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Old November 21st 03, 05:03 PM
John Doty
 
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In article , "Wes Stewart"
wrote:

Antennas are reciprocal, if they wouldn't work well for transmitting,
they will work equally poorly for receiving.


The reciprocity principle is usually good physics (but watch out for
Faraday rotation). However, the engineering virtues of a good transmitting
and good receiving antenna are different. At HF and below, efficiency is
much less important for receiving than it is for transmitting. The reason
is that the natural noise level is high at these frequencies: at 10 MHz
it's 30 dB above thermal, while a good receiver's noise floor is 10 dB
above thermal. This leaves plenty of room for inefficiency without SNR
degradation. At lower frequencies the natural noise is higher. In practice
10 meters of untuned inverted L into a 500 ohm input suffices to reach the
natural noise floor from 100 kHz to 30 MHz with a good receiver.

Back in the days of the omega navigation system, we used tuned 2 meter
whips to receive signals from around the world in the 10 kHz band.

For the results of quantitative engineering calculations on this subject,
see:

http://anarc.org/naswa/badx/antennas/SWL_longwire.html

--
| John Doty "You can't confuse me, that's my job."
| Home:
| Work:

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Old November 21st 03, 07:17 PM
John Doty
 
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In article , "w4jle" W4JLE(remove this
to wrote:

Believe what you will, the law of reciprocity will ignore your beliefs
and continue to function.


1. It's only a "law" for scalar radiation (like sound), not vector
radiation (radio). To be sure, it's a fine approximation for most HF
antenna systems, but watch out a microwave frequencies, especially if your
antenna system contains a "circulator".

2. In the cases where reciprocity applies you would be correct to say that
it requires that the antenna directivity and efficiency are the same for
transmitting and receiving. It does not follow, however, that a poor
transmitting antenna is necessarily a poor receiving antenna. Efficiency
matters much more when transmitting than it does when receiving.

Franks's observations are correct, and can be verified if you do a
detailed signal to noise calculation. You could also try the experiment
yourself.


"Frank" wrote in message
news:01c3b0a2$989de120$0125250a@cqvdqntcxxawvjpo.. .
Wes Stewart ...

^ Antennas are reciprocal, if they wouldn't work well for
^ transmitting, they will work equally poorly for receiving.

I don't believe that. It's been my experience that an antenna used for
receiving will function satisfactorily over a much broader range of
conditions (environment, antenna length, etc.) than it will if used for
transmitting under those same conditions.

Frank




--
| John Doty "You can't confuse me, that's my job."
| Home:
| Work:

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Old November 21st 03, 07:37 PM
A.Pismo Clam
 
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Default Outwitting Home Owner Associations/Condo Associations Regarding Antennas

Hello All!

I live in San Diego and have been a PBS supporter for many years. An
article in this months "On Air" PBS magazine has made my day! The
article is on page #3. It is written by the General Manager of the tv
station. I have not read the document in question, but it does sound too
good to be true. How curious are you? If you live in San Diego, you
might find a copy in your local library.

In essence he says that the:

"...[Federal] government will defend your right to crawl up on the roof
and put up a BIG, HONKING antenna, despite the protests of nosy
neighbors, community planners, rental management companies, local
governemnt bureaucrats and other meddlesome busybodies."

Want to know how? Here is the URL:

www.fcc.gov/mb/facts/otard.html

Now you may have to prove to "the opposition" that the antenna you have
erected can indeed receive "local" television stations, but that should
not be that difficult to do...

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Old November 21st 03, 09:05 PM
 
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Thank you.... .......

I am moving into a housing plan with such antenna restrictions. But
what housing plan doesn't have them. There is always someone trying to
tell some else how to live their lives, or knows what's best for you.

"A.Pismo Clam" wrote:

Hello All!

I live in San Diego and have been a PBS supporter for many years. An
article in this months "On Air" PBS magazine has made my day! The
article is on page #3. It is written by the General Manager of the tv
station. I have not read the document in question, but it does sound too
good to be true. How curious are you? If you live in San Diego, you
might find a copy in your local library.

In essence he says that the:

"...[Federal] government will defend your right to crawl up on the roof
and put up a BIG, HONKING antenna, despite the protests of nosy
neighbors, community planners, rental management companies, local
governemnt bureaucrats and other meddlesome busybodies."

Want to know how? Here is the URL:

www.fcc.gov/mb/facts/otard.html

Now you may have to prove to "the opposition" that the antenna you have
erected can indeed receive "local" television stations, but that should
not be that difficult to do...

