Harmonics, from a transmitter, behave exactly like "regular radio waves" because that's what they are. Radio waves are radio waves and propogation depends of the usual characteristics, such as frequency etc. It does not matter how they were generated. So, a 2nd harmonic from a transmitter around 100 MHz will behave exactly like a signal from a 200 MHz transmitter.

For a given location and terrain, www.tvfool.com calculates received signal levels.
You should click on the call letters of each station of interest to compare the ERP power
levels assumed by TVFool (extracted from the FCC database) with what you think is
actually being transmitted (e.g. from the Canadian database)...adjust if necessary.

Impact of interference across an entire REGION can be calculated by various FREE programs,
including an FCC/NTIA program, Radio Mobile and SPLAT! Or by various commercial S/W.

Next-Adjacent, 2nd Adjacent (N+/-2), and other "Taboo" signals can be much stronger than
the desired signal, usually expressed as a NEGATIVE Desired to Undesired (D/U) power ratio. Co-channel (same channel) signals must be AT LEAST 15 dB weaker than Desired
station. However, in practice for all types of interference, it is advisable to add another
10+ dB of Fade Margin to ensure the Desired signal remains locked when subject to
multipath fading.

ATSC A/74 Receiver Performance Guidelines tells you what GOOD receivers SHOULD be
capable of in bench tests, although many older DTVs weren't quite that good and ONLY
the CECB (NTIA coupon eligible low-rez) DTV Receivers were REQUIRED to "meet spec":
http://www.atsc.org/cms/index.php/standards/recommended-practices

Tests REPORTS on actual DTV Receivers can be found here:
http://www.fcc.gov/oet/info/documents/

=================================================
Second harmonic interference from FM stations into the VHF TV band are nearly
always due to non-linearities ("overload") in the receiver system, rather than
being generated in the heavily filtered and monitored transmitter. Hence the
expected signal strengths can be calculated using www.fmfool.com.

Non-linear Interference generation explained:
http://www.odyseus.nildram.co.uk/Systems_And_Devices_Files/Linearity.pdf
http://www.fiber-span.com/Application_Note_Spurious%20Free%20Dynamic%20Range.pdf
http://www.arl.army.mil/arlreports/2007/ARL-TR-4235.pdf

The effect of FM interference for DTV reception was discussed here:
http://www.tvfmtranslators.com/PastPapers/2009/CharlesRhodesNTA2009FMixtoTV.pdf
http://tvtechnology.com/article/82716
http://www.tvtechnology.com/article/93086
http://www.tvtechnology.com/article/88282

Narrow-band Notch Filters targeted against Adjacent or Next-Adjacent interference will
degrade the desired signal due to excessive envelope delay & freq response non-linearity.
Steerable Nulls from a dual antenna system, or physically blocking the undesired station
are effective remedies....depending on how much "help" is needed....as usual...YMMV....

Narrow-band Notch Filters targeted against a strong FM station can be effective, BUT it
will also degrade Ch6 if tuned to the lower part of the FM band. A more expensive,
FM Full-Band Stop Filter would be needed if there are multiple strong FM stations.

Second harmonic interference from FM stations into the VHF TV band are nearly always due to non-linearities ("overload") in the receiver system
... and therefore special care needs to be taken when amplifying antenna signals, i.e., limiting amplification to just the amount required for stable reception of a channel? Can amplifiers with high gain figures (e.g., CM 7777) therefore magnify or even create the problem of second harmonic interference?

A more expensive FM Full-Band Stop Filter would be needed if there are multiple strong FM stations. Is the FM trap feature, advertised by some (pre-)amplifiers, equivalent to an FM Full-Band Stop Filter?

Is the FM trap feature, advertised by some (pre-)amplifiers, equivalent to an FM Full-Band Stop Filter?
Depends on the specs of the FM band stop filter.

The Channel Master 7777 FM trap has about 20dB of attenuation. I believe the FM Band stop filter by Tin Lee of Toronto offers greater than 50dB of attenuation.

Can amplifiers with high gain figures

All amplifiers have some amount of non-linearity, which is what causes distortion (harmonics) of the amplified signal. The higher the gain, the more likely this is to be a problem. Careful design can minimize, but not eliminate non-linearity.

The inexpensive FM Trap Filter built into some Preamps is a simple, tunable Notch Filter,
which has a very limited frequency range.

Tin-Lee charts illustrate difference between a CR7-HQ 88.3 (25) Notch Filter
and a more expensive CR7-FM Band Stop Filter (you get what you pay for):
http://www.tinlee.com/Graph_ALL_FM_filters.php
For the Notch Filter, 25 dB of attenuation is provided across only 1 MHz of bandwidth.
Notch Filters are typically tuned to the bottom of the FM band to improve reception on Ch6,
rather than trying to solve the more difficult second harmonic problem on Ch7-13.

Notch Filters are typically tuned to the bottom of the FM band to improve reception on Ch6,
rather than trying to solve the more difficult second harmonic problem on Ch7-13.

