HDTV xfmr

[WA3VJB]

So I am getting a new "UHF" outdoor ant for the HDTV, and it looks like they all suggest a transformer at the antenna end, then feed coax to the house.



20 years ago, I put 300 ohm foam twin lead up there to the screw terminals on the TV at the time. A newer TV was the "new" F jack, and I transformered the twin lead at the television.

So for today's upgrade, is there any difference in loss whether the transformer (4:1 balun) goes at the head end into coax, or at the tail end from twin lead?

I've got new coax laying around, or could even use some 70 ohm semi-rigid hard on line for most of the 50 foot run.

But if I can leave lower loss balanced line up there that would seem to make sense to minimize the amount of unbalanced coax on the path.

[Ed/KB1HYS]

since the active element in the picture is the folded dipole, it should match 300 ohm twinlead with out a transformer, though you will have to modify your attachment points to the ends of the loop.
 I'd run twinlead as far as possible. (all the way to the back of the set if able).  and transform to 75 ohms there.

[Tom WA3KLR]

As far as I see, the 300 Ohm line is not used much anymore.  The latest RG-6 is lower loss than in the past.  As you know, balanced line is much more influenced by the outside world and vice-versa than coax.

What I do here is have a mast-mounted pre-amp and use the coax, having my cake and eat it as far as I am concerned.  With a mast-mounted pre-amp your SYSTEM noise figure will be the lowest and the transmission line loss becomes an almost insignificant factor.  You'll be able to drive multiple sets with a splitter with the amplified signal.

[WA1GFZ]

If you decide to bring twin lead into the house to the back of the set make sure you have a good ground on the coax shield. A common mode lightning pulse could nail the TV. The transformer at the antenna
with the shield terminated to ground outside may help for lightning.
ane everything Tom said.

[Tom WA3KLR]

By the way Paul, my UHF antenna straps yours, HI.

[flintstone mop]

Tom, Paul's aerial looks sexier.
With all of the hot UHF signals around you, Paul, you shouldn't have any problem with 90 and better signal readings with the HD tuner. Make it 75 ohm all the way into the house. Remember the need for shielding once inside the house. Twin lead won't give you shielding when it starts running near/around the house wiring. HD from terrestrial stations (1080i) is beautiful!!! The satellite is next for a wow pic and cable is ok for HDTV. Watch out for the PBS stations that like to multicast 4 crummy NTSC pic on one carrier. Really diversified programing going there.
Fred

[WU2D]

I agree with Tom. The latest versions of RG-6 are comparable to the best of the RG-8 types including LMR-400 and RG-213 for loss (not power handling).

They are double shielded and poly foam insulated.

http://www.tessco.com/products/displayProductInfo.do?sku=47444&eventPage=1

Mike Wu2D

[flintstone mop]

I had a panel type of UHF antenna that gave me 14db gain.
Just think when you see a sporting event you will see people's faces in the crowd not a blur of humanity as with NTSC. And no ghosts!!! Digital was the only way to get rid of an ancient old problem. Digital is either there or not there no half way stuff.
I hope you got an LCD TV not Plasma.
Fred

[WA3VJB]

Fred, I got a plasma and it's better than the LCD competition in a 42 inch variety. 1080p besides. TH-42PZ700U Panasonic.

The antenna is a disappointment. I picked up more stations on the OLD combination antenna (a non-swept version of yours, Tom), and those I pick up on the new one are not as strong. NO other changes.

I can lay the RG-6 down for a temporary test, and if it proves better than I will switch over, otherwise, will have to get an 8-bay or some other variety. Lots of trees on the property, and the signals are not stable as shown on the unit-measure menu.

Pixelates quite a lot at times.

[Pete, WA2CWA]

Fred, I got a plasma and it's better than the LCD competition in a 42 inch variety. 1080p besides. TH-42PZ700U Panasonic.

The antenna is a disappointment. I picked up more stations on the OLD combination antenna (a non-swept version of yours, Tom), and those I pick up on the new one are not as strong. NO other changes.

I can lay the RG-6 down for a temporary test, and if it proves better than I will switch over, otherwise, will have to get an 8-bay or some other variety. Lots of trees on the property, and the signals are not stable as shown on the unit-measure menu.

Pixelates quite a lot at times.

You probably need one of these:

[flintstone mop]

Withou knowing your elevation, I guess the trees will be attenuators until Fall. The panel antenna I had did all right through trees, but I was pretty high up in Oxon Hill.
Plasma ehhh?? Better color?? sharper?? What was decision for Plasma?
Fred

[Steve - WB3HUZ]

All other things being equal, 72/75 line should be lower loss than 50 Ohm line. This is why 75 Ohm lines exist - they produce the lowest loss for reasonable coaxial cable designs. The 50 Ohm lines trade of some loss for better power handling capability.

