Antennae Booster

Do you mean that a "bigger" box is your idea of a better TV antenna amplifier? This looks plenty big: Dimension: 498mm (W) x 360mm (D) x 280mm (H) Or, perhaps you mean't something other than size?

Higher gain does not buy you much in the way of a performance improvment. At best, all you need for gain is a bit more than the coax cable loss between the amp and the TV (or distribution amp). Too much gain just generates intermodulation products, AGC overload, and other receiver problems caused by too much signal.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann
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Unless you're dealing with weak signals and fringe coverage, a high gain (26dB in this case) amp is an invitation to overload problems. Quoting the Channelmaster data sheet: The Titan 2 High Gain Preamplifier is recommended for professional installers only. Due to the high gain output of this product, it can result in over amplification if not used in the appropriate scenario. Over amplification

receive and display some or all channels. Note that there were 3 radically different versions of the CM-7777 amplifier. Which version do you have?

The original Titan 2 amp had a phenolic PCB. V2 had separate VHF and UHF outputs, while V3 has them combined into one output. Therefore, my guess is that it's a V2.

Are you trying to measure amplifier gain using an OTA (over the air) signal? The amplifier gain is not the same for the VHF and UHF sections. It's also has some intentional "tilt" in the frequency response intended to compensate for the higher coax cable losses at the higher UHF channels.

Due to intentional "tilt" in the frequency response, that's too much "tilt" for the amplifier. CH3 = 60 MHz, CH21 = 512 MHz. Cable loss for 100ft of RG-6/u is 1.6dB at 60 Mhz and 5.2dB at

512 MHz. Therefore, I would expect to see a corresponding: 5.2 - 1.6 = 3.6dB difference in gain between CH21 and CH3. Comparing with your measurement: 27.1 - 15.6 = 11.8dB Yep, way too much "tilt" in your measurement. Do it again, this time with a spectrum analyzer and an RF sweep generator.

What is a bypass braid? I've never heard of the term. Neither has Google search. Do you mean something like quad shielded RG-6/u?

Large height or large girth?

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Bypass braid for a rotator is for lightning protection. You put a piece of wire to the mast above the rotator and then to the mast below the rotator. That is suppose to make a good connection from the top mast to the bottom mast.

It is not so much the actual gain of the amplifiers, but the noise figure. If just feeding one or two tv sets all the gain needs to be is just to make up for the loss of the feedline if the amp is very near the antenna and a little more depending on the noise figure of the TV set. If the amp is near the TV, it needs very little gain (maybe 10 db) and better have a noise figure much lower than the TV tuner.

Hopefully a tall tree will get hit first,but no guarentee.

Reply to
Ralph Mowery

It was a piece of heavy braid to connect the upper mast to the lower mast f or grounding. It was supposed to prevent lightning or static discharges fro m damaging the ball bearings or their races. The grease wasn't conductive, and would harden into an insulating layer of varnish. That forced the downl ead to carry the discharge current.

Reply to
Michael Terrell

Thanks. Even with the magic buzzwords, I wasn't able to find any rotator or tower installation instructions that involved such a bypass braid. I don't think it will do much to prevent 20,000 Amps from turning a big antenna rotator into a metal recycling candidate. I double if it will do much to prevent arcing from pitting the bearings. The are a large number of bearings in the rotator and it only take a decent connection through one bearing to discharge a static electricity buildup. I've taken apart a few rotators and found plenty of rust, considerable loss of grease, but no pitting (except from the rust).

The bypass wire might also protect against an unusual situation where a ham operator uses a tower or mast as both a monopole antenna and a rotator mount. In transmit, the RF current will go through the rotator bearings. That's not a problem if the rotator is not in motion, but potentially a big problem if the bearings are moving, arcing merrily as they roll along. To be fair, I haven't proven that this is happening, but I'm fairly certain it could easily be tested.

