attenuate 2 UHF OTA TV channels

tahlyn · 17-Jan-2017, 1:02 AM

hi,

I have a situation where I have 2 channels that come in extremely strong, but all other channels (2 hi-VHF and 2 UHF) are very weak, so weak, that those channels can only be tuned with a preamp. However, because the preamp also "boosts" the extremely strong channels, I'm getting pixelation and other distortion issues, probably due to overload on the TV tuners.

So, I'm thinking that I'd like to attenuate the 2 UHF OTA TV channels that have extremely strong signals. Both ABC (RF 16 - UHF) and CW (RF 34 - UHF) are only around 9 miles away and the signal from both are always 98%+ signal strength either directly to the TV or through the HDHomeRun Extends. I can actually put the antenna on the ground in the opposite direction of the tower and still easily get the signals from ABC and CW.

Since the weak channels are both VHF and UHF, I can't just have separate VHF & UHF antennas, and then only use a preamp on one of them like you usually could. I think I need a way to attenuate the extremely strong UHF channels, but not the weak VHF & UHF channels.

What do I need in my situation? Are there inline filters that can attenuate specific channels and adjust independently for the 2 separate channels?

thanks for any information in advance.

===============================

TV Fool Report
http://www.tvfool.com/?option=com_wr...e6a484469c67df

===============================

EQUIPMENT

- Winegard HD7698P antenna on 20ft mast.
- 2 different outdoor preamps that I can experiment with:
- currently using Winegard LNA-200 Boost XT Outdoor Digital TV Antenna Amplifier (max gain 18 dB).
- Channel Master CM-7777 Titan 2 High Gain Preamplifier (max gain 30 dB).
- 3 HDHomeRun Extends.
- rg11 outdoor direct burial coax between antenna and house.
- quad shielded rg6 from attic to 3-way split to 3 HDHomeRun Extends.
- HDHomeRun Extends connect to home network (all cat6 cabling) to Win10 server with NextPVR software which can be output to any TV/device in the house either wired or wireless with proper app.
- Fire TVs are wired to home network with HDMI connection to TVs.

===============================

SETUP

- in Florida, obviously very flat, but in a slight depression, next to a canal with hundreds of 50ft+ pine trees on either side of the canal.

- Antenna is pointed south toward towers, mostly parallel to canal and slightly upwards over the pine trees. After lots of experimentation, I found this brings in the best signal. I've spent hours moving & pointing the antenna in lots of different locations, directions, angles, and heights.

- antenna is pointed almost due south, directly at the NBC and CBS tower, which have the weakest signals. There's about 150ft opening between the pine trees on the back of my property that I point the antenna up and through.

- I tried smaller antennas, but because of my situation with the canal and pine trees, only a large antenna like the HD7698P worked with NBC and CBS (and I still need a preamp for that to work).

- I have a neighbor with an antenna setup that is 1 mile farther away from the towers, but not on a canal or in a depression, and his channels come in perfect with no preamp, and, with a much smaller antenna (Denny's HD Stacker antenna).

===============================

SIGNAL STRENGTH (ss), SIGNAL QUALITY (snq) and SYMBOL QUALITY (seq)

- without and with Winegard LNA-200 Boost XT Outdoor Digital TV Antenna Amplifier (max gain 18 dB)

- getting numbers from TVs, HDHomeRun Tuner Status page, and the "Signal GH" iPad app. Numbers match from all sources. Obviously, signal is slightly stronger directly from antenna to TVs.

- without an outdoor preamp, I only get 2 channels, ABC and CW. With an outdoor preamp, I get all channels, even in most bad weather.

- However, with preamp, I'm getting occasional pixelation and distortion on all channels.

- I don't think any of the percentages can go above 100% so I really don't know what the peak ss/snq/seq are.

