Passive Relay's


Nick Gregory G0HIK
 

Living in a valley, I've been interested in using a passive relay and have talked about them several times over the years with local amateurs.

When I was working, on one of the sites we had tanks that were refurbished WWII fuel dumps with chambers underground. To enable the UHF radios to work we had a folded dipole in the chamber with LDF4-50 feeding and 18 ele jaybeam. This gave comms back to the control room (Less than a mile).

While working on the rigs, we had a blind spot, I installed a system with two folded dipoles back to back. This was not perfect, but was a great improvement.

As I walk on the Fells around here there, I often come across community TV repeaters. They are always been powered, not sure if they are simply a pre-amplifier or they frequency shift.

I have been told that you cant have the passive repeater anywhere near the middle of the link and has to be right at one end of it. Not sure how the logic works, as several of the communities fed by these are not that close to them, say up to 2 to 5 miles away.

Finding a site locally that I could use that is on a hill and secure was a problem. But recently a radio friend who lives the other side of the valley, around 5 miles away said I could install one on the roof of his shack for me to try out. I was thinking of 144MHz because I was talking about this with another chap in the club whom I would like to communicate with who has Two metres. But it could be any band, maybe 23cm's might be a good one to try out.

Nick G0HIK

 


Iain Young
 

Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

I have been told that you cant have the passive repeater anywhere near the middle of the link and has to be right at one end of it. Not sure how the logic works, as several of the communities fed by these are not that close to them, say up to 2 to 5 miles away.
I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain


Andy G4JNT
 

I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !



On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain




Nick Gregory G0HIK
 

Thanks for the PDF's, no time today, but I'll print them off and read later.

All sounds good though.

I'll have to dig some aerials out and see what I have and can throw up for a quick and dirt test.

Nick G0HIK


Andy G4JNT
 

Correction:
If the repeater is exactly on the direct line from Tx to Rx,  MAXIMUM loss occurs if it is placed mid way
Better to have it close to one end or the other

Spreadsheet for a simplistic view will follow shortly



On Tue, 19 May 2020 at 11:29, Andy Talbot <andy.g4jnt@...> wrote:
I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !



On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain




Andy G4JNT
 


This assumes Line of Sight Tx to passive repeater, and from there to Rx
All antennas see terrestrial noise temperatures



On Tue, 19 May 2020 at 12:11, Andy Talbot <andy.g4jnt@...> wrote:
Correction:
If the repeater is exactly on the direct line from Tx to Rx,  MAXIMUM loss occurs if it is placed mid way
Better to have it close to one end or the other

Spreadsheet for a simplistic view will follow shortly



On Tue, 19 May 2020 at 11:29, Andy Talbot <andy.g4jnt@...> wrote:
I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !



On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain




Phil Guttridge G3TCU
 

Andy,

So why does Airscout suggest the optimum place for a plane is mid way on the path then? And that seems to work in practice, if you're ever lucky enough to have a plane flying exactly along the path.

I'm aware there are special cases, like when one station is in a valley and can only 'see' the plane when it's pretty close.

I assume an aircraft must be a form of passive reflector or is there a difference between aircraft *scatter* and a passive repeater that is a deliberate reflector?

Thanks & 73, Phil G3TCU



On 19/05/2020 12:11, Andy G4JNT via groups.io wrote:
Correction:
If the repeater is exactly on the direct line from Tx to Rx,  MAXIMUM loss occurs if it is placed mid way
Better to have it close to one end or the other

Spreadsheet for a simplistic view will follow shortly



On Tue, 19 May 2020 at 11:29, Andy Talbot <andy.g4jnt@...> wrote:
I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !



On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain




Virus-free. www.avg.com


Andy G4JNT
 

Probably because it gives maximum distance rather than maximum signal.
? ? ? ?  ...



On Tue, 19 May 2020 at 14:21, Phil Guttridge G3TCU <p.guttridge@...> wrote:
Andy,

So why does Airscout suggest the optimum place for a plane is mid way on the path then? And that seems to work in practice, if you're ever lucky enough to have a plane flying exactly along the path.

I'm aware there are special cases, like when one station is in a valley and can only 'see' the plane when it's pretty close.

