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Antennae Booster...

J

Jeff Liebermann

Guest
On Fri, 25 Sep 2020 01:15:02 -0700 (PDT), Chris K-Man
<thekmanrocks@gmail.com> wrote:

>My idea of a \"booster\" or \"signal amp\" is a bigger/higher gain antenna.

Do you mean that a \"bigger\" box is your idea of a better TV antenna
amplifier? This looks plenty big:
<http://www.ambery.com/rfmp-w50.html>
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.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
A

amdx

Guest
On 9/25/2020 10:50 AM, Jeff Liebermann wrote:
On Fri, 25 Sep 2020 01:15:02 -0700 (PDT), Chris K-Man
thekmanrocks@gmail.com> wrote:

My idea of a \"booster\" or \"signal amp\" is a bigger/higher gain antenna.
Do you mean that a \"bigger\" box is your idea of a better TV antenna
amplifier? This looks plenty big:
http://www.ambery.com/rfmp-w50.html
Dimension: 498mm (W) x 360mm (D) x 280mm (H)
Or, perhaps you mean\'t something other than size?
 I stored a rack mount Wingard distribution amplifier for years before
I tossed it.

I was about 19\" x 6\" x 3\".

I always thought it would be good for something, but never ran across
that something.

                                         Mikek






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.
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
 
R

Ron D.

Guest
jeff:

Antenna is pretty big, A Winegard HD-8200U and the CM-7777 antenna mounted amp.

The reason why I don;t TRUST is I did gain measurements using a Sencore 8VSB tester. My gain measurements were not consistant, but they were not done at the same time. I measures the signal at the antenna and the NEXT day the signal after the power injector (about 30\')

Gain varied from 15.6 (physical channel 3) and 27.1 for channel 21. I\'m at least 30 miles outside of Philly and aimed toward Philly stations.

The rotor also has a bypass braid around it which many people forget. A large tree is going to hit by lightning first.
 
J

Jeff Liebermann

Guest
On Fri, 25 Sep 2020 12:36:44 -0700 (PDT), \"Ron D.\"
<ron.dozier@gmail.com> wrote:

>Antenna is pretty big, A Winegard HD-8200U and the CM-7777 antenna mounted amp.
<https://winegard.com/products/hdtv-digital-antennas/hdtv-antenna-amplifiers/boost/hd8200u-platinum-hd-series-antenna>
<https://www.channelmaster.com/TV_Antenna_Preamplifier_p/cm-7777v3.htm>

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
can cause issues with the television tuner’s ability to
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?

<https://photos.imageevent.com/holl_ands/files/ota//CM7777%20Ckt%20Brd%20Rear%20Photo%20-%20damaged%20rlongfield.jpg>
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.

The reason why I don\'t TRUST is I did gain measurements using
a Sencore 8VSB tester. My gain measurements were not consistant,
but they were not done at the same time. I measures the signal
at the antenna and the NEXT day the signal after the power
injector (about 30\')
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.

Gain varied from 15.6 (physical channel 3) and 27.1 for channel 21.
I\'m at least 30 miles outside of Philly and aimed toward Philly
stations.
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.

The rotor also has a bypass braid around it which many people
forget.
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?

>A large tree is going to hit by lightning first.

Large height or large girth?

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
R

Ralph Mowery

Guest
In article <sljvmflff4bfi51udegldlovgb03cg13s5@4ax.com>,
jeffl@cruzio.com says...
h a spectrum analyzer and an RF sweep generator.

The rotor also has a bypass braid around it which many people
forget.

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?

A large tree is going to hit by lightning first.

Large height or large girth?
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.
 
M

Michael Terrell

Guest
> What is a bypass braid? I\'ve never heard of the term.

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

Jeff Liebermann

Guest
On Sat, 26 Sep 2020 17:21:21 -0700 (PDT), Michael Terrell
<terrell.michael.a@gmail.com> wrote:

What is a bypass braid? I\'ve never heard of the term.

It was a piece of heavy braid to connect the upper mast
to the lower mast for grounding. It was supposed to prevent
lightning or static discharges from damaging the ball
bearings or their races.
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.

