Old TV Antenna to HDTV? - Page 1
Forum section: electronics / general

author: TimNJ
author_rank: Super Contributor
timestamp: April 28, 2013, 05:21:28 pm
content: Hi guys,My grandfather passed away a few months ago. We aren't selling the house anytime soon. But we still want internet, phone, and TV for when we come over and work on the house or landscape etc.So instead of paying for TV, we were going to cancel and use his big old antenna, that is probably from the 60s. It has a twin-lead 300ohm connection. He also has a 720p Panasonic set from 2008/2009. It has a coax connection in the back labled antenna.My question is: Can we get a 300ohm >> 75ohm converter device and plug straight from the antenna to the TV?I'm confused as to who need to get one of those ADC boxes and who doesn't. I don't have one of those converters at the moment so I'm just curious before I do that.Thanks.Tim

author: tom66
author_rank: Super Contributor
timestamp: April 28, 2013, 05:34:02 pm
content: I thought 300 ohm was the characteristic impedance of the cable (and maybe the antenna?) You could recable it and that may work fine, or you could see if the TV will just work with it, but I would be surprised because the mis-match would cause some strange transmission line effects (I think?)

author: TimNJ
author_rank: Super Contributor
timestamp: April 28, 2013, 05:44:12 pm
content: I'm not sure really. I know next to nothing about TV transmission.Would a modern digital TV know what to do with a "raw" signal from the antenna?

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 28, 2013, 06:10:09 pm
content: It would work just fine, although you might need an amplifier as close to the antenna as possible and maybe a highpass filter since HDTV signals (in the US at least) are UHF or high VHF.

author: SeanB
author_rank: Super Contributor
timestamp: April 28, 2013, 06:15:19 pm
content: The old TV set used VHF t get signals, and this was sent down the 300R flat cable to the set. Newer HDTV sets use UHF for the transmitter, so you in all likelyhood need a new antenna ( pointed at the same transmitter) and a new cable run to the TV set. Then it will most likely work for OTA digital TV transmissions. There are websites that give coverage maps for the HDTV transmitters, but the easiest will be to look up local TV antenna installers and find out.If the TV worked with the antenna then leave it, otherwise first try using a FM balun to connect the flat lead to the coax connection on the set, it may get enough signal to work.

author: IanB
author_rank: Super Contributor
timestamp: April 28, 2013, 06:15:56 pm
content: I was going to ask if the US switched from VHF to UHF TV signals at some point in the past?You'd want to confirm that the Panasonic TV has a built-in digital tuner for broadcast HDTV. Some older TV's may only have had an analog tuner included and expected to get digital signals from cable.Usually, even if everything is in place it may be necessary to adjust the alignment of the antenna to get the best signal. HDTV is quite sensitive to signal quality.

author: tom66
author_rank: Super Contributor
timestamp: April 28, 2013, 06:31:51 pm
content: If it's a 2008/2009 Panasonic 720p, it's probably one of their earlier plasmas, TH-xxPX70, TH-xxPX80. Nice TVs. Digital tuner built in. I think only the PX60 doesn't have a digital tuner.

author: TimNJ
author_rank: Super Contributor
timestamp: April 28, 2013, 07:29:24 pm
content: It's an LCD. I'll look up its datasheet and see what kind of tuner it has. The 300ohm goes from the antenna to the basement where it goes into a preamplifier. It has inputs for both 300ohm and 75ohm. It also has outputs for 300ohm and 75ohm.What I tried to do was use the 300ohm input with the 75ohm output and hook it up to the TV. We actually found some channels, but something isn't right. The channels we were getting were majority foreign language (Japanese, Polish, Korean) and then only a single English channel which was NJ public television. But none of the major stations like NBC or CBS or FOX or anything like that.Fishy. We've left his house now so I'm not sure where that leaves us.

author: kxenos
author_rank: Frequent Contributor
timestamp: April 28, 2013, 07:34:48 pm
content: Sorry for your loss. To the point, I think you have to use a balun (balanced-unbalanced) to convert from 300 to 75Ohm.

author: oPossum
author_rank: Super Contributor
timestamp: April 28, 2013, 07:41:12 pm
content: Go here:http://www.antennaweb.org/Address.aspxand put in the zip code. It will show a map of the TV stations nearby and the RF channel they are on. The FCC tried to free up the low VHF and high UHF TV channels during the digital transition, so the existing antenna may not cover the needed RF channels.The 300 to 75 ohm balun should be installed at the antenna and a 75 ohm coax downlead used from the balun to the TV set. You can put the balun at the TV, but the old 300 ohm twinlead will not perform as well as new coax especially at UHF.

author: eKretz
author_rank: Frequent Contributor
timestamp: April 28, 2013, 08:07:07 pm
content: Sorry to hear about your grandfather, I still miss mine. As the others have said, the antenna might work fine if the set has a built-in digital tuner. The panels that don't have tuners usually say "monitor" somewhere on the back. Can't hurt to give it a shot and see what happens. Try re-aiming the antenna to get better reception, if he hadn't used it for 40 years it probably isn't optimally aligned. I think the antenna web site linked below has a section that gives you compass headings to aim for based on your location.

