Need Help with KERA Dallas TX

[jayinc1]

I am failing to get reception from KERA TV channel 14 in dallas Texas. my TVFool.com radar plot here indicates my home town of mesquite is about 25miles from the station. That with a set top ant. i should get this station. well the little coby tv in my upstairs BR cannot get this station but the bigger one in LR pick it up just fine.

i am using home made youtube coat hanger antenna mounted in the attic. i have added a dipole antenna on top of it (rabbit ears antenna). but it's not helping as yet with kera. however, all the other channels have an extremely strong signal.

my understanding is the youtube antenna is a uhf ant. and has no vhf solution/cabability. i have been searching for a vhf solution. i came across this page which indicates how to build a simple dipole antenna. i am thinking i should move the dipole further in the attic to be on it's own, i don't know if this will this help?

i need help to find the exact measurements i should use for this ant.

or if you do have a different way to effect a vhf solution please let me know.

btw tvfool.com shows it as channel 14 and my tv downstairs indicates kera as ch 13.1 (it used to be channel 13 before dtv transition). i don't know what is it's transmission frequency, etc.

this is the antenna type that i built. i only added rabbit ears at the top

[mtownsend]

[QUOTE=jayinc1;632]my TVFool.com radar plot here

Hello and welcome!

This tvfool report was only done to zip code level accuracy. To best understand your signal situation and any possible terrain blockage, it would help if you could post a report for your exact location and antenna height.

The address lookup engine might not be able to provide an accurate fix for your location, so sometimes it's better to start out with the Interactive Maps tool (located here). With it, you can map your location, switch to "satellite" view, zoom in to your house, and adjust the location being analyzed (drag the orange marker to the correct location). You can also play with antenna height. Any time you move the marker or edit the antenna height, the channel list will automatically be recomputed based on the new information. Once you are done editing the location to be analyzed, press the "Make Radar Plot" button. This will create a new report with the current setting and you can post that report back here.

i have added a dipole antenna on top of it (rabbit ears antenna). but it's not helping as yet with kera. however, all the other channels have an extremely strong signal.

FYI, KERA is on channel 14, which is a UHF station and should be picked up by your 4-bay antenna.

The important column for antenna selection is the "Real" channel. That's the frequency the transmitter is broadcasting. The "Virt" channel is the virtual channel that is shown on your screen when you watch the channel. Most stations have chosen to set their virtual channel to match their old analog broadcast channel. The virtual channel number has nothing to do with antenna selection and is merely being provided for informational purposes.

Before we try to figure out what is causing problems on KERA, please post a more accurate tvfool report for your location. There might be something blocking the signal that isn't showing up in the generic zip code level analysis.

[jayinc1]

ok really appreciate your help. makes me feel welcome as a newbie.

anyways my analysis is here or here http://www.tvfool.com/?option=com_wr...27ee4fa2d4b1dd

as my antenna is in the attic in a regular 2 storey home i would approximate the height to be 25ft.

[mtownsend]

Thanks for updating your tvfool report.

Well, it still looks like all your signals are VERY strong and all coming from one direction. That's about as good as you could hope for in OTA television! Many people would be jealous of your situation.



Are you having any trouble on any of your VHF stations (WFAA or KFWD)? If not, then your rabbit ears are probably doing their job.

When you connected the rabbit ears, how did you join the signals with the ones coming from the 4-bay antenna? The best way to combine signals from separate VHF and UHF sources is through a diplexor like the UVSJ. This merges the signal from two bands onto a signal coax with minimal loss and it also minimizes cross-interference between the two antenna types. If you are using a regular 2-way splitter/combiner to join the signals, I recommend that you try replacing it with a UVSJ.



Now, in regards to KERA... It's hard to say why you're not getting reliable results on this channel. It's strong and line of sight, so it ought to be easy to receive. However, here are some things to check for:

1) If you haven't already, use a UVSJ to combine your VHF and UHF feeds instead of a standard splitter/combiner.

2) Don't use any amps. Your strongest signals are probably too strong for most amps to handle. If you have any amps in your setup, remove them completely. With signals this strong, amps can make things worse rather than better.

3) What is the spacing between your bowties and the reflector screen? The sweet spot for this kind of antenna is to keep about a 4 to 5 inch gap between the bowties and the screen. The way it's shown in the graphic of your original post, the spacing looks way too small. Each of the whiskers of the bowties should be about 8 inches long. These rough parameters should get you pretty well set up for good UHF performance. If you're not sure about your antenna build, then post some pictures and we can take a look at it.

4) Are you splitting the signal to multiple rooms? If so, make sure you don't have any open unused ports (either open ended cables or open ports on a splitter). All unused ports should be terminated with a 75 ohm terminator (like this). Any paths left open-ended can cause signals to reflect back into the coax, creating signal "echos" within your distribution network that makes the signal harder for receivers to decode.

5) Try turning or relocating your antenna to see if that makes any difference. Some places might be plagued with signal multipath (reflections from surrounding objects, buildings, terrain, etc.). By re-aiming or moving the antenna, you might be able to find a spot that has less multipath getting into your antenna. If this helps clean up the signal, your receivers might then be able to lock on to the channel.

[jayinc1]

"Are you having any trouble on any of your VHF stations (WFAA or KFWD)? If not, then your rabbit ears are probably doing their job."


