I don't like amplifiers.
Ones you can afford are single ended which means they will have beat products that may fall on a channel you like. The best ones are push-pull like professional CATV amps and don't have this problem.
So I use a high gain antenna (10 dB gain) and feed that to an 8 way splitter (10dB loss) to provide one output for each room in the house.
Now the antenna has to match to free space impedance. What is free space impedance? Its about 277 ohms which is how the twin lead impedance (300)was chosen.
Ones you can afford are single ended which means they will have beat products that may fall on a channel you like. The best ones are push-pull like professional CATV amps and don't have this problem.
So I use a high gain antenna (10 dB gain) and feed that to an 8 way splitter (10dB loss) to provide one output for each room in the house.
Now the antenna has to match to free space impedance. What is free space impedance? Its about 277 ohms which is how the twin lead impedance (300)was chosen.
I will find out eventually.....
There is a commercial ham wire antenna sold at hamfests everywhere called the "W5GI Mystery Antenna". I have been using one for about 3 years. It uses a "Euro strip" for the connection between the twin lead and the RG59. It is hanging in free space where all the salty rain water that runs down the twin lead drips off. So far so good. I think the center lead of the coax is going to fail first from wind abuse.
The old rhombic that I talk about used a black terminal block like the one on this antenna. All that stuff is OK the PVC pipe got brittle from UV exposure and broke apart.
US DTV allows the broadcaster to use his 6 MHz channel in several different ways. Many chose to run ONE single TV broadcast with 1080 lines and use all of the bandwidth to achieve sufficient data rate so that motion artifacts are visible if you nkow what to look for but not terribly obtrusive at full speed. DVR them and watch frame by frame to understand how the compression algorithm builds a total sceen change over 10 or 20 frames.
Other broadcasters run one 720 line TV broadcast, AND several 480 line broadcasts with low data rates. Our local NBC franchise runs a 24 hour sports channel featuring running, cycling, swimming, and other fast motion events. It is totally unwatchable. You can even read the numbers on the competitors jerseys or see who they are.
The characteristic impedance of a folded dipole is 300 ohms, or 288 ohms, or 277 ohms depending which book you read.
There are some good single ended broadband amplifier chips out there for reasonable money. I got my test board back today. Maybe I'll fire it up tomorrow.
In the UK the BBC seems to use more bits than commercial broadcasters. The 'lesser' commercial channels are particularly low on bit rate, and some have trouble even getting lip sync correct.
The impedance of a thin folded dipole will be four times a normal halfwave dipole, about 290 ohms? Most folded dipoles are thicker, so will resonate at a shorter length and have a slightly smaller impedance. The impedance of free space is not relevant, except in the sense that it appears in the impedance formula for all antennas so sets the scale of likely impedances.
The impedance of a thin folded dipole will be four times a normal halfwave dipole, about 290 ohms? Most folded dipoles are thicker, so will resonate at a shorter length and have a slightly smaller impedance. The impedance of free space is not relevant, except in the sense that it appears in the impedance formula for all antennas so sets the scale of likely impedances.
My first paying job was installing TV antennas. It was 1967. The budget antennas of the day were mostly folded dipoles with a reflector and one or two directors. They were made of thin walled aluminum tubing with a bend radius of about 1.5 inches making them quite thick. A folded dipole was used because it is balanced and easilly fed by connecting 300 ohm twin lead across the open ends. Coaxial cable wasn't used for TV antennas yet. It didn't show up until color TV got a stronghold which was early to mid 70's. NTSC color didn't like multipath or twin lead blowing in the wind.
There are two reasons why folded dipoles are often used in TV Yagi antennas. One is bandwidth. The other is to raise impedance. The director and reflectors lower the dipole impedance; folding the dipole multiplies it by four. It is unlikely to be anywhere near 300 ohms, more like 50-100ohms in a Yagi. Are you sure the twin feeder was 300, as lower impedance versions (80?) were available too?
Funny. My 2nd or 3rd paying job was installing TV antennas. 1979, Palm Beach county. A lot of CATV work for condos.
Cable was not omni-present, even that late.
Cable was slow to come to south Florida due to the problems getting easement rights to run the cable. Many new developments were cabled up as they were built out, but older developments got cable based on their economic status. It has been the same way with DSL and fiber to the home.
