU-75XR.JPG (47.8 KB, 1587 views)
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Last edited by rabbit73; 7-Apr-2016 at 3:44 AM.
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Old 7-Apr-2016, 12:21 AM   #8
chris1379
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I didn't know WOUL was that close! I think the tower in the distance is theirs. That means it's directly in line with all of the TV stations we want. I guess we are all supposed to support our poor starving (Time Warner) cable company.

I'll try the HLSJ and try to find a ground. The power lines are on the opposite corner of the house but there might be a copper water pipe. The FM stations would also explain why I can't use an amplifier at all. The Radio Shack amp even has an FM trap but that doesn't work. That same amp helped with rabbit ears.

Back to the antenna, a half wave dipole on CH 13 is 26 inches total, right? That's 13 inches per element, right? That would make this one a full wave at 13 if the elements are 26 inches each and 52 total, right?

Thanks for everyone's help. I'll update with progress.

Last edited by chris1379; 7-Apr-2016 at 12:58 AM.
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Old 7-Apr-2016, 2:02 AM   #9
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If you don't find a good ground for the coax shield using a grounding block, the FM signals can get directly into the TV cabinet, bypassing the FM filter. The FM signals are so strong that even with a good ground you might need two HLSJs in series.

Folded Dipole



Quote:
The FM stations would also explain why I can't use an amplifier at all.
The FM stations would overload a preamp, but you could put the filter(s) between the antenna and the input of the preamp. However, your strongest TV signal WKAS would also overload most preamps and the TV tuner after it.

It is possible to buy a custom filter (expensive) that would attenuate WKAS so that you could use a preamp for the very weak WCHS. Without that custom single channel bandstop filter for real channel 26 to make WKAS weaker, all you can do is use an antenna with more gain for WCHS.

So, you have three issues that are making TV reception difficult.
1. Very strong FM signal interference
2. A very strong TV signal WKAS, that limits your use of a preamp to help you with WCHS ABC.
3. The hill, that makes your desired signals weaker from that direction.



Here is a close up of the WCHS coverage map for your area. Where there is red, the signal is weak. Where there is no color, it is even weaker, which is why WCHS has a NM of -11.1 dB. Any channel with a Noise Margin of less than -10 dB is difficult to receive. If you are able to receive them, you have an excellent antenna system, your tvfool report is wrong, or they have been enhanced by Tropospheric Propagation.



WOWK also has to make it over the hill, but VHF signals can do it better than UHF signals.
Attached Images
File Type: jpg chris1379TVFp2WCHS.JPG (103.4 KB, 1514 views)
File Type: jpg chris1379covWCHScu.JPG (106.2 KB, 1546 views)
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Last edited by rabbit73; 12-Sep-2017 at 12:24 AM.
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Old 7-Apr-2016, 1:52 PM   #10
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Quote:
As for the antenna, is there a way to modify the VHF section so it works better on channel 13? I believe 13 inch elements would be a half-wave dipole.
The design of the VU75 is of a different type than you're referring to.
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Old 7-Apr-2016, 3:07 PM   #11
rabbit73
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Before I forget, thanks for the photo; it helped a lot.

I think you have a good chance of getting WOWK with your antenna, if you use an FM filter and ground the coax.

Ant > coax > grounding block > coax > HLSJ or 2 > coax > TV

If that works, I have some ideas to try for WCHS; let me know.
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Old 7-Apr-2016, 5:24 PM   #12
chris1379
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Quote:
Originally Posted by rabbit73 View Post
Before I forget, thanks for the photo; it helped a lot.

I think you have a good chance of getting WOWK with your antenna, if you use an FM filter and ground the coax.

Ant > coax > grounding block > coax > HLSJ or 2 > coax > TV

If that works, I have some ideas to try for WCHS; let me know.
Wow, thank you. That coverage map helps a lot. Where do I find that for other channels?

Would it be OK to ground the HLSJ and omit the grounding block to avoid another connection? I only ordered one HLSJ so I'll see how it does first. I don't think I'll find one locally. I do have a grounding block.

I found this diagramon my antenna. It seems to have more gain on higher VHF channels so that's good.