I have been having trouble with WFAA, KFWD and KTXA KDFI but no KERA. Let me explain. with this ant i was not able to pick up the first 2 and KDFI. i don't know know what i might have done then i would pick up 1 and 3 and not 2 and 4. i don't know how and if adding a dipole helped/or had anything to do with that. so i changed the ant to this one here which has a balun connecting into the coax cable leading to tv set. now i have all the channels except KERA. this little antenna picks up 52 channels total and the other one 42.

"When you connected the rabbit ears, how did you join the signals with the ones coming from the 4-bay antenna?"
I used a simple splitter/combiner as you can see here.
it has 4 screws 2 for uhf and 2 for VHF input respectively. then i plugged it into a USVJ diplexor with 2 outputs to connect 2 tv sets. now even if i connect either ant directly i still don't pick up KERA on the bedroom tv, my current issue.

i am not using any amplifiers. eventually once i get the KERA signal i would like to split to two different rooms. the cables leading to the 2 tv sets were left over after i cancelled dish tv. afaik there's no open unused ports on the 2 cables leading to each tv.

the measurements are just 1.5" bet the bowties and the reflector, obviously falls short of 4-5". the length of my whiskers is 9" longside on the upperside and 8" for the short ones on the lower side. should i cut those to be 8" even?

a pic of the bigger ant with a dipole at the top is here. does it matter how long should i extend the dipole, if so how long should they be extended?
i have a bunch of these usvj's 2 marked 5-1000mhz (one is connected on the antenna) another one is marked 5-600mhz. they are here do these numbers make a difference? would one have an advantage over another?

i have more images of the antenna here http://picasaweb.google.com/jayinc1/ANTENNA#

[mtownsend]

Thanks for the pictures. That does help...

That black box you have that had separate terminals for UHF and VHF is a diplexor. It performs the same function as a UVSJ. The only difference is that it takes in twin-lean inputs (the screw terminals) instead of the "F-type" connectors. It looks like the output is an F-type connector. Since this component is going from twin-lead to F-type connectors, it must also have balun functionality built into it.

The Monster Cable gold colored splitter you have is a simple two-way splitter. It is not a UVSJ and does not have the ability to separate or combine UHF and VHF signals.

When separate VHF and UHF antennas are combined through a diplexor (like the UVSJ), there is very little signal loss (about 0.5 dB) on the way through the device. When a plain splitter is used instead, the loss will be more (about 3.5 dB) and there is the potential for some cross-talk / interference going between the antennas (that is, the VHF antenna might pick up a little UHF signal and the UHF antenna might pick up a little VHF signal, and when combined, the resulting signal might not be so clean).



With the components that you have, the connections look like they are in the correct order. Just for completeness, here's how everything ought to go together...

1) Connect the 4-bay antenna to the UHF input on the diplexor (black unit) using twin-lead.

2) Connect the dipole antenna to the VHF input on the diplexor using twin-lead.

3) Use RG6 coax to connect from the diplexor down to a convenient place where you want to split the signal. In your photos it looks like you have the splitter attached directly to the diplexor. This also works, but puts a lot of wires and components close to the antenna. Any objects near an antenna can alter its performance. If you run a section of coax between the diplexor and the splitter, you can get some of the clutter away from the antenna.

4) Use RG6 coax to go from the splitter to each of your TVs. These connections can go straight into your receiver with no other components necessary (i.e., no other converters, baluns, splitters, or anything else).



The bowtie whiskers are nominally 8" long to roughly cover the UHF band. If your whiskers are a little longer, the antenna will favor lower channel numbers (like channels 14-35). If your whiskers are shorter, the antenna will favor higher channel numbers (like 36-69). The differences from 7" to 9" is gradual, so anything within this range should yield pretty good performance for most of the UHF band.

The bowties work best if all the whisker sets have identical lengths, or at least very symmetrical (e.g., the top/bottom pair should be the same and the middle pair should be the same, and each set should be symmetrical left-to-right). The feed point (where you connect the twin-lead) should be exactly in the middle.

You should definitely increase the spacing between the whiskers and the reflector screen. Having the reflector screen too close to the whiskers will degrade their effectiveness. You can have no reflector at all, or have one that is at least 4" behind the whiskers. With a proper reflector, you get about 3 dB better gain than having no reflector.

Since your VHF stations are in upper VHF (channels 8 and 9), the ideal setup for the rabbit ears is to have them laid out in a stright line horizontally with a tip-to-tip length of about 40-45 inches (longer elements will favor lower channels). Both elements should be equal length. If you can, you should also put some space between the bowtie antenna and the rabbit ears (at least a couple of feet). This will minimize the interaction between the antennas and keep them close to their ideal performance.




All the antenna elements should be kept far away from any other objects. An antenna functions by resonating at certain frequencies. Any time there are objects (especially conductive materials) close to the antenna, the entire behavior of the antenna can change.


Hopefully, some of this information will help you clean up your reception.

[jayinc1]

thx much for clear, concise and ez to understand advice. i will make these adjustments and revert. thx again!

[Dave Loudin]

The primary problem with the bow-tie design you used is the spacing between elements. At the low-end of UHF, the SWR (measure of how well power is transferred between antennas and cables) goes up and the overall gain of the antenna goes way down. At KERA's RF channel (14), there's almost as much signal power bouncing around the antenna as being delivered into the cable. Use the plans documented here to improve KERA and have actual positive gain for channels 7-13, similar to or better than a dipole. You can even buy pre-made parts from the designer. Good luck!