A better way to describe this is if you don't care about channel 6, use a full FM band stop filter. It will cut out the entire FM band, but will also kill channel 6. Another option would be to get a high pass filter that will kill FM, VHF-LO and everything else beneath that.

If you do care about channel 6, use a band shifted FM band stop filter (Tinlee also makes one of these) which will filter out most but not all of the FM band and thus won't hurt channel 6. You can then buy sharp notch filters for any strong FM stations not covered by the band shifted stop filter that are still causing problems.

There are 3-way splitters where each leg is a 5db loss.

Just found one of these in the junk bin from many moons ago, and it dawned on me
I could use one of these to further notch out a strong local FM Station nearby
(possibly beyond what ur typical Preamp FM Trap can do alone).

Tell me someone else remembers these Tunable Notch Filter Kits besides me?
I can't believe they are still available. I may buy a new one just for kicks,
since I have an FM Broadcast Transmitter within 1/2 a mile.

A fun little kit to put together.

http://www.dewtronics.com/tutorials/descramblers/notchfilter/notch.html

Link to details regarding parts per specific frequency ur trying to notch out
In my case, I'd be shooting for "Bullet/Snooper" (4 Pole) to eliminate an FM Broadcast Station.
But the one I had was tuned to Channel 11 (3 Pole, and slightly diff parts).
As it is without replacing any parts, tuning it to Channel 9 (able to totally wipe out ch9 CFTO from TO), still quite a ways a way
from FM Broadcast but seemed to stop some of the strong FM Transmitter noise here.

http://www.dewtronics.com/tutorials/descramblers/notchfilter/df222.html

Link to Rainbow Kits
http://www.rainbowkits.com/kits/df-222p.html

For 15 bux, how can ya go wrong? Especially if ur in an attic install scenario
where ya wouldn't need to weatherproof it inside a weatherproof housing?
could come in handy for some of them Big city Apartment dwellers (i.e near the CN Tower,
or the Hamilton Transmitter sites?)
Myself, I'd have to find a way to get it in to a Metal Bud Box, to insert it between the antenna
and Preamp Input.

I know you can buy pre-tuned notch filters for specific frequencies, in a shielded case like the cable co would use,
for like twice that amount + shipping, but DIY seems more fun to me. And, u'd have to be aware of the
specific freq ahead of time to specify it, which ya may not always know ahead of time.

GeoStar has posted a link in the Grounding thread to a very interesting company in Indianapolis that carries a wide range of RF filters, signal gear, and other stuff:

http://www.digitalhome.ca/forum/showthread.php?t=62265 Post #734

Right on, some cool stuff there, unless I missed sumthin,
seemed mostly for ham community, saw a lot of 50 ohm stuff.
Thx for the additional link Stampeder.

I found two of these BUD boxes in the junk bin at home.
Knew I had some, somewhere. Looks like just the right size.

Now to try and get a new one of them filters,
install inside this before soldering in the F-connectors,
drill a few small holes for the alignment, and cover the
holes with some tape. This should work for outdoors by the pre-amp.
use a little bit of caulk on the cover & the screws, to keep the moisture
out. When I get a chance to giving this idea a whirl, I'll let ya'll know
how / if it works out for filtering a single strong FM Transmitter in the
FM Broadcast Band at the Pre-AMP input.

Digikey 6253-box-alum-3-62-x-1-5-x-1-21-nat-cu-123.html

Can someone tell me what filter I could use to drop some of the signal coming from Hamilton's channel 11-1 tower. Thanks!

Tom Thumb: The cheapest solution is probably a VHF/UHF diplexer, or UVSJ. The device attenuates the alternate band...usually by 20db or more. The majority of the signal interference that you're experiencing is coming from analog CHCH on channel 11, and not digital channel 11 (actual channel 18).

How do I get the DB4 signal to run throught the splitter and diplexers. I'm running diplexers to to allow my analogue and satellite to utilize the same wiring and feed the 3 tv rooms in my home. Direct from the antenna to the Hi Def TV I get signal, through the satellite wiring I do not.

The diplexer were put in place to allow the rabbit ear feed (non digital) through to my TV's via one cable. All my TV's were non digital units.

Now I have one digital TV and a digital antenna and of course a digital satellite; are diplexers (one or both) required in the run that feeds the digital tv?

If diplexers are needed my next step would be to feed the coax from the digital antenna directly into the UHF input on the diplexer (bypass splitter) that feeds signal to the digital tv.

Current set up (x3);

Sat Feed In ------------------------- antenna feed in from 4 way splitter
---------------------Diplexer--------------------


---------------------Diplexer--------------------
Sat Feed Out-------------------------- UHF/VHF Out (to TV)

Power pass is on satellite side.

The above setup is x 3 as I'm feeding three rooms. As mentioned there is a 4 way splitter (1 in/ 3 out) at the front of this. Each of the out legs feeding the UHF/VHF port of the in diplexer. Of course the antenna is hooked to the in port on the splitter. The diplexer is a 40 - 2050Mhz combiner/splitter Satellite diplexer with one power pass leg and signal can flow through both ways.

