There was a question posted to another group about connecting to a distant
antenna.
The post reminded me of another article (perhaps in QST) where someone who
lived behind a mountain used 2 rhombic antennas as a "passive repeater" on
uhf. He mounted both antennas at the summit of the mountain with one
pointed to the repeater and the other pointed into the valley where he
lived. As I recall, he was then able to communicate via the repeater.
This brings up other possibilities - like doing the same thing for
inside-outside of a metal bldg.

'Corse, consider that there are certain constraints-- one being that
the antenna must be within a small distance from one end of the loop.
(for passive reflectors, at microwave, believe, they state 2-3 miles
(MAX)). and two, consider that at VHF, there is an effect called
"KNIFE EDGE REFRACTION" that tends to bend a signal over a hilltop
to a distant target on the other side of that ridge of hills!
But, for cell phones in a vehicle, those thru the glass antennas
on cars, with a whip on the outside , and what looks like a PAWN
BROKERS 3 ball symbol on the inside, do exactly what you describe
(or at least are susposed to)! as info, Jim NN7K

Hal Rosser wrote:
There was a question posted to another group about connecting to a distant
antenna.
The post reminded me of another article (perhaps in QST) where someone who
lived behind a mountain used 2 rhombic antennas as a "passive repeater" on
uhf. He mounted both antennas at the summit of the mountain with one
pointed to the repeater and the other pointed into the valley where he
lived. As I recall, he was then able to communicate via the repeater.
This brings up other possibilities - like doing the same thing for
inside-outside of a metal bldg.

"Jim - NN7K" wrote in message
. com...
'Corse, consider that there are certain constraints-- one being that
the antenna must be within a small distance from one end of the loop.
(for passive reflectors, at microwave, believe, they state 2-3 miles
(MAX)). and two, consider that at VHF, there is an effect called
"KNIFE EDGE REFRACTION" that tends to bend a signal over a hilltop
to a distant target on the other side of that ridge of hills!
But, for cell phones in a vehicle, those thru the glass antennas
on cars, with a whip on the outside , and what looks like a PAWN
BROKERS 3 ball symbol on the inside, do exactly what you describe
(or at least are susposed to)! as info, Jim NN7K

Hi Jim,
Yes, I've heard of knife-edge refraction, but the instance I was referring
to in the article had a real positive benefit. As I recall, the operator
went from zero contact to satifactory contact by hooking up 2 beams
back-to-back at the summit, with one beam pointing back at him - and the
other beam pointed to the otherwise unreachable distant repeater.
I wouldn't have thought something like that would work without some
signal amplification. But it does.

It certainly works Hal

I use to live in a half below ground block of flats that had a 1/4 wave
for 2M way up on the roof. One day I experimented plugging the coax end
into my field day 5 element positioned at the end of the hallway and
used my handheld maybe 30ft away. Having the yagi connected vs not was
in the vicinity of 12dB but this was a real rough measurement.

Recently I had cause to model a passive repeater on 400MHz. We had a
situation with a base station positioned on a plateau but at maybe 1km
away had a deep valley (railway cutting) that at the base of was
(measured) at around -95dBm. We needed about -85 so we put up a back to
back yagi at the valley edge and with it receiving an approx -10dBm
signal the valley floor was now at around -80dBm at 200M away inside the
cutting. Its actually pretty easy to model. Just find the pathloss of
one link and add it to the other. Allow maybe 3dB loss for the passive
coupling and there is your answer!

Cheers Bob VK2YQA



Hal Rosser wrote:
There was a question posted to another group about connecting to a distant
antenna.
The post reminded me of another article (perhaps in QST) where someone who
lived behind a mountain used 2 rhombic antennas as a "passive repeater" on
uhf. He mounted both antennas at the summit of the mountain with one
pointed to the repeater and the other pointed into the valley where he
lived. As I recall, he was then able to communicate via the repeater.
This brings up other possibilities - like doing the same thing for
inside-outside of a metal bldg.

well, yes, and no ! when still working for R.R., in the Sierras,
had such , on 2 GHz, dish's on a hillside to Colfax ,CA -- It worked-
sorta, was quite noisy, and had bad fade problems, even tho only
useing it to channel A-6 (highest freq was 32KHz for channel assignment)
and that was until coax link between the dishes leaked (water)!
A-6 is the lowest 6 channels in a multiplex system, and consider:
this was tied to a 300 channel (up to around 1.5 MHz) bandpass system!
(each channel = a voice channel, or up to 15 data channels (low speed))
To summerize, It can work, but most likely, not very effeciently.. Have
fun-- Jim NN7K

Hal Rosser wrote:
"Jim - NN7K" wrote in message
. com...

