[holl_ands]

It's probably a FILTER....and the Cable Tech would use a SPECIAL TOOL to remove it. Fol. TOOL is "probably" what is used to remove it [unless it is designed to use some other type TOOL:
https://www.amazon.com/Cable-Security-Shield-Filter-Removing/dp/B00NGZGQRW

1) Filter could be a PASS BAND FILTER which only allows Internet Freqs to pass....so you can't watch regular TV...ONLY ON THAT PORT...which begs the questions as to why it wasn't attached to Splitter INPUT so it blocks watching TV on ALL ports....

OR:

2) Filter PASSES ALL CATV Freqs (up thru 860 or 1002 MHz, depending on your CATV System) and BLOCKS the higher MOCA Freqs used for Multi-Room DVR's and User Owned File Servers (i.e. PC or Network Attached Storage Device) to DLNA Player Devices (i.e. DTV and/or BD/UD-Player).

 

[majortom]

further, if internet only service, why would they install a splitter at all??
incoming cable should just go directly to the modem, shouldn't it?
Around here, for Internet + TV they also used a 3 way splitter with the modem connected to the -3.5 dB down port,
and the TVs to the -7 dB down port. Later, when I got my own modem, I put my own 4 way splitter in instead,
and ran two modems (mine for data plus theirs for voice) and two TVs, so all are equal -7 dB down now.

 

[arnyc]

The splitter was added due to line signals levels too high for the modem spec. However, this attached component doesn't look like a filter used to block certain frequencies, since there is no way to attach coax cable to it. Its threaded probably for attaching the removal tool only. Given this, can it be a hack component, like traffic mirroring? Or its a noise (return path) filter on an unused splitter connector?

 

[majortom]

I guess I am confused why your photo shows a splitter and the filter standalone sitting on a table or sumthin. Take a picture of exactly what you have in YOUR installation now and post a picture of it as is.

 

[arnyc]

Its just one cable in, 2 out - the whole installation. This component reminds me a G-trap or noise trap, but inside there are no visible locking elements one can use to remove it.

 

[classicsat]

Open terminator. Its purpose is to prevent unauthorized connection to a coax port, in this case the 3.5dB port, because that signal is too hot to reliably use for anything. 7dB is enough attenuation of the signal.

 

[ADTech]

It's a coax security lock/terminator as "classicsat" indicated.

If you look down inside the open hole, you'll probably see two notches on opposite sides. If so, you can make a removal tool out of an old metal 4-prong fork (Google it). Just make sure that you don't use one out of the "good" set of dinnerware.

 

[Jase88]

As mentioned above, a classic locking terminator. If you don't intend to use this spigot on the splitter, leave the terminator on to prevent signal leakage. Signal leakage (from cable TV systems) is tested for by both the cable company and the government, to prevent interference with licensed radio services. If leakage at your home is detected, a cable tech will eventually visit to investigate.

 

[majortom]

an example of using a 1/4 wave open circuit stub to kill a strong channel in the uhf band without disturbing much else.
tvfool:
TV Fool

Looking at that TVfool report you can see distant signals at 334 degrees with single digit or less noise margins... that's the CN tower in Toronto. Thus CN tower reception isn't possible from here without a preamp to improve the noise figure of the system. A local Transmitter farm is at the same azimuth however with high power transmitters. At ~ 310 degrees is the tallest building downtown with a couple low power tv stations on it, but in close proximity. So the CN Tower is like looking for a faint star near a full moon...

Normally, with the preamp in-line, one has to steer well away from the CN tower / local antenna farm azimuth to prevent the preamp from overloading causing intermod distortion. So, cutting a 1/4 wave stub for ~ 83 MHz to rely on the null at the 7th harmonic to knock a small chunk of UHF spectrum down. The signal level of RF 29 local LPTV station (563 MHz) is now 23 dB down from the RF 17 LPTV station (491 MHz on the same bldg at the same power) without too much disturbance elsewhere in the UHF spectrum that I am interested in. Will probably trim it a little more to get closer to the rf ch 32 flamethrower, but where it sits now is doing OK. As rf ch 32 is about 3 dB lower than usual and I can pretty much aim right in to the local antenna farm / CN tower Az. now without raising havoc in the preamp.

Pretty simple solution to a common problem, accomplished with nothing more than an old two way splitter, gutted to convert it to a 'Tee' with F connectors, re-sealed to weather proof, and a short length of coax to use as a stub. Without spending hundreds of $$$ on custom one off notch filters.

