Salem OR Reception issues

[Conju]

Greetings!

TV Fool Report

So I ran GroundUrMast's a-b-c method last night to quantize my reception, and had some interesting results. My goal is to pull the "big 4" (ABC,NBC,CBS,Fox) + PBS and Ion would be nice but not required. Of those, I was able to pull:

KPXG-TB 22 (75% nominal)
KATU-TV 43 (56% nominal)
KGW 8 (77% Nominal)

What was interesting to me is I was able to pull the low end of the VHF Hi band but received blackouts on 10 and 12 with similar NM and identical transmitter locations.

I built this antenna and am currently using it indoors (Living room only, HAG ~15ft). The antenna is currently obstructed by a fir tree (tall, distance 30 ft) to the north and my exterior wall. It would be possible to position an antenna around the tree, but there are additional trees in the distance.
ApeWeek Dual Bowtie Antenna


At this point, I am wondering if it might be worthwhile to place it in the attic, I am also going to test the antenna's radiance via network analyzer (EE by trade) to see if there are any obvious reasons why I might be missing 10 & 12, but I also wanted to ping the forum for other ideas. Do you guys think that I might be better served by a Yagi setup mounted externally in this case? If that were the case I suppose I should just target a ch 22 center frequency then?

Thanks in advance for your advice and help!

[Jake V]

Attics are not antenna friendly. But it's certainly worth a try. I'd run a line of coax from the antenna in the attic to one television and experiment. Be prepared to try a million or so locations in the attic until you find a sweet spot (it it exists). Keep at least 3 feet away from anything metal, have no metal in the line of sight. And if you have concrete, stucco over metal, or anything else metal, don't expect much.

If you were installing outdoors I'd start with an ANT-751 aimed north, and then keep nudging it west to see if you get the stations at 313 degrees. The ones in green are pretty strong, so it's possible.

[ADTech]

am also going to test the antenna's radiance via network analyzer (EE by trade)

...scratches head.... I've tested numerous antennas with a VNA, but I've never tested "radiance".

to see if there are any obvious reasons why I might be missing 10 & 12,

The obvious thing is that the antenna you built is a UHF antenna (it's a copy of an old Radio Shack/Channel Master design) operating between 450 and 800 MHz. Channels 7-13 occupy 174-216 MHz. Antennas that are too small electrically do not resonate well and you usually suffer extreme return loss which, in an ATSC system, results in significant reflections in your cable and at the input to the tuner. Such reflections behave the same as short-delay multipath and, if excessive, can cause the tuner's function to fail.

Indoor reception of VHF is often complicated by:
1) Lower transmitter power which doesn't yield enough field strength to adequately penetrate construction materials.
2) Localized sources of RFI from in-home electrical/electronics stuff, even the TV set itself, can readily wipe out VHF reception.
3) Effective VHF antennas require 2X-4X size increase over a comparable UHF antenna making them unwelcome in consumer's living space. Smaller VHF elements are therefore usually implemented which, combined with lower signal powers indoors, often causes erratic reception.

[Conju]

Originally Posted by Jake V

Attics are not antenna friendly. But it's certainly worth a try. I'd run a line of coax from the antenna in the attic to one television and experiment. Be prepared to try a million or so locations in the attic until you find a sweet spot (it it exists). Keep at least 3 feet away from anything metal, have no metal in the line of sight. And if you have concrete, stucco over metal, or anything else metal, don't expect much.

If you were installing outdoors I'd start with an ANT-751 aimed north, and then keep nudging it west to see if you get the stations at 313 degrees. The ones in green are pretty strong, so it's possible.

Thanks Jake! Out of curiosity, what prompted you to suggest an ANT-751 for starters? RCA is showing very little in terms of technical data on this one. Is there a reason the suggested antenna doesn't include a reflector?

[Conju]

Originally Posted by ADTech

...scratches head.... I've tested numerous antennas with a VNA, but I've never tested "radiance".

Yeah sorry, I meant to just say S11 measurement. It was interesting though looking at the analyzer plot that there was a narrow pole (maybe 6MHz BW) around 220Mhz. The system was however impedance mismatched (50/75 at load), but I don't think that would affect the locations of the poles themselves, just the amount of power transmitted to the load.

Originally Posted by ADTech

The obvious thing is that the antenna you built is a UHF antenna (it's a copy of an old Radio Shack/Channel Master design) operating between 450 and 800 MHz. Channels 7-13 occupy 174-216 MHz. Antennas that are too small electrically do not resonate well and you usually suffer extreme return loss which, in an ATSC system, results in significant reflections in your cable and at the input to the tuner. Such reflections behave the same as short-delay multipath and, if excessive, can cause the tuner's function to fail.

Indoor reception of VHF is often complicated by:
1) Lower transmitter power which doesn't yield enough field strength to adequately penetrate construction materials.

But isn't the governing factor here the apparent power at the load? In terms of raw dBm, the VHF signals are largely on-par with those in the UHF band for my geographical location.

