amigo@milton.u.washington.edu (The Friend) (12/11/90)
Anyone have some hints to improve TV reception from a TV Antenna?
I bought a Rat-Shack 100 mile antenna, and set it up properly (avoiding
things like the in-bound cable(s), power lines, etc.). Its fully
grounded, and static discharge surpressed.
My problem is that it won't pick up much at all. Well at least it seems
"picky" about what it does want to pickup. I've compared its results
to a old rabit ears antenna, and I can get some stations (especially
UHF ones) that won't even show up on the outdoor antenna. I've
tried to point it in the right direction for viewing (having
someone watch the TV), and yet I still can't get anything...
I know UHF is very directional over VHF, but yet I've had
some stations that are much further away (say 125 miles) come in
clean, while the one I'm trying to get is only 30 miles away, and I don't
get anything- both are UHF channels that should pickup in the same
general direction.
Some things I'm looking at:
1. antenna rotator - gets to be a hassel rotating the antenna.
2. amplifier for VHF/UHF/FM - generally the one I have in mind
has something like 25 dB gain...I'm wondering if this will
help at all?
3. Definitely reading some books on TV Antennas.
I'm wondering if some gizmo like that of the rabbit ears's "dial"
that helps pull the signal in exists for outdoor antennas as well..
Seems like this could be the key to locking the station in or not.
My main goal is to get two major stations in the Seattle area in:
[ KVOS - CH 12 Bellingham. This station has some great shows,
and being by the border, you see some Canadian stuff that's real
different. >not to mention being the one recognized Dr. Who station
in the country<.
RANGE: by maps standpoint, as the crow flies it should be near
straight to the tower over much lower terrain then the
hill I'm on (tower's on a 2,000 ft mtn), or less then 75 mi. ]
[ KTPS - CH 28, Tacoma. Unknown exactly where this is, but
its due south-east, all downhill from my place, about 35 mi away ]
(my biggest problem? both are in opposite directions!)
Our cable service has closed both of these channels off thier service,
so I've since went to my own means to tune in..
thanks for any help anyone can provide. I've invested enough in this that
I'm sort of bummed out that nothing works (didn't expect miracles, but at
least it could have one of the two stations I was after up).evans@decvax.DEC.COM (Marc Evans) (12/11/90)
In article <12765@milton.u.washington.edu>, amigo@milton.u.washington.edu (The Friend) writes: |> 1. antenna rotator - gets to be a hassel rotating the antenna. Although your initial experiments would require manual adjustment of the rotors direction, I feel that I should point out that it is pretty easy to build a unit which engages the rotor to a preset position based on the channel being watched (you will need to modify the TV a bit to get this information). I have built one which even has the ability to let the VCR channel override the TV channel, so that if you are watching the TV and recording on the VCR, the VCR will get the better picture. |> 2. amplifier for VHF/UHF/FM - generally the one I have in mind |> has something like 25 dB gain...I'm wondering if this will |> help at all? I have found this to be the key to most setups. The key here is to get the amplifier as close the the signal source as possible. Rat-Shack sells a model of amp which is mounted at the antenna, and use the coax to get voltage from a power unit located in your house. This is the best setup I have seen, as compared to the amps which are located many feet away from the antenna. - Marc -- =========================================================================== Marc Evans - WB1GRH - evans@decvax.DEC.COM | Synergytics (603)635-8876 Unix and X Software Contractor | 21 Hinds Ln, Pelham, NH 03076 ===========================================================================
mb@sparrms.ists.ca (Mike Bell) (12/12/90)
In <12765@milton.u.washington.edu> amigo@milton.u.washington.edu (The Friend) writes: > Anyone have some hints to improve TV reception from a TV Antenna? > I bought a Rat-Shack 100 mile antenna, and set it up properly (avoiding > My problem is that it won't pick up much at all. Well at least it seems Quick suggestions: (1) Is the polarisation correct for the stations? Eg. in Toronto area Ch 49 from Buffalo is vertically polarised, all the other channels are horizontally polarised. Worth a check. (2) Is the coax cable very long or very lossy? If so, a mast mounted amplifier is one possibility. (3) Antenna correct for bands in question? Ch 12 is one end of VHF band Ch 28 is low UHF (4) Antenna not accurately pointed. (OK, you said it was, but check. The higher the antenna gain, the smaller the acceptance angle...) Just a thought: since Ch 12 is VHF, Ch 28 is UHF, and both stations are in opposite directions, you might be able to split the antenna... Also, a cheap VHF antenna might be an alternative to a rotator. Best of luck. -- Mike --
simnet@ssc-vax.UUCP (Mark R Poulson) (12/17/90)