The system is split 8 ways here. Preamp driving 2way splitter, driving two 4 way splitters.

spectrum screenshots from updateDVB while aimed at 314 degrees.
before: 491 & 563 MHz equal. co-located on the same bdlg, at the same power levels.


after: 563 MHz is 23 dB down from 491 MHz.


pic of stub:

 

[majortom]

trimmed it another 1/4" after the rain stopped this AM. Another two CN tower channels came to the party. 3 of the weakest signals off the CN tower are like Low Power UHF TV stations by US standards and normally only come in under extreme ducting conditions, so have to keep an eye on them, even though I don't watch 'em (just ethnic stuff).

increased rf 29 back up by 12 dB, and reduced rf 32 further 5 dB. Getting closer to the sweet spot.
Judging by the null in the 700 MHz LTE spectrum ~ the 9th harmonic, wanna say it's fundamental is tuned to about 82 MHz now. RF 32 is about 12 dB down from nominal, while RF 29 is about 8 to 9 dB down from RF 17 now.

 

[majortom]

next experiment, made another one to reduce ch 14 (473 MHz). It is located at the same antenna farm as ch 32 (581 MHz). Took apart an old pansat 4x1 diseqc switch and removed the circuit board, which has a fried transistor anyway. Wired all 5 ports together internally with copper braid, and sealed it back up with JB Weld epoxy. This will allow a line from antenna, a line to preamp, and up to 3 stubs to hang off of it. Just gonna use 2. One for between ch 29 and ch 32 like I had, and one for 14 / just below 473 MHz.

So far, was able to reduce Ch 14 by 13 dB without much fine tuning, and had to trim the one for ch 32 a bit more due to the additional length of braid inside the new "tee" compared to the old one. Ch 32 is about 13 db down from it's original nominal of -16 dBm when it was peaked. And when panning thru the Grand Island / CN tower azimuth, the CN tower stations are peaking snr. Where as originally, they would degrade when passing thru there, due to the intermod / noise created in the preamp. Without measuring the preamp input directly, if I back my way in to it from estimated losses, preamp gain, when RF 32 & 14 was approaching -16 dBm at the tuner, the preamp input was probably ~ -22 dBm.
Which I think is consistent with the intermod numbers holl_ands has listed in the first post of the preamp thread / preamp chart.

new "tee" with 2 stubs hanging off it. stubs calculated for 3rd harmonic of 473/3 for ch 14, and 7th harmonic of 581/7 for ch 32.


new spectrum_scan while aimed at grand island / cn tower

 

[hamiltonOTA2.0]

SDR FM bandstop

I picked up a popular FM bandstop for 12 bucks from ebay plus a couple of extra bucks for a SMA to F adapter for testing. Specs are [email protected], [email protected], [email protected] and 122MHz

Test is done with a GH8n3 aimed toward Buffalo, mounted in attic of a two story home.
Known strong signals are RF15(-30dB) RF36(-25dB) FM94.7(-20dB) FM95.3(-13dB) directly at the main lobe.
RF35(-6dB) a little over a kilometer away in a null.
Toronto stations are at about 65* in the side lobe.
Kitchener stations are from the back lobe.

Testing with a UVSJ, the three local UHF stations come in along with VHF9 and CHF13. Adding an amp kills VHF9 from the second harmonics from the FM stations. Adding the FM bandstop to the mix restores SNR to normal.
Testing with the full TV band, the amp kills or degrades a lot of the channels due to overload from the three local TV stations and FM stations. Adding the FM notch fully restores the SNR for the VHF stations and partially or fully restores the SNR for some of the UHF stations.

I have a bandpass and UHF notches coming from JJ antennas. Hopefully the SDR stick I ordered arrives as well then I can post results from those.

 

[holl_ands]

DIDJA Notice that RTL-SDR did NOT mention the IMPEDANCE of the FM Band Filter????
And they are even less clear in the fol. found on their website....maybe it's 50-ohm (like most SMA)....and maybe it's 75-ohm....just as unclear as the S/W Defined Radio Specs posted on their website. PS: 50-ohm load on a 75-ohm Antenna (or Tuner) is SWR of 1.5...which will make original SWR even WORSE....so you are fore-warned:
https://www.rtl-sdr.com/about-rtl-sdr

"What is the RTL-SDR input impedance?
Since these dongles are intended for TV, most dongles will have an input impedance of approximately 75 Ohms, although it is unlikely to be exactly 75 Ohms over the entire frequency range.
Remember that the mismatch loss when using 50 Ohm cabling on a 75 Ohm input will be very minimal at less than 0.177 dB.
The 75 Ohm impedance for the R820T can be checked on the datasheet which can be downloaded here.
However, newer dongles that come with SMA connectors will be 50 Ohms."