Originally Posted by ADTech

2) Localized sources of RFI from in-home electrical/electronics stuff, even the TV set itself, can readily wipe out VHF reception.

Ahh yes, that would make sense.

Originally Posted by ADTech

3) Effective VHF antennas require 2X-4X size increase over a comparable UHF antenna making them unwelcome in consumer's living space. Smaller VHF elements are therefore usually implemented which, combined with lower signal powers indoors, often causes erratic reception.

Thanks for your response. I should also mention that I am not opposed to mounting outdoors, I just don't want to add additional hardware to the exterior if it can be avoided.

[Jake V]

Originally Posted by Conju

Thanks Jake! Out of curiosity, what prompted you to suggest an ANT-751 for starters? RCA is showing very little in terms of technical data on this one. Is there a reason the suggested antenna doesn't include a reflector?

Your signals are pretty strong, and numerous people have had great success with the ANT-751. Plus, it's generally under $50.

Alternates I would consider (which I should have listed) include the Antennacraft HBU-11 or HBU-11K ($35, not including mounting), or, for a few dollars more, the HBU-22, and the Antennas Direct C2V would also be good choices (but is quite a bit more in cost).

I'd probably start by aiming at about 7 degrees on a compass, scanning for channels a few times, and then adjusting a little each way until you have everything you want.

Home antennas are fun to build and play with. But, if they don't work very well in the attic, then the wife factor enters the picture. She's probably allow a smallish outdoor antenna if she got her favorite channels. But a home made anything on the roof is asking for trouble.

[ADTech]

he system was however impedance mismatched (50/75 at load),

That causes some really funky S11 traces. Only way to eliminate them is to (generally) use a min loss pad then calibrate using a 75 ohm call kit at the F-connector plane. Unfortunately Keysight wants about $5G for a 75 ohm cal kit, so I don't have on here (our designer has one at his lab).

But isn't the governing factor here the apparent power at the load? In terms of raw dBm, the VHF signals are largely on-par with those in the UHF band for my geographical location

You have to have both adequate power and adequate signal quality for the ATSC signal to be decoded. The apparent power of the signal at the tuner input is only half the equation, so to speak. Excessive VSWR at the antenna creates mismatch loss which must be treated as insertion loss in terms of absolute power. You still have to keep under consideration the effects of the reflected signals when they get to the tuner's input and how they affect the demodulation scheme.

Another factor to consider indoors is that, as well as pure signal penetration of construction materials by the incoming signals, there may be window openings that admit (or, if the window has a low-e coating or a metal window screen, block) incoming signals which may substantially increase the randomness of the signals inside the living space.

Frankly, after discussing all the things that could go wrong, I'm about ready to declare this to be a bumblebee which, as everyone knows, shouldn't be able to fly.

[Conju]

I have to thank you Jake for your recommendation of the 751. Installed it in my attic last weekend, was about a 2 hr job. Was especially apprehensive as I ended up having to install it looking through shingles, instead of one of the gables I had which ended up being too shallow, but I am getting clear reception on all the channels available to me (haven't yet done a detailed audit on the fringe channels, but so far I have pulled in 47 virtual channels, aimed directly at 18°). Hopefully it will continue to work through our foul NW rain

[Conju]

Update:

We had some stormy weather here over the last weekend where I was experiencing significant reception issues on CBS (6.1/40) only. The signal meter was jumping around between 50 -95% (sometimes instantaneously). I'm not sure I quite comprehend this behavior, as I would have assumed that rain would attenuate a broad spectrum of signals.

If it makes a difference I was receiving through a wet 12/5 roof, but the problem persisted even when we dried out for a bit over the weekend, so I am wondering if it was storms at or along the path of transmission that was causing the attenuation, rather than my attic wall.

Thoughts?

[ADTech]

I'm not sure I quite comprehend this behavior,

That's a common manifestation of multi-path interference, most commonly caused by wet, moving trees in front of or near the antenna, from the signal echoing around in an attic, or from electrical or electronic interference.

[Conju]

Originally Posted by ADTech

That's a common manifestation of multi-path interference, most commonly caused by wet, moving trees in front of or near the antenna, from the signal echoing around in an attic, or from electrical or electronic interference.

So I suppose at that point, my options are roof mount and/or cut the tree down? Short of turning my attic into a directional anechoic?

[GroundUrMast]

Ideally, there would be nothing obstructing the path between the transmitting and receiving antennas. The elimination of a roof deck often improves the situation a great deal. Still, trees are a big deal when they move about.

In either case, wet roof/changing weather conditions or moving tree limbs, the signal quality is affected far more than the raw signal strength. If you have ever been in a place that has a significant echo problem, you can understand how making the sound louder does not resolve the echo problem... Your difficulty understanding spoken words in such a situation is not a problem of sound level (signal power) but sound quality.

Your tuner may be satisfied if you can eliminate just one source of signal quality impairment... Or, you may need to go all out, mount outdoors and get over/around the trees.