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The Official AVS Antenna and Related Hardware Topic! - Page 81

post #2401 of 16112
Quote:
Originally Posted by Bill Johnson View Post

Definitely the words of a 60 ft tower man! But here again are some attic advantages that I'm happy about (and in no particular order):

1. No wind
2. No lightning
3. No falling to the ground and breaking one's neck or leg
4. "Ease of installation"
5. No deterioration due to weather
6. Adjustments made in any weather
7. No HOA or neighbor problems
8. No wife problems
9. Shorter cable run

I'd take issue with both 3 and 4. I've personally seen people who've fallen through the rafters in their attic (don't worry, I'll admit to seeing falls from roofs as well). It's typically poorly lighted, cramped, hot, potential for wasps, etc, i.e. no picnic. Many have never even seen the inside of their own attic. I'll take a good ladder, firm footing on a dry roof, and a cool breeze any day. Of course, I *do* have a particular disdain for insects that fly and sting as well.

By the way I can add another one to your list for the *vast* majority of people at greater than 40-50 miles out:

10. No signal
post #2402 of 16112
Hi,
Does anybody in a apartment in Willimantic Connecticut have a indoor Antenna that can pick up all the HD Channels in Connecticut,Boston and Providence? If so what kind of indoor Antenna do you use? This is what antennaweb said the map is below.

DTV Antenna
Type Call Sign Channel Network City State Live
Date Compass
Orientation Miles
From Frequency
Assignment
violet - uhf WVIT 30 NBC NEW BRITAIN CT 284° 31.8 30
violet - uhf WWLP 22 NBC SPRINGFIELD MA 331° 36.2 22
violet - vhf WPRI 12 CBS PROVIDENCE RI 90° 49.5 12
violet - uhf WPXQ 69 PAX PROVIDENCE RI 137° 26.7 69
violet - vhf WLNE 6 ABC NEW BEDFORD MA 112° 53.6 6
violet - uhf WTIC 61 FOX HARTFORD CT 284° 31.8 61
violet - uhf WHPX 26 PAX NEW LONDON CT 192° 19.9 26
violet - uhf WGGB 40 ABC SPRINGFIELD MA 344° 43.2 40
violet - uhf WUVN 18 UNI HARTFORD CT 294° 30.5 18
violet - uhf WEDH 24 PBS HARTFORD CT 293° 30.7 24
violet - uhf WEDN 53 PBS NORWICH CT 183° 13.0 53
violet - vhf WJAR 10 NBC PROVIDENCE RI 91° 49.1 10
violet - vhf WFSB 3 CBS HARTFORD CT 294° 30.8
LL
post #2403 of 16112
Quote:
Originally Posted by milehighmike View Post

CEB II,
On July 11, you started a new thread to the HDTV Hardware forum regarding your ability to lock KMGH, the one channel you can't get indoors, by temporarily mounting an antenna outside on your chimney. In that thread, it was quite clear, at least to me (since I posted to it), that the sole reason for not mounting an outside antenna was spousal disapproval.

That is correct, that is my personal situation.

Quote:


You never once mentioned the various reasons you have posted on this thread that you perceive as negatives to outdoor antennas. I'm not saying some of your points are not valid (other than I have a $500 deductible on my house insurance - Liberty Mutual) but it makes me wonder why you didn't mention any of these negatives on the thread you started.

Just because I preceive them as negatives doesn't mean that I'm not willing to risk them to get what I want, if it is the only option. That is why, I've been toiling in the attic for a year and a half to see if I can achieve my objectives. Working from the attic I've managed to lock all of the channels everyone else north of I-70 gets and get good analog reception for the various NTSC tuners available in my hardware. I've been frustrated by not getting one channel that is generally regarded as not available in my area. Before investing any more time and money in trying, I went outside to see if that channel could be locked under the most optimal conditions. I found out it could. I'm not sure I can ever lock it from in the attic, but because the wife says no to the roof antenna, I'm going to try.

I offered the defense of Bill Johnson's points because he is correct. If I can get channel 17 from the attic, I'll never think about an outside antenna again because the issues Bill raised are correct.