I agree with Tom. The latest versions of RG-6 are comparable to the best of the RG-8 types including LMR-400 and RG-213 for loss (not power handling).

They are double shielded and poly foam insulated.

http://www.tessco.com/products/displayProductInfo.do?sku=47444&eventPage=1

Mike Wu2D

[W1DAN]

Paul:

A couple of things to keep in mind:

1) todays sets are a lot more sensitive than even the early 1980's. You may or not need a preamp. These sets overload easily and have relatively poor IMD and adjacent and even non-adjacent signal handling capability. Most receivers are not superhets these days, but are direct conversion with little front end filtering.

2) Reflections kill the DTV receiver's ability to decode an ATSC signal (as well as COFDM IBOC and DRM for that matter) faster than low signal level. If you get the analog stations with snow but little reflection you may be all set.

Enjoy your TV..I am jealous!

73
Dan
W1DAN

[WA3VJB]

Thanks all. I haven't laid the RG-6 to test yet. This weekend.
Fred the plasma screens have better black/dark gradations than LCD, but if you have a room with a lot of ambient light, the LCD's illumination is more strapping than plasma.

Dan I am about fed up with this part of the process and am ready to try Verizon FiOS television. I've already got their internet light pipe and it's friggen magic.  In our area we would get about 25 channels of high def, between the local channels and the movie networks. Directv that we now have (on regular def) is offering only 5 HD channels, and I may not be able to see their other satellites carrying high-def. By the time I upgrade the box and get a new multi-LNB dish, I then may find out I can only see the one main bird I've been on the past ten years.

Comcast sucks and is not considered.

But if I persue over-the-air HD,

Steve are you comparing 72/75Ω coax with 50Ω coax? I wasn't really going to waste any of my 50Ω stuff on a mere television. My options are between the existing 300Ω foam twinlead and some new Belden RG-6 coax.

All other things being equal, 72/75 line should be lower loss than 50 Ohm line. This is why 75 Ohm lines exist - they produce the lowest loss for reasonable coaxial cable designs. The 50 Ohm lines trade of some loss for better power handling capability.

Pete,
I've used up my good husband credits with this last winter.

No way she'd let this go up on the roof.

[Steve - WB3HUZ]

Steve are you comparing 72/75? coax with 50? coax? I wasn't really going to waste any of my 50? stuff on a mere television. My options are between the existing 300? foam twinlead and some new Belden RG-6 coax.

Someone else mentioned 50 Ohm types. Yes, don't waste any 50 Ohm cable on this application unless you have a ton of low loss stuff around. The 75 Ohm cables will likely be lower loss and less expensive. I use 75 Ohm cable for my receive antennas (loops, beverages, etc) for this very reason. The SWR/mismatch doesn't matter on receive.

[N3DRB The Derb]

i have the biggest RCA OTA they make up here in WV,  the boom is 25 ft long; combined with a wineguard mast mounted preamp > 25 db of gain, 80 miles from dc I get typically >85%~95% signal strength. I get about 18~19 OTA stations, and some comcast stuff, but most of that is encrypted. I am hookin the cable back up today, so I'll get about 6 more channels off of that.

I use a EL GATO eye TV 500 to record in HD to the hard drive, from there I can convert the files to quicktime sized as needed from HD to native iPod. I use iMovie HD or FCP HD to produce with, Soundtrack or Garageband..... I just haven't been feeling well enough to mess with it. The whole Mac side of the room i torn Down.

[WA3VJB]

It was the 300 ohm foam twinlead.
I guess 20 years took its toll.

Hooked up the little weatherproofed balun onto the antenna wingnuts, spun the F connector to it, then dropped the Belden RG-6 off the roof and ran it through the downstairs slider to the back of the TV.

VOILA !!

Even pointed at Baltimore, I could pick up the Washington DC stations nearly full strap. Baltimore were bone-crushing signals.

So it's time to thread some coax through the walls using the old twinlead as fish wire.

Tnx for all suggestions / advice.

Friday we are getting Verizon FiOS television besides, but I'm not sure they power up their head end if the region loses power, so the coax OTA will be the backup.

Just got a new generator this weekend too, an 8Kw Briggs & Stratton, strapping replacement for the old Coal Man Powermate 4000. Many AM Expeditions on that old machine, I'll miss it.

[W2JBL]

way up in the Adirondack Mountains at my secret compound i'm a minimum of 60 miles from major market TV transmitters on VHF, and farther on many UHF stations. Ok, i may be cheating being at 2000 feet up but i use a large Radio Shack TV ant, and last year went from twinlead to RG6, with a balun at the antenna end. results? UHF stations from Rochester and Binghamton (120-150 miles airline) are now out of the noise and solid at night. on a good day inversion/tropo) i get NYC market stations on 2,4 and 5. best DX this season was a VHF in Cleveland area advertising a car dealer down the street from Buddly WD8BIL. it was worth dumping the twinlead for sure.