ABC (RF 16 - UHF)
485 MHz
- path LOS
- 9.3 miles to tower
- ss74%/snq100%/seq100% no preamp
- ss100%/snq100%/seq100% with preamp

CW (RF 34 - UHF)
593 MHz
- path LOS
- 9.3 miles to tower
- ss68%/snq98%/seq100% no preamp
- ss100%/snq98%/seq100% with preamp

FOX (RF 28 - UHF)
557 MHz
- path LOS
- 47.9 miles to tower
- ss27%/snq41%/seqNONE no preamp (no channel reception)
- ss94%/snq89%/seq100% with preamp

PBS (RF 27 - UHF)
551 MHz
- path LOS
- 47.9 miles to tower
- ss25%/snq41%/seqNONE no preamp (no channel reception)
- ss92%/snq89%/seq100% with preamp

NBC (RF 12 - hi VHF)
207 MHz
- path 1Edge
- 47.3 miles to tower
- ss18%/snq40%/seqNONE no preamp (no channel reception)
- ss80%/snq85%/seq100% with preamp

CBS (RF 13 - hi VHF)
213 MHz
- path 1Edge
- 47.4 miles to tower
- ss17%/snq40%/seqNONE no preamp (no channel reception)
- ss73%/snq81%/seq100% with preamp

Again, thanks for any insight into my situation.

skatingrocker17 · 20-Jan-2017, 8:01 PM

Not too long ago I saw someone post about attenuators that you could order for certain frequencies. I think it was an ebay where you ordered the part the messaged the user what frequency you wanted to attenuate.

Maybe someone else knows what I'm talking about or could point you in the right direction.

GroundUrMast · 20-Jan-2017, 8:13 PM

Check with www.tinlee.com for custom tuned filters. Be prepared for sticker shock, as their product is generally custom work that requires expensive test gear and skilled labor to produce.

tahlyn · 20-Jan-2017, 9:14 PM

thanks for the help. Including help from here, and my posts here:

https://www.reddit.com/r/ota/comment...a_tv_channels/

and here:

https://forum.silicondust.com/forum/...?f=113&t=63763

I've got all the information needed to move forward with my issue.

For the notch filter, I contacted 2 companies:

===============================

Tin Lee

the TLE rep suggested installing a notch filter before the pre-amp if the 2 UHF channels are overloading the pre-amp.

He said TLE can build 2 UHF bandstops (channels 16 and 34) and it could be built into one enclosure. Attenuation would be fixed and user-specified between 15dB to 25dB. He also noted that the bandstop would affect the signal +/-10MHz on either side of each bandstop, which in this case, would affect potential channels 15, 17, 33 and 35. Since I don't have or watch any of these channels, that wouldn't be an issue for me.

He said one filter with two UHF bandstops would be around $195.00.

===============================

PAR Electronics

I also contacted another company called PAR Electronics out of North Carolina, www.parelectronics.com.

They said the filter could go inside- post preamp- as long as your preamp is not being overloaded. If the preamp is being driven into distortion then the filters must be in a weather proof enclosure between the antenna and preamp.

They also said the 593MHz filter, 605mHz would take about a 6dB hit. Filters w/ F/F type F are $42 dollars each. They are a dual stage and factory preset on their network analyzer at about -20dB attenuation. Not adjustable.

I sent a follow-up question about the easiest/cheapest way to measure the UHF signal as well and he said a Jerrold or Leader Field Strength Meter might be found used for $400 under.

===============================

After doing a lot of research based on information from everyone, I've come to the conclusion that it's really difficult to get at hard numbers like dBm without a meter. At first, I thought I could get the numbers from my HDHomeRun, but only the commercial HDHomeRuns display "dBmV signal level", and, at that point, I could just get a Digiair Pro ATSC TV Antenna Signal Meter for less money (but still over $300US).

I even found software called TSReader that outputs information from an HDHomeRun, but like one of the devs told me, "it's down to the demodulator and the only HDHomeRun that gives you the dBm is the HDHomeRun Pro".

If I get over the fact about hard numbers and just solve my own issue, and like more than one person has mentioned at this point, just keep attenuating until the signal drops below 100% on the HDHomeRun Extend and then run the math that dev Nickk supplied from Silicondust. That's what I'll do, I just wish it was easier/cheaper to get at the dBm numbers.