We didn't get cable until 1981 in my neighborhood, DSL wasn't available until 2000. AT&T started advertizing U-verse service about 2 years ago, but it wasn't available until last month at my house. By that time AT&T and Comcast's attitude and customer "satisfaction" policies have convinced me that antenna TV is just fine. I do miss some of the Discovery Channel shows like Mythbusters.
Some areas in Miami didn't have cable until the late 80's. They did have the private channel club, HBO on 2.154 GHz. Yes, I made antennas and downconverters for this too. They also had a scrambled UHF channel with nasty movies late at night. Strong signal, a suitable antenna could be made from #12 solid wire. The descrambler was a little harder to make.
When I was in high school I walked into the TV repair shop near my house and asked the owner to hire me because I could fix TV's better than he could. He laughed and said that I could put up antennas for $1 per hour. Within 6 months I was fixing TV's and he was putting up antennas.
300 ohms was the standard TV input impedance in the US from the first CRT glow until well into the 90's. In fact some TV's and TV accessories still come with the 300 ohm balanced to 75 ohm SE transformer that I used on my antenna.
Many "old style" TV antennas are still 300 ohms and you can still buy 300 ohm twin lead, or the transformer. Radio Shack sells the transformer for $6 and their ad copy states "The reversible Indoor/Outdoor Matching Transformer matches 300-ohm screw terminals on antenna to 75-ohm round coax cable downlead."
Indoor/Outdoor Matching Transformer : Antenna Transformers | RadioShack.com
That's pretty much what I remember. I went to work for a cable company a year later and in some new neighborhoods we were going into, there were 3 competing companies! Imagine having a choice of 2 or 3 cable providers.
There was a lot of "accidental" cutting of the other guy's feeder lines back in those day. Ooops! It was the Wild West (Palm Beach).
Hurray!
Fired up the breadboarded first stage of my amp today. Very simple circuit. RFMD SPF-5122Z chip, 4 caps and a coil. I think I can eliminate all but the chip and one cap once I switch to DC up the coax cable.
Performance is as good as the data sheet says. NF is .5 db at VHF rising to .6db all the way up to 1.3 GHz and hitting .9db in the 2 to 2.5 GHz region. Gain is a slope from 26 db at 100 MHz (too much, but probably OK with the low antenna gain at VHF) to 20 db at 1GHz and 11 db at 2.5 GHz. Measured with an Agilent N8975A noise figure analyzer.
IIP3 is +8dbm at 100 MHz, +15dbm at 400 MHz, and +19dbm at 1GHz. Measured with two Agilent E4438C ESG's and an Agilent E4440A PSA.
Input return loss is at least -10db across the TV band and drops to -8 at 100 MHz. Measured with an HP 8753 network analyzer.
I plan to test both amps cascaded with 40 feet of cable between them before deployment.
I will not have much more time to play with this until after I return from my road trip in late May. Will hit the Dayton hamfest on the way home to collect more tubes, and other toys.
Performance is as good as the data sheet says. NF is .5 db at VHF rising to .6db all the way up to 1.3 GHz and hitting .9db in the 2 to 2.5 GHz region. Gain is a slope from 26 db at 100 MHz (too much, but probably OK with the low antenna gain at VHF) to 20 db at 1GHz and 11 db at 2.5 GHz. Measured with an Agilent N8975A noise figure analyzer.
IIP3 is +8dbm at 100 MHz, +15dbm at 400 MHz, and +19dbm at 1GHz. Measured with two Agilent E4438C ESG's and an Agilent E4440A PSA.
Input return loss is at least -10db across the TV band and drops to -8 at 100 MHz. Measured with an HP 8753 network analyzer.
I plan to test both amps cascaded with 40 feet of cable between them before deployment.
I will not have much more time to play with this until after I return from my road trip in late May. Will hit the Dayton hamfest on the way home to collect more tubes, and other toys.
I made two prototype boards 4 years ago. One had a 4 to 1 balun transformer on the input, and the other didn't.
