FM Trap layman question
Daniel
I am currently looking to install an omnidirectional TV/FM antenna in
my attic (unfortunately I don't have space for a directional one with
a rotator).
Ideally, I would like to have a single antenna feeding the single coax
cable run throughout the house (a condo), fulfilling the needs of both
my TV set and FM stereo system.
I found on the web a few such antennas offered by Winegard and Radio
Shack. However, all of them have a FIXED FM trap. That is, even if I
wanted to switch it off, I couldn't.
My first question is: Why? Why isn't anyone making an omnidirectional
antenna WITHOUT an FM trap? Is there an inherent problem in
omnidirectional antennas that mandates an FM trap?
My second question is: If I combine the RF signals (using a coupler
similar to the Winegard CA-8800 in
http://www.winegard.com/products/accessories/acc_ant_seperator_joiner.html)
from two omnidirectional antennas (one FM, one VHF/UHF), in order to
feed the combined signal through the single coax run - will I
essentially re-introduce the very same problem that the FM trap in the
VHF/UHF antenna was trying to solve? Is this solution better or worse
than having a single VHF/UFH antenna that does not have an FM trap?
(assuming I can actually find one...)
Please reply directly to this newsgroup (my email address is bogus, to
prevent spam).
Many thanks in advance,
Daniel
Richard Clark
>
>I found on the web a few such antennas offered by Winegard and Radio
>Shack. However, all of them have a FIXED FM trap. That is, even if I
>wanted to switch it off, I couldn't.
Hi Daniel,
You don't need to. The "switching" comes free and is only noticeable
at the receiver (working correctly for the correct one). That is the
point of traps.
>
>My first question is: Why? Why isn't anyone making an omnidirectional
>antenna WITHOUT an FM trap? Is there an inherent problem in
>omnidirectional antennas that mandates an FM trap?
No
>
>My second question is: If I combine the RF signals ... - will I
>essentially re-introduce the very same problem that the FM trap in the
>VHF/UHF antenna was trying to solve?
It isn't a problem in the first place - but you can turn it into a
problem.
Start with the simplest solution first, and THEN add complexity.
73's
Richard Clark, KB7QHC
Tarmo Tammaru
indoor antennas. The FM trap is there , supposedly, to keep a strong FM
station from overloading your TV front end. Probably, it is there to keep
from overloading the the amp in the antenna. Havent't looked at the
Wineguard, but the RS is an amplified rabbit ear. You are better off putting
the biggest outdoor TV antenna that will fit in your attic up there.
Generally, they don't have FM traps. Remember though, the more gain, the
more directional the antenna will be. FM gain will be low on any of them.
Normally, you can combine a TV antenna and FM antenna on to one coax with
the proper filter (not 2 way coupler), but that may not work with the
amplified antenna because it sends DC up the coax. For the price of the
filters, you could just buy the extra coax and keep the antenna separate.
This will also have less signal loss.
If you really need the amplified antenna, and single coax, make sure the
combiner will work with that antenna. Don't assume you can also use an
amplified FM antenna. Buy the stuff as a package, and have the salesman
reassure you that it will all work together.
Tam/WB2TT
"Daniel" <dan...@my-deja.com> wrote in message
news:b73f7787.0305...@posting.google.com...
WB3FUP (Mike Hall)
antenna (15-2164) that sells for less than $20.
It is two "folded dipoles" stacked at right angles
to each other, separated by 3 - 5 inches. Each of
the dipoles is about 5 feet long, and should mount
easily in your attic. The antenna's nominal
feedpoint impedance is 300 ohms, so you will need
a balun (15-1230) to match to coax. If you need
further amplification there are a number of
distribution amplifiers available. However I
would try the antenna barefoot first, just split
the output 4 ways at the antenna and see what kind
of reception you have.
73 es cul
wb3fup
a Salty Bear
"Tarmo Tammaru" <t-ta...@home.com> wrote in
message news:4YidnbcwIIK...@comcast.com...
Crazy George
This was discussed here in some detail several months ago. To summarize, FM
stations tend to be nearer homes, and thus produce higher field strengths.