In article <12765@milton.u.washington.edu>, amigo@milton.u.washington.edu (The Friend) writes: > > Anyone have some hints to improve TV reception from a TV Antenna? Some things to consider: 1) Just because the station is in Bellingham doesn't mean that that's where the antenna is. You may want to call the station and ask where their antenna is located. Another poster mentioned that some stations are polarized differently. In the US, almost every station is horizontally polarized (i.e. their antenna dipoles are parallel to the ground). Check to make sure the station is NOT vertically polarized, because if it is you should mount your antenna with its dipoles perpendicular to the ground (which will screw up reception of all normal horizontally polarized stations.) 2) Go sit on your roof with a TV and a short peice of coax. Loosen your antenna and find out in which directions specific stations come in the best. Hopefully the antenna is outside (not in the attic behind foil insulation!) and is as high as possible. All you need is line of sight with your target tower and they are usually pretty high. Try to find an orientation that works for all the stations you watch. A horizontally polarized dipole will have a reception pattern that looks like a figure 8. The higher the "gain" of your antenna the more streached the 8 becomes (crude drawing): . . . Sources in here are received -.-* . . . . . ._. <- Antenna is here and looks like: . . . . _+_ <- UHF dipoles . . __|__ . . ___|___ <- VHF dipoles . ____|____ The higher gain antenna you purchased, the more difficult this becomes. Also note that your worry about ch. 12 and 28 being opposite directions is not a problem, but being perpendicular is. This assumes that the UHF dipoles are oriented the same as the much longer VHF ones. Needless to say, don't do this in the rain, but doing it in the weather you watch in will help (i.e. cloudy, clear (not around here!), cold,...). If this step is impossible, you can use two antennas each with notch filters that remove the bad stations from a given antenna. Combine the outputs with an RF combiner (same as a passive splitter but used backwards) to give one downlead to the TV. 3) Once you have a decent picture on the roof, connect your downlead to inside the house. If you don't have similar reception you have: a) Used lousy Rat-Shack cabling (you need >400MHz bandwidth). b) Terminated it poorly or are using the wrong impedance cable (you'd better be using 75 ohm coax (not 50 ohm!) or 300 ohm twin lead). c) Used good cable, but may have bent it excessively, cut it, or anything else you can to bad to coax... d) Have too weak a signal to make it over the cable (twin lead is worst with loss). Your idea of getting a book is probably the best. The Radio Amateurs Handbook usually has a rather complete section on antennas. The above information is from memory and I may have made a few errors, so please don't flame me if I royally screwed something up (but corrections are welcome)!. Mark ...uw-beaver!ssc-vax!simnet
depolo@eniac.seas.upenn.edu (Jeff DePolo) (12/17/90)
In article <3561@ssc-bee.ssc-vax.UUCP> simnet@ssc-vax.UUCP (Mark R Poulson) writes: >In article <12765@milton.u.washington.edu>, amigo@milton.u.washington.edu (The Friend) writes: >> Anyone have some hints to improve TV reception from a TV Antenna? >Some things to consider: > >The higher gain antenna you purchased, the more difficult this becomes. Also >note that your worry about ch. 12 and 28 being opposite directions is not a >problem, but being perpendicular is. This assumes that the UHF dipoles are >oriented the same as the much longer VHF ones. Most VHF/UHF antennas that are purely log-periodic antennas will have a decent front-to-back ratio, so signals coming from the back of the antenna, particularly those higher in frequency than the frequency the rear-most elements are designed for, will be attenuated. THis is because the longer elements will act like a reflector ala a yagi reflector. Most VHF/UHF combo antennas have log-periodic elements for VHF, and a corner reflector yagi for UHF, so the same holds true. Stations coming in from the rear and sides will be heavily attenuated. >3) Once you have a decent picture on the roof, connect your downlead to inside >the house. If you don't have similar reception you have: > > a) Used lousy Rat-Shack cabling (you need >400MHz bandwidth). Bandwidth that varies with brands of cable? I don't get it. Cheap cable may be more lossy, but it doesn't have a self-contained band-pass filter. Loss graphs for transmission cables generally follow a linear plot on log-log paper, so you need only compare the loss figures at one frequency (e.g. at 200 MHz) to determine which cable will work better. > b) Terminated it poorly or are using the wrong impedance cable > (you'd better be using 75 ohm coax (not 50 ohm!) or 300 ohm twin > lead). You'll realize little difference between 75 ohm and 50 ohm coax. When you consider what a wide range of frequencies you are attempting to receive, even with a well designed log periodic, the feedpoint impedence is going to vary over quite a wide range. Choose the cable with the lowest loss that fits into your budget. Typically, RG59 (75 ohm) is about the same price as RG58 (50 ohm), but has lower loss figures. On the other hand, RG8-foam (50 ohm) is probably cheaper and also has a lower loss than RG-11 (75 ohm). The only problem you might run into is trying to find F connectors that will work on RG8 (I've never seen them). > d) Have too weak a signal to make it over the cable (twin lead is > worst with loss). To the contrary. Twin lead (aka ladder line or open wire line) is much lower in loss than most types of coax. Just be sure you keep the twin lead away from metallic objects (e.g. aluminum siding), and keep it as much out of the weather as possible. If you have to run your cable in places where it will be near metal or will be heavily exposed to the elements (e.g. running it across the length of your roof instead of having it come into your attic below the antenna), get good coax. Belden makes a version of RG59 that has an aluminum shield in addition to a few strands of braid and has good loss figures for the price. Most cable companies use this type. Stay away from Radio Shack cable - get Belden, Saxton, Times Wire and Cable, or Intercomp. As a last resort, get a mast-mounted preamplifier. This isn't going to make stations that were previously invisible suddenly show up, but if you have long cable runs (like over 100'), it will make a noticible difference, particularly on UHF. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104