I live in Arvada. After a particularly nasty storm in the mid-'90s, where over half of my sub-division got a new roof from their insurance company, the minimum deductibles were raised. I'm w/ USAA and have been since 1967. If one of the top rated insurers won't give their long-term customers under a $1K deductible, I don't think many others will for my area. I just paid $1K out of my pocket this spring to replace 50 feet of cedar fence knocked down during the late December wind storm.

Quote:


So my question is do you really feel very strongly against outside antenna mounts or is it really a spousal issue?

I'd prefer to not have to deal with an outside antenna, but I will if that is what it takes to get what I want. However, the wife doesn't value channel 17 HDTV as highly as I do (maybe not at all) and says no way.

Quote:


I'd also be interested in the low power channel you receive (apparently from the north) from 100 miles away. The only DT station I'm aware of north of us is KGWN. It's barely 100 miles away from me and I live 25 miles south of you, I do receive it, and it's hardly low power at 95.5 ERP even though it's still on an STA.

Okay, so it is only 88.59 miles away according to w.2150.com, and yes it is channel 30 KGWN. I get a steady 49, no lock, on it through the back screen pickup of a Yagi corner reflector pointed SW. During one of my experiments last year, I mounted a Winegard PR-9018 w/ pre-amp in my attic facing north. Couldn't get much else that way, but locked channel 30. Don't care about channel 30 and combining the signal caused a lot of new problems, so I took it down.

95.5 ERP may not be low power compared to our puny downtown broadcasters, but it is far less than our, not at full power, local channels 32 (223 kw) and 34 (450 kw), and no where near the full power license for KGWN at 630 kw. So, I don't think my previous post was deceptive or highly inaccurate as you seem to be implying.
post #2404 of 16112
MGT & I are going to hook up in a week or so after some replacement test equipment arrives. (I busted my minimum loss pads up in Phili a couple of weeks back.) If he is as much a a gentlemen, as I think he is, I'll get a chance to fly the 3671, 4228, 91x, and the 7120. It's summer in Houston, I don't think I'll have to the energy to get the rest of the fleet up the mast.

By the way, sane Texans don't go into the attic until 'winter' anyway. (We only have two seasons - damn hot & damn cold.) So even if he has an attic, we won't be trying it out. This winter I have a few more attics scheduled for testing. As always, I will share the data no matter which way the dB crumbles.

Bob Chase
post #2405 of 16112
Quote:
Originally Posted by Bill Johnson View Post


At 8.7 kW and 70 miles, is there any antenna that would?

.

I have a PBS that has an official STA of 5kw (the station told me via email they're actually only about 1kw) that I can get fairly consistently at 65 miles. My antenna can take a little credit I suppose but the most important factor is that the transmitter is up around 4000ft ASL. Power can help but transmitter height and line of sight is probably more important.
post #2406 of 16112
Quote:
Originally Posted by cpcat View Post

By the way I can add another one to your list for the *vast* majority of people at greater than 40-50 miles out:

10. No signal

Now this is the way it should be! Even in strongly arguing some point, cp brings humor into the mix and makes us all laugh! After all, this is only television we're talking about and when it comes to our faith, family, friends, and failings (or successes) in life, TV doesn't amount to a hill of beans.

Quote:
Originally Posted by sregener View Post

The problem I have with the way you usually present it is that you say something like, "Here's what I did, and I think it will work for a lot of people, and these other guys don't know what they're talking about."

Putting down forum members is certainly not my intention and, going over past posts, I think I've at least tried not to. However, there may be kind of a dogmatic way in my posting language and I feel bad they're perceived as putting anyone down.

Unfortunately, perception is reality and I guarantee HENCEFORTH no one will be able to fairly level a putting down forum members charge against me.
post #2407 of 16112
Quote:
Originally Posted by CEB II View Post

I just have to wade in on this one.



So, I say, unless you absolutely know something won't work, try the cheapest and easiest possible solution first. Rule of thumb for engineers, mechanical at least, not medical doctors. From my attic I get 7 of 8 locals available to me at ranges from 10 to 37 miles. The seventh, at 10 miles, is a real bugger that few in my area get indoors or out. OTOH, if I turn my attic antenna around, I can lock a low power DTV station 100 miles away. It all just depends on your situation.