I've seen grease turned to varnish, usually in salty marine atmospheres or after using the wrong type of grease to lubricate the rotator. I sometimes find some water in the bearing race. In my never humble opinion, what's happening is the grease is getting washed away by rain, fog and condensation. The idea grease would be something that can (in order of most important to least important):

  1. Will not wash out (i.e. marine grade grease).
  2. Inhibits galvanic corrosion and rust formation.
  3. Does no "foam" or create abscesses that collect water.
  4. Slightly conductive to discharge static electricity.
  5. Tolerates high temperatures by NOT evaporating or dripping.
  6. Handles a heavy load. What I've been using are various marine lithium based grease concoctions such as WD-40 Specialist Marine-Grade Grease: Note that this is lithium based and not white-lithium grease.

Please note that very little of this has much to do with a receive only TV antenna, rotator, and mast/tower.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Methinks it has more to do with discharging a static electricity buildup (St Elmo's Fire) than protecting against a lightning hit or lightning induced current.

Well, I've never seen such a thing, never had anyone request it, and couldn't find with Google any installation instructions recommending such a practice.

Agreed. I think I mumbled something about too much gain causing intermod problems further up this thread. Another problem is loss of dynamic range when the added gain also raises the noise floor but not changing the overload point. Way back in the dark ages of TV, the receivers were stone deaf and any kind of RF preamplifier offered a performance improvement. These days, with GaAs low noise front ends, the best that a preamp can offer is to compensate for coax cable losses.

We don't get much lightning here on the left coast[1]. I live in a forest full of 100ft and higher trees. I know of three local trees (out of millions) that were hit by lightning in the past 40 odd years. Both were in rather odd locations, such as the bottom of a canyon or surrounded by taller trees. My best guess is the tree holding the most water has the highest conductivity and therefore gets hit first.

[1] Mother nature delivered our accumulated savings (with interest) of lightning on Aug 15, 2020, with a really impressive display of flashing lights, and starting 500+ big fires that are currently trying to incinerate California, Oregon, and Washington states. 5 million acres burned and climbing.
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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Measurements: The CM-7777 has only one input. I used an OTA signal, no t on the same day. I measured before the pre-amp one day and after the power injector (about 3

0') on another day. Cable is copper clad RG6QS. Measured with a Sencore SLM 1453i
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These measurements were don e before the re-assignment of channels.

The measurement is problematic because of 1) Tilt and 2) different days.

"Evaluation of a Winegard HD8200U Antenna with a Channel Master CM-7777 30 dB mast mounted Preamp" FM trap is enabled in the antenna pre-amp. May 2019 Voltages in Columns C and F are in dBuV Gain is just Column F minus Column C @antenna (N3) @In Attic (N4) Gain(N5) 2 53.6 73.5 19.9 3 42.4 58.0 15.6 4 47.5 67.5 20.0 5 29.9 54.1 24.2 6 59.5 80.6 21.1 7 Fail 37.4 Fail 8 16.1 Fail 41.6 Fail 9 22 Fail 38.1 Fail 10 * * 46.5 Fail 11 * 39.4 Fail 12 36.7 58.4 21.7 13 * * 35.0 Fail 14 * * 28.5 Fail 15 * * 29.2 Fail 16 * * 31.6 Fail 17 * * N5 49.2 18 * * 27.7 Fail 19 * * 39.5 Fail 20 * * 28.9 Fail 21 27.6 Fail 27.6 22 43.4 63.6 20.2 23 * * 25.9 Fail 24 * * 28.4 Fail 25 * * 34.3 Fail 26 32.2 55.2 23.0 27 * * 29.2 Fail 28 * * 27.6 Fail 29 * * 25.8 Fail 30 * * 26.8 Fail 31 21.2 48.7 27.5 32 32.3 56.7 24.4 33 * * 30.1 Fail 34 34.4 * 56.0 21.6 35 * * 27.4 36 * * 30.2 37 * * 30.7 38 * * 39.0 39 * * 28.7 40 * * 33.1 41 * * N1 31.2 42 U U N6 55.5 43 * * 31.3 44 U U N7 Missed a few here, "I think the reason for the * @antenna is that the Sencore didn't find any thing Using 8VSB modulation. Not sure."

TVFool data from Highest to lowest NF

6 (6.1) ABC NM: 42.6db Pwr -48.2dbm 2Edge, 28.8 miles ... 42 (29.1) Fox NM: 21.5 Pwr: -69.4 2Edge, 28.9 miles

On one TV using a converter box, it shows 29/100 for signal strength on it' s internal meter for 29.1 and 91 for channel 6.1. This includes another am p at 35 feet (unknown gain) from the 7777, then 65 feet to a 2-way splitter and about 35' to the TV.