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Old November 21st 03, 09:25 PM
Richard Clark
 
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On Fri, 21 Nov 2003 10:37:02 -0800, "A.Pismo Clam"
wrote:

... I have not read the document in question, but it does sound too
good to be true.


Such feelings are generally indications of dreaming.

In essence he says that the:

"...[Federal] government will defend your right to crawl up on the roof
and put up a BIG, HONKING antenna..."


The government will DO NOTHING! Which means you won't get arrested.
The converse notion of their helping is dreaming in technicolor.

Want to know how? Here is the URL:

www.fcc.gov/mb/facts/otard.html

Now you may have to prove to "the opposition" that the antenna you have
erected can indeed receive "local" television stations, but that should
not be that difficult to do...


Hi Pismo,

Big honkin' antennas? This completes the picture with dreaming in
surround-sound:
(1) A "dish" antenna that is one meter (39.37") or less in diameter
(2) An antenna that is one meter or less in diameter or diagonal measurement
(3) ... Masts higher than 12 feet above the roofline
may be subject to local permitting requirements.


Such interpretation of the law, while asleep, has created a vast
culture of lawyers who are willing to do follow-up work.

The trick is to design your antenna to within the law.
1. Choose the highest point of your roof line and erect the allowed
12
foot mast;
2. Place suitable dish or simple TV antenna (remember, local means no
40 element booms);
3. Run your favorite coax STRAIGHT UP (as nearly you can) to the top;
4. Ground to radial system and AC earth ground at bottom;
5. Gamma match to coax shield at the bottom (hidden).

Antenna does not have to be functional. It only needs to look
functional (do not point at the northern star, Polaris, for example).
If it is functional, you may need to provide for a choke at the
feedpoint to the antenna (to separate the two functions - your hobby
from your TV). Try to place this effort away from major home
interference sources (TV's and computer monitors, fish tanks,
fluorescent fixtures, and so on).

To extend the service frequencies in the HF region (because the mast
is still too short), then add guy wires attached at the top
electrically and physically, which are insulated about halfway down
with egg type insulators, or use rope the rest of the way to ground.
This top-load skirt may also serve as the choke, but don't count on it
without figuring in the time to experiment and confirm.

73's
Richard Clark, KB7QHC


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Old November 21st 03, 09:56 PM
'Doc
 
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The only one you can blame for this problem is your
self. You signed the lease...
'Doc
  #7   Report Post  
Old November 21st 03, 10:09 PM
Frank Dresser
 
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"A.Pismo Clam" wrote in message
...
Hello All!

I live in San Diego and have been a PBS supporter for many years. An
article in this months "On Air" PBS magazine has made my day! The
article is on page #3. It is written by the General Manager of the tv
station. I have not read the document in question, but it does sound

too
good to be true. How curious are you? If you live in San Diego, you
might find a copy in your local library.


[snip]

Why do you want to live in a neighborhood in which all the homes have a
dress code? I suppose renters are stuck with such restrictions, but
what do "owners" "own" if they can get hassled for stringing a wire?

Frank Dresser


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Old November 21st 03, 10:31 PM
Dave Holford
 
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Frank Dresser wrote:

"A.Pismo Clam" wrote in message
...
Hello All!

I live in San Diego and have been a PBS supporter for many years. An
article in this months "On Air" PBS magazine has made my day! The
article is on page #3. It is written by the General Manager of the tv
station. I have not read the document in question, but it does sound

too
good to be true. How curious are you? If you live in San Diego, you
might find a copy in your local library.


[snip]

Why do you want to live in a neighborhood in which all the homes have a
dress code? I suppose renters are stuck with such restrictions, but
what do "owners" "own" if they can get hassled for stringing a wire?

Frank Dresser



The thought occurs to me that in the "good old days" aircraft used to
have wire antennas, either strung around the airframe or trailing below
and behind.

Modern, high speed, aircraft can't do this so they have various
solutions including HF probes and conformal antennas (I have seen
unpainted panels on some large military aircraft which were identified
as HF antennas) and it is not difficult to receive their signals over
distances of several thousand miles. I wonder why no one has, at least
as far as I am aware, attempted to adapt these solutions to Ham Radio?

I have personal experience, some 40 years ago, with an HF antenna which
consisted of the top half of the tail (about a 15 to 20 foot square
metal surface) which was tuned by a remote ATU (Collins CU-351 ISTR) and
performed at least as well as a fixed wire over the range of 2.5 to 30
MHz. I had considered at one time covering one end of the house with
foil and trying the idea against ground, but for some reason I
encountered some opposition from another member of my household. I think
she figured 15 antennas was enough!


