Coax for OTA
Coaxial cabling for OTA
- 1 Antenna selection and installation
- 2 Aligning the antenna
- 3 Preamps for antennae
- 4 Distributing the feed to tuner(s)
Antenna selection and installation
Indoor / Rabbit-Ears
The first choice for situations where a traditional antenna cannot be used. The traditional "rabbit-ears" style can be found at nearly any electronics store. The telescoping ears are used to tune the low and high VHF channels (2-13). The UHF channels (14-69) are received by the loop at the rear.
A very good quality indoor antenna is the Silver Sensor. It is made in the UK and marketed in the US by Zenith. This type of design is for the UHF band (14-69) only. For ATSC reception, this shouldn't be a problem for most North American users. There are very few cases where the FCC has assigned a VHF frequency for ATSC transmission. One exception is Chicago's WBBM-2 which was allocated channel 3 making reception even more difficult having to cope with it's own analog broadcast on the adjacent channel.
<edit> WBBM has been approved to move to channel 12.1 (VHF) post-transition, Feb 17, 2009. At that time, typical indoor antennas rated for VHF reception should work without issue. </edit>
Roof or mast mounted
Shown here are the Winegard PR8200 UHF/VHF/FM, PR9032 UHF-only and PR9010 FM dipole antennae mounted on the chimney of a three story building. While line-of sight to the transmitters is excellent, one particular UHF channel was un-tunable using the the 8200. The narrow beamwidth 9032 is used solely for that channel by aiming toward a nearby five story building, using the building as a reflector. Sometimes multipath can be your friend.
The 2-inch mast is attached using universal strut and threaded rod. Coaxial feeds enter access hatch bulkhead -- holes are drilled at an upward angle from outside of bulkhead to inside to prevent rainwater seepage. Notice the ground bonding clamp. In the US, National Electric Code requires proper grounding for antenna masts. A 4-gauge grounding wire was eventually run to edge of the roof, down the building's exterior and attached to a 1/2-inch ground rod driven 9 feet into the earth.
View of the Sear's Tower approximately fourteen miles to the NNE. The Hancock Tower where additional transmitters are located is just to the left of the Sear's building behind some trees. The clouds on that particular day were the very first to arrive in Chicago when the remaining air mass of hurricane Katrina swept north.
Aligning the antenna
Portable TV method
Laptop with WiFi and HD HomeRun method
Getting the initial readings
Before tweaking you need some baseline readings. Without these you won't know if the changes you're making are for the better or worse. Start with a channel scan to identify the frequency for each station you care about. Put these into a table along with the initial signal strength and signal to noise numbers:
hdhomerun_config FFFFFFFF scan /tmp/ota_initial_scan.txt
- From the
/tmp/ota_initial_scan.txtfile record the frequency, channel, signal strength, and signal noise of each station you care about
FRQ STATION Scan ===================================== 707 5.1 WRAL DT CBS 61/56 719 17.1 NBC17HD NBC --/-- 683 50.1 WRAZ HD FOX 67/63 701 11.1 WTVD HD ABC 70/69
Channel scan on the HDHR doesn't always accurately show the signal strength and signal noise. I recommend you tune to each station and watch the status output for about 20 seconds to get an accurate picture of signal strength and signal noise.
hdhomerun_config FFFFFFFF set /tuner0/channel 8vsb:707000000
watch -n 1 hdhomerun_config FFFFFFFF get /tuner0/status
- Keep an eye on the signal strength (ss) and signal noise (snq) for about 20 seconds. You want them to be as close to 100 as possible. Add this info to your table Use CTRL-C to stop the watch command.
FRQ STATION Scan 132deg ===================================== 707 5.1 WRAL DT CBS 61/56 65/62 719 17.1 NBC17HD NBC --/-- 43/04 683 50.1 WRAZ HD FOX 67/63 65/62 701 11.1 WTVD HD ABC 70/69 77/69
Notice my initial readings indicate that NBC17 isn't coming in well. On the channel scan the HDHR saw it but didn't get a good SS/SNQ reading. On the manual tune I was able to see some SS but had a very poor SNQ reading. Everythign else isn't to bad however ideally we would see SS/SNQ closer to 75/80 on all channels. Also, watch for wild fluctuations in SS and SNQ. If you see that chances are you are experiencing a multipath signal problem and will need to move the location of the antenna
Here is where the laptop comes in handy. You should head into the attic with the laptop, marker, and mapping compass. Connect to your system where the hdhomerun_config program lives (or install a copy on the laptop!) and tune in the weakest channel in the table from your initial scan. Turn the antenna until you see a SS/SNQ of 75/80 or there about. I've had good results with any station showing 70/75 SS/SNQ or better as long as it doesn't fluctuate much!
- Start by tuning weakest channel with
hdhomerun_config FFFFFFFF set /tuner0/channel 8vsb:719000000
- Monitor for 20 seconds with
watch -n 1 hdhomerun_config FFFFFFFF get /tuner0/status
- Turn the antenna making small adjustments and note the change in real time
- Record the new information in your table. Use the mapping compass to get an idea of the direction in case you want to use it again later.
- Repeat the first three steps for each channel until all channels are showing a good SS/SNQ reading that is stable
FRQ STATION Scan 132deg 128deg ============================================= 707 5.1 WRAL DT CBS 61/56 65/62 78/88 719 17.1 NBC17HD NBC --/-- 43/04 69/85 683 50.1 WRAZ HD FOX 67/63 65/62 71/88 701 11.1 WTVD HD ABC 70/69 77/69 60/69
Preamps for antennae
Distributing the feed to tuner(s)