Simply due to the signal structures and receiver designs, FM interferes with
TV channels about 100X as often as TV interferes with FM. Thus, the traps
you have encountered. If you had access to a good spectrum analyzer, you
would see that even with the traps, the FM band output from the antenna is
plenty high enough to distribute to several FM receivers. On one leg of my
home CATV system (distant channel 2), I have 3 FM traps in different
locations, but electrically they end up being in series, and there is still
enough FM signal from that leg to provide full quieting signals from locals
on any tuner I have connected.
So, a suggestion. Install the TV antenna and check the FM signal levels.
If they aren't strong enough, add the FM antenna through the coupler. The
only way to get omnidirectional gain is at the expense of a physically
taller structure, or by amplification. But, a couple of strong FM signals
may overload the amplifier and cause herringbone interference on one or more
TV channels.
--
Crazy George
Remove NO and SPAM from return address
Roger Halstead
>Greetings,
>I am currently looking to install an omnidirectional TV/FM antenna in
>my attic (unfortunately I don't have space for a directional one with
>a rotator).
<snip>
Be careful with amplified antennas. The Wineguards have been causing
interference although they may have cleared that up by now.
Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)
Crazy George
hundreds by RatShack, among many others. It has been fixed once, broke
twice. There are so many in the distribution pipe that it is impossible to
guess whether one bought somewhere today will be good, or noisy (spurious
noisy). The FCC, FAA, Coast Guard, and Institute of Navigation all know the
full story.
--
Crazy George
Remove NO and SPAM from return address
"Roger Halstead" <rdha...@tm.net> wrote in message
news:mg9ecvgn2957nmkpr...@4ax.com...
Roger Halstead
<muns...@attglobal.net.SPAM> wrote:
>Not just the Winegards. That has become a generic design sold in the
>hundreds by RatShack, among many others. It has been fixed once, broke
>twice. There are so many in the distribution pipe that it is impossible to
>guess whether one bought somewhere today will be good, or noisy (spurious
>noisy). The FCC, FAA, Coast Guard, and Institute of Navigation all know the
>full story.
Yup.
Like the FCC action against the RV owner telling them to quit using
the antenna , "or else".
Crazy George
what was said to the group in the RV park at the airport where the pilots
"using" GPS reported problems in the landing approach? I keep forgetting to
find out exactly where that was. You being a pilot may know, was that
reported in the AOPA magazine?
--
Crazy George
Remove NO and SPAM from return address
"Roger Halstead" <rdha...@tm.net> wrote in message
news:ce6fcvg7ilkoqba2u...@4ax.com...
Daniel
> So, a suggestion. Install the TV antenna and check the FM signal levels.
> If they aren't strong enough, add the FM antenna through the coupler. The
> only way to get omnidirectional gain is at the expense of a physically
> taller structure, or by amplification. But, a couple of strong FM signals
> may overload the amplifier and cause herringbone interference on one or more
> TV channels.
George, thank you for your answer (and thanks to all other who
replied). I do have a pretty strong FM radio station near my house
(can be heard over my ordinary (non-wireless) phone...) and I would
like to filter it out as closer to the antenna as possible. Do you
know where I can purchase such single-frequency (98.9 MHz) filters?
The idea that I had in mind for my antenna installation was this:
+-----------------+ +-----------------+
| Amplified | | |
| Omnidirectioanl | | Omnidirectioanl |
| VHF/UHF Antenna | | FM Antenna |
| with FM Trap | |(can I find one?)|
+-----------------+ +-----------------+
| |
| RG6/U RG6/U |
+-------------+ +--------- +
| |
| |
+-----------------+
| |
| RF combiner |
| |
+--------+--------+
|
| RG6/U
|
+-----------------+
| |
| Ant. Amplifier |
| |
+--------+--------+
|
| RG6/U (runs
| throughout
| house walls
| to basement)
+--------+--------+
| |
| Splitter |
| |
+--+--+--+--+--+--+
| | | |
| | | |
| | | |
| | | | +----------+
| | | | | FM |
+------+ | | | +--------+ Receiver |
| | | | | | |
| TV +-----+ | | +----------+
| | | |
+------+ | |
| | +----------+
| | | FM |
| +-----------+ Receiver |
| | |
| +----------+
|
|
| +----------+
| | FM |
+--------------+ Receiver |
| |
+----------+
However, I saw your other posting that suggested that the amplified
omnidirectional VHF/UFH antenna may be causing some interference. (one
would think that after learning about the problem, Winegard would fix
the problem and recall all its faulty antennas...)
