See the several posts I added to the fol. Las Vegas Thead, starting with this one:
Very large DIY RF Ch2 antenna is combined with ANT-751 using a LHSJ Lo-VHF/Hi-VHF Combiner (from Hollands Electronics, Blonder-Tongue and Tin-Lee):
Preamp probably won't help to receive RF Ch2, but first you need to tell us if you are using any RF Splitters and coax lengths. And post the Results URL (webaddress at top of browser) AFTER you enter your location into www.tvfool.com
You need the longer, resonant elements for the low-band RF channels.
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Try this - works great1
A simple, efficient, low cost, stackable, low-band VHF antenna for HDTV channel 2 (3.1 virtual)
Jeff Winkelhake, K6JWK
A folded dipole is an efficient TV antenna that is easy to construct. It will not compete with a good high-gain directional antenna, but it sure beats rabbit ears (which are dipole antennas, should not be used outdoors and would have to open 4.2 feet on each ear to be optimal for channel 2). Importantly, the dipole antenna can be conveniently linked or ‘stacked’ with your existing digital HDTV antenna to aid reception of low-band vhf signals such as those from Channel 2 (3.1 virtual) KVBC (NBC) HD, 3.2 CoZi TV & 3.3. Antenna TV Las Vegas.
This dipole antenna is optimized for a single channel, though it will often work acceptably on others, and it is modified to work via a coaxial connection. The overall idea here is to improve the reception capabilities of your current HDTV antenna (indoor or outdoor) since the signal for low-band VHF is often difficult for smaller high-band VHF/UHF digital HDTV antennas to capture (depends on slight nuances of location and requires a relatively big antenna to capture the long 5M wavelength).
The dipole antenna is made from 300 ohm twin-lead cable - the brown or black ribbon-like TV line that we all used before the days of cable and digital television. There are two conductors running along the edges of the ribbon.
What you’ll need:
· 10 -15 feet of 300 Ohm twin lead tv cable [100’ is $14.00 at Radio Shack – if you can find a source which sells by the foot (difficult in this day of digital tv), it should cost about $1.50]
· 1 x 300-75 ohm transformer ($4.00)
· 1 x 2-way coaxial cable splitter ($6.00) – you’ll looe about 3.5dB gain per antenna with one of these, but signal strength for tv stations in the Las Vegas area is plenty strong as most locations are no more than 20 miles from the transmitters
· 2 short lengths of RG6 coaxial cable (quad-shielded is best for all TV signals) – one will go from your HDTV antenna to the splitter, the other will link your new dipole antenna to the splitter. Lengths will be determined by antenna locations… use patch cables or make your own from scratch. Patch cables range in price from $4 to $10 depending on length and quality. Build your own is the least expensive and better-fit way to go as you can put the $$ into a crimping tool.
For determining the length of the dipole antenna, you need to know the frequency of the station, which you can find out by calling the station. But, pretty much the frequency of Rf channels can be calculated as follows:
For channels 2 - 4, the frequency is given by: f (in MHz) = (6 x channel_number) + 45.
For channels 5 and 6, the frequency is: f (in MHz) = (6 x channel_number) + 49.
For channels 7 -13, the frequency is: f (in MHz) = (6 x channel_number) + 135.
For channels 14 and above: f (in MHz) = (6 x channel_number) + 389.
Cut off a piece of twin lead one-half wavelength long, where wavelength on twin lead (in meters) = 0.95 x 300 / freq. (in MHz).
(The factor of 0.95 is the assumed velocity factor of the common mode signal on the twin lead.)
(Example: for channel 2 (NBC in Las Vegas), the frequency is (6 x 2) + 45 = 57 MHz, so the wavelength on twin lead is 0.95 x 300/57 = 5.00 meters, and the antenna should be 5.00 meters/2 = 2.5 meters or 98.4 inches)
Strip the insulation off just enough of each end to be able to twist the conductors together and solder. This is the "folded dipole" antenna.
The next step is up to you. You can connect the antenna directly to the 300-75ohm transformer or to a short section of twin lead and then add in the transformer. (pictured above in outdoor format, but the rubber boot where the coax attaches on the bottom is not needed for indoor antenna use) in order to stack the signal onto those from your digital antenna.
To attach either the transformer, or a twin lead transmission line then transformer, cut ONE of the two conductors of the antenna at the midpoint, and strip a half inch or so of insulation from each piece. Strip insulation from a half inch of insulation from the conductors of the long piece of twin lead. Attach the wires from the transmission line or, alternatively, the leads of the transformer to the wires at the midpoint of the antenna. Solder.
If you choose to use twin lead transmission line, then attach the opposite end of the transmission line to the 300
ohm leads of the transformer (cut off the u-shaped fittings on the 300 ohm end and strip the insulation off. Solder.
The dipole antenna should be mounted broadside to the transmitting tower for NBC. To find out where the tower is in relation to you ck.: www.tvfool.com The higher it is mounted, the better it will perform. Do not mount the antenna near metal or behind too many walls. Do not leave excess transmission/coaxial line in a coil: trim it close to the desired length.
Attic or even a garage installations work pretty well. If you are in a dorm room or apartment, you can tape or thumbtack the antenna to a wall or ceiling, though in-wall wiring may degrade performance. Move it around to find the best reception. Attic ceiling is good if you want to add ‘further improvements’ (see below).
Next you will need to ‘stack’ the new dipole with your existing indoor or outdoor HDTV antenna. There are all sorts of ways to do this, but the basic aim is to keep the total length of cable between the two antennas and your TV as short as possible. For example, for an attic installation of both antenna’s, I mounted the dipole on the ceiling just above my small (1M) yagi HDTV antenna (RCA ANT751) and used two short lengths of RG-6 coaxial cable attached to the two antennas and inserted into the splitter. Then I attached the splitter’s single (third) lead to my already installed coax going to the tv. This also worked well outside on the roof… just tacking the dipole antenna to the roof perpendicular to the transmitter station (117 degree is my case) below the yagi (which, in my location, did not receive channels 3.1, 3.2 or 3.3).
Signal strength and ghost rejection (if you get ghosts) can be improved significantly by adding a reflector and perhaps a director. For the spacings below, use the formula for wavelength in air, not wavelength in twin lead: 5M
Cut a single piece of wire about 5% longer than your antenna. Do not use twin lead for this wire; use a single uninsulated wire. Mount it parallel to the antenna, about 0.2 wavelengths (for Ch. 2 that would be 0.2x5 = 1M) away on the side opposite the TV station. There is NO electrical connection between this wire and the antenna.
For some additional improvement in reception, cut a similar piece of wire about 5% shorter than the antenna, and mount it parallel to the antenna on the side toward the station, about 0.15 wavelengths from the antenna.