The grease wasn\'t conductive, and would harden into an insulating
layer of varnish. That forced the downlead to carry the discharge current.
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:
<https://www.amazon.com/WD-40-Specialist-Marine-Grade-Resistant-Grease/dp/B071R943VS/>
<https://www.wd40.com/products/water-resistant-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.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
J

Jeff Liebermann

Guest
On Sat, 26 Sep 2020 20:13:15 -0400, Ralph Mowery
<rmowery28146@earthlink.net> wrote:

In article <sljvmflff4bfi51udegldlovgb03cg13s5@4ax.com>,
jeffl@cruzio.com says...
h a spectrum analyzer and an RF sweep generator.

The rotor also has a bypass braid around it which many people
forget.

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?

A large tree is going to hit by lightning first.

Large height or large girth?

Bypass braid for a rotator is for lightning protection.
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.

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.
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.

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.
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.

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

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.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
R

Ron D.

Guest
Measurements: The CM-7777 has only one input. I used an OTA signal, not on the same day.
I measured before the pre-amp one day and after the power injector (about 30\') on another day. Cable is copper clad RG6QS. Measured with a Sencore SLM1453i http://salestores.com/sencor01.html. These measurements were done 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 anything
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 amp 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 less, 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 because of a broken amplifier)
Locations are around 40\' away.

The gain is unknown because the AMP and attenuator WAS prior to the 2-way splitter and it was recently moved to the attic as is. performance is definitely 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 attenuator. I think the CM-7777 might overload with cellular signals.

Why copper clad? Friends that were in the satellite TV industry gave me 1000 feet.
 
R

Ralph Mowery

Guest
In article <5ac1d4c4-3a0b-4602-9ff1-4df219d352c6n@googlegroups.com>,
ron.dozier@gmail.com says...
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 amp 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 less, 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 because of a broken amplifier)
Locations are around 40\' away.

The gain is unknown because the AMP and attenuator WAS prior to the 2-way splitter and it was recently moved to the attic as is. performance is definitely 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 attenuator. I think the CM-7777 might overload with cellular signals.

Why copper clad? Friends that were in the satellite TV industry gave me 1000 feet.
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.
 
M

Michael Terrell

Guest
On Saturday, September 26, 2020 at 11:14:26 PM UTC-4, Jeff Liebermann wrote:
On Sat, 26 Sep 2020 17:21:21 -0700 (PDT), Michael Terrell wrote:


What is a bypass braid? I\'ve never heard of the term.

It was a piece of heavy braid to connect the upper mast
to the lower mast for grounding. It was supposed to prevent
lightning or static discharges from damaging the ball
bearings or their races.
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.
The grease wasn\'t conductive, and would harden into an insulating
layer of varnish. That forced the downlead to carry the discharge current.
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:
https://www.amazon.com/WD-40-Specialist-Marine-Grade-Resistant-Grease/dp/B071R943VS/
https://www.wd40.com/products/water-resistant-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, rotor, and mast/tower.
I haven\'t seen one used in decades. I think that it was an article in the late \'60s that recommended it. Some really cheap TV rotors used sleeve bearings, 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 already 30 years old. A new seal, a new run cap and new control cable put them back into service.

A direct strike would vaporize that strap, but if it was a lesser hit, it would help. I had a CATV tower hit once. The audio wiring at the site was unsheilded. The EMP from the high current pulse fried the aural inputs of every 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 building without ground blocks. The equipment used the building\'s neutral for grounding. They had punched holes in the ceiling tiles to run cable all over the place. I had to replace the RCA CA3240 ICs in every modulator, then I rewired the site. Ground rods under the equipment racks. A 19\" relay panel was used to make a grounding plate for all the Coax entering or leaving the building. Large Panduit wire duct ran from the Microwave racks to the equipment 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. Insert them, one per foot. Run the cables. Snap on the covers and remove the pencils 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 cable to replace it, it left the tower about 50 feet up, and sloped to the roof of the building to allow plenty of room for big trucks to pass underneath.

