Antenna for HDTV

[Space Varmint]

You said you just wanted to improve what you have. That is why you should try an rf amp. I have seen amplified antennas at Walmart so they might work. You need to make it a broadband amplifier. That means you don't want a tuned tank circuit. What is usually done in order to obtain the high impedance in the collector circuit, you will use just a coil with no capacitor. Use a piece of ferrite to wind the coil onto (coil form). The ferrite will give you the extra impedance "Z". If you happen to use Amidon Corp. which I do. Then I know that number 63 material is the best for that frequency. Use voltage divider bias maybe 10K to power and 2.2K to ground. And try say 470 ohms in the emitter. You may want to bypass the emitter with some capacitance. Not too much. About 100 to 220pf. Have to play with it. That will increase your signal strength several DB. If your problem does not involve RFI then that should do the trick.

 

[MikeMl]

My experience with "preamps" (especially ones from Walmart) is that they just produce susceptability to intermod from other signals. A high quality low-noise preamp such as are used by weak-signal Ham Radio operators on 430Mhz might help as long as it is broadband.

 

[gary350]

I bought an antenna amp from Radio Shack last summer. It pretty much doubled the signal strength.

Today I rebuilt my antenna. HALF of the antenna is a UHF antenna. The other HALF is the bow tie antenna is also basically a UHF antenna too. I used this web site Amateur Dipole Antenna Calculator to calculate the length of each leg and each element for channel 2, 4, 5 and 8 and changed only the bow tie antenna. The antenna has 8 elements so I changed it so it now has 2 elements for each frequency. The change has made a 45% improvement in VHF but UHF has dropped about 30%. VHF channel 5 has always been the hardest station to received signal went from 50% to 90% today after the change. Now I am receiving channel 5 excellent. The local stations 2, 4 and 5-1 don't have much worth watching. But channel 5-3 has non stop movies with NO advertisements. Channel 8 has Nova, discovery, Master Piece Theater, Master Piece Mystery, History Detectives, and several others but signal has dropped from 95% to 65%. Channel 17-1, 28-1, 28-3 and 30-1 have movies too, signal has dropped from 98% to 65%. The change I made today improved channel 5 and screwed up 8, 17, 28 and 30.

Now I need to make another change to get 8, 17, 28 and 30 back up to about 95% strength. I change I made today has caused me to lost 1/2 of my UHF antenna and given me a VHF antenna I never had.

This is what I have now.

Antenna #1 pointed 310 degrees.

16 legs = 11", 8 elements = 22.5" long. Channel 17, 28, 30 Signal 60 to 65%......was 98%



Antenna #2 pointed 320 degrees.

Element 1 and 2 = 204" long Channel 2 Signal strength 98%

Element 3 and 4 = 168" long Channel 4 Signal strength 98%

Element 5 and 6 = 146" long Channel 5 Signal strength 98%

Element 7 and 8 = 62" long Channel 8 Signal strength 65%


Antenna Photo **broken link removed**

Close up view. **broken link removed**

According to www.antennaweb.org OOPS. Antenna web information has changed. Information I wrote down last summer is different than what is listed now.

Channels 5, 17, 28, 30 are at 322 degrees.

Channel 4 is at 305 degrees.

Channels 2, 8 are at 295 degrees.

The half way point is about 310 degrees but reception is better at 320 degrees probably because reception is always low on channel 5 so antenna needs to be pointed right at channel 5. This gets channel 2, 4, 5 excellent reception, strength meter reading is 98% but reception is 65% on channel 8.

 

[mneary]

Don't forget to translate channels. Your "channel 2" is on RF channel 27 and your "channel 4" is on RF channel 10. Your 204" and 168" elements probably aren't' contributing anything.

 

[mneary]

Antenna web information has changed. Information I wrote down last summer is different than what is listed now.

Yes, when the stations stopped transmitting analog, a lot of them changed frequency (again). To confuse matters further, stations still use their old "channel number" but many are now using an entirely different frequency.

This really threw me a curve ball last summer because all digital stations in my area were initially UHF. So when I got my digital TV I also went to a UHF-only antenna. But in June four of them went back to VHF and my UHF antenna didn't give a usable signal.