I did manage to find a non-amplified version of the MS-2000, called
MS-1000 at: http://www.winegard.com/products/vhfuhf_tv_products/general_antennas.html
Do yo think this would be a better solution for me? It seems that it
might save me from investing in another antenna and a combiner. I
already have a 26dB antenna amplifier in my attic (radio-shack
#15-1108).
Thank you so much for your advice!
Daniel
Daniel
need a fixed-size font (courier or similar).
Daniel
multiple posting):
Crazy George
To give you a credible answer, I would need 2 things, one of which you can
give, the other, I suspect not. To do an analysis, I need the frequencies
and amplitudes of the stations. Since I suspect you do not have a
calibrated spectrum analyzer, let me take a WAG from the channels in your
area, and frequencies of the FM stations. And, lacking amplitudes, a rough
guess as to distance to the closer ones (any less than 25 miles). The
likely problem will be the lower amplifier, where both the TV and FM will be
present.
Omni FM antennas used to be common, there were two designs, a halo version
for RVs and a folded dipole which was lazy "S" shaped when viewed from
above.
I wasn't clear on your nearby FM problem. There are phone filters
advertised in the ham magazines which will take care of the phone, and
Winegard used to make a FM trap with one tunable notch, but I have no idea
of the model number. And, I have had only marginal success tuning one of
those without an analyzer of some type, as there are secondary effects which
may or may not let you get effective performance. Which is probably why
they are not more widely used. The RatShack FM filter is pretty good for
the price, I looked at a handful of them a few weeks back, and was amazed at
how similar they all were, and the amount of attenuation across the band.
Unfortunately, they are not too good at the low end, so as to not attenuate
channel 6 audio at 87.75 MHz, and based on the now incorrect premise that
educational stations below 92 MHz will be running lower power. That was
changed over 10 years ago, and there are plenty of class A stations near the
low end now, and channel 6 vs. FM interference issues have again bubbled to
the surface in the broadcasting industry. Unfortunately, no one has a good
way to defeat the laws of physics, even though the lawyers legislate against
them.
WB3FUP (Mike Hall)
--
73 es cul
wb3fup
a Salty Bear
"Daniel" <dan...@my-deja.com> wrote in message
news:b73f7787.03051...@posting.google.com...
Tarmo Tammaru
I think you have too much gain in the TV path. Put the FM distribution amp
after the TV and FM signals have been separated. Also, do not use a 2 way
splitter to do that. They make filters with separate outputs for TV and FM.
This will keep the strong FM signal from getting into the TV. This would be
the same thing you used to combine the two antennas, except hooked up
backwards. Keep the gain of the FM amp on the lowest seting, probably 10 -15
db.
Since the FM station you are concerned with is around the middle of the FM
band, filters should do a good job.
Tam/WB2TT
Daniel
> Omni directional FM Antenna # Radio Shack 15-2164
Thank you. I did find it on Radio Shack's web site
(http://support.radioshack.com/support_audio/doc61/61405.pdf), but
with all the detailed information I couldn't find out how big it is. I
need to make sure it can fit in my attic (unfortunately a small one).
Daniel
P.S. Anyone had bad experience with this antenna? How would you rate
it comparing to other **omnidirectional** FM antennas that can be
found in the market?
Daniel
> Radio Shack sells a omnidirectional outdoor
> antenna (15-2164) that sells for less than $20.
> It is two "folded dipoles" stacked at right angles
> to each other, separated by 3 - 5 inches. Each of
> the dipoles is about 5 feet long, and should mount
> easily in your attic. The antenna's nominal
> feedpoint impedance is 300 ohms, so you will need
> a balun (15-1230) to match to coax. If you need
> further amplification there are a number of
> distribution amplifiers available. However I
> would try the antenna barefoot first, just split
> the output 4 ways at the antenna and see what kind
> of reception you have.
Thank you very much for this information. I missed this posting and so
I mistakenly posted (elsehwere in the thread) a question about the
antennas size. Please ignore it.
Daniel
> I think you have too much gain in the TV path. Put the FM distribution amp
> after the TV and FM signals have been separated. Also, do not use a 2 way
> splitter to do that. They make filters with separate outputs for TV and FM.
> This will keep the strong FM signal from getting into the TV. This would be
> the same thing you used to combine the two antennas, except hooked up
> backwards. Keep the gain of the FM amp on the lowest seting, probably 10 -15
> db.