=================================================
FYI: Inexpensive MCM FM Full-Band Filter with 75-ohm Type-F Connectors is still available at fol. source, providing more than 33 dB Attenuation across ENTIRE FM Band....compare Measurements found in my below imageevent link:
In-Line FM Trap

BTW: I've posted Frequency Response for alternative FM Band Reject Filters here, incl. the exceptional Tin-Lee CH7 CH.FM 40 FM Bandstop Filter, providing 40+ dB Attenuation across ENTIRE FM Band:
https://imageevent.com/holl_ands/files/ota

 

[hamiltonOTA2.0]

DIDJA Notice that RTL-SDR did NOT mention the IMPEDANCE of the FM Band Filter????
And they are even less clear in the fol. found on their website....maybe it's 50-ohm (like most SMA)....and maybe it's 75-ohm....just as unclear as the S/W Defined Radio Specs posted on their website. PS: 50-ohm load on a 75-ohm Antenna (or Tuner) is SWR of 1.5...which will make original SWR even WORSE....so you are fore-warned:

Yes I did notice it's 50 ohms. However, except for Tin Lee stuff, these kinds of things are not easy to source in Canada. The UVSJ I have I had to buy from the US for $15 with another 15$ for shipping so :smile $12 is cheap enough to waste for an experiment.

 

[ADTech]

FYI: Inexpensive MCM FM Full-Band Filter with 75-ohm Type-F Connectors is still available at fol. source, providing more than 33 dB Attenuation across ENTIRE FM Band....compare Measurements found in my below imageevent link:
In-Line FM Trap

FWIW, I'd be VERY skeptical about that website. They're advertising stuff of ours that we ran out of stock 4-6 years ago. If you do a Google Street View drive-by of their street address given on their website, there's a Farmer's Insurance agent's office there. Image is from Sep, '18.

 

[hamiltonOTA2.0]

JJ antennas

The order from JJ took a couple of days to fulfill once the details were confirmed and a little over a week to arrive. Items were nicely padded for transit.

Here's a quick scan with the SDR and its rinky dink antenna indoors to give an idea of the strong signals in the area.

The three local UHF stations clearly show up along with the expected FM band. None of the -45dB TV stations from Toronto show themselves. You can see activity on the 730-740Mhz cellular band. It spikes higher than shown when the scan runs continuously. I marked out the various other peaks for the curious. I'm suprised at the VHF low band results. It seems like a lot of noise considering there are no VHF low TV stations around here.

The filters

Double band pass 174-216, 470-698
50EUR

The regular version on ebay had a higher passband loss on the UHF band I assume due to the extra attention given on the upper 440-460 ham/pager frequencies. I asked for a different design that ignores those to get an improved UHF passband.

Regular notch -30dB for UHF14
22EUR

Come mid 2019, the two channels located on the same tower infront of the main lobe of the antenna will move to UHF 14 and 15. A regular notch on 14 should also still have enough impact on 15 to get an acceptable SFDR and MaxSignalIn based on the preamp chart found earlier in the thread.

Specialty notch -40db centered on UHF35
30EUR

This is a sharp notch filter to try to tame UHF35. For the moment the two Buffalo stations are second and third adjacent to it. Come 2020 they will be directly adjacent so might need to think about a Tin Lee version at that point.

Results

 

[ADTech]

The stuff in the 730-740 MHz range is the downlink for LTE band 12. Here in the US, that *usually* AT&T. North of the border, I think it's Rogers.

It seems like a lot of noise considering there are no VHF low TV stations around here.

Yeah, that's why low-VHF generally does poorly, especially indoors. The background noise level from all the electrical and electronic stuff around us tends to drown it out, even without any TV stations using it in the vicinity.

 

[rabbit73]

Here's a quick scan with the SDR and its rinky dink antenna indoors to give an idea of the strong signals in the area.

I'm suprised at the VHF low band results. It seems like a lot of noise considering there are no VHF low TV stations around here.

Nice display.

Yes, the noise level on VHF-Low is very high, requiring stronger signals to have sufficient SNR above the noise.

 

[orbot]

Are there any other uhf combiners / two-way splitters out there where all the ports are on the same side, like the DB8e uhf combiner? I contacted Antennas Direct but they don't sell the db8e combiner bundle on its own. They do sell a vhf/uhf combiner bundle with weatherproof case and mounting hardware, so if there's an appropriately-sized uhf combiner/splitter out there then maybe I could swap it with the AD vhf/uhf combiner and still use the weatherproof case and mounting hardware. This would be for the holl_ands horizontally stacked HFF8: Horiz-Stack 2xFF4 + DoubleAng Refl - RFC

 

[rabbit73]

Are there any other uhf combiners / two-way splitters out there where all the ports are on the same side, like the DB8e uhf combiner? I contacted Antennas Direct but they don't sell the db8e combiner bundle on its own.

I don't know of any. You could try sending a PM to ADTech who might make a special arrangement for you.

If that doesn't work out, you will have to use a weatherproof electrical enclosure large enough to avoid sharp bends in the coax so that they can all come out the bottom. The enclosure doesn't need to be tightly sealed; it needs to breathe to evaporate internal condensation. Usually a small opening at the bottom (weep hole) does it.

Don't forget, the two baluns must be connected in phase. If they are not, the main lobe will split in two, with a null between the lobes.