Help With Weak Upper-VHF Digital? - Page 2

Yes, it is a difficult situation.

Thanks for reading through this thread. Considering all the installation experience that you have, I might have overlooked an obvious solution.

It could be worse. The strongest and weakest signals could be on adjacent channels!

A less expensive (about 1/3) alternative to the bandstop filter might be the Jointenna (if it's properly tuned):
http://www.warrenelectronics.com/Ant...Jointennas.htm
http://www.tvantenna.com/support/tut...combining.html
http://www.avsforum.com/avs-vb/showt...8#post10911738
http://www.avsforum.com/avs-vb/showt...9#post13766389
http://www.avsforum.com/avs-vb/showt...1#post13766891 (AntAltMike #7182)

The Jointenna that I have in mind is the model 0585-2 tuned for CH32. Using it in the conventional way you would connect a UHF antenna to the CH32 input. But, since you want less CH32 instead of more you would not use it in the conventional way (if I correctly understand what's inside), keeping in mind that analog WVIR on CH29 would still be a problem before the transitition.
The tvantenna/tutorial link above says that the Jointenna can also be used as a single channel -20dB trap & warren says it can be used for blocking or passing. You would connect your CH11 antenna to the all-channel input and connect the output to the tuner.
If CH40 & 46 were too weak, you would have to use a VHF & UHF antenna and a UVSJ, with the CH11 antenna going to the VHF input and the Jointenna trap in the line between the UHF antenna (to all-channel input) and the UHF input of the UVSJ.
Instead of the Jointenna, you might try a quarterwave open stub for CH 32 connected by a T in the UHF line. If the Q of the stub trap was too high it might make a notch in the signal that would be just as harmful as a notch caused by multipath. I don't know how to lower the Q of a trap stub if this is a problem.

I have been making measurements of digital signals with my Sadelco 719E signal level meter (SLM) for about a year. Even though it is calibrated for peak reading of analog signals, I have found that it is very useful for making comparative measurements of antennas and digital signals.

I would like to have a new SLM that is designed for digital signals, but it is not now in the budget. But what about the people that don't have either? I keep thinking of a poster who lived close to the transmitter towers and had an attic antenna. He was having trouble receiving signals. Was it that the signals were so strong they were causing overload because they only had to go thru wooden siding or were they too weak because they were blocked by aluminum siding or an aluminum foil vapor barrier?
I made some signal measurements with my Apex DT502 to see how it would do as a SLM. After the antenna, I used a switched attenuator with 3dB steps (as in the Kelvin link in my signature) going to a splitter and then to the DT502 and the SLM; first in a strong signal location:
I next added a preamp to simulate a very strong signal bringing it up to +36 dBmV, but the DT502 signal strength never went any higher than 84%. I was also looking for signs of overload, but didn't see any. I would have to drive about 100 miles round trip to pick up an extremely strong signal, but it doesn't seem worth the trouble right now. The ultimate test of a tuner would be to see how it would handle a very weak signal when other very strong signals are on the band. That's for another day.

and then in a weak signal location:
I was able to test a 2nd DT502, and the results were similar: It maxed out at 87% strength at +2.2 dBmV with an increasing signal, and held 100% quality down to 51% strength just below -30 dBmV with a decreasing signal.

It looks like the DT502 can be used as a SLM. Its tuner is even more sensitive than my SLM.

CAUTION: As Trip correctly pointed out to me, this CECB doesn't allow you to add other channels after the scan. See wiki other features note code "-N" of CECB comparisons:
http://en.wikipedia.org/wiki/Comparison_of_CECB_units

Update: I have received some positive feedback from IDRick:



Downunder in .au land, they have a good understanding of the importance signal quality, BER, and MER:
http://www.dtvforum.info/index.php?showtopic=18627 see post #11
http://www.dtvforum.info/index.php?s...=360&start=360 #366 & 369
http://www.hillsantenna.com.au/arbitrage/pages/61 BER
http://www.hillsantenna.com.au/arbitrage/pages/60 MER
http://users.tpg.com.au/bitek500/Dow...M%20instal.pdf p4 DVB-T digital cliff
http://www.bbc.co.uk/rd/pubs/papers/.../crn-dvbtm.pdf ATSC vs DVB-T, excellent charts on p3
http://www.wowvision.tv/signal_strength_meters_BER.htm Signal strength meters and BER

How long did you make the whiskers? I will be curious to see how it performs.

It is a simple antenna to make, but can be rather unwieldy do to the additional width required for a bow-tie over a dipole.

What did you use to protect the ends? I ended up using twist on wire connectors.

Nice job, Trip!
I'm looking forward to hearing about the test results.
The plastic tubing for end protection is a good idea!

That's too long for channel 11.

Hey Trip,
Can you hang something lightweight from the ceiling that has about a 3" vertical profile?

A five or ten element highbander suspended by a couple of eyescrews and small wire or string.

That is the electrical half wavelength.

The physical half wavelength depends on the size and shape of the element. In the case of a bow tie, the physical length varies from 65% to 85% of the electrical length. It depends on how far you spread the tips of the wires.