Dave
VE3HLU
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Old November 21st 03, 11:58 PM
Stinger
 
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Homeowners associations are a good thing! They are basically an agreement
that you and your neighbors will follow some clearly defined rules for the
specific purpose of maintining optimum property values for everyone. In
other words, you won't have to worry about buying an expensive house and
having your next-door neighbor decide to use his yard to store a dozen
wrecked automobiles while he builds a hot-rod or runs a car-repair business.
Common sense should tell anyone that their rights end when they start to
infringe on anyone else's, but sometimes you need it in writing. ;^)

Receiving antennas are easily concealed. If you can find mine from the
street, you were born on Krypton. I think this is an overly-hyped problem.

Broadcasting antennas are another animal, though. For instance, nobody
wants to live next to some clown running a bunch of linear amps through a CB
"base station." It will literally be "seen" on well-shielded cable
television connections, and is a nuisance. I think that's a lot of what the
"external antenna" rules are meant to curb.

-- Stinger

"Frank Dresser" wrote in message
...

"A.Pismo Clam" wrote in message
...
Hello All!

I live in San Diego and have been a PBS supporter for many years. An
article in this months "On Air" PBS magazine has made my day! The
article is on page #3. It is written by the General Manager of the tv
station. I have not read the document in question, but it does sound

too
good to be true. How curious are you? If you live in San Diego, you
might find a copy in your local library.


[snip]

Why do you want to live in a neighborhood in which all the homes have a
dress code? I suppose renters are stuck with such restrictions, but
what do "owners" "own" if they can get hassled for stringing a wire?

Frank Dresser




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Old November 22nd 03, 01:33 AM
Wes Stewart
 
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Default

On Fri, 21 Nov 2003 16:58:40 -0600, "Stinger"
wrote:

|Homeowners associations are a good thing! They are basically an agreement
|that you and your neighbors will follow some clearly defined rules for the
|specific purpose of maintining optimum property values for everyone. In
|other words, you won't have to worry about buying an expensive house and
|having your next-door neighbor decide to use his yard to store a dozen
|wrecked automobiles while he builds a hot-rod or runs a car-repair business.
|Common sense should tell anyone that their rights end when they start to
|infringe on anyone else's, but sometimes you need it in writing. ;^)

I happen to subscribe to Fine Homebuilding Magazine and in one of the
latest issues there is some discussion about people who will not make
any changes to their house without considering resale value. They
could be eight feet tall and planning to remodel the kitchen, but will
they think of raising the height of the countertops to make it easier
on themselves? Nooooo. It will affect resale value. They might be
planning to die in the house but they worry that their heirs will have
a hard time selling.

The same mentality prevails in people who willingly submit to the
whims of the homeowners' association board. If I want to leave my
garage door open while I use my woodworking tools or work on my car, I
don't want the guy across the street getting his panties in a bunch
over it. Likewise, I don't want to be told when to mow the grass.

Of course, in my case, across the street is 80 acres of Sonoran Desert
and my landscaping is whatever grows here. (I gave the lawnmower to
the guy that bought my last house.) And I'm not trying to keep up
with Jones either because where I live, *I'm* Jones. Heh heh.

|
|Receiving antennas are easily concealed. If you can find mine from the
|street, you were born on Krypton. I think this is an overly-hyped problem.


If you don't want to hear anything, by all means conceal your antenna.
Antennas are reciprocal, if they wouldn't work well for transmitting,
they will work equally poorly for receiving.

|
|Broadcasting antennas are another animal, though.

Broadcasting is done by broadcasting stations. Broadcasting is
one-way communication.

Hobbists; licensed radio amateurs (hams), and CBers (not to be
confused with hams) are operating transmitting stations designed for
two-way communications.

|For instance, nobody
|wants to live next to some clown running a bunch of linear amps through a CB
|"base station."

Nobody? That is an all-encompassing term. "Few", "some", "not too
many" might be better. Not that I'm in favor of CBers running illegal
stations.

|It will literally be "seen" on well-shielded cable
|television connections, and is a nuisance.

A "well-shielded" system will not "see" anything of the sort. The
problem will more likely be from some upstanding homeowner, who
wouldn't dare leave his garage door open and violate association
rules, making an illegal tap on the cable.

| I think that's a lot of what the
|"external antenna" rules are meant to curb.

No, most antenna restrictions have nothing to do with the possibility
of interference. The restrictions are for the same reasons as not
wanting the garage door open, the grass an inch too high, painting the
house the wrong shade of white, etc...

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