I assume an aircraft must be a form of passive reflector or is there a difference between aircraft *scatter* and a passive repeater that is a deliberate reflector?

Thanks & 73, Phil G3TCU



On 19/05/2020 12:11, Andy G4JNT via groups.io wrote:
Correction:
If the repeater is exactly on the direct line from Tx to Rx,  MAXIMUM loss occurs if it is placed mid way
Better to have it close to one end or the other

Spreadsheet for a simplistic view will follow shortly



On Tue, 19 May 2020 at 11:29, Andy Talbot <andy.g4jnt@...> wrote:
I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !



On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain




Virus-free. www.avg.com


Dave G8KHU
 

?? Civil aircraft try to fly level. therefore wings parallel to the ground, and for reflection the angle of incidence = angle of reflection ??
Dave


Neil Smith G4DBN
 

Airscout misses the case where a plane is beyond the target and you often get a very good reflection.  I see that a lot with omni beacons that I can't see direct, but I do see via planes further away.  I have to fool Airscout by picking a target 200km further way on the same heading. If anyone fancies doing some detailed verifications of the mechanism, we should be able to ask the author to add the functionality.  It is a bit counter-intuitive to beam AWAY from the station you are trying to work, but it does seem to work with omni beacons, and might be useful for stations in the Midlands to work into Scotland via planes to their south.  I can feel a project proposal on The Signal Lounge coming together...

On the higher bands, planes near to one end of the path are often in one of the nulls or just too high an angle unless you have elevation. I enable the additional info on Airscout so I see both elevation angles as well as just squint.  Once you use elevation, that means the reflection angle is steeper, and generally I find that reduces the level of the reflection compared with those in the middle half of the path.

I can usually get a decent return from GB3KBQ on 10 GHz when planes are more than 80km from Taunton so long as they are not at 4km or higher, I guess that is because of the vertical beamwidth of the antenna. I can usually get reflections from planes within 40km of here if I use elevation, but again only if they are relatively low  High planes that are close don't seem to reflect as well, perhaps because glancing incidence gives a stronger specular reflection.

There is also a huge dependency on plane type and angle of approach to the line of sight for those brief specular reflections, but for shorter paths with big signals, I suspect there is more of the classical scatter going on rather than brief glints.

Mid-path reflections from planes over the North Sea directly in line with the path between here and endpoints in PA/DL/OZ are usually stable for a minute or more, with almost no doppler, but are subject to periodic deep fades.  Those where the plane is at right angles to the path have maximum rate of change of doppler and are usually brief.  You can sometimes see the 'S' shaped curve of doppler shift if both stations are tracking the plane from 50km out as the geometry of the path changes and tan(theta) becomes almost equal to theta (in radians).  You see that 'S' very clearly with GRAVES reflections from the ISS.

On 19/05/2020 14:25, Andy G4JNT wrote:
Probably because it gives maximum distance rather than maximum signal.
? ? ? ?  ...



On Tue, 19 May 2020 at 14:21, Phil Guttridge G3TCU <p.guttridge@...> wrote:
Andy,

So why does Airscout suggest the optimum place for a plane is mid way on the path then? And that seems to work in practice, if you're ever lucky enough to have a plane flying exactly along the path.

I'm aware there are special cases, like when one station is in a valley and can only 'see' the plane when it's pretty close.

I assume an aircraft must be a form of passive reflector or is there a difference between aircraft *scatter* and a passive repeater that is a deliberate reflector?

Thanks & 73, Phil G3TCU



On 19/05/2020 12:11, Andy G4JNT via groups.io wrote:
Correction:
If the repeater is exactly on the direct line from Tx to Rx,  MAXIMUM loss occurs if it is placed mid way
Better to have it close to one end or the other

Spreadsheet for a simplistic view will follow shortly



On Tue, 19 May 2020 at 11:29, Andy Talbot <andy.g4jnt@...> wrote:
I feel a spreadsheet coming on ..
Seem to recall doing this calculation back in the dim and distant past for work, and IIRC the mid point gave furthest range extension.   But that would have been for a naval scenario and no hills !