I just tried a 4 way digital splitter (5 - 2300 MHz) spliced into the line from the antenna to the TV direct and the picture froze. I put the male coupler back in and we were up and running again. Reading the article there was a lot of talk about signal loss using connections, would guess the strength of my signal is borderline to start with.

Unless you are close to one or more FM/TV towers, you should use Preamp mounted
next to the DB4. You would need to hook up the Preamp's Power Insertion Module
(typically 18 VDC) BETWEEN the Diplexer and the DB4, rather than at your TV,
meaning you'll need access to an inconveniently located AC outlet.
FYI: A 4-Way Splitter has AT LEAST 7 dB of loss....plus the coax & Diplexer losses....

You might consider using the DC Voltage coming from the SAT Receiver, if you
used Diplexers with DC PASS on BOTH ports....but many DirecTV systems change
between 13 and 17 VDC to select Right Hand or Left Hand Polarized signals, which
could cause Preamp problems.....

BTW: Some (but not all) DirecTV systems occupy some of the OTA TV frequencies
and hence are NOT compatible with Diplexer coax sharing schemes....
Dishnet doesn't have this shortcoming....although redistributing their "TV2"
UHF signal can be tricky....

As you can see, your options may be severely limited, depending on what you have....
Check SAT threads for more info....or bite the bullet and RUN ANOTHER COAX!!!!

My diplexers (201-254) have powerpass through the Sat side only

Must the preamp be mounted close to the DB4 or can I run 20 feet of coax before putting the preamp in the system.

The goal is to run the 75 ohm cabling from the DB4 into my attic and then hook into a 4 room splitter (feeding the sat wiring /diplexer runs or independent antenna runs). Unsure of the fix, when there is two separate 75 ohm feeds (antenna and satellite) and only one 75 ohm connection at the TV??????


As mentioned in my earlier posts I tried my RCA VH368 amplifier to no avail. Looking back, looks like the piece I tried (had the two 75 ohm connections) was the power supply. The piece that had amplifier written on it (looks like a bird-house) only allowed twin lead to connect to the antenna side (connected to my rabbit ears). From the amplifier (bird-house) to the power supply then out of the power supply to the TV could have been done with 300 ohm twin lead or 75 ohm coax which ever was required. Bottom line, seems I don't have the correct amplifier to connect 75 ohm coax to the DB4, unless Im able to replace the black box on the DB4 with twin lead and then hook into the booster, where the rabbits ears are currently connected. There is a switch on the booster telling it whch out feed to run 75 or 300 ohm. The nice thing about this unit is the booster and the power supply are separate, this eliminates the need for an inconveniently located AC outlet.


Running new coax to my HDTV is not a huge issue. As noted in my last post, at this point, signal will not pass through the splitter itself. Down the road I would like to be able to feed 3 - 4 TV's, even if I run new cable to each tv location by-passing the diplexer system the signal still has to pass through a splitter, I hope a pre-amp will solve this issue, what are the specifics when looking for a device (booster/amplifier/pre-amplifier) to solve this problem.

If the preamp does not fix either (diplexer / splitter) or both I guess I'm down to one antenna per TV.

Next comes your last point re: "redistributing" please explain, don't know if it applies here.

Tom Thumb: The cheapest solution is probably a VHF/UHF diplexer, or UVSJ. The device attenuates the alternate band...usually by 20db or more. The majority of the signal interference that you're experiencing is coming from analog CHCH on channel 11, and not digital channel 11 (actual channel 18).
Thanks Jase88. Do you know where I can pick one of these UVSJ's up? I'm in Hamilton.
Thanks!

Check in here: OTA: Ontario Parts, Sales, Service, Installers (https://www.digitalhome.ca/forum/showthread.php?t=23984) and ask in that thread if you don't find what you're looking for in previous posts there.

Stampeder's 2005 input

Your Satellite receiver has to power the dish's LNBs, so that connection has to have "DC Pass" capability all the way from one end to the other. Your OTA antenna preamp has to be powered by its own DC "power injector". This means you need to make sure that the Sat. and OTA lines do not accidentally share any DC power across them, which could damage everything including your ATSC tuner. If you're using an AC-powered signal amplifier on the antenna line instead of a preamp-power injector pair, just substitute them in my layouts below.

The solution is to let the Sat. receiver run its DC power all through the diplexed connection, while giving your OTA gear its own DC power only on its own isolated branches with the antenna and with the ATSC tuner. If your diplexers do not allow DC Pass on either line you need to get two that have at least 1 line that can do that. Your layout will have to be like this:

LNB(s) -> LNB switch (if more than one LNB) -> diplexer #1 DC Pass input -> incoming coax line -> diplexer #2 DC Pass output -> Sat. receiver
+
Antenna -> preamp -> preamp's power injector -> diplexer #1 non-DC Pass input -> incoming coax line -> diplexer #2 non-DC Pass output -> ATSC tuner


I think this answers my questions and what I have for the rabbit ears; so inputing a HD antenna DB4 in place of the rabbit ears should do the trick ??????????? Questions is does the Rabbit ears preamp out put enough dB gain for the DB4