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 wires have to be repaired quite often. The tallest tower I\'ve worked at was 1700\' with two TV stations, five FM stations a Motorola Trunking system and a bunch of government radios on it in North Central Florida.
 
R

Ron D.

Guest
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 between 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 moving. 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 hardware went that route. The antenna mount is an eve mount made with Unistrut and I guy every 120 degrees using a non-conductive guy wire called Phillystran. 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 do that, I install a 2 piece shaft collar under the antenna and loosen the antenna and remove the connections. The tree guy in the bucket truck just plucked the antenna off the mast. He did his thing and plopped it back on the mast and I could finish it after the install. I had to do some more important 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 rotor brackets although I had plenty of time if i had planned it during the original install.
 
M

Mike S

Guest
On 9/23/2020 3:06 AM, Pimpom wrote:
On 9/23/2020 1:02 PM, Pimpom wrote:
On 9/23/2020 3:26 AM, Dave Platt wrote:
Stu jaxon  <stankowalski02@gmail.com> wrote:
Hi Group, can someone help please, I have an antenna booster that
requires a power supply of 6v 100ma, can i use a
variable power supply 6v 300ma???

Assuming that they\'re both DC supplies, and assuming that you get the
polarity correct (positive-supply to positive-load, negative-supply to
negative-load), and assuming that you\'re careful to not turn the
variable power supply up to higher than 6 volts... yes, it should
work.  The 300 mA capacity of the variable supply is greater than the
100 mA which the booster will draw, and that\'s OK.  However, turning
up the supply to above 6 volts may damage the booster.  I\'d recommend
checking the supply voltage with a voltmeter before you connect it to
the booster.

Do be aware that \"antenna booster\" amplifiers can cause more problems
than they solve.  In most cases you\'ll get better results by improving
your antenna setup.

Agreed on all points except that, in certain situations, using an
antenna booster is the only way to get an acceptable reception.

TV came to this remote corner of India in 1980 when some army
people discovered that it was possible to receive stations in
neighbouring Bangladesh. Due to the very hilly terrain, reception
varied from fair to unusable within tens of meters, all with
outdoor yagi antennas. Antenna boosters were a must.

The boosters were all alike, made up of 4 or 5 bjt amplifier
stages. Power was fed to the booster via twin 300-ohm cable from
an indoor 12V AC supply and gain was adjusted by means of a
series potentiometer.

I was the local \"expert\" and I experimented with different
antenna types, including yagi arrays and helical antennas with a
6-foot plane reflector. Some people claimed that reception was
noticeably improved by hanging aluminium pans on their yagis.

Once I even rigged up a passive re-radiator with a back-to-back pair of
yagis on a hilltop for a client who had no reception at all in his house
which was located on the blind side of the hill. It worked somewhat but
was not really satisfactory.

What I couldn\'t really explain was that reception slowly but steadily
degraded in the decade from 1980 to 1990 (when cable TV arrived). In
1980, I could often get excellent reception in my house with literally
an aluminium coat hanger plugged into the antenna socket. By contrast, I
could watch the 1990 FIFA World Cup only with an array of four yagis
*and* an antenna booster.
Is it possible there was construction going on somewhere between the
source antenna and your work?
 
J

Jeff Liebermann

Guest
On Wed, 23 Sep 2020 15:36:58 +0530, Pimpom <nobody@nowhere.com> wrote:

Once I even rigged up a passive re-radiator with a back-to-back
pair of yagis on a hilltop for a client who had no reception at
all in his house which was located on the blind side of the hill.
It worked somewhat but was not really satisfactory.
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.
<https://www.proxim.com/en/products/knowledge-center/calculations/calculations-free-space-loss>
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.

What I couldn\'t really explain was that reception slowly but
steadily degraded in the decade from 1980 to 1990 (when cable TV
arrived). In 1980, I could often get excellent reception in my
house with literally an aluminium coat hanger plugged into the
antenna socket. By contrast, I could watch the 1990 FIFA World
Cup only with an array of four yagis *and* an antenna booster.
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?


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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