thats correct

no balun

4 lines of 50 ohm coax only ... 2 fed with a extra qtr wave to get the phasing

rgds

Simon



--- In GEO-Subscribers@yahoogroups.com, Barry Smith <baz@...> wrote:
>
> In message <20091125170947.M89600@...>
>           "Ruud Jansen" <ruud@...> wrote:
>
> > Sorry Folks, My ^C and ^V action of the GEO-Q article was not
> > sucsesful.
> > The beginning text must be:
>
> >  Hi Barry,
> >  A point of consideration. If you a use antenna with a
> > impedance (at 137.5 Mhz) that have NOT  the correct BALanced-
> > UNbalanced matching circuit, you can get many problems. If the match
> > is incorrect, a "skin" current will flow along the outside of the
> > coaxial-cable. The outside braid etc....
> > ---------------------------------------------------
> > And remember Barry, there is a big difference between theory and
> > practice (more than 40 years antenna experiments and measurments).
>
> OK. To mee it is like magic!
>
> On the DCA antenna, I do not think there is a balun. Maybe it doesn't
> need one? Maybe Jerry can answer that?
>
> Barry
> --
>

--- In GEO-Subscribers@yahoogroups.com, Barry Smith <baz@...> wrote:

> I did find a website some time ago that had a list of transmitter
> sites, but I can't find it now.

> Barry

Hi Barry and All,
Don't forget you can check what kind of mast it is here:
http://www.sitefinder.ofcom.org.uk/
click on the uk map and then the blue triangle which will give you
operator,power,type of emission etc.

Rob Denton

P.S. Sorry if this msj comes through twice, just setting up a temporary internet
system in UK.

Hi Barry,


---------- Original Message -----------
From: Barry Smith <baz@...>
To: GEO-Subscribers@yahoogroups.com
>
> Interesting ideas.
>
> The first has the practical problem of locating the yagi. If
> the distance pager-APT and pager-yagi is not the same, could
> it be adjusted with a different length of coax?

SEE MY TEXT:
"You can also shift this yagi antenna (to en from) in the direction
of the pager. Then there is no need for 180 degrees phaseshift
circuit. Simply shift for a minimum of pagersignal.


> The second takes the fun out of having your own
> installation. For me, getting good pictures is just as
> interesting (possibly more interesting?) as what they show.

SEE MY TEXT:
"I think that with 1 or 2 "I and Q" circuits and with specified
  software, also this "APT+pager" signal can be improved."

So NOT receiving APT via Internet but receiving APT from the air and
then use one or two homebrew circuits and somesoftware (DAVIT T ?).
The given site WEBSDR is only a demonstrating example using this
technics.

> Barry
> --
>
> In message <20091127140508.M38206@...>
>           "Ruud Jansen" <ruud@...> wrote:
>
> > Some whirling thoughts.
> > 1e.
> > If there is a very strong pagersignal, receive this signal with a
> > vertical 2, 3 or more  elements yagi-antenna in the direction
and at
> > the same distance from the pager as the APT receive-antenna,
reduce
> > this signal and combine this, after a phaseshift of 180 degrees,
> > with the signal you receive with your APT-antenna. Maybe is then
> > bandfiltering necessarily.
> > You can also shift this yagi antenna (to en from) in the
direction
> > of the pager. Then there is no need for 180 degrees phaseshift
> > circuit. Simply shift for a minimum of pagersignal.
>
> > 2e.
> > I saw a demonstration with Software Designed Radio and has made
some
> > experiments with SDR.
> > http://www.websdr.org
> > I think that with 1 or 2 "I and Q" circuits and with specified
> > software, also this "APT+pager" signal can be improved.
>
> > Be curous for comments,
> > Ruud PA0ROJ
> ------------------------------------
>
> Paypal - Paypal - Paypal - Paypal - Paypal
>
> GEO now accept Paypal for subscription renewal and shop purchases
>
> See the web site for details
>
> *** RENEWAL of SUBSCRIPTIONS REMINDER  ***
>
> Check your status by looking at the label on your latest
> issue or contact members@... by email
>
> ** AUTOMATIC CREDIT CARD RENEWAL  **
>
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> you time and reduce our administration.  If you wish to
> convert to automated renewal contact members@...
> by email.  Also a tick box is provided on the application
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> Clive Finnis shop@... *** GEO SHOP ***
> Yahoo! Groups Links
>
>
>