I stuck the transformer version on the coat hanger antenna 2.0 to see what it would do. It was mounted outside at the antenna so the feedline losses would not add to the system noise figure. It rammed so much signal into the Radio Shack distribution amp that it was overloaded with its gain turned all the way down. I removed the distribution amp and connected the output up to one TV. The low noise amp allowed excellent reception of the two TV stations in Port Saint Lucie that were previously seen on the spectrum analyzer, but too week to be decoded by the TV set. There were a few new weak TV signals visible on the spectrum analyzer that were not visible before. The Radio Shack amp with 50 feet of cable in front of it had virtually no gain above 700 MHz but cellular LTE was very strong at 720 Mhz and two way radio and cellular CDMA were strong at 850 MHz. The new amp displayed all sorts of signals with the twin coat hanger antenna up to 2.4 GHz. IMD products were still visible on the spectrum analyzer from the strong local two way radio and cellular signals, but they were weaker than those produced in the Radio Shack amp
I removed the outside amp and returned the system to its previous configuration because I had no suitable enclosure for the outside amp. Since then I have not used either of the prototype amps. I lost my 41 year job at Motorola last year, packed up and moved 1200 miles north.
We had a new house built in rural West Virginia, and finally moved in two weeks ago. It will take me a while to build a new basement lab, then I can get back to building stuff again. For now those little amps are stuffed in a box somewhere. The locals tell me that there is NO antenna TV reception here, no cell phone either, so for now we are paying Comcast far too much money......my spectrum analyzer says that there is some hope, but only time , and amp or two, and antenna 3.0 will tell. It will be several months before I have time to experiment.
I stuck the transformer version on the coat hanger antenna 2.0 to see what it would do. It was mounted outside at the antenna so the feedline losses would not add to the system noise figure. It rammed so much signal into the Radio Shack distribution amp that it was overloaded with its gain turned all the way down. I removed the distribution amp and connected the output up to one TV. The low noise amp allowed excellent reception of the two TV stations in Port Saint Lucie that were previously seen on the spectrum analyzer, but too week to be decoded by the TV set. There were a few new weak TV signals visible on the spectrum analyzer that were not visible before. The Radio Shack amp with 50 feet of cable in front of it had virtually no gain above 700 MHz but cellular LTE was very strong at 720 Mhz and two way radio and cellular CDMA were strong at 850 MHz. The new amp displayed all sorts of signals with the twin coat hanger antenna up to 2.4 GHz. IMD products were still visible on the spectrum analyzer from the strong local two way radio and cellular signals, but they were weaker than those produced in the Radio Shack amp
I removed the outside amp and returned the system to its previous configuration because I had no suitable enclosure for the outside amp. Since then I have not used either of the prototype amps. I lost my 41 year job at Motorola last year, packed up and moved 1200 miles north.
We had a new house built in rural West Virginia, and finally moved in two weeks ago. It will take me a while to build a new basement lab, then I can get back to building stuff again. For now those little amps are stuffed in a box somewhere. The locals tell me that there is NO antenna TV reception here, no cell phone either, so for now we are paying Comcast far too much money......my spectrum analyzer says that there is some hope, but only time , and amp or two, and antenna 3.0 will tell. It will be several months before I have time to experiment.
Thanks very much for the update, very sorry to hear about your job, it sounds like you were the best engineer there.
I'm in Connecticut about 65 miles from the NYC area towers, part of the path is over water, and I'm getting decent reception with a fairly small Clearstream 2 antenna:
Antennas Direct C2 ClearStream2 Outdoor Digital HD TV Antenna With Winegard DS-3000 39 J-Mount (C2) from Solid Signal
I need a better antenna, and I get a small number of channels without an amp but with a CM-7777 I get most of the NY channels and a few local just because they are so strong. I'm not using a rotator:
Antennas Direct C2 ClearStream2 Outdoor Digital HD TV Antenna With Winegard DS-3000 39 J-Mount (C2) from Solid Signal
The CM-7777 seems to get good user reviews but I have a feeling that your amp is much better.
I'm getting just enough signal that I can split it with a passive splitter to two sets, an active distribution amp just overloads and probably has so much IM that it is just not workable.
It is still on my list to get one of the better commercial bow ties and then I hope to be able to split 3 or 4 ways, or perhaps an even better antenna. I have it in the attic by the way.