Guess I'll be waiting patiently by the mailbox.
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Old 7-Apr-2016, 7:05 PM   #13
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Quote:
Where do I find that for other channels?
It's a little involved. I'll take you through it for WOWK step-by-step:
http://www.rabbitears.info/
First Section, Web Listings
Type wowk in Find: Call Sign box and click Search which will take you here:
http://www.rabbitears.info/market.ph...&callsign=wowk
Digital TV Market Listing for WOWK
scroll down to WOWK
click on Technical Data and Screencaps in yellow band which will expand the yellow band
click on RabbitEars TV Query which will take you here:
http://www.rabbitears.info/tvq.php?r...ms&facid=23342
RabbitEars TV Query for WOWK
WOWK-TV - HUNTINGTON, WV, US - Main Listing
scroll down to Area: and click on Longley-Rice Coverage Map which will take you here:
http://www.rabbitears.info/contour.p...=2001528&map=Y
Coverage Maps
WOWK-TV (13-1) BLANK-0000003187
Look for Ashland; it is half way out from the center of the circle toward 9 o'clock
zoom in on Ashland
Ironton is NNW of Ashland
Your location is just SW of where 141 meets 52
You will see more signal color in your area because WOWK is stronger than WCHS but there is a dead zone around S 10th and Adams St near the Holiday Inn



Keep in mind that field measurements are made for the contour circles, but the color patches are the result off the Longley-Rice computer simulation which gives an impression of greater accuracy than what actually exists. Your tuner will tell you the truth, especially with 2Edge signals.
Quote:
Would it be OK to ground the HLSJ and omit the grounding block to avoid another connection?
It would work, but it doesn't meet NEC requirements, if you care about that.
Quote:
It seems to have more gain on higher VHF channels so that's good.
Yes, the pattern shows more gain on VHF-High than on VHF-Low, which agrees with the specs.
Attached Images
File Type: jpg chris1379covWOWKcu.JPG (106.3 KB, 1533 views)
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Last edited by rabbit73; 7-Apr-2016 at 8:11 PM.
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Old 8-Apr-2016, 4:49 AM   #14
chris1379
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I was thinking earlier that I wish I had a Spectrum Analyzer. Then I wondered if anything would show up on an oscilloscope. It did and this should not be happening. That's 10 cycles marked so it's really showing 107MHz. But look at the voltage. That is straight off the coax.
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File Type: jpg 20160407_231440.jpg (273.8 KB, 299 views)
File Type: jpg 20160407_231824.jpg (239.8 KB, 305 views)
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Old 8-Apr-2016, 3:18 PM   #15
rabbit73
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0.433Vpp = 0.153Vrms = 153mVrms

That is a lot of RF voltage coming from your antenna!

Or as Mr. Spock would say, "Fascinating!"

Thanks for making the test; good detective work. I also wish you had a spectrum analyzer, to confirm the frequency and check for other possible interference like cell phone transmitters from above TV CH 51.

That is waaaaay too much. It does look like it is coming from WLRX, but why not from WOUL-FM that is 15 dB stronger at +4dBm; they are both in about the same direction? Maybe it has something to do with the gain curve of your antenna. The specs say FM band gain -0.8 dB.

So, 153mVrms = -5.1 dBm in a 75 ohm system; about what you would expect after looking at your FM signal report:
http://www.fmfool.com/modeling/tmp/2...f/Radar-FM.png

Quote:
Originally Posted by chris1379 View Post
I have experience in CB and a little Amateur radio (friends) so that helps. I just don't have practical experience with TV in weak signal areas.
You are getting the experience now. Maybe you can borrow a spectrum analyzer if you have ham friends. If you do borrow a SA, be careful not to blow out the front end with that hot signal. Look at the analyzer specs and use an attenuator if necessary.

Quote:
Originally Posted by rabbit73 View Post
Extreme measures are sometimes necessary, even if your equipment is operating properly, if you have very strong EMI.

John Stanley, K4ERO, was able to operate a ham station when he was living at the transmitter site of HCJB in Quito, Ecuador. A 40 meter dipole collected enough RF to light a 100 watt bulb. See Front-End Overload, A Worst Case Example on p214 of The ARRL Antenna Compendium, Vol. 3.

