Splitters, Attenuators, Filters, Diplexers, Other Signal Gear - Page 113 - Canadian TV, Computing and Home Theatre Forums

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post #1681 of 1748 (permalink) Old 2016-02-21, 04:40 PM
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Quote:
Originally Posted by SCChris View Post
TV Fool

Real channels 27 and 29 are adjacent to real channel 28, which is my desired channel. These are seemingly, potentially interfering with the reception of 28. How do I determine if these are interfering?
43% quality seems marginal.

The remote 28 is 24 dB weaker and in another direction; it shouldn't interfere unless the tropo propagation is unusually strong that day.

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2016-02-21 at 04:58 PM.
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post #1682 of 1748 (permalink) Old 2016-02-21, 05:06 PM
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I'd like to get 28 but it may be economically unrealistic..

Thanks Rabbit!

Chris
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post #1683 of 1748 (permalink) Old 2016-02-22, 02:14 PM
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Per your TVFool Report, Ch29 is only a few dB Stronger than Ch28...and Ch27 is much weaker. ATSC signals tolerate Adjacent Channels that are 20-40 dB STRONGER than the Desired Ch28 (depending on changing Fading conditions), so a Filter on Ch29 is NOT NEEDED and the extra Insertion Loss would reduce Sensitivity.

To receive Ch28, you'll need to improve the overall Sensitivity with a higher Gain (preferably Stacked to provide 10+ dB Space Diversity Combining Gain) Antenna System, perhaps on a Taller Mast and perhaps a Lower Noise Figure Preamp.....

Although your signal levels aren't strong enough to pose an "Overload" threat to the CM7777, the much higher levels going into the 8-Way DistroAmp MIGHT be causing 3rd Order Intermod's which would De-Sensitize SOME Channel positions. I would recommend inserting a SMALL amount of Attenuation on the Input of the DistroAmp to see if there is any improvement. For example, inserting a spare 2-Way RF Splitter would reduce the signals levels by 4 dB....and the 3rd Order IMD's by 3x4=12 dB, a Sensitivity Improvement of about 8 dB if NOT already operating at the Maximum Spurious Free Dynamic Range (SFDR) point.

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #1684 of 1748 (permalink) Old 2016-02-23, 11:52 AM
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Thank you holl_ands! inserting a 2-way is an easy experiment, it'll need to wait till the weekend. On a plus note, the hdhomerun metrics helped me to aim the antenna, done prior to the first posting, and 28 is available more of the time than it was prior to the adjustment.. What i found interesting is the strength stays high over a 20 or more degree arch directly related to the direction of broadcast antenna, expected, but the best quality was about 7 degrees or more out of direct alignment, not expected.

My antenna is about 6Ft off the roof and the height from the street is about 50 feet. I may replace the 5ft mast with a 10ft mast, this would give me a bit more headroom over distant roofs and trees.

RE, "Lower Noise Figure Preamp".. Any suggestions?

Thanks

Chris

PS the quote for the filter was an eye opener.. Not cheep.. and I'm happy not to go there.

PSS - Look and you shall receive. I found your "Preamplifier Comparison Chart v.2.1"

Thanks again!

Last edited by SCChris; 2016-02-23 at 01:23 PM. Reason: Accuracy and additional information
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post #1685 of 1748 (permalink) Old 2016-02-23, 03:11 PM
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See my earlier post re Low NF Preamps:
Signal Amplifiers (Amps, Preamps, Distro Amps)

BTW: Since CM7777 has LOTS of Gain, it is ALSO worth trying an 8-Way Splitter instead of 8-Port Distro Amp....and you COULD use that 2-Way Splitter Prior to DistroAmp to drive a "Favored" DTV.

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #1686 of 1748 (permalink) Old 2016-02-23, 03:50 PM
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I'm working my way through the "Signal Amplifiers (Amps, Preamps, Distro Amps)" forum and I'm in line with your suggestion about splitting the main after the pre-amp power and before the 8-way distro amp. This'll allow me to get a picture of what I really have at this point in the line and, if it looks good, take one of the lines and send it to a preferred tuner and send the other to the 8-way distro. If nothing else I'll get more info..

The cheapest next move will be to add 5' to the mast.