In message <20091127140508.M38206@...>
           "Ruud Jansen" <ruud@...> wrote:

> Some whirling thoughts.
> 1e.
> If there is a very strong pagersignal, receive this signal with a
> vertical 2, 3 or more  elements yagi-antenna in the direction and at
> the same distance from the pager as the APT receive-antenna, reduce
> this signal and combine this, after a phaseshift of 180 degrees,
> with the signal you receive with your APT-antenna. Maybe is then
> bandfiltering necessarily.
> You can also shift this yagi antenna (to en from) in the direction
> of the pager. Then there is no need for 180 degrees phaseshift
> circuit. Simply shift for a minimum of pagersignal.

> 2e.
> I saw a demonstration with Software Designed Radio and has made some
> experiments with SDR.
> http://www.websdr.org
> I think that with 1 or 2 "I and Q" circuits and with specified
> software, also this "APT+pager" signal can be improved.

> Be curous for comments,
> Ruud PA0ROJ

Interesting ideas.

The first has the practical problem of locating the yagi. If the
distance pager-APT and pager-yagi is not the same, could it be
adjusted with a different length of coax?

The second takes the fun out of having your own installation. For me,
getting good pictures is just as interesting (possibly more
interesting?) as what they show.

Barry
--

In message <d5c.5238714e.384140c2@...>
           geojohnt@... wrote:

> Barry,

> Pager transmission antenna look just like a flag pole - a vertical pole
> atop a building or standing off from a mast.

In that case the lattice mast (like a small version of Blackpool
tower) that I've been looking at may not be the pager.

> The frequencies (here in the UK) we are interested in are:

> 137.975 MHz.
> 138.075 MHz.
> 138.150 MHz.
> 138.175 MHz.

Thanks.

> More than one of these channels can be radiated at the same time from the
> same site.

I did find a website some time ago that had a list of transmitter
sites, but I can't find it now.

> The transmitters are 100 W erp and spaced at 18 km usually - closer in
> urban areas.
> And are designed to 'blast through' buildings of course to small pocket
> receivers.

Barry
--

Some whirling thoughts.
1e.
If there is a very strong pagersignal, receive this signal with a
vertical 2, 3 or more  elements yagi-antenna in the direction and at
the same distance from the pager as the APT receive-antenna, reduce
this signal and combine this, after a phaseshift of 180 degrees,
with the signal you receive with your APT-antenna. Maybe is then
bandfiltering necessarily.
You can also shift this yagi antenna (to en from) in the direction
of the pager. Then there is no need for 180 degrees phaseshift
circuit. Simply shift for a minimum of pagersignal.

2e.
I saw a demonstration with Software Designed Radio and has made some
experiments with SDR.
http://www.websdr.org
I think that with 1 or 2 "I and Q" circuits and with specified
software, also this "APT+pager" signal can be improved.

Be curous for comments,
Ruud PA0ROJ

In a message dated 26/11/2009 00:11:25 GMT Standard Time,
baz@... writes:

Apart  from the nearby pager - I assume it's a pager - it could just be
a  cellular phone mast, but in my experience a mast can have dozens of
services on it...

I'm going to locate the mast (again) on Google  maps and work out
bearing and distance.


Barry,

Pager transmission antenna look just like a flag pole - a vertical pole
atop a building or standing off from a mast.

The frequencies (here in the UK) we are interested in are:

137.975 MHz.
138.075 MHz.
138.150 MHz.
138.175 MHz.


More than one of these channels can be radiated at the same time from the
same site.


The transmitters are 100 W erp and spaced at 18 km usually - closer in
urban areas.
And are designed to 'blast through' buildings of course to small pocket
receivers.

Regards,
John.






[Non-text portions of this message have been removed]

Form ESA:

_________________________________________
This Envisat image features western North America, one of the most
extensive mountainous regions on Earth.


More at:

http://www.esa.int/esaEO/SEMLV470A2G_index_0.html
_________________________________________


Cheers,
David
--
SatSignal software - quality software written to your requirements
Web:  www.satsignal.eu
Email:  davidtaylor@...