This is where the quad loop antenna was invented (patent no. 2,537,191) by Clarence C. Moore, W9LZX, because of problems with corona discharges from the previous four-element antennas that were fed by high power transmitters located at 10,000 feet altitude in the Andes. The aluminum elements got so hot that pieces melted and fell to ground.
Quad antenna - Wikipedia, the free encyclopedia
from this original post:
http://www.digitalhome.ca/forum/186-...ml#post1307146

If K4ERO was able to operate a ham station at HCJB and receive signals, I think your chances of receiving at least WOWK are good with the right filters and a good ground.

There are some tests you can do with your 'scope now. Insert a HLSJ, high and common ports, in the coax and take more voltage readings. Try it with and without grounding the coax. You can also try inserting a UVSJ (not the MCM UVSJ), high and common ports, which will limit reception to UHF. You should get a reading from WKAS.

WKAS -27.5 dBm + ant gain 5 dB = -22.5 dBm = 0.02 Vrms across 75 ohms = 20mVrms = 56.6 mVpp if your 'scope reads that low at 545 MHz.
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Last edited by rabbit73; 9-Apr-2016 at 2:05 PM.
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Old 9-Apr-2016, 2:06 AM   #16
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My primary TV is a newer CRT with an RCA DTA800B1lL digital converter. I have a Samsung LCD but it needs a board replaced. If I connect the antenna directly to the Samsung, I can receive WOWK and WCHS but with a weak signal. The WCHS signal is only good for a few degrees of antenna rotation but does correspond with WVAH as expected. Is it possible that the Samsung has filters to block the FM band or is the RCA tuner just junk? I'll find out when I get HLSJ. I wish there was a filter I could make just for some tests.

By the way, I am still puzzled as to why I have more problems from the 3100W WLRX than the 50,000W WOUL. I further confirmed the strength by using a C. Crane FM transmitter and my stereo. I can interfere with WOUL 89.1 from 3-4 feet away. The only way I can interfere with WLRX is by electrically touching the antennas. The only reason I can think of is that WLRX has a directional antenna pointed this way.

Last edited by chris1379; 9-Apr-2016 at 3:22 AM. Reason: added to post
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Old 9-Apr-2016, 11:49 PM   #17
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I received the HLSJ today. I am happy to report that the RCA converter finally detected WCHS. It doesn't receive it clearly but at least I can work on it now. I even got signals through the amplifier and it may be helping a little. I plan to order another HLSJ and try to optimize the signal. If I still have issues, what kind of antenna would be recommended? Not giving up yet.
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Old 10-Apr-2016, 12:30 AM   #18
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Glad to hear the HLSJ makes a difference. Is that with the coax grounded?

What is the voltage measurement on the oscilloscope with the HLSJ?
Quote:
If I still have issues, what kind of antenna would be recommended?
An antenna with more UHF gain for WCHS.
Quote:
Not giving up yet.
That is the true spirit of an antenna experimenter.

Is WOWK better with the HLSJ? That's why you ordered it.
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Last edited by rabbit73; 10-Apr-2016 at 12:35 AM.
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Old 10-Apr-2016, 3:44 AM   #19
chris1379
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Quote:
Originally Posted by rabbit73 View Post
Glad to hear the HLSJ makes a difference. Is that with the coax grounded?
No, I didn't get to that yet

Quote:
Originally Posted by rabbit73 View Post
What is the voltage measurement on the oscilloscope with the HLSJ?
Not an exact measurement but 17mV P-P

Quote:
Originally Posted by rabbit73 View Post
Is WOWK better with the HLSJ? That's why you ordered it.
Not picking it up at all right now. I'm going to try raising and lowering the antenna again as well as moving it around a few feet. The cold, wet weather probably isn't helping.
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Old 10-Apr-2016, 11:04 PM   #20
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OK, the HLSJ is blocking channel 13. I don't understand. It's a Skywalker SKY26802. Mine passes DC on the Hi side but is otherwise the same. If anything, I would be afraid of it blocking UHF but it doesn't. Sound like it's defective?
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