author: TimNJ
author_rank: Super Contributor
timestamp: April 28, 2013, 10:23:25 pm
content: Thank you all. I should have paid more attention to the orientation of the antenna today, but from what I remember, I think it's about 90 degrees off. We should be aiming at the empire state building about 25 miles away but I don't recall it being orientated that way. However, I do have a feeling that most stations were broadcasted from there 40 years ago and that it should be orientated that way, though I guess it is totally possible that's not true and that the antenna could have moved.Next time I go back, would it make more sense to run 300ohm to the preamp in the basement, and then continue running 300ohm upstairs to the TV, and then using a balun at the TV?I was also on the roof and I noticed that there was a small box left unconnected by the antenna. I have a sneaky suspicion that it was actually a balun because it was a passive unpowered device, but it had two lugs, and then a coax and two more lugs. Not sure it's condition. It looks quite weathered and the contacts are rusted. But if bought a new one, maybe it would be better to run coax directly from the balun near the antenna?Thanks.

author: IanB
author_rank: Super Contributor
timestamp: April 28, 2013, 11:01:15 pm
content: I think you would want to run modern UHF coax from the antenna to the TV. The antenna will pick up whatever signal it can; it may not be optimal if it is not a UHF antenna, but whatever UHF signal it captures you want to preserve. So feed the antenna output into your coax and run that to the TV. Then, even if the antenna is no good and eventually needs replacing with a modern one, the coax will be in place and ready to connect to it. I don't know without research whether the antenna output needs matching to the coax with a balun. It may depend on exactly what antenna is installed.Also, I would try first with the shortest run direct to the TV. Don't go via the basement and the preamp unless the direct connection fails. Even then, I suspect a modern UHF preamp or a modern antenna would serve you better than an old VHF amplifier.

author: TimNJ
author_rank: Super Contributor
timestamp: April 28, 2013, 11:26:27 pm
content: Alright thanks. I guess the coax isn't too expensive so I'll see if I can get some.

author: SeanB
author_rank: Super Contributor
timestamp: April 29, 2013, 03:31:02 pm
content: Point the antenna at Empire State, there are still a lot of transmitters for TV on it, and most are digital now. All are on the 87'th floor and feed up to the top antenna arrays.

author: Strada916
author_rank: Frequent Contributor
timestamp: April 29, 2013, 06:13:22 pm
content: Quote from: TimNJ on April 28, 2013, 05:21:28 pmHi Tim sorry to hear of your Grandfathers passing. What you need is a BALUN (BALance UNbalance). It's basically a small transformer which matches the impedance between Coax = 75Ohm and the ribbon cable or antenna 300 Ohm. If it works keep using it. However I strongly recommend replacing any of the ribbon cable with Quad to Tri shield. There are only a few 75 Ohm antennas out there. Most are LOG periodic

author: TimNJ
author_rank: Super Contributor
timestamp: April 30, 2013, 01:26:42 am
content: Thanks it means a lot. I will definitely do that!

author: TimNJ
author_rank: Super Contributor
timestamp: April 30, 2013, 02:20:31 am
content: Anyone have any resources for good UHF antenna designs? Perhaps that will be better than the old VHF antennas?

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: April 30, 2013, 03:01:43 am
content: Fractal hdtv antennas work, and they're small.http://www.ruckman.net/home/news-archives#FEATURED

author: vk6zgo
author_rank: Super Contributor
timestamp: April 30, 2013, 03:14:52 am
content: Quote from: oPossum on April 28, 2013, 07:41:12 pmActually,all things being equal,the twin line will be less lossy than coax--especially the stuff which is currently used.Most of the "RG6" & the like,is really designed for cable use,where the desired signal is quite high level,& the extra screening is required to prevent radiation into other services.It looks great,compared to the shoddy looking TV coax which was commonly used in earlier times,but its losses are higher at UHF ---about the same as "real RG59".(not the crud they try to sell as RG59 now)The "shoddy cable" was air cored,with much better loss figures.I had occasion some years back to try RG59 for a long run in a TV distribution system after we ran out of the cable we had been using---the signal was unuseable with RG59!All that said,the stuff currently used is cheap,rugged,& in most cases the additional loss is of no consequence.If the original installation is 40 years old, most of the connections will have corroded,the insulation crumbled off the twinlead,& any splitters will be blobs of corroded copper.Digital TV is very rugged,so the stations you are getting may be from random pickup on a broken length of twinline.When I bought a Digital TV,we got some stations OK on the old antenna & coax.The old antenna was quite literally falling apart,so I fitted a new one & temporarily connected it to the old feeder.NO change!--still the same group of stations.When I fitted the new cable,I got all the stations OK.I'm not sure how they did it in your country,but we stopped using the low VHF channels ,so a Digital antenna is quite compact compared to the old one.If you are going to climb around on the roof,you may as well fit a new antenna & cable & be done with it!

author: ptricks
author_rank: Frequent Contributor
timestamp: April 30, 2013, 04:14:29 am
content: Quote from: TimNJ on April 28, 2013, 10:23:25 pmThe interesting thing many may not be aware of is 300 ohm twin lead is actually better performing and has less loss than coax. The downside of twin lead is that performance suffers if it is routed poorly down the mast and into the home which is why stand off supports for the wire were produced. The box you are describing sounds a lot like a pre-amp. Pre-amp are to be placed as close to the antenna as possible and will amplify the signal to make up for line loss between the antenna and the tuner. The power supply for a pre-amp goes inside the home and it uses the same wiring for power and signal. A balun will just have a coax fitting on one side and twin lead on the other, no box for it is needed.