>>>>   http://www.satsignal.eu/wxsat/filters/HelicalNotch.htm

> Your notch filter sounds the best option.
>
> Barry
> --

Barry,

Thanks for your comments.  One source of copper for the coils may be
petrol pipe for cars.  I don't know the best source for cavity filters,
but perhaps eBay might be worth checking, or the more major Amateur Radio
rallies.

Cheers,
David
--
SatSignal software - quality software written to your requirements
Web:  www.satsignal.eu
Email:  davidtaylor@...

In message <152840CF36AC49C699860A5592F5E97C@narvik>
           "David J Taylor" <gm8arv@...> wrote:

>>>   http://www.satsignal.eu/wxsat/filters/HelicalNotch.htm
>>
>> Ah! That makes sense and is something I had missed reading and/or
>> understanding when I glanced at the web page.

> OK, Barry, I've added a sentence to clarify the aims of that particular
> filter.

I think even with that sentence *I* may have missed the point, due to
having a bandpass filter and them looking similar physically. I saw
the picture and thought "I already have one of those". I should have
read the heading and text more carefully.

I need to look in the loft and see what bits I have. I'll probably
need to buy a box. I think I have some piston trimmers. Enamelled
copper wire is not a problem. If the wire is too "flexible" I could
stiffen it up with hot melt glue.

>> I'll take another look and get the bits together to build one.
>>
>> And without sophisticated test equipment, the notch will be easier to
>> align than a bandpass, because the pagers radiate a constant power
>> (almost) 24/7 whereas the APT signals vary in strength and are only
>> available for, at most, a couple of hours/day.
>>
>> Barry

> Yes, it's much easier to adjust for a minimum on a continuous signal!  I
> found that I had two major interfering signals and one minor one, so I
> adjusted the two resonators so that one notched out each of the major
> interfering signals.  This meant that they could not mix together in the
> receiver non-linearities and generate further in-band interference.

I've tried (but not recently) using my scanner to determine the pager
frequency/frequeuncies but even with its telescopic aerial not
extended it's difficult to home in on the exact frequency/frequencies.

> Mind you - if you have really bad interference you may want to be on the
> lookout for ex-police or ex-air-traffic-control cavity filters for
> modification.....

I would imagine they are not easy to find.

Your notch filter sounds the best option.

Barry
--

No. 24 arrived here too. Thanks Les and all others.

One comment: the website of Planet Earth must be www.planetearth.nerc.ac.uk. For
me a new one. Thanks Francis.

Greetings

Fred

Hi Ruud
got mine yesterday and was delighted to find one of my images on the
front cover.
Agree Les has done a great job over the last 6 years. I'm sure I speak
for all of us when I say a huge thanks to Les for all his work and I
trust he enjoys all that new free time he will have.
Best wishes

Alan

Ruud Jansen wrote:
> Hi folks,
> Found 1 hour ago the new GEO-Quarterly in my (solid-state (postbox).
> Again a lot of information. Thanks to Les H. for the giant job you
> have doing the last years

Hi folks,
Found 1 hour ago the new GEO-Quarterly in my (solid-state (postbox).
Again a lot of information. Thanks to Les H. for the giant job you
have doing the last years and all the other people who send their
submissions to the geoeditor@....

ruud 73's PA0ROJ

Ruud Jansen
Saeftinge 102
2036 GC Haarlem
Nederland

website ruud:
http://www.jendela.nl

website adri:
http://www.kookadri.nl


---------- Original Message -----------
From: "David J Taylor" <gm8arv@...>
To: <GEO-Subscribers@yahoogroups.com>
Sent: Thu, 26 Nov 2009 07:08:29 -0000
Subject: Re: [GEO-Subscribers] GEO preamp - variable/reduced gain?

