Antenna installation

lower mast section

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My advice is to leave well enough alone. Mount your big antenna where you planned to remount your compact antenna, rather than going through all this fabrication. Add a section of mast tubing to raise the rotor if this spot is too low for good reception.

Why not a basic satellite receiver ?

Before blundering forward, I suggest you do a little research.

1. Go thee unto:

Enter your location and have it calculate which stations you can expect to see at your camp location. Print the results and post them on the wall as it will save much effort in antenna pointing.

1. Set your TV or converter to rescan for digital channels. They sometimes move in frequency. With a directional antenna, you may need to aim it in a probable direction, scan, scribble down the usable channels, and then do it again with the antenna pointed in another likely location.

1. If you have a converter, please check for reviews and user comments. Many of the rush to market converters are little better than junk.

2. Compare the gain and performance of your proposed antenna at:

Your existing antenna and amplifier may already be theoretically sufficient.

two channels. TV fool says that there are more possibilities for that addre= ss. Also the neighbor put up an all band POS Radio Shlock antenna with no p= reamp and he gets a few channels. And he used 300 ohm wire and taped it to = the mast! As for satellite, for just a few weeks out of the year it's not feasible. Besides we're not looking for that type of TV entertainment for a Summer camp anyway. During the day we listen to the radio or swim, hike, etc. Rainy days we might go to a museum or watch a DVD. Evenings we might watch a show or the news or weather. TV is not a big thing for us but a few more channels would be nice. I don't want to lose my FM though and the new HD antenna will not have a low band VHF section. Lenny

Bingo. What I'm trying to get you to do is figure out what a reasonable receiver and antenna should see at your location. If your current derangement isn't working up to estimated coverage, it might easily be a receiver or converter problem. If your neighbor, with his marginal system, gets good reception, you may have a problem with your hardware.

I can't tell from your description if you have the preamp mounted on the antenna, or if it's next to the receiver. It belongs near the antenna.

You could carry a satellite receiver back and forth between your residence and summer camp. With DirecTV, it is also possible to add a

Then, find a better antenna that covers FM or add a separate FM yagi. I live in the hills and a big FM yagi is the only antenna that really works for OTA reception. My former VHF/UHF TV antenna (destroyed in a storm in Jan 2012) had only about 5dBi gain in the FM band. The 8ft long FM band yagi (partly mangled in the same storm) has about 10dbi gain. The difference in reception quality and stability was very noticeable.

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You don't want to tape 300 ohm twinlead to the mast, it killls the signal. Use standoffs or coax cable. 300 ohm has lower losses on average than coax, but does have to be kept at least a couple of inches away from anything metallic and thus is more of a pain to install.

Agreed. However, I would recommend double shielded RG-6/u coax cable instead of twinlead.

Yep. I dunno about the low loss part. For the feed lines by themselves: 300 ohm RG-6/u MHz twinlead coax

Most antennas are 300 ohms, while modern TV's are all 75 ohm. Add a

However, when I tried to measure the losses at 100Mhz, with a few impairments added. Losses are approximate as I can't fine where I scribbled down the results.

Coiling the entire 100ft of twinlead into about a 2ft dia coil resulted in an additional 3dB loss due to radiation. While this is unlikely to happen in a real install, it does indicate that you cannot store extra wire in a loop in the attic.

Running the twinlead through a nearby metal object (i.e. my bench vise) resulted in an additional 2dB loss. This was intended to simulate running through the opening in a metal framed window or door.

Running the twinlead, with one wire close to a handy metal object (10ft of steel rain gutter) resulted in an additional 3dB loss. This demonstrates what happens with the balanced line becomes unbalanced by different capacitance from each wire to ground.

A simulated wet bird, in the form of a plastic bag filled with 2 cups of water straddling the twinlead, resulted in 2dB loss.

Doing the same with the coax cable, showed no changes in loss.

Bottom line: Twinlead is lower loss, but only if you have an ideal installation, which I have yet to see. Use coax so that you don't have to worry about such things.

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Jeff - I installed antennas in the mid-1950's in Ft Pierce, FL. Nearest tv broadcast station was Miami @ 125 miles. We used antenna- mounted signal vacuum tube boosters, and 300 ohm twinlead with standoffs to get the maximum possible signal to the tv sets. When West Palm Beach came on the air, only 50 miles away, we were able to drop the boosters, but kept the 300 ohm twinlead. There was also a hollow tube 300 ohm twinlead that claimed slightly lower losses in wet weather, but that required sealing the tube at the top or it could act like a small pipe and be worse than regular flat twinlead. Coax losses were just too great at those signal levels/distances.

In the 1950's, antenna mounted tube amplifiers were all you could buy. In the mid 1970's, I inherited some Jerrod tower mounted amps (6AG5 tubes) that I used for the local do it ourself CATV system receivers. They worked, but when proper dual gate MOSFET amps arrived, I junked them.