On Tue, 19 May 2020 at 10:58, Iain Young <g7iii@...> wrote:
Hi Nick,

On 19/05/20 10:24, Nick Gregory G0HIK via groups.io wrote:

> I have been told that you cant have the passive repeater anywhere near
> the middle of the link and has to be right at one end of it. Not sure
> how the logic works, as several of the communities fed by these are not
> that close to them, say up to 2 to 5 miles away.

I beg to differ. While this was done on 144MHz, and 433MHz, last time I
checked the rules of physics don't change at 1.2GHz and up,so here are
a couple of links tto a presentation that I did based on an experiment a
couple of years ago:

http://hal.g7iii.net/ppt/Passive_Repeater_Experiment.pdf
http://hal.g7iii.net/ppt/Passive_Repeater.pdf

Personally, I think it's all about overcoming the extra path loss, so
you need gain in the antennas. I must try it on 23cms and up sometime...


73s

Iain




Virus-free. www.avg.com

-- 
Neil
http://g4dbn.uk


Chris Bartram G4DGU
 

Hello Dave,

?? Civil aircraft try to fly level. therefore wings parallel to the ground, and for reflection the angle of incidence = angle of reflection ??
I suspect that Airscout is predicated on the assumption that people wish to us it as an aid to extending the range of tropo systems. If that's the case, it makes sense to assume that the centre point of the path is also the point of minimum loss as asymmetric illumination wouldn't reduce path losses significantly.

I played with the end illumination of MS paths on 2m back around 1979-80 and found it very effective, once I'd persuaded people that it wasn't black magic! It often took longer on the then 20m VHF net to do that than to make the QSOs. That work predates a certain PhD by a few years ...

73

Chris G4DGU


John E. Beech
 

Back to back dishes have been used in commericial links on the microwave bands.
de John G8SEQ

-------Original Message-------
From: Nick Gregory G0HIK via groups.io <nickg0hik=googlemail.com@groups.io>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: [UKMicrowaves] Passive Relay's
Sent: May 19 '20 10:24

Living in a valley, I've been interested in using a passive relay and
have talked about them several times over the years with local
amateurs.

When I was working, on one of the sites we had tanks that were
refurbished WWII fuel dumps with chambers underground. To enable the
UHF radios to work we had a folded dipole in the chamber with LDF4-50
feeding and 18 ele jaybeam. This gave comms back to the control room
(Less than a mile).

While working on the rigs, we had a blind spot, I installed a system
with two folded dipoles back to back. This was not perfect, but was a
great improvement.

As I walk on the Fells around here there, I often come across
community TV repeaters. They are always been powered, not sure if they
are simply a pre-amplifier or they frequency shift.

I have been told that you cant have the passive repeater anywhere
near the middle of the link and has to be right at one end of it. Not
sure how the logic works, as several of the communities fed by these
are not that close to them, say up to 2 to 5 miles away.

Finding a site locally that I could use that is on a hill and secure
was a problem. But recently a radio friend who lives the other side of
the valley, around 5 miles away said I could install one on the roof
of his shack for me to try out. I was thinking of 144MHz because I was
talking about this with another chap in the club whom I would like to
communicate with who has Two metres. But it could be any band, maybe
23cm's might be a good one to try out.

Nick G0HIK


Roger Ray
 

A local farmer uses vhf to link his people, farms and tractors.  He has several farms up to 30 miles away. He had good coverage except one, which was in a valley. We used a gain antenna 8el I think, pointing to the base. A few metres of coax, feeding a 2el to cover the valley. Worked a treat.....

Roger


On 19 May 2020, at 10:24, Nick Gregory G0HIK via groups.io <nickg0hik@...> wrote:

Living in a valley, I've been interested in using a passive relay and have talked about them several times over the years with local amateurs.

When I was working, on one of the sites we had tanks that were refurbished WWII fuel dumps with chambers underground. To enable the UHF radios to work we had a folded dipole in the chamber with LDF4-50 feeding and 18 ele jaybeam. This gave comms back to the control room (Less than a mile).

While working on the rigs, we had a blind spot, I installed a system with two folded dipoles back to back. This was not perfect, but was a great improvement.