The "stupid" Samsung "Smart TV" only shows s/n ratio. I do have a "tuner" that will show both in real units.

The system is/will be: Mast amp (currently CM-7777, plan to change to a Kitz lower NF amplifier)

30'; RG-6QS copper clad Power injector in attic Variable 0-18db gain amplifier using an attenuator 65'; RG-6QS copper clad to basement; About 40' to each TV location (some le ss, some more)

Currently: A 2-way splitter to two TV's about 40' away.

Planned: Blonder Tongue BIDA 75-43a (30-45 db Gain with tilt compensation cards and variable) that replaces a Tin Lee amplifier four 24 db 4-way taps to 12 locations (existing, but not currently used bec ause of a broken amplifier) Locations are around 40' away.

The gain is unknown because the AMP and attenuator WAS prior to the 2-way s plitter and it was recently moved to the attic as is. performance is defin itely better.

My main distribution amp died and I'm planning to replace it with a Blonder

-tongue BID 75a-43 for 12 locations fed by four 4-way 24 db taps.

This has available various "tilt cards", but might consider a custom VHF at tenuator. I think the CM-7777 might overload with cellular signals.

Why copper clad? Friends that were in the satellite TV industry gave me 10

00 feet.
Reply to
Ron D.

The day and time of day can make much difference. I monitored a ham repeater all the time that is about 40 miles away by air. It normally showed a 3 on a scale of 0 to 10. Some days there were no signal (about two or three times a month), and about the same number of times it pinned the meter on the high side. That was on 220 MHz.

There is very little loss in the copper clad cable (as long as the copper is not broken or missing) at TV frequencies due to the skin effect compaired to solid copper. If there was much loss it would not be used. The iron core does make for a stiff center pin for the connection.

The S/N is really more important that the signal strength. You may be boosting the noise along with the signal and the TV will not be able to decode the signal.

Reply to
Ralph Mowery

On Saturday, September 26, 2020 at 11:14:26 PM UTC-4, Jeff Liebermann wrote :

t.

I haven't seen one used in decades. I think that it was an article in the l ate '60s that recommended it. Some really cheap TV rotors used sleeve beari ngs, that corroded. Pot metal against brass with crap lube didn't last very long. OTOH, the old Alliance rotors often had a crumbling rubber top seal that let water into the housings. I rebuilt a lot of those that were alread y 30 years old. A new seal, a new run cap and new control cable put them ba ck into service.

A direct strike would vaporize that strap, but if it was a lesser hit, it w ould help. I had a CATV tower hit once. The audio wiring at the site was un sheilded. The EMP from the high current pulse fried the aural inputs of eve ry modulator. Nothing was done right when the site was built. The tower was well grounded, with three concrete pours that went 60' into the ground for the self supporting tower, but the lines from the tower entered the buildi ng without ground blocks. The equipment used the building's neutral for gro unding. They had punched holes in the ceiling tiles to run cable all over t he place. I had to replace the RCA CA3240 ICs in every modulator, then I re wired the site. Ground rods under the equipment racks. A 19" relay panel wa s used to make a grounding plate for all the Coax entering or leaving the b uilding. Large Panduit wire duct ran from the Microwave racks to the equipm ent racks. The idiot manager tried to tell me that there was no way to hold the wires in it, with the bottom open. A case of pencils solved that. Inse rt them, one per foot. Run the cables. Snap on the covers and remove the pe ncils if you want to. We never had another problem indoors, but we did lose some coax coming down the tower. A 1400 pound Ch4 antenna was at the top, to pick up a distant TV station. Rather than rip out all the underground ca ble to replace it, it left the tower about 50 feet up, and sloped to the ro of of the building to allow plenty of room for big trucks to pass underneat h.

As a Broadcast engineer, I've seen more than one tower take a direct strike . It plays hell with the power lines for the tower lights. The stations are too cheap to use a transformer for isolation at the tower base, so the wir es have to be repaired quite often. The tallest tower I've worked at was 17

00' with two TV stations, five FM stations a Motorola Trunking system and a bunch of government radios on it in North Central Florida.
Reply to
Michael Terrell

terrell. Nic

At the university where I worked, they had a ground potential across about

200' in their computing center built duting the big mainframe ERA. A motor

-generator fed the building.