The free demo copy of EZNEZ may be helpful.

http://www.eznec.com/demoinfo.htm

Good news on the UHF. It looks like the CH11 antenna is acting like an attenuator for UHF, reducing the overload problem.

Bad news on CH11. You need more CH11 signal coming from your antenna; more gain or a better location for the antenna, or both. Do you have a window that faces the tower, or did you already answer that question?

I don't think amplification for VHF only will help, but it's worth a try.

To position the VHF antenna in the best location, what did you think of my floor-to-ceiling spring loaded pole idea?---- no screw holes needed.

I'll give it some more thought.

Trip, wasn't that question on the test still? A simple wire dipole or driven element in a yagi if not too thick (like a homemade wire yagi, not commercial tubbing) is .95

The reason is the speed of light is slower in a wire than free space. So it's not as long. The thicker the diameter of the element the shorter you make it.

Now since a whisker antenna is like a dipole that on each side the conductor on each side starts narrow and gets wider. Imagine the area between whiskers on one side filled in. You have probably seen bowties indoor made like this. Well the whisker simulates a solid bowtie on each side. It's easier to think of a solid bowtie as a conductor that gets thicker as it leaves the feed point.

So it takes a lot of math or a good program to figure out the length of the whiskers. So don't ask me to figure out Channel 11!

Maybe dipoles used to be on the general class test. What ever! you can google anything these days!

Ok, in a total vacuum EM waves travel at C.

Anytime they move through matter they interact with that matter and are slowed down my a Constant we will call X

So the speed of light in another medium is always less than free space and simple equation of

Speed of Light = XC where X is a equal to or less than 1, where 1 is free space (not air, though air slows it down so little it's ignored).

Radio waves do the same thing, but here is an article on light
http://en.wikipedia.org/wiki/Dispersion_(optics)

This is why lens work to focus light and why prisms break light into it's component colors.

It is also why a fish is not where it appears in a lake if you are looking at any angle except straight down.

Same reason light is blue in the sky.

Or Brewser's Angle where you see what looks like water on a road in the distance.
http://en.wikipedia.org/wiki/Brewster%27s_angle
Or the reason radio waves skip off the ionosphere and not penetrate them. Or the same on tropo skip off air layers.

Ok, I will shut up now!

Piggie :@)

Trip,

First off, thank you so much for your work with the Rabbit Ears site! The FCC, NAB and CEA owe you a debt of gratitude as do many OTA enthusiasts.

Most of the advice you have received on RF propagation and wave theory is spot-on. I'll offer somewhat more pedestrian advice: Colgate white toothpaste is your friend.

You can put a couple small nail or screw holes in a drywall or masonry wall or ceiling and likely cover them up quite well by filling with grout or even something as simple as white toothpaste. I'm not advocating intentional property damage, but a couple small holes to suspend an upper VHF antenna shouldn't compromise the structural integrity of your dorm room.

As some of the other posters have suggested, get in touch with a professor or grad student in the Electrical Engineering department and see if you can borrow some metering equipment to test out RF reception in your dorm room. If the department doesn't trust you with $80,000+ worth of test equipment, offer your room as a complex real world test environment for signal reception optimization from a weak transmitter with intense multipath in a near Faraday's cage. Someone in the EE department might buy it or at least be somewhat sympathetic.

Once again, thank you for your great contributions over the last few years. Best of luck with your last semester. Please tell me you have a job lined up at the FCC or in industry for when you graduate.

According to:
http://www.kyes.com/antenna/rabbitear.html

Reduce to 91%

I'm still interested in getting WVPT here in Afton, Hokie Jim said his friend in Greenwood gets WVPT, but there is no way to tell if it is coming from Carter's Mtn or from Elliot Knob since they are both on Channel 11 (or is there a way to tell?).

I am going to try a homemade antenna and see what happens.

Would one of those home made VHF bowties mounted outdoors work for high VHF at say 55 miles from the transmitter?

I currently have a DB4 mounted on a floor lamp post sitting on my South facing balcony, it receives pretty much all the Chicago (55 miles) and Milwaukee (30 miles) UHF stations reliably. However I am unable to receive channel 10 from Milwaukee (VHF channel 8 IIRC) right now.

Channel 7 from Chicago is going back to VHF 7 after the transition so I suspect I'll also lose that. Channel 10 has also been received by me in the past with a CECB and the DB4 so I imagine it should easily be doable with a purpose built VHF antenna.

I have some fence wire the previous owner left, so I think I have everything I need.

I just made a 4 bowtie antenna and posted my results on the Richmond thread. I had everything except washers. Total cash outlay: $ 0.95.

I made a big mistake about a year ago; I purchased a YA-1713, and cut a short length of RG6 to test the antenna from the roof into the closest window. I wasn't getting any signal, and I returned the antenna. It was only months later I discovered the cable I made was bad.

TV fool says I have some signal from Elliot Knob, and I'm unsure how much signal arrives from Carter's Mtn.

Is there any benefit to a 2 bay design ala the UHF bowtie arrays but cut to VHF length? Would there be a noticeable improvement in gain?

How would I go about figuring out what the optimal length for receiving channels 7, 8 and 12 would be? I would consider myself mathematically challenged, constructing it looks incredibly simple though.