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My DTV is like HF??

post #1 of 13
Thread Starter 
Hi, guys. This might be simple for somebody here so here goes. I've set up my old analogs with the converter boxes and did the autoprogram. I'm using a Phillips outdoor amplified antenna mounted in various spots on a pole. I live on Melrose Mt. in Tryon, about 2300' elevation but heavily wooded. At first it seemed like I hooked up to a dish, showing about 50 channels and most were godlike. However, as nighttime rolls around some of our favorite channels lose signal strength like crazy and come and go. It reminds me of my years on HF, shortwave, when daytime signals faded and you had to change freqs. Somebody at RS told me that some stations are not at full power yet on HD and also reduce power at night. Any ideas? Thanks in advance....Ed.
post #2 of 13
Topic title changed and topic moved to correct forum.
post #3 of 13
Quote:
Originally Posted by Ed Foster View Post

Hi, guys. This might be simple for somebody here so here goes. I've set up my old analogs with the converter boxes and did the autoprogram. I'm using a Phillips outdoor amplified antenna mounted in various spots on a pole. I live on Melrose Mt. in Tryon, about 2300' elevation but heavily wooded. At first it seemed like I hooked up to a dish, showing about 50 channels and most were godlike. However, as nighttime rolls around some of our favorite channels lose signal strength like crazy and come and go. It reminds me of my years on HF, shortwave, when daytime signals faded and you had to change freqs.

Digital TV reception can be similar to HF & shortwave, as you have observed.


Quote:
Somebody at RS told me that some stations are not at full power yet on HD and also reduce power at night.

Most DTV stations are already at full power, but they will be optimising in other ways for digital after 2/17/09.

Quote:
Any ideas?

Get a real antenna, directional and mounted as high as possible.
post #4 of 13
It's probably more common to have improved reception on some channels at night because of atmospheric temperature inversions. I have a couple of stations about 85 miles away that I almost never see during the day, but usually become watchable around sunset. Other stations in the 65-75 mile range also usually come in better at night.
post #5 of 13
I've found the best reception happens early in the morning, between midnight and 5 a.m. Once the sun rises, then reception diminishes.
post #6 of 13
post #7 of 13
Quote:


It's probably more common to have improved reception on some channels at night because of atmospheric temperature inversions.

Yep. The reverse is very unusual and is most likely due to his antenna. Like noted above, he should get a real antenna.
post #8 of 13
Are you going to give him $200 to cover the cost?

Or are you willing to refund the money if the new antenna does not work as you promised it would?

It's waaaay too easy to just say "get a new antenna" rather than fix the actual problem. It sounds like he already has an outdoor antenna. He just needs to raise it to the FCC-recommended height of 30+ feet. I'm not sure that will fix the problem, but it's a lot cheaper suggestion then "go waste your money buying a new antenna".
post #9 of 13
Sounds like tropo is causing Ed's signals to fade. I have 3 fairly reliable stations(40-65 miles) during the day, that are lost on some nights; particularly one.(Almost every night) They are usually overtaken by strong tropo from the back of the antenna.

A highly directional (real) antenna would help Ed more than anything else.
post #10 of 13
And Ed is at the southern edge of the North Carolina mountains, where there are a lot of translators for analog signals. Maybe some of them are interfering with his desired signals at night because of tropospheric enhancement.

I have a similar problem with WUNF-DT out of Asheville, which is on ch 25. Out of Columbia, WOLO (analog) is also on channel 25, and I'm in the middle. During the day, I can usually get decent reception on WUNF-DT if I aim my antenna carefully, because I have line-of-sight to its transmitter on Mt. Pisgah, whereas there's a slight rise in terrain between me and Columbia. At night, however, the signal from WOLO increases and usually swamps out WUNF-DT.

Which specific channels are giving you problems, Ed?
post #11 of 13
I ran across this link today. http://guidetouhf.blogspot.com/2007/...echniques.html

Quote:


UHF advantages

Fringe or DX UHF TV reception has unique technical challenges, which leave little room for error. Let's consider some of the advantages for UHF verses VHF TV reception:

1. Man-made and external ambient noise levels at UHF are at least 20dB less than VHF band I (45-70 MHz).
2. Low noise masthead preamplifiers are very beneficial at UHF.
3. UHF antennas are smaller and compact, hence relatively easy to produce high gain aerials.
4. Due to the small wavelength size, it is more practical to stack high gain UHF antennas, but with manageable physical space.
5. Height gain is significant at UHF. Usually one obtains about 0.5dB gain for every foot heigher, for heights between 25 and 35ft. In other words, the same aerial will provide about 5dB more signal at 35ft than at 25ft.
6. UHF transmitter powers are very high, typically 500kW to 1000kW.

UHF disadvantages

1. UHF TV tuner noise figures are around 10dB (typical). VHF tuner noise figures are typically 6dB. This means UHF tuners are 4-6dB less sensitive than VHF tuners.
2. Signal path loss is much greater at UHF.
3. Trees, foliage, buildings, etc, greatly absorb UHF signals.
4. Transmission coax cable line losses are far greater at UHF compared to VHF band I.
5. UHF TV aerials need to be positioned higher than VHF aerials.
6. The voltage developed by a dipole element decreases inversely with frequency. For example, a band I dipole will develope from a given field strength about 15 times as much signal voltage as a high band V UHF dipole.

To help compensate for UHF disadvantages, we need to observe the following points:

1. Use high gain (13-18dB) 'deep fringe' type UHF only TV aerial(s) (see list below).
2. Use a quality low noise (2dB or less) masthead UHF preamplifier.
3. Use low loss 75 ohm coax cable (see table below). For example, RG-11 coax. Never use RG-75U coax!
4. Position the UHF antenna at least 30 ft above ground level. Within constructional limits, the higher the better.
post #12 of 13
I agree with a lot of the above variables. There is one simpler one that I haven't seen mentioned yet.

Condensation.

The preamp in the outside unit may be experiencing moisture buildup. That would corospond with the effect only being at nigth when it grows cooler. Feedwires have been known to show adverse effects from moisture too, but are less likely to follow a tempreture induced condensation cycle. Sure is easier to test for though (By swapping out for a known good feedwire).

Ed, could you comment on the analog signal at night?
Does it fade noticibly too on the same troubled channels?

That would help indicate if atmospheric conditions are causing an effect that contributes to the newer ATSC standard failing.
post #13 of 13
I'm going to go out on a limb and guess that he's seeing amplifier overload; propagation generally improves at night (as noted), so interfering sources which weren't a problem during the day may become a problem at night. I googled a spot on Melrose Mountain and plugged it into TV fool, and there's stations receivable with -26dBm (!) signal strength. If the OPs spot is similar, bypassing the amplifier might do the job.
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