FM Radio Antennas, Reception Gear

[bentoronto]

There's a company in Rochester, I think, that sells in-line 75-ohm filters very sharp for single stations. Used it to cut out CBC-5 in Toronto years ago to be able to get Channel 4 Buffalo (so as to watch 60-Minutes Sunday night).

At the time, nice folks, quick service, and like $10.

Ben

[ExDilbert]

The signal on CIII 6 is quite weak so I wouldn't be concerned. TVFool tends to overestimate it's signal level. The analog signal might have been a problem but it had 10 times the ERP.

[roger1818]

^^^TVFool doesn't over estimate the signal level, it over estimates the Noise Margin (the amount of signal required to receive the broadcast) for VHF.

Also, the analog broadcast didn't really have 10 times the ERP, as the ERP for analog was the peek power where as for digital it is the average power, so comparing them is like apples and oranges. On top of that, the luma carrier (which would cause the most problems) for an NTSC broadcast for channel 6 is at 83.25MHz, but in ATSC, almost the entire 6MHz band is used, so it extends almost to 88MHz. Pictures comparing the two are shown below:


Image courtesy of HDTV Primer

[mrvanwinkles]

Yes, thank you Roger, with these pictures, you are showing us that the digital transmission, spreads it's power more evenly across it's 6 Mhz channel band, than the old analog.

So, there is more signal up closer to the 88.5 FM station - to possibly cause interference.

( the analog trails off, becomes weaker as you get closer to the FM band, but the digital stays almost level / square )

The pictures / the spectrum use - gives the true story.

If the FM receiver is not very good at rejecting nearby frequencies, or if those nearby frequencies are very strong ... you'll have interference.

[ExDilbert]

Even so, VHF-lo channels received a significant reduction in power with the switch to ATSC. Those charts represent a UHF signal with roughly equivalent ERP. Cut the left side down to about 5% of the current illustration and it will demonstrate what happened to CIII in Paris. It received an approximate 98% cut in power, despite what that ATSC vs analog chart shows.

I also realize that noise levels were underestimated but that's reflected in a ridiculously high NM(dB) level for CIII. A 4Kw ATSC signal is in no way as strong as the former 200Kw or so analog signal. I also suspect that the TVFool power levels (Pwr dBm) shown for CIII are too high. They don't make sense unless correction for wavelength is factored in. That makes reception even more difficult for people in urban areas who are using compact, fractional wavelength antennas.

mrvanwinkles, it's the peaks that cause the problems. They cause tuner overload and harmonics that affect other frequencies. Even though a digital signal may have more effective power, the fact that it is spread out will cause fewer problems.

[roger1818]

I have modified the picture I posted above to highlight the difference between the way ERP is measured for NTSC signals and ATSC signals. As ExDilbert said, these signals have roughly equivalent ERP in practice, but the measured value is significantly different.

[hoopitup2000]

Winegard has discontinued the excellent 6055 FM antenna. Looks like there are some still available with a google search.

[majortom]

Further to what Roger's pointing out, if ur interested there's some old spectrum screenshots in the below album from when there was analog still around. The only "Local" analog signal (2nd page) at the time around here was WBNF-CA, which was low power and adjacent to WUTV. That signal was always snowy here (Buffalo). The others ya see are distant analogs coming from either the CN tower or Hamilton.

http://www.digitalhome.ca/forum/album.php?albumid=467

Probably the best example of what Roger's talkin about is pic 25 of 28, with TVO CH19 analog in the center, a portion of CHCH-DT was on ch 18 (at the time) to the left, and CBLT-DT was on CH20 to the right. TVO analog was almost always snowy even though the peak level of the video carrier is way above CHCH-DT and CBLT-DT. 10 dB/div on the vert scale.

I should take some new ones of the current spectrum sometime.
might be an interesting comparison.

[bentoronto]

Are those pictures of the signal spectrum, showing peaks at the frequency of stations?

I sure would like to see a picture like that, esp for my location. TV/FM Fool charts (like the circular "radar" chart) kind of reveal that information but hardly as meaningful to my eyeball and mind as just a plain spectrum image. I suppose I could take the Fool TV and FM data for my location and create such an image in Excel???

Ben