Mrtbig is 67 miles out. That's what we're talking about here. No one is saying don't try the attic if you're relatively close in (as you are). For Mrtbig it's a waste of time and effort and telling him to "just try it, it works for me" is just bad advice plain and simple.
post #2408 of 16112
Quote:
Originally Posted by the_bear89451 View Post

It is possible for a high water content tree to be next to a rooftop antenna not connected to anything (electrically floating antenna). The tree will be more attractive to lightning, because the water in the tree is conductive, unlike the dry wood used in home construction. The problem arises once you connect the antenna to a receiver and reduce the antenna's resistance to ground. The a grounding line does not reduce an antennas chance of getting hit by lightning (does not raise the resistance), but rather makes the strike safer. The grounding line provides a path for the current to travel more attractive than through your home.

This has been dealt with ad nauseum in other forums. Antennas are not a single metal component, but two - the active element and the directors/reflectors. Most people ground the coax and ignore mast/inactive elements. As wind passes by metal objects, static electricity forms on the metal. Enough of that charge, and suddenly, you're attracting lightning! That's the principle behind lightning rods, which have pretty much been discredited as not helping with lightning strikes.

Anyone who has had a lightning strike even *near* their home will tell you that grounding to protect the equipment in your home in the event of a strike is a useless gesture - everything electrical in your home will be fried, grounded or not.
post #2409 of 16112
Quote:
Originally Posted by cpcat View Post

I have a PBS that has an official STA of 5kw (the station told me via email they're actually only about 1kw) that I can get fairly consistently at 65 miles. My antenna can take a little credit I suppose but the most important factor is that the transmitter is up around 4000ft ASL. Power can help but transmitter height and line of sight is probably more important.

Perhaps missed in all this is that the 8.7kw ERP station is hi-VHF, which is dramatically more effective than 8.7kw ERP in UHF.
post #2410 of 16112
Quote:
Originally Posted by sregener View Post

Perhaps missed in all this is that the 8.7kw ERP station is hi-VHF, which is dramatically more effective than 8.7kw ERP in UHF.

Yep. Missed that entirely.

Mine is channel 41 BTW. I have another PBS at 65 miles (ch. 17, 100kw) but I'm blocked by Jellico MTN to the south and I've yet to get stable reception even with the Band A's.

Of course, the fact that I can tune the Soap Channnel (cable 68, roughly the same freq as uhf 17) when my antenna is pointing toward the cable amp on the utility pole on my street may have something to do with that as well.
post #2411 of 16112
Outdoor/Rooftop is best.
post #2412 of 16112
There is no 'equivalent' to the SvS for VHF. Plain old 'rabbit ears' work for VHF.

OTOH... refer to the post above.
post #2413 of 16112
Quote:
Originally Posted by cpcat View Post

Mrtbig is 67 miles out. That's what we're talking about here. No one is saying don't try the attic if you're relatively close in (as you are). For Mrtbig it's a waste of time and effort and telling him to "just try it, it works for me" is just bad advice plain and simple.

The world would be more backward place and with far fewer rags to riches stories if everyone who was told someone wouldn't work that actually hadn't be tried, simply threw in the towel.

I agree with the earlier post that there are some basic principles for antennas that generally will improve the probability of success (e.g., higher rather than lower, outdoors rather than indoors, more metal in the air versus less, narrow beamwidth versus wide, etc.). But, until someone has actually put a large, pre-amp'd antenna in Mrtbig's attic and found out what is receivable and what isn't, no one can say he won't receive a given channel in his area.

Yes, his probability of doing so is raised by going outside. But, maybe for the multitude of reasons cited, he doesn't really want his antenna outside. Why tell him it won't work when you don't know if it will. BTW the 37 mile distance channel I get is only 7 kw, in the upper half of the UHF band (46), with no LOS, and with only a medium size, wide beamwidth antenna. It happens!