During a storm, there was a potential that developed across the ground betw een one side and the other side of the building. They had to replace those lines with fiber.

The rotor is an Eagle Aspen ROTR-100 which is pretty cool, but going to be repairable if it fails. min uses a coax for power/positioning. You can, but I didn't use it for the antenna feed too. You can even use it to power a pre-amp. it send DISEQ/C signals on the coax for positioning.

One bad thing is that the readout is not real-time when the antenna is movi ng. The readout "pretends" to know where the antenna is.

I did use a thrust bearing which isn't available anymore and I did replace the studs with stainless studs. 318 SS and anti-sieze if possible. All har dware went that route. The antenna mount is an eve mount made with Unistru t and I guy every 120 degrees using a non-conductive guy wire called Philly stran. I never got a chance to replace the aluminum mast wth fiberglass,

When we had the tree trimmed, I offered to help take down the antenna. To d o that, I install a 2 piece shaft collar under the antenna and loosen the a ntenna and remove the connections. The tree guy in the bucket truck just p lucked the antenna off the mast. He did his thing and plopped it back on t he mast and I could finish it after the install. I had to do some more imp ortant antenna stuff and I was unable to change the mast to fiberglass.

I changed all of the U-bolts to stainless too. I didn't powdercoat the rot or brackets although I had plenty of time if i had planned it during the or iginal install.

Reply to
Ron D.

Is it possible there was construction going on somewhere between the source antenna and your work?

Reply to
Mike S

Passive repeaters like that don't work. For example, let's take an over simplified situation.

This is for a direct path (no repeater) between the TV station and the receiving antenna. UHF 14 channel at 500 MHz. 10 mile path. 12 dBi antenna gain on the receiver end. The 10 mile path produces a 110.6 dB path loss at 500 MHz. Add the 12 dBi antenna gain and the station to receiver path loss is: 110.6 - 12 = 98.6 dB loss

Next is with a passive repeater installed at 9 miles from the TV station and 1 mile to the receive antenna. At the 9 mile point, there are two back to back 12dBi UHF antennas. This splits the calculation into two parts (9 miles and 1 mile). Note that there are three 12dBi antennas involved:

The 9 mile path has a loss of 109.7 dB. The first 12dBi antenna reduces the 9 mile loss to: 109.7 - 12 = 97.7 dB loss The 1 mile path has a loss of 90.6 dB. The 2nd and 3rd 12dBi antennas reduce the 1 mile loss to: 90.6 - 12 -12 = 66.6 dB loss The total end to end loss (including the three 12dBi antennas) is: 97.7dB + 66.6dB = 164.3 dB path loss

164dB is a *MUCH* larger path loss than the original direct path of 98.6dB even though it includes the gain from 3 antennas (+36dB). Specifically, the direct path signal through such a passive repeater arrangement would be: 164.3 - 98.6 = 65.7dB or about 4 million times stronger (in terms of power gain) than the passive repeater derangement. This is why you don't see many passive repeaters, passive cell phone boosters, or flat panel reflectors, in service.
1990 was before repacking and DTV (about 2009), so that wouldn't explain the signal loss. What seems odd is your "slowly but steadily degraded". That seems like some kind of TV receiver problem, mechanical problem (squirrel chewing coax, water in the coax, antenna rot), that gets worse over time, rather than a sudden change. Were the neighbors experiencing the same problem with the same station? Are you on a shared community or building distribution system? Were you listening directly to the unspecified TV transmitter, or were you listening to a station owned UHF repeater?
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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

The UK spoke like Americans and Canadians until some time prior to the 1900s. Where else would they get the accent from? Pluto?

Canada and Mexico. This is North America we're talking. Forget?

Reply to
Transition Zone

With the understanding that the proper job of the Village Idiot is to make the rest of the villagers look good by contrast, I ask all of you to join me in recognizing the masterful performance of our new incumbent!

Peter Wieck Melrose Park, PA

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Peter W.

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