 

[gary350]

Don't forget to translate channels. Your "channel 2" is on RF channel 27 and your "channel 4" is on RF channel 10. Your 204" and 168" elements probably aren't' contributing anything.

OOPS.......I forgot about that.

I have been searching the web of almost an hour I can not find RF frequencies for HDTV channels. Does anyone know where to fine them??

Channel 2 is RF 27 does that mean the frequency of analog 27 which is 548 to 554 MHz

There is 2 channel 2s, we have 2-1 and 2-2. Same thing with all the channels. There is 4 channel 28s.

My book says Meg Cycles. That was changed in 1969 to MHz.

 

[blueroomelectronics]

tvfool.com shows the actual vs virtual channel numbers. If you want really long range a Yagi might be a better choice, I use a pair of Yagi's (one per tuner) on my HTPC DVR and can reliably pull in everything but VHF and these are mounted in my attic (-3db loss when behind shingles). Combing them on a single tuner made things worse when pointing in two directions.
Antenna height makes a huge difference unless your house is on top of a hill. It also looks like your reflector is too close to the antenna elements. Having the antennas arranged like your pair isn't the norm, usually they must be side by side to increase gain.
Take a look at the Antennas Direct DB8 to see a typical arrangement.
PS antenna preamps also amplify the noise, better just to keep your cable runs as short as possible.

 

[gary350]

Everytime I go to AntennaWeb it tells me the HDTV stations are located in a different place. Now it is telling me channel 2 and 8 are located 20 degrees south of where they were 15 minutes ago. And before that it was telling me channel 2 and 5 are located 15 degrees north of where they were before that. This crap is not helpful.

I am still having a problem finding the actually RF frequency of each channel. I have channels 2-1, 2-2, 4-1, 4-2, 5-1, 5-2, 5-3, 8-1, 8-2, 17-1, 28-1, 28-3, 30, 58. There are more a total of 24 but the others are trash I have no interest in.

I tried a Yagi and it works good but drift is very bad. The antenna is too sensitive. It has to be pointed exactly at the station to get a strong signal. If the wind blows then the stations drift in and out over and over and the channel are not watchable. Wind never stops blowing in Tennessee and it is Gusty all the time. I have lived in TN for 31 years it is impossible to fly a Kite here wind is blowing 10 mph all the time with gusts to 20 mph then dead calm for 30 seconds, then more 20 mph wind gusts.

 

[blueroomelectronics]

Try tvfool.com

also can you mount an antenna in your attic?

 

[gary350]

This is what I know for sure. But I still need to know more. Is the RF channel = to the old RF frequency? My 40 year old book and the online chart both say RF 27 is 548 to 554 MHz. There can not be 2 channel with the same frequency. If 2-1 = 548MHz what about 2-2, and 4-2 and 5-2 and 5-3 and 8-2 and so on.

Channel.......RF...........Degrees..........Miles

2-1.............27..............295..............26.8
2-2..............?.................?................?

4-1.............10..............305..............31.4
4-2..............?.................?................?

5-1..............5...............322..............33.7
5-2..............?.................?................?
5-3..............?.................?................?

8-1..............8...............295.............26.8
8-2..............?.................?................?

17-1...........15...............321.............33.8

28-1...........36..............321...............34
28-2............?.................?................?
28-3............?.................?................?
28-4............?.................?................?

30-1...........21..............321.............33.8

58..............23..............321.............33.8

 

[mneary]

The RF channel (e.g. 27) is divided into data streams, so 2-1, 2-2, etc. are on the same RF channel. One transmitter, up to 8 "channels" on the same frequency.

 

[Nigel Goodwin]

The RF channel (e.g. 27) is divided into data streams, so 2-1, 2-2, etc. are on the same RF channel. One transmitter, up to 8 "channels" on the same frequency.

They are called 'multiplexes' - each multiplex contains a number of channels, which can be HD, SD, radio, text, or a combination of all of them. The more channels per multiplex the lower the quality, the recently started HD multiplex in parts of the UK will have four multiplexes, which (in my opinion - and many others) is too many, and quality will be relatively poor.

