How to install your new antenna [Instructions]
 

On May 13, 12:58*pm, Grimly Curmudgeon
wrote:
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Grimly Curmudgeon
saying something like:

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "
saying something like:

I have been fascinated by the idea of using parabolas for UHF ever
since UHF was invented. When we went to the maternity hospital for the
birth of out first child (now 35) I anticipated a long wait and took a
notebook and a textbook, and set about planning the construction of a
monster. However the child was born very rapidly, and thereafter was
such a drain on time and resounces that I soon had to abandon the
project. Still in my loft to this day are some curved members. the
start of the prototype.

Not unknown for old sat dishes to be used as wi-fi and 3G antennas.

To follow up...
UHF and VHF on an old 1.8m dishhttp://www.dtvforum.info/index.php?showtopic=84979
The pics from that post...http://i46.tinypic.com/scwd1h.jpghtt...com/necpjl.jpg

This has got my juices flowing and I've stuck an old 1m MMDS dish up in
my attic space, pointing out through the roof structure with a folded
dipole cut for ~580MHz at the focal point. My reasoning is that the gain
of the dish will compensate for the roof thickness. Last night it was
providing a cracking signal to my PC telly card and today I intend to
connect it to the digitelly and see what I can pull in.
This avoids ****ing around with poles and external antennas on top of
them.

Somewhere I've got some info on this. I believe there's something
about a parabola not acting properly as a parabola below a certain
number of wavelengths -- about 20?

Bill

Bill

How to install your new antenna [Instructions]
 

On Thursday, May 13th, 2010 at 05:54:55h -0700, Wrights Aerials wrote:

Somewhere I've got some info on this. I believe there's something about
a parabola not acting properly as a parabola below a certain number of
wavelengths -- about 20?

But some people claim that the Channelmaster CM 4251 UHF 7 foot parabolic
antenna was the best and most powerful production consumer UHF TV antenna
ever manufactured.

http://www.rocketroberts.COM/cm4251/cm4251.htm

I have always been fascinated at what would be the results of comparing
one of these to a Plemi-Margon 103 element or Fuba 92 element UHF wideband
antenna for long distance (80 miles or more) reception, or with the closest
currently available equivalent, the AntennasDirect 91XG.

http://www.antennasdirect.COM/91XG_HDTV_Antenna.html

How to install your new antenna [Instructions]
 

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "
saying something like:

Somewhere I've got some info on this. I believe there's something
about a parabola not acting properly as a parabola below a certain
number of wavelengths -- about 20?

I dunno, maybe it all goes to cock at certain freqs but it's working
well enough now. I hooked it up to the digitelly and it's just fine,
which actually surprised me.

This is pretty much the type of dish I have
url:http://www.wi-pipe.com/24sd27-24dbi-...85022ece8707f7
with a folded dipole of 1.5mm insulated wire taped to a wooden former
and connnected to an old 300/75 matcher salvaged from the back of an
ancient portable. Over here the old MMDS dishes are to be found laying
around as a lot of people ditched the system and moved to Sky/Freesat.
Previously, I was using this dish as a 3G link for across-field treetop
datalinkage, with a flat plate antenna mounted at the focal point.

Talk about cheekiness - get this for a price...
http://www.dtvs.co.nz/index.php?main...oducts_ id=85
Same idea, but with a log-periodic. Now, I just happen to have an old
indoor LP set-top antenna and the backbone of it just happens to be the
right size to insert into the boom of the MMDS dish. I'll leave that for
another day.

How to install your new antenna [Instructions]
 

On Thu, 13 May 2010 05:54:55 -0700 (PDT), "
wrote:

Somewhere I've got some info on this. I believe there's something
about a parabola not acting properly as a parabola below a certain
number of wavelengths -- about 20?

I was hoping someone would add to this.

I used a parabolic reflector with a microphone before the days of
shotgun mikes and can remember *something* about the frequency
response drop-off being related to the distance of mic to dish or
similar, but the brain no longer recalls the details

http://en.wikipedia.org/wiki/Parabolic_reflector

http://www.antenna-theory.com/antenn...ctors/dish.php

How to install your new antenna [Instructions]
 

On May 15, 1:56*pm, Albert Ross wrote:
On Thu, 13 May 2010 05:54:55 -0700 (PDT), "

wrote:
Somewhere I've got some info on this. I believe there's something
about a parabola not acting properly as a parabola below a certain
number of wavelengths -- about 20?

I was hoping someone would add to this.

I used a parabolic reflector with a microphone before the days of
shotgun mikes and can remember *something* about the frequency
response drop-off being related to the distance of mic to dish or
similar, but the brain no longer recalls the details

Don't you have to apply bass boost and treble cut when you use a
parabolic mike, for that reason?