Finally, the only reason I posted was my irritation at the all-out, personal assault on Bill Johnson for making what I believe to be reasonable suggestions. As a result the pack came after me with the equal vigor. There obviously isn't any room in this thread for anything but dogma, so this will be my last post in this thread. I'm sure that will make some very happy.
post #2414 of 16112
Quote:
Originally Posted by CEB II View Post

But, until someone has actually put a large, pre-amp'd antenna in Mrtbig's attic and found out what is receivable and what isn't, no one can say he won't receive a given channel in his area.

Why tell him it won't work when you don't know if it will.

Finally, the only reason I posted was my irritation at the all-out, personal assault on Bill Johnson for making what I believe to be reasonable suggestions. As a result the pack came after me with the equal vigor. There obviously isn't any room in this thread for anything but dogma, so this will be my last post in this thread. I'm sure that will make some very happy.

You are absolutely right that no one can tell him for sure what he will or won't get. But we can say what the odds are, and frankly, they're not good for a multitude of reasons. Having a station engineer in his market rate his chances of success as low with an outdoor antenna makes it even more likely that an attic antenna is not a good idea for him. The problem I've had since the beginning is those who present the odds as better than they are for attic antennas, or those who think that it's worth trying every half-baked idea before doing what common sense, conventional wisdom, sound physics, and expert advice all agree is the thing to do.

I can't find anything that was an all-out assault on you in the thread. I never intended to attack you personally, or treat your advice as worthless. I, for one, will miss your input if you choose to leave this thread, even if I don't always agree with it. From a multitude of counselors, wisdom comes.
post #2415 of 16112
Quote:
Originally Posted by CEB II View Post

The world would be more backward place and with far fewer rags to riches stories if everyone who was told someone wouldn't work that actually hadn't be tried, simply threw in the towel.

I agree with the earlier post that there are some basic principles for antennas that generally will improve the probability of success (e.g., higher rather than lower, outdoors rather than indoors, more metal in the air versus less, narrow beamwidth versus wide, etc.). But, until someone has actually put a large, pre-amp'd antenna in Mrtbig's attic and found out what is receivable and what isn't, no one can say he won't receive a given channel in his area.

Yes, his probability of doing so is raised by going outside. But, maybe for the multitude of reasons cited, he doesn't really want his antenna outside. Why tell him it won't work when you don't know if it will. BTW the 37 mile distance channel I get is only 7 kw, in the upper half of the UHF band (46), with no LOS, and with only a medium size, wide beamwidth antenna. It happens!

Finally, the only reason I posted was my irritation at the all-out, personal assault on Bill Johnson for making what I believe to be reasonable suggestions. As a result the pack came after me with the equal vigor. There obviously isn't any room in this thread for anything but dogma, so this will be my last post in this thread. I'm sure that will make some very happy.

I think there are probably two mindsets at work here. There's the person who wants advice on how to get something done with the least fuss possible and then there's the person who obviously needs it to work but also enjoys the quest and the hobbyist side of it. Most who ask for advice for the first time are of the former group and many who give the advice (like maybe you and me) are of the latter.

Conventional wisdom has to be the most beneficial advice for the former although certainly speculative experimentation must be allowed it's place(and is even part of the fun for many in the latter group).
post #2416 of 16112
Quote:
Originally Posted by sregener View Post

As wind passes by metal objects, static electricity forms on the metal. Enough of that charge, and suddenly, you're attracting lightning!

In many Yagi antennas, there is no easy way to ground the director elements because the are connected to the boom with an isolator. Are you saying that type of Yagi is especially dangerous? If so, why don't all antenna manufacturers connect the director elements to the boom with a conductor?
post #2417 of 16112
Quote:
Originally Posted by CEB II View Post

Finally, the only reason I posted was my irritation at the all-out, personal assault on Bill Johnson for making what I believe to be reasonable suggestions. As a result the pack came after me with the equal vigor. There obviously isn't any room in this thread for anything but dogma, so this will be my last post in this thread. I'm sure that will make some very happy.