Thanks for your answer. If I understand you correctly, you meant the
following configuration (please use a fixed font to view this
properly):
+-----------------+ +-----------------+
| Amplified | | |
| Omnidirectioanl | | Omnidirectioanl |
| VHF/UHF Antenna | | FM Antenna |
| with FM Trap | |(can I find one?)|
+-----------------+ +-----------------+
| |
| RG6/U RG6/U |
+-------------+ +--------- +
| |
| |
+-----+----+------+
| |
| FM/TV combiner |
| |
+--------+--------+
|
| RG6/U (runs
| throughout
| house walls
| to basement)
|
+--------+--------+
| |
| FM/TV splitter |
| |
+--+-----------+--+
| |
| |
| +------+----------+
| | |
| | Ant. Amplifier |
+------+ | | |
| | | +--------+--------+
| TV +-----+ |
| | |
+------+ |
+--------+--------+
| |
| Splitter |
| |
+--+--+--+--+--+--+
| | |
| | | +-------------+
| | +--------+ FM Receiver |
| | +-------------+
| |
| | +-------------+
| +-----------+ FM Receiver |
| +-------------+
|
| +-------------+
+--------------+ FM Receiver |
+-------------+
But how about the following one:
+-----------------+ +-----------------+
| Amplified | | |
| Omnidirectioanl | | Omnidirectioanl |
| VHF/UHF Antenna | | FM Antenna |
| with FM Trap | |(can I find one?)|
+-----------------+ +-----------------+
| |
| RG6/U RG6/U |
| |
| +--------+--------+
| | |
| | Ant. Amplifier |
| | |
| +--------+--------+
| |
+-------------+ +--------- +
| |RG6/U
| |
+-----+----+------+
| |
| FM/TV combiner |
| |
+--------+--------+
|
| RG6/U (runs
| throughout
| house walls
| to basement)
|
+--------+--------+
| |
| Splitter |
| |
+--+--+--+--+--+--+
| | | |
| | | |
| | | |
| | | | +-------------+
| | | +--------+ FM Receiver |
+------+ | | | +-------------+
| | | | |
| TV +-----+ | | +-------------+
| | | +-----------+ FM Receiver |
+------+ | +-------------+
|
| +-------------+
+--------------+ FM Receiver |
+-------------+
Intuitively, I would think that it is better than the first one, since
I amplify the FM signal right at the antenna (before picking up noise)
and I also save the FM/TV splitter. What do you think?
Daniel
Tarmo Tammaru
I agree that the second would be best from the FM sensitivity standpoint.
There are two things against it though: you have to get DC power to it
through the splitter, and you are combining a boosted FM sgnal with your TV
signal. I am concerned about your super strong 98.X. How are you powering
the TV antenna? Is there AC in the attick, like a light you could put a
cheater socket on?
Tam/WB2TT
"Daniel" <dan...@my-deja.com> wrote in message
news:b73f7787.03051...@posting.google.com...
WB3FUP (Mike Hall)
tip. It folds in half, so out of the box it is a
packages about 6" square and 2 1/2 foot long.
73 es cul
wb3fup
a Salty Bear
"Daniel" <dan...@my-deja.com> wrote in message
news:b73f7787.03051...@posting.google.com...
Daniel
> I agree that the second would be best from the FM sensitivity standpoint.
> There are two things against it though: you have to get DC power to it
> through the splitter, and you are combining a boosted FM sgnal with your TV
> signal. I am concerned about your super strong 98.X. How are you powering
> the TV antenna? Is there AC in the attick, like a light you could put a
> cheater socket on?
I have a fully fledged AC outlet in the attic - installed by a
licensed electrician. However, I just received by email a thorough
analysis of my particular situation (several strong FM stations
nearby, and not so strong TV stations scatterd in different
directions...), which doesn't leave much hope for anything. :-(
I guess I'll have to pay the cable company (a monopoly in my state)
for monthly subscription...
Thanks,
Daniel
Tarmo Tammaru
You will get TV like you never got it before. I was never able to get rid of
all ghosts with the antenna. Cable looks perfect. Wonder if your cable has
FM on it.
Tam
"Daniel" <dan...@my-deja.com> wrote in message
news:b73f7787.03052...@posting.google.com...