As I walk on the Fells around here there, I often come across community TV repeaters. They are always been powered, not sure if they are simply a pre-amplifier or they frequency shift.

I have been told that you cant have the passive repeater anywhere near the middle of the link and has to be right at one end of it. Not sure how the logic works, as several of the communities fed by these are not that close to them, say up to 2 to 5 miles away.

Finding a site locally that I could use that is on a hill and secure was a problem. But recently a radio friend who lives the other side of the valley, around 5 miles away said I could install one on the roof of his shack for me to try out. I was thinking of 144MHz because I was talking about this with another chap in the club whom I would like to communicate with who has Two metres. But it could be any band, maybe 23cm's might be a good one to try out.

Nick G0HIK

 


Dave G8KHU
 

Hi Chris

It's funny how we tend to approach things based on our experience and make assumptions that may not be correct. The more l learn the more I realise how much more there is to learn - good grief, philosophy at 6 am  :)

I, probably falsley - mea culpa, assumed that the reflections were to allow relatively local communication over a path where the direct path was obscured ie as bistatic radar problem in which the bistatic angle is relatively acute. In which case the midpoint geometery with a horizontal reflector would probably give the highest target return. However If you're looking at dx, where the bistatic angle approaches 180 degrees, then I should have looked at it as a forward scattering radar system where the geometry gets a bit more fuzzy. Duh!

PS  i agree there is no black magic in end illumination of MS paths....  but there is black magic in calling up a shower of meteorites just when you nedd them!  (Images of mad professor like amateurs dancing round a burning PSU holding up a 4CX250B in supplication ....)

73
Dave G8KHU
******************
Hello Dave,

?? Civil aircraft try to fly level. therefore wings parallel to the ground, and for reflection the angle of incidence = angle of reflection ??
I suspect that Airscout is predicated on the assumption that people wish to us it as an aid to extending the range of tropo systems. If that's the case, it makes sense to assume that the centre point of the path is also the point of minimum loss as asymmetric illumination wouldn't reduce path losses significantly.

I played with the end illumination of MS paths on 2m back around 1979-80 and found it very effective, once I'd persuaded people that it wasn't black magic! It often took longer on the then 20m VHF net to do that than to make the QSOs. That work predates a certain PhD by a few years ...

******************


Ian White
 

As Chris well remembers, back in the days of the 2m Es telephone tree we had our own real-life mad professor. If the phone rang in the middle of a tutorial, he would make some excuse to the students, jump on his bike and pedal like mad for North Oxford.

It won't surprise anyone to learn that he was a psychology don.

73 from Ian GM3SEK


On 20/05/2020 06:36, Dave G8KHU wrote:
Hi Chris

It's funny how we tend to approach things based on our experience and make assumptions that may not be correct. The more l learn the more I realise how much more there is to learn - good grief, philosophy at 6 am  :)

I, probably falsley - mea culpa, assumed that the reflections were to allow relatively local communication over a path where the direct path was obscured ie as bistatic radar problem in which the bistatic angle is relatively acute. In which case the midpoint geometery with a horizontal reflector would probably give the highest target return. However If you're looking at dx, where the bistatic angle approaches 180 degrees, then I should have looked at it as a forward scattering radar system where the geometry gets a bit more fuzzy. Duh!

PS  i agree there is no black magic in end illumination of MS paths....  but there is black magic in calling up a shower of meteorites just when you nedd them!  (Images of mad professor like amateurs dancing round a burning PSU holding up a 4CX250B in supplication ....)

73
Dave G8KHU
******************
Hello Dave,

?? Civil aircraft try to fly level. therefore wings parallel to the ground, and for reflection the angle of incidence = angle of reflection ??
I suspect that Airscout is predicated on the assumption that people wish to us it as an aid to extending the range of tropo systems. If that's the case, it makes sense to assume that the centre point of the path is also the point of minimum loss as asymmetric illumination wouldn't reduce path losses significantly.

I played with the end illumination of MS paths on 2m back around 1979-80 and found it very effective, once I'd persuaded people that it wasn't black magic! It often took longer on the then 20m VHF net to do that than to make the QSOs. That work predates a certain PhD by a few years ...

******************