I'm thankful for CEB's show of support (bless you) and with that I too will officially sign out with my last post in this thread.
post #2418 of 16112
I have a basic question now that I am interested in using an antenna in my HT. I recently bought a LG 4200A, it seems to be a nice unit. I want to play with antenna placement and I see that people are talking about signal strength. What sort of device measures signal strength? Is it something that sits between the antenna & the tuner's antenna input? Is this something that can be picked up at Radio Shack?

Also, I live in an area between 2 metropolitan areas - can I mount two different antennas to the same mast & have a combiner of some sort to share the same cable coming into the house?

Thanks!
Bets
post #2419 of 16112
Quote:
Originally Posted by betsy c View Post

I have a basic question now that I am interested in using an antenna in my HT. I recently bought a LG 4200A, it seems to be a nice unit. I want to play with antenna placement and I see that people are talking about signal strength. What sort of device measures signal strength? Is it something that sits between the antenna & the tuner's antenna input? Is this something that can be picked up at Radio Shack?

Also, I live in an area between 2 metropolitan areas - can I mount two different antennas to the same mast & have a combiner of some sort to share the same cable coming into the house?

Thanks!
Bets

Signal strength is measured through the receiver. Some have a meter that quantifies it to a number while others (like your LG) will just have a meter which indicates "weak, medium, strong" or something to that effect.

It's sounds like your best option will be a rotator for access to both markets. The other option would be to run two separate downleads into an indoor A/B switch.

Combining like you refer to is prone to creating signal killing multipath unless you diplex the two antennas. If one is vhf and the other is uhf that's easy to diplex, but if you're talking multiple channels on both vhf and uhf in both directions it's very difficult/expensive or even impossible.
post #2420 of 16112
Quote:
Originally Posted by cpcat View Post

Signal strength is measured through the receiver. Some have a meter that quantifies it to a number while others (like your LG) will just have a meter which indicates "weak, medium, strong" or something to that effect.

It's sounds like your best option will be a rotator for access to both markets. The other option would be to run two separate downleads into an indoor A/B switch.

Combining like you refer to is prone to creating signal killing multipath unless you diplex the two antennas. If one is vhf and the other is uhf that's easy to diplex, but if you're talking multiple channels on both vhf and uhf in both directions it's very difficult/expensive or even impossible.

On my LG Plasma, the signal strength indicator appears really to be a signal quality indicator -- BAD -- NORMAL -- GOOD. When it hits the BAD/NORMAL boundary, it drops to zero. I believe the signal really doesn't drop to zero but drops down to a level where the quality isn't good for decoding. I sort of proved this by adding a Winegard AP-4700 pre-amp which boosted the levels a few percentage points and reduced the signal quality dropping to zero on some channels. This pre-amp is excellent for overload protection, since my external CM4228 picks up both locals (in the order of 10-12 miles) and and distant channels (60 to 90 miles).
post #2421 of 16112
Although there may be at least one HDTV/STB that actually provides a signal strength display,
for the most part what is displayed is NOT signal strength, but a percentage measurement based on the detected MPEG2 data error rate.

Hence you could have a very strong signal with lots of multipath that has a very low % display and vice versa.
post #2422 of 16112
Hey gang,

I'm 60 miles west of Chicago, and one thing I have noticed is that I saw the
dreaded drop of signal from my attic antenna in early May from the leaves
growing on all of the trees. Some roughly 100' north of where my townhouse is.

Having said that...since then the reception has slowly gotten better...to the point
where it used to be in winter! Now, the drop in reception was about 10%, or
more accurately, the MPEG2 error rate on my Zenith DVR420 went up by that
amount. Since then, gradually, over the last two months, it has come back to my
winter signal levels, pretty much.

I put forth the theory that while leaves do absorb rf...I would argue that it may be
more of a function of the *water/sap content* in the leaves that does it.
Today, we had wind speeds here over 20 MPH. In May, the signal levels would
be going up and down, as one would expect from trees being nearby. Now,
that effect is barely noticeable...and it WAS unexpectedly breezy here, with
100 degree temps and southwest winds with gusts to 30 MPH!

Based on these observations, I want to throw this out to the engineers on the
list, and the advanced members who have either seen it or know about it.