Bill

How to install your new antenna [Instructions]
 

On Sat, 15 May 2010 06:27:57 -0700 (PDT), "
wrote:

On May 15, 1:56*pm, Albert Ross wrote:
On Thu, 13 May 2010 05:54:55 -0700 (PDT), "

wrote:
Somewhere I've got some info on this. I believe there's something
about a parabola not acting properly as a parabola below a certain
number of wavelengths -- about 20?

I was hoping someone would add to this.

I used a parabolic reflector with a microphone before the days of
shotgun mikes and can remember *something* about the frequency
response drop-off being related to the distance of mic to dish or
similar, but the brain no longer recalls the details

Don't you have to apply bass boost and treble cut when you use a
parabolic mike, for that reason?

Yes, and the bass cutoff especially relates not only to the diameter
of the dish but to the depth AFAICR (or think I can remember).

The Grampian was a yard in diameter (pre-metric I suspect) and
relatively flat compared to some of the smaller more tulip-shaped
jobbies which had a sharp loss of lower frequencies.

How to install your new antenna [Instructions]
 

Ian Jackson wrote:
In message , J G Miller
writes
On Monday, May 3rd, 2010 at 20:22:29h +0100, Adrian C wrote:

Put simply, in an _urban area_ the device isn't bling enough.

Maybe not. But how about this one?

http://www.kathrein-scala.COM/catalog/PR-TV.pdf

I would be most interested to know the proprietor of Wright's Aerials
opinion on this type of design and its performance compared to the
Yagi-Uda.

If I'm not mis-reading the information, that's a single-channel aerial,
available for your specified UHF channel. Not much good for
multi-channel TV use.

Not very small either, 5ft 8 tall, 3ft wide and 18" deep. Fnarr..

How to install your new antenna [Instructions]
 

In article , Albert Ross
wrote:
On Thu, 13 May 2010 05:54:55 -0700 (PDT), "
wrote:

Somewhere I've got some info on this. I believe there's something about
a parabola not acting properly as a parabola below a certain number of
wavelengths -- about 20?

I was hoping someone would add to this.

Afraid I've only just noticed the thread and this topic, and the interest
in mic parabolas rather than EH ones.

FWIW I have two AES publications on this. One a Journal paper from 1985,
the other a (better, I think) Convention Paper from 2002.

Parabolic Reflector Microphones
Juha Backman
Paper 5499
112th Convention Munich 2002 May 10-13


I used a parabolic reflector with a microphone before the days of
shotgun mikes and can remember *something* about the frequency response
drop-off being related to the distance of mic to dish or similar, but
the brain no longer recalls the details

The gain will depend on how close the mic is to the actual focus produced
by the reflected source. In part due to the real source not being at
'infinity' but also because the mic may not be at the parabolic focus.
Also, as you'd expect, due to the relationship between the size/shape of
the parabola and the wavelength. The above gives both theory and some
measurements.

I was surprised, looking at it, to see that the gain behaviour seems to
hold up fairly well until you reach almost down to the wavelength being
similar to the size of the parabola. i.e. much longer wavelengths than
assuming a parabola needs to be twenty times the wavelength. However again
as you'd expect the gain does vary with wavelength. Just that the simple
scaling breaks down when you approach long wavelengths.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

How to install your new antenna [Instructions]
 

On Wed, 19 May 2010 18:23:34 +0100, Jim Lesurf
wrote:

In article , Albert Ross
wrote:


Afraid I've only just noticed the thread and this topic, and the interest
in mic parabolas rather than EH ones.

FWIW I have two AES publications on this. One a Journal paper from 1985,
the other a (better, I think) Convention Paper from 2002.

Parabolic Reflector Microphones
Juha Backman
Paper 5499
112th Convention Munich 2002 May 10-13


I used a parabolic reflector with a microphone before the days of
shotgun mikes and can remember *something* about the frequency response
drop-off being related to the distance of mic to dish or similar, but
the brain no longer recalls the details

The gain will depend on how close the mic is to the actual focus produced
by the reflected source. In part due to the real source not being at
'infinity' but also because the mic may not be at the parabolic focus.
Also, as you'd expect, due to the relationship between the size/shape of
the parabola and the wavelength. The above gives both theory and some
measurements.

It's beginning to come back to me now! Yes the source isn't really at
infinity and the mic diaphragm is *near* the focus but it's close
enough to work in the Real World.

I was surprised, looking at it, to see that the gain behaviour seems to
hold up fairly well until you reach almost down to the wavelength being
similar to the size of the parabola. i.e. much longer wavelengths than
assuming a parabola needs to be twenty times the wavelength. However again
as you'd expect the gain does vary with wavelength. Just that the simple
scaling breaks down when you approach long wavelengths.

Ah yes that was the interesting bit where the wavelength was involved.
Thanks! I think what I may have been semi-remembering was to do with
phase relationships. Or I may just be confused . . .