Chris
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post #1687 of 1748 (permalink) Old 2016-02-23, 08:00 PM
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I inserted a 2-way split between the power inserter for the CM7777 and the 8-way distribution amp. The free leg numbers for Channel 28 are;
98% Signal Strength
74% Signal Quality
100% Symbol Quality

The numbers for one of the 4 populated ports on the 8-way distribution amp are;
100% Signal Strength
81% Signal Quality
100% Symbol Quality

A few minutes separate the measurements, and I didn't get a baseline just before the 2-way splitter was inserted.. I know that time will tell but I have to say the numbers are very heartening..


Chris
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post #1688 of 1748 (permalink) Old 2016-02-23, 11:25 PM
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So ch 28 is coming in no problem in either case.
~24 dB SNR (74%) vs ~ 26 dB SNR (81%),
What's the issue again??

If you had a pc running linux there, you could get even more meaningful measurement
reports from your hdhomerun using forum member 905shmick's bash script, where we extrapolate the signal strength measurements beyond 100%
to dBm.

Can be useful when trying to figure out why a signal is being impaired. But in this case, with the data presented so far
I don't see much of an impairment. See the hdhomerun thread for more info if interested.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #1689 of 1748 (permalink) Old 2016-02-24, 11:34 AM
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@majortom
Apparently channel 28 has no issue other than my past assumptions and misunderstandings of the black art of antennas and cable plant technologies..

I have to say the Hdhomerun has been worth every nickel, dime and quarter paid..


Thank you all very much for the help and suggestions!


Sincerely

Chris

PS now back to the "Signal Amplifiers (Amps, Preamps, Distro Amps)" forum
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post #1690 of 1748 (permalink) Old 2016-02-29, 09:37 PM
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Question Would splitter loss be too much?

Hello All,

I'm combing through this form looking for some recommendations. Current setup is a DB8e with original CM7777 on a 60ft cable run to a single TV. Finishing my basement and would like to add a splitter and send the OTA signal to my new TV. Any recommendations for a high quality, low insertion loss splitter? I'm pretty remote so even with the CM7777 some of my channels are marginal (16db-18db). Worried a splitter will add just enough losses to lose those marginal channels.

Thanks
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post #1691 of 1748 (permalink) Old 2016-02-29, 10:17 PM
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Don't be shy, just pick up a splitter and try it. If that doesn't work out quite right, try another.

Chances are any issues you run in to will be more related to not all tuners perform the same and nothing to do with the splitter. The downstream losses are irrelevant to the overall system when the preamp is installed upstream at the antenna. One two way splitter isn't a big deal. I use a 4 way splitter here.

The only caveat would be to ensure it's a DC passive splitter,depending on where your feeding the DC power to the preamp.
If you fed the DC power via the DC injector on the Antenna side of the Splitter up towards the antenna, even that won't matter.
Not familiar with channel master so ur on your own there. Read the manual.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #1692 of 1748 (permalink) Old 2016-03-01, 07:22 AM
 
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The original CM7777 had around 23-25 dB gain. That's enough for 200' of RG6 and a two port splitter or 100' of RG6 plus an 8-way splitter, both with left over margin.
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post #1693 of 1748 (permalink) Old 2016-03-06, 08:52 PM
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Oh that's a good point. I guess I should have a power injector before the splitter? Don't have a manual for the cm7777.
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post #1694 of 1748 (permalink) Old 2016-03-07, 07:14 AM
 
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All pre-amplifiers operate in the same manner.

You cannot put just any old splitter between the amp and the injector. Only a DC-pass splitter may be used in that position, otherwise, you will block operating power to the amp and turn it into a brick. Downstream from the power injector, it no longer matters.
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post #1695 of 1748 (permalink) Old 2016-05-09, 02:01 PM
 
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300Ω suggested combiner?

So I have all the kit, and finally the weather, to complete my ganged antenna. Holl_ands strongly suggested using 300 twinlead to link the two, but at first I thought I'd avoid that for simplicity's sake. Now having read a bit more it's clear that I'm better off buying $5 of twinlead and doing it the right way.

In the case of 75 ohm, the whole idea of the splitter/combiner is that the parallel leads have lower impedance than a single lead, so you have to use a balun (etc) to fix that. The same is true for 300 ohm as well, but the problem is finding a combiner that's useful. I did come across this:

UHF/VHF Signal Combiner Transformer 300 Ohm to 75 Ohm | VANCO International

This seems perfect except for those VHF and UHF labels, which may, as I see it, be completely bogus. Has anyone used something similar to this and might have a suggestion?
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