What do you think?
post #2423 of 16112
Quote:
Originally Posted by sebenste View Post

I put forth the theory that while leaves do absorb rf...I would argue that it may be more of a function of the *water/sap content* in the leaves that does it.

Based on these observations, I want to throw this out to the engineers on the
list, and the advanced members who have either seen it or know about it.

Water content in the leaves definitely makes a difference. And if your weather has been anything like it has been here in Minnesota lately, your leaves would be very dry.
post #2424 of 16112
For background, I live pretty close to the major towers, about 5 miles. We are surrounded by many trees, however there are no major structural obstacles between us and the towers. Originally, we had rabbit ears for our TV, reception was alright, but some stations were a bit snowy. After reading some comments here, we bought a Silver Sensor & that made a bit of difference. The SS was mounted on top of our TV.

Over the last year, I've been building a HT in our basement, it became functional a month ago. The room has a projector, since I wanted to receive HD OTA, I bought a LG 4200A tuner. I also wired the house so I could take an antenna signal and distribute it anywhere in the house. I then tried the following (over a month):

1. I put the SS in the basement - the 4200 only picked up a few stations, and those poorly.

2. I then moved the SS to the attic and positioned it (based on the antennaweb orientation information). The reception improved significantly, although things were far from perfect. I'd get drop-outs on occasion & sometimes a channel couldn't be tuned.

3. I purchased a 4-bay antenna (antennasdirect.com DB4) and mounted that in the attic. I played some with placement, but probably could have spent more time (however it is an oven up there). Anyhow, my reception improved somewhat, although dropouts were still present. Doing an auto scan with the 4200 produced 20 stations.

4. We have an old antenna on our house, I had tried it earlier without good results. I went up on the roof recently and found the problem was the cable was poorly connected. I replaced some cabling (using the old, directional antenna) and hooked it into my system. The results were on par with the 4 bay, 20 stations & a few drop outs.

5. Lastly, I took my 4 bay from the attic and attached it to my existing antenna mast. It was a simple process, it sits slightly below the existing antenna. Here things improved pretty significantly. When I scan now, I pick up 6 new stations and so far the majors are better, no drop outs. Having the additional stations aren't the big deal, I'm just assuming that all signals are stronger - at least that's what I'm experiencing.

I haven't done anything else to the signal, it isn't amplified, etc. So in my experience, in my situation, outside placement made a big difference. When I say big, maybe less that a 20% improvement, but when it comes to a digital signal, it made big difference in my case.

Of course, YMMV - if I were to move, I'd try the same thing over again as I know of people to are satisfied with their attic install.

Bob
post #2425 of 16112
Quote:
Originally Posted by bob md View Post

Of course, YMMV - if I were to move, I'd try the same thing over again as I know of people to are satisfied with their attic install.

Basically, you're confirming what we've been saying - an outdoor install gives you the best chance for success. Not that it can't work indoors or in an attic, just that it is less likely. You're only 5 miles from your targets, so your problem was probably attic-induced multipath. An amplifier is practically guaranteed to ruin what good reception you get - inddors or out.
post #2426 of 16112
Quote:
Originally Posted by sebenste View Post

Hey gang,

I'm 60 miles west of Chicago, and one thing I have noticed is that I saw the
dreaded drop of signal from my attic antenna in early May from the leaves
growing on all of the trees. Some roughly 100' north of where my townhouse is.

Having said that...since then the reception has slowly gotten better...to the point
where it used to be in winter! Now, the drop in reception was about 10%, or
more accurately, the MPEG2 error rate on my Zenith DVR420 went up by that
amount. Since then, gradually, over the last two months, it has come back to my
winter signal levels, pretty much.

I put forth the theory that while leaves do absorb rf...I would argue that it may be
more of a function of the *water/sap content* in the leaves that does it.
Today, we had wind speeds here over 20 MPH. In May, the signal levels would
be going up and down, as one would expect from trees being nearby. Now,
that effect is barely noticeable...and it WAS unexpectedly breezy here, with
100 degree temps and southwest winds with gusts to 30 MPH!