'Corse, consider that there are certain constraints-- one being that
the antenna must be within a small distance from one end of the loop.
(for passive reflectors, at microwave, believe, they state 2-3 miles
(MAX)). and two, consider that at VHF, there is an effect called
"KNIFE EDGE REFRACTION" that tends to bend a signal over a hilltop
to a distant target on the other side of that ridge of hills!
But, for cell phones in a vehicle, those thru the glass antennas
on cars, with a whip on the outside , and what looks like a PAWN
BROKERS 3 ball symbol on the inside, do exactly what you describe
(or at least are susposed to)! as info, Jim NN7K


Hi Jim,
Yes, I've heard of knife-edge refraction, but the instance I was referring
to in the article had a real positive benefit. As I recall, the operator
went from zero contact to satifactory contact by hooking up 2 beams
back-to-back at the summit, with one beam pointing back at him - and the
other beam pointed to the otherwise unreachable distant repeater.
I wouldn't have thought something like that would work without some
signal amplification. But it does.

well, yes, and no ! when still working for R.R., in the Sierras,
had such , on 2 GHz, dish's on a hillside to Colfax ,CA

Familiar territory, I used to live in Dutch Flat.

Couldn't hit anything in sacramento, but I could hit repeaters in the bay
area..
Except on a few days when I 'd knife-edge into sac.

Hi Jim,
Yes, I've heard of knife-edge refraction, but the instance I was referring
to in the article had a real positive benefit. As I recall, the operator
went from zero contact to satifactory contact by hooking up 2 beams
back-to-back at the summit, with one beam pointing back at him - and the
other beam pointed to the otherwise unreachable distant repeater.
I wouldn't have thought something like that would work without some
signal amplification. But it does.



How critical would the matching on those beams have to be? I am
wondering if maybe a 300 ohm wire could run from DE to DE on the two
beams.


--
73 for now
Buck
N4PGW

Buck wrote:
"How critical would the matching of those beams have to be?"

Very.

Recall that a perfectl;y matched antenna delivers only 50% of its
received energy to its load. The other 50% is re-radiated. In the case
of back-to-back antennas, the load of one antenna is the other antenna.
The source resistance of one antenna is the antenna resistancce of the
other antenna.

If one antenna is shorted or open, 100% of the energy it receives is
re-radiated.

So if all antennas are in far-fields, and if all antenna connections are
lossless, and if all antennas are properly aligned, and if the match of
all antennas is perfect, overall system gain is the sum of the antenna
gains minus the path losses (both paths with a pair of antennas
back-to-back). Recall that the radiated signal loses 22 dB in the first
wavelength and 6 more dB exery time the distance doubles after that.

Best regards, Richard Harrison, KB5WZI

Many years ago, when costs were quite different:

The British police used a hybrid system to extend the range of their low
power 400 MHz transceivers. They found some large almost flat roofs located
near the edge of coverage. At the edge of the roof most near to the base
station they erected a high gain antenna pointed at the base station. Coax
was run to a BPF + mixer + narrow BPF + mixer + amplifier where the LO for
both mixers is the same. (This scheme cleans the signal and adds some
amplification.) From the active device, coax was run to the distal edge of
the roof to a second gain antenna pointing to the sector of interest. Both
antennas had grid reflectors/shields so as to reduce to a minimum their
"behind" coupling, which had to be less than the gain added by the active
device.
The scheme worked.

I have used passive schemes where a high gain antenna on a roof captures
signals that are distributed in basements and tunnels through a TL made
deliberately leaky. Have coverage where none was available before.

The sub-theme of Richard is that one needs to calculate the numbers to
see if such systems will work.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Richard Harrison" wrote in message
...
Buck wrote:
"How critical would the matching of those beams have to be?"

Very.

Recall that a perfectl;y matched antenna delivers only 50% of its
received energy to its load. The other 50% is re-radiated. In the case
of back-to-back antennas, the load of one antenna is the other antenna.
The source resistance of one antenna is the antenna resistancce of the
other antenna.

If one antenna is shorted or open, 100% of the energy it receives is
re-radiated.

So if all antennas are in far-fields, and if all antenna connections are
lossless, and if all antennas are properly aligned, and if the match of
all antennas is perfect, overall system gain is the sum of the antenna
gains minus the path losses (both paths with a pair of antennas
back-to-back). Recall that the radiated signal loses 22 dB in the first
wavelength and 6 more dB exery time the distance doubles after that.

Best regards, Richard Harrison, KB5WZI

In this Rigless Repeater, would an antenna made up of Dir5, Dir4,
Dir3, Dir2, Dir1, Driven, Dir1, Dir2, Dir3, Dir4 Dir5 make up a
similar antenna to two 7 element beams phased together pointing back
to back?

THanks.

Buck

On Mon, 28 Mar 2005 16:15:12 -0600, (Richard
Harrison) wrote:

Buck wrote:
"How critical would the matching of those beams have to be?"

Very.

Recall that a perfectl;y matched antenna delivers only 50% of its
received energy to its load. The other 50% is re-radiated. In the case
of back-to-back antennas, the load of one antenna is the other antenna.
The source resistance of one antenna is the antenna resistancce of the
other antenna.

If one antenna is shorted or open, 100% of the energy it receives is
re-radiated.

So if all antennas are in far-fields, and if all antenna connections are
lossless, and if all antennas are properly aligned, and if the match of
all antennas is perfect, overall system gain is the sum of the antenna
gains minus the path losses (both paths with a pair of antennas
back-to-back). Recall that the radiated signal loses 22 dB in the first
wavelength and 6 more dB exery time the distance doubles after that.

Best regards, Richard Harrison, KB5WZI

--
73 for now
Buck
N4PGW