According to theory, as long as your antenna mounted amplifier has a reasonable noise figure, and your amplifier gain is a few dB more than your coax cable losses, it will work as well as if the receiver was on top of the tower. The purpose of the RF amp (not normally called a booster) is to eliminate the effects of the coax cable. Had you left the amp up the tower, you would not have needed to squeeze every last dB out of the twinlead. Coax would have worked.

However, since you enjoy living in lightning country, I suspect that tower mounted electronics have a short lifetime. Maybe mounting the amplifier a few feet below the top the of the tower might be better.

Incidentally, I worked with the low loss twinlead. The center "core" was filled with some kind of foam rubber. Judging by the density, it was probably open cell foam. Left open to the atmosphere, it would absorb water from the air, wick it into the coax, and eventually fill with water. I used some of that stuff in the Smog Angeles area. That was when I was into using the best, not matter how much it cost my parents. I sealed the top of the twinlead, but didn't think I needed to seal the bottom. After a few months, it was dripping water out the bottom. Oddly, the reception wasn't affected, but we were in a strong signal area, so a few dB didn't matter.

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In message , Jeff Liebermann writes

Coiling the coax shouldn't make a scrap of difference.

True for coax cable. However, coiling twinlead added 3dB in loss. It's common practice to coil the excess cable rather than cut it. Not a problem with coax, but potentially a bad idea with twinlead. Nobody is going to coil 100ft of twinlead into a 2ft diameter coil, so the

In message , Jeff Liebermann writes

Ah yes, sorry. I missed the 'twinlead'. I've never really thought about what happens what happens if you have a roll of twinlead coiled up. It's simply something you don't do!

Unless you use shielded twin lead. I used it on an antenna way back. Seems like strange stuff, but didn't require transformers.

Greg

I think you mean Twinax:

The stuff is about 75 ohms between pairs. Strictly speaking, it doesn't require a matching transformer, but really should have a 1:1 balun to deal with the balanced Twinax to unbalanced (F connector) system.

The stuff was designed for data, not RF. Impedance, balance, capacitances, and data performance are specified in MlL-STD-1553B, attenuation at RF frequencies is not. I'm surprised that it worked at FM/TV(?) frequencies.

You could fake shielded twinlead with two runs of 75 ohm line. That will give you 150 ohms between center conductors, which can be converted to either 75 or 300 ohms with a 2:1 (trifilar) balun. Unfortunately, the loss would be twice that of a single run of RG6/u, so there's no benefit.

The stuff was 300 ohms. I'm pretty sure the name was belden super permaohm. This was back in the 60's . The only reference I find, is my own. I do find another name, city color by belden. Twin 26 gauge wires with foil shield.

Greg

It was called Belden "Permohm" and later changed to Belden "City Color". Belden recommended it for locations with high interference levels. The loss is about the same as the equivalent length of coax cable. I checked the online Belden catalog and didn't find any manner of twinlead. Belden allowed the Permohm trademark to expire in 2001:

City Color is a listed trademark, but not by Belden.

Scroll down to "WR-TWIN-TV" and "WR-TWIN-TV-100":

That's not a Belden part number. I don't know where they got the stuff. Belden may have sold the product to someone else.

Drivel: We had a local ham that spent some time characterizing the HF transmission line characteristics of 12-2 Romex power cable. It actually worked reasonably well until the price of copper made it uneconomical. Ummm... not recommended for TV or FM use.

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Never thought of using Romex for RF. It would indeed be interesting to see what it's characteristic impedance would be at different frequencies though. I wish I had the time to experiment with that. Too busy trying to pay the electric bill. I suppose if I'm ever on a desert island and have to get the transmitter on the air and all I have is Romex well, I suppose I'd give it a try.

I used that shielded 300 ohm Belden Permohm back in the 60's when I lived in The Bronx. I think I still have a bunch of it around here too. I had a Vbeam antenna, (just about everyone did). All NYC TV stations were VHF except for 31 which was municipal and 47 which was Spanish. I received them all on my Vbeam. All but 47 which was from New Jersey and mostly ran test patterns, (remember test patterns), broadcast from the Empire State Building 15 miles away in Manhattan. Reception was never a problem. I had no pre amplifier but used a rotor for DX'ing. I sometimes could get low band from Boston and Connecticut and once pulled in 13 from Prince Edward Island Canada. We had a 1951 TV/FM console receiver made by Pilot Radio. This was like the wild west of TV. That was pretty thrilling for a kid. Lenny

Nope. It's quite constant. As I vaguely recall (and can't find my notes), it's about 110 ohms between outside conductors for 14-2 NM-B. There's nothing in the dielectric and insulation to absorb power, so the impedance is going to be constant up through UHF frequencies. However, the insulation breakdown voltage is only about 600V making Romex rather useless for high power RF.

The big problem is what to do with the "extra" ground wire in 12-2 cable. Grounding or floating the extra ground wire allegedly didn't seem to do anything, but I'm suspicious.

I haven't tried to design an antenna that would take advantage of this ground wire. Perhaps a motorized yagi that uses the feed line to supply power. With all that copper, the IR losses will be small.

Hint: LMR-400 about $0.80/ft