If I do determine that I need to attenuate my 2 extremely strong UHF channels, how much to attenuate, and the attenuation needed for each channel is at least 15dB, then I'll need to decide if it's worth purchasing a notch filter with two UHF bandstops from places like Tin Lee or Par Electronics (which will probably be between $100 - $200 like I mentioned earlier).

I think at this point, I've bothered everyone possible and have all the information needed to move forward.

I appreciate all the help.

ADTech · 21-Jan-2017, 12:25 PM

Quote:

Originally Posted by skatingrocker17

Not too long ago I saw someone post about attenuators that you could order for certain frequencies. I think it was an ebay where you ordered the part the messaged the user what frequency you wanted to attenuate.

Maybe someone else knows what I'm talking about or could point you in the right direction.

That would Jan Janca Electonics in Slovakia, ebay username "jan_jenca". They can whip just about anything needed, you'd have to work directly with them to communicate your precise requirements including amount of attenuation required in each of the notches and how selective the filters must be in order to maximize how many adjacent channels are to be preserved. It usually takes a filter with very steep skirts to limit their effect to only one or two adjacent channels and that sort of selectivity gets more expensive very quickly.

Here's their current link to a single/dual notch filter: http://www.ebay.com/itm/UHF-channel-...oAAOSwMVdYGwdY

rabbit73 · 21-Jan-2017, 3:04 PM

http://www.antenne-komponenty.eu/eng...zlucovace.html

http://www.antenne-komponenty.eu/eng...ct/filtre.html

WIRELESS ENGINEER · 21-Jan-2017, 11:19 PM

Yes, reducing the level of the strong channels is necessary before the preamp.

The 7777 is too much gain so the winegard would be a better choice.

Either way, preamps will also amplify interference as well so only use one if you have to and only use enough gain to compensate for coax loss

Vhf signals generally don't need to be boosted at all or very little due to much lower coax loss at those frequencies

The winegard ap4700 preamp was ideal since it only amplified UHF signals and passed the vhf.
But they quit selling them.

The notch filters are a good idea and will also introduce loss so be aware of that fact

All these guys have provided great info on filters already and I have nothing to add there

Tower Guy · 22-Jan-2017, 3:17 PM

I have a suggestion to try without using special filters. Remove the amp from the antenna. Get two UVSJ splitter joiners. Install one on the antenna. Feed the VHF port to the preamp input. The preamp output goes to the VHF port of the second UVSJ. Install a short jumper between the UHF ports of the two UVSJ's. This will amplify the VHF, but not the UHF.

rabbit73 · 22-Jan-2017, 7:41 PM

That might work, but the VHF port of the second UVSJ would need to be power passive for the preamp. The Radio Shack and Antennas Direct UVSJs are power passive on the UHF port, not the VHF port.
https://mjsales.net/products/tru-spe...ant=1198505857

Code:

       UHF> Jumper> UHF 
        /             \
7698> UVSJ           UVSJ> coax> grounding> power> tuner
        \             /            block   inserter
       VHF> Preamp> VHF

Another possible solution is to attenuate the UHF and amplify both. The attenuator value would be selected by trial and error. Too much attenuation would make WXEL 27 too weak; not enough attenuation would cause overload from 16 and 34. I suggest 15 dB as a starting point to make it as weak as the VHF channels before amplification.

Code:

      UHF> Attenuator> UHF 
       /                \
7698> UVSJ            UVSJ> preamp> coax> grounding> power> attenuator> tuner
       \                /                  block    inserter
      VHF> FM Filter > VHF

You might also need an FM filter between the VHF port of the first UVSJ and the VHF port of the second UVSJ. You have a strong FM signal coming from the south.
http://www.fmfool.com/modeling/tmp/f...a/Radar-FM.png

I suggest a HLSJ, High and Line ports, as an FM filter and an Antennas Direct Juice preamp because it is resistant to overload.

http://www.solidsignal.com/pview.asp?p=zhlsj

You might need some attenuation after the preamp power inserter to prevent tuner overload. The signal dynamic range between CH 16 and CH 12 will be about 36 dB, for a required SFDR (Spurious-Free Dynamic Range) of 52 dB after adding the minimum required SNR of 16 dB for CH 12.