I'm in Connecticut about 65 miles from the NYC area towers, part of the path is over water, and I'm getting decent reception with a fairly small Clearstream 2 antenna:
Antennas Direct C2 ClearStream2 Outdoor Digital HD TV Antenna With Winegard DS-3000 39 J-Mount (C2) from Solid Signal
I need a better antenna, and I get a small number of channels without an amp but with a CM-7777 I get most of the NY channels and a few local just because they are so strong. I'm not using a rotator:
Antennas Direct C2 ClearStream2 Outdoor Digital HD TV Antenna With Winegard DS-3000 39 J-Mount (C2) from Solid Signal
The CM-7777 seems to get good user reviews but I have a feeling that your amp is much better.
I'm getting just enough signal that I can split it with a passive splitter to two sets, an active distribution amp just overloads and probably has so much IM that it is just not workable.
It is still on my list to get one of the better commercial bow ties and then I hope to be able to split 3 or 4 ways, or perhaps an even better antenna. I have it in the attic by the way.
Are you familiar with the discontinued CM-4251: ?
Channel Master 4251 Tribute Page
I'd think that someone could figure out a way to DIY a CM-4251 using different construction methods.
They say that the Stacked Super-G-1483 UHF antenna is almost as good:
Stacked Super-G-1483 UHF antenna collinear package
This page covers how some of the better antennas have gotten worse in later production:
Temporary page
The Super-G-1483 is a Hoverman design, here is an improved DIY version, the Gray-Hoverman:
http://www.digitalhome.ca/ota/superantenna/index.htm
Channel Master 4251 Tribute Page
I'd think that someone could figure out a way to DIY a CM-4251 using different construction methods.
They say that the Stacked Super-G-1483 UHF antenna is almost as good:
Stacked Super-G-1483 UHF antenna collinear package
This page covers how some of the better antennas have gotten worse in later production:
Temporary page
The Super-G-1483 is a Hoverman design, here is an improved DIY version, the Gray-Hoverman:
http://www.digitalhome.ca/ota/superantenna/index.htm
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I was far from the best, but I worked far below my abilities. I did this on purpose to prolong my career. I chose to do the work that nobody else wanted to do, designing and building prototype high tech devices! I was good at it and I enjoyed my job, but the environment was changing, and it became clear to me that corporate wanted the older higher paid people out, and I found out that the building had been sold, so when corporate offered me a buyout, I said goodbye! After 41 years in the same place, I was well past my corporate expiration date.
About 3 weeks after signing my exit papers, most of my friends, including those who refused to sign, were laid off.
Yes, they were all over Miami.....to receive the blacked out Dolphins games from WINK TV channel 20 across the everglades in Fort Myers. Those things were out of my budget, so I had a home made 4 antenna Yagi array made with broom sticks and welding rod. This was in the early 70's. That ended when Tampa got an NFL team in 1976. WINK chose to broadcast the Bucs instead of the Dolphins. I built a C band dish in 1981.
I did things a bit backwards. I walked into Motorola in 1972 at age 20 to answer a "technicians wanted" ad in the Miami newspaper with only a high school diploma. Out of about 500 applicants, 3 of us were hired. The HR guy said that odds were 2 of us would be gone in a month, the turnover rate was that high. He was right.
20 years later, they paid me to go to college and get a degree. When I joined the advanced development group, they sent me to school for a masters degree. Neither included any RF course work.
The amazing work was done by whoever designed the IC chip. It is 50 ohms in and 50 ohms out. The "amp" is just the chip, two 50 ohm striplines, and a blocking cap. You add a choke and a bypass cap if you don't want power through the output coax. 50 ohms is close enough to 75 ohms, so that the mismatch losses are about 0.5 db. Most of the details are given in the device data sheet. No fancy RF techniques needed. There are more and more "RF building blocks" types of chips like these appearing on the market every day.
Here in the middle of nowhere there are two VHF stations that "cover" this area IF you are on high ground. We are down in a "holler" where there is little RF period. If I climb the 100 foot hill behind our house with a portable TV, I can receive both of them. Channel 7 Wheeling has CBS and ABC. Channel 9 Steubenville has FOX and NBC.
I see two possibilities. I will make a Yagi cut for channel 8 and see if there is any signal to be found on the property somewhere. If that doesn't work out I can always design a repeater with a battery and a solar panel to go up on the hill. It will only need to transmit a few hundred feet, a few milliwatts of power is all that is needed, but DTV signals require extreme linearity.
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