The UK was the first country in the world to have terrestrial digital, and we're currently going through a phased shutdown of the analogue transmitters, which is due to finish in 2012 - where I live is due May 2011.

 

[gary350]

Ok....that is excellent. Thanks

What is the frequency of RF 27?

Is RF 27 the same as before 548 to 554 MHz?

 

[Nigel Goodwin]

In the UK (and Europe) ch27 is listed as 519.25MHz.

 

[gary350]

Don't forget to translate channels. Your "channel 2" is on RF channel 27 and your "channel 4" is on RF channel 10. Your 204" and 168" elements probably aren't' contributing anything.

I am getting conflicting information. I see AntennaWeb shows channel 2 = RF 27, 4 = RF 10, 17 = RF 15, 28 = RF 36, 30 = RF 21, 58 = RF 23.

The HDTV antenna forum is saying, channel frequencies have not changed channel 2 is still 54 to 60 MHz, channel 8 is still 180 to 186 MHZ, 17 = 488 - 494 MHz, 28 = 554 - 560 MHz, 30 = 566 - 572 MHz. Only difference is multiplexing 8 different channels can now be transmitted on each frequency.

If that is so then what does the RF channel mean? If channel 2 = RF 27 what does that mean???????

 

[mneary]

I would go with the FCC: The Digital TV Transition: Reception Maps since they are the regulating agency. People on forums might provide information local to themselves, or simply outdated or mistaken.

 

[Nigel Goodwin]

I would go with the FCC: The Digital TV Transition: Reception Maps since they are the regulating agency. People on forums might provide information local to themselves, or simply outdated or mistaken.

I would imagijne they are purely theoretical maps?, what you need is local 'real' advice.

 

[mneary]

The maps are theoretical, but the assigned frequencies aren't.

 

[gary350]

I am thinking about buiding this antenna. After doing a lot of reading I found out the way this antenna is put together determines the bandwidth and bean width. A dipole calculator can be used to determine the length of the elements. The book shows an antenna with 4 sections each section can have 2, 3 or 4 elements. 4 elements with 4 sections = 16 elements. A dipole has a gain of 2.15 dBi, 4 elements have a gain if 8 and 16 elements has a gain of about 20 dBi. Beam width is wide enough to cover all 8 stations I want to receive, 5 stations are at 320 degrees the other 3 stations are between 295 to 305 degrees. If I aim the antenna at the half way point 307.5 degrees beam width is wide enought to receive them all. A bow tie is slightly better than a straight element so I plan to have 16 bow tie elements.

I found some information where it shows building one 8 element array instead of building two 4 element arrays and connected them in parallel. I found it also shows attaching the 75 ohm cable to the end rather than the center of the antenna. I am not sure what the difference would be between one 8 element antenna or two 4 element antennas in parallel both have 8 elements total seems like the 8 would be easier to build.

I also don't know what is the difference between attaching the 75 ohm cable to the center of the antenna or the end of the antenna???

If it is OK to build this as 1 antenna with 8 elements on each side that is the way I would like to build it.

The book says each antenna should be matching. What if I build TWO 8 element antenna each antenna contains 1 of the following elements. I have 7 channels to receive and channel 5 is the hardest one to pick up. For channel 5 I will have 2 elements on each 8 element section of the antenna. This gives me a total of 8 elements. Will this work?

Channel 8 = 186 MHz.........element total length = 60.4"

Channel 4 = 198 MHz.........element total length = 56.75"

Channel 17 = 482 MHz.........element total length = 23.3"

Channel 30 = 518 MHz.........element total length = 21.6"

Channel 2 = 554 MHz.........element total length = 20.3"

Channel 28 = 608 MHz.........element total length = 18.5"

Channel 5 = 692 MHz.........element total length = 16.25"

Channel 5 = 692 MHz.........element total length = 16.25"

Dipole calculator http://www.csgnetwork.com/antennaedcalc.html

 

[mneary]

This is a narrowband design, but it can be broadened by using large diameter elements or even triangular sheets of metal. It's very difficult to calculate the performances of different frequency antennas connected together.

If channel 5 is your worst signal, then an antenna cut for 692 might work pretty well. Another worthy experiment might be to build one at 3x the size (3/2 wavelength instead of 1/2).