Based on these observations, I want to throw this out to the engineers on the
list, and the advanced members who have either seen it or know about it.

What do you think?

You are on the right track with your thinking but you need to factor in something else. Yes, foliage does attenuate the signal somewhat, with long needle conifers (pine , fir, etc.) being particularly harmful to UHF reception. (Doug Lung, of TV Technology fame, often kids me about the -30 dB pine trees up in the northeast Houston area.) I don't think that we would see gross variations of signal strength due to the winds blowing and causing all of the leaves to line up one moment and pass the signal, then block the signal the next.

The factor most people don't consider with TV reception is the moisture content of the air. They will think of raining vs. not raining but most people ignore the importance of humidity. Relative humidity (RH) will change as the temperature changes even when the moisture content stays the same. So Meteorologists, and engineers who study propagation, often use Dew Point (DP) as a determinate of moisture content of the air. (DP is directly proportional to vapor pressure (VP) and is much much easier to get data on and to work with.)

If we measured your dew point temperature in the winter, it would be very low compared to the air temperature. Your trees were also bare.

If we measured your dew point in the summer, the air temperature and the dew point would be very close, perhaps only a few degrees apart. In the mornings, a car left outside often has dew on the windows because the air temperature went below the dew point and condensed on the cool glass & metal. The air in the summer is often still with no breeze until late afternoon, if then.

In the spring, the north winds often fight the south winds causing large variation in the water content of the air. The north wind brings in dry air; the south wind brings moist air. There is mixing of the two winds right over your house and all the way over the to the transmitter. Pockets of air develop with high moisture content, perhaps moving through the viewing area. Meanwhile, you see the spring breezes blow the branches around.

So how does moisture content affect radio propagation? Radio waves only travel in a straight line when they are in a vacuum. Our air (the lower atmosphere) causes the radio wave to slow down and to bend by refraction. While there are many factors that cause the bending, moisture content is the biggest factor, swamping out all the other factors combined.

We refer to this as the K-factor in our calculations. K-factor is the radius of the earth for the the TV signal as opposed to the actual radius of the earth. The greater the K-factor, the 'flatter' the earth becomes allowing reception at greater and greater distances. (Bending a wave around the earth has the same affect as flattening out the earth.)

The increased K-factor allows over the horizon reception of TV signals by folks who live further than the FCC stations service area, as you often see posted here on the forum. It also causes the signal strength of a station to increase or decrease for folks who live within the stations service area. I think you may be seeing moisture moving through the viewing area.

Bob Chase
KHWB-TV
post #2427 of 16112
Thanks for the explanation, Bob - we newbies are always looking for such info.
post #2428 of 16112
Yes, thanks Bob. Finally an educated explanation for the observations I have made the last three years, from about 70 miles from the Memphis towers. Over the years some of the self proclaimed "experts" on this forum have called me crazy for believing that I would get better reception during the summer than in winter, even citing water content in the atmosphere as a reason summer reception should be worse. But your clear explanation of the effects of dew point on reception coincides exactly with what I have observed.
post #2429 of 16112
I'm sorry if these question has been asked but I didn't find any information searching this thread. Now the question....

What would be the general affect on signal reception when there is a water tower directly inline with the transmission towers? The water tower is approximately 1/4 mile away and the transmission towers are 14-15 miles from my home.

The tower looks like this one: http://www.ci.wixom.mi.us/YourCommun...watertower.jpg

Thanks,

Alan

[edited to add photo link]
post #2430 of 16112
Quote:
Originally Posted by Alan Curry View Post

I'm sorry if these question has been asked but I didn't find any information searching this thread. Now the question....

What would be the general affect on signal reception when there is a water tower directly inline with the transmission towers? The water tower is approximately 1/4 mile away and the transmission towers are 14-15 miles from my home.

The tower looks like this one: http://www.ci.wixom.mi.us/YourCommun...watertower.jpg

Thanks,

Alan

[edited to add photo link]

If it blocks line of sight the result could be multipath. If you're analogs are from the same towers and are ghost free you're likely o.k.
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