> >>   http://www.satsignal.eu/wxsat/filters/HelicalNotch.htm
> >
> > Ah! That makes sense and is something I had missed reading and/or
> > understanding when I glanced at the web page.
>
> OK, Barry, I've added a sentence to clarify the aims of that
> particular filter.
>
> > I'll take another look and get the bits together to build one.
> >
> > And without sophisticated test equipment, the notch will be
easier to
> > align than a bandpass, because the pagers radiate a constant
power
> > (almost) 24/7 whereas the APT signals vary in strength and are
only
> > available for, at most, a couple of hours/day.
> >
> > Barry
>
> Yes, it's much easier to adjust for a minimum on a
> continuous signal!  I found that I had two major interfering
> signals and one minor one, so I adjusted the two resonators
> so that one notched out each of the major interfering
> signals.  This meant that they could not mix together in the
> receiver non-linearities and generate further in-band interference.
>
> Mind you - if you have really bad interference you may want
> to be on the lookout for ex-police or ex-air-traffic-control
> cavity filters for modification.....
>
> Cheers,
> David
> --
> SatSignal software - quality software written to your requirements
> Web:  www.satsignal.eu
> Email:  davidtaylor@...
>
> ------------------------------------
>
> Paypal - Paypal - Paypal - Paypal - Paypal
>
> GEO now accept Paypal for subscription renewal and shop purchases
>
> See the web site for details
>
> *** RENEWAL of SUBSCRIPTIONS REMINDER  ***
>
> Check your status by looking at the label on your latest
> issue or contact members@... by email
>
> ** AUTOMATIC CREDIT CARD RENEWAL  **
>
> GEO will be operating automatic credit card renewal to save
> you time and reduce our administration.  If you wish to
> convert to automated renewal contact members@...
> by email.  Also a tick box is provided on the application
> form to indicate your preference.  The form can be found
> here :- http://www.geo-web.org.uk/join.pdf   Your credit
> card details will be held securely.
>
> Contact details    ### GEO is run by volunteers ###
>
> David Anderson members@... Membership enquiries
> Ray Godden webmaster@... GEO website
> Les Hamilton editor@... GEO Quarterly Editor
> John Tellick info@... General enquiries
> Peter Wakelin meteo@... Meteorological matters
> Francis Bell francis@... Public Relations and Education
> Clive Finnis shop@... *** GEO SHOP ***
> Yahoo! Groups Links
>
>
>

> Just my luck! I'm teaching on Thursday morning. Let's hope I don't miss
> the next one.
> Thanks for the reminder David.
> Robert

Robert, I got this message about a recording of today's briefing, which I
found quite interesting:

__________________________________________________________
Hi, all,

here comes the recording link of today's weather briefing. Thanks for
joining! See you again in 17 December!

Vesa


https://sas.elluminate.com/p.jnlp?psid=2009-11-26.0049.D.0AE36C18D8F94A2CFC3DB41\
7575F81.vcr
__________________________________________________________


I expect you would need to install the conferencing software to be able to
play it.  The URL is all on one line.

I hope you can make the week before Christmas.

Cheers,
David
--
SatSignal software - quality software written to your requirements
Web:  www.satsignal.eu
Email:  davidtaylor@...

>>   http://www.satsignal.eu/wxsat/filters/HelicalNotch.htm
>
> Ah! That makes sense and is something I had missed reading and/or
> understanding when I glanced at the web page.

OK, Barry, I've added a sentence to clarify the aims of that particular
filter.

> I'll take another look and get the bits together to build one.
>
> And without sophisticated test equipment, the notch will be easier to
> align than a bandpass, because the pagers radiate a constant power
> (almost) 24/7 whereas the APT signals vary in strength and are only
> available for, at most, a couple of hours/day.
>
> Barry

Yes, it's much easier to adjust for a minimum on a continuous signal!  I
found that I had two major interfering signals and one minor one, so I
adjusted the two resonators so that one notched out each of the major
interfering signals.  This meant that they could not mix together in the
receiver non-linearities and generate further in-band interference.

Mind you - if you have really bad interference you may want to be on the
lookout for ex-police or ex-air-traffic-control cavity filters for
modification.....

Cheers,
David
--
SatSignal software - quality software written to your requirements
Web:  www.satsignal.eu
Email:  davidtaylor@...

In message <20091125232935.28ff4342@...>
           Andy Eskelson <andyyahoo@...> wrote:


>> north, but I tend to lose enough signal to see noise on the picture
>> once it drops below about 10 degrees.

> I would not be too surprised at that, but the camera is a good idea, at
> least you sound as if you have something to look at rather than the
> frigging 60+ft block of maisonettes I have just west of north which is
> what blocks the signal. No camera or maps necessary to work that one out.

Apart from the nearby pager - I assume it's a pager - it could just be
a cellular phone mast, but in my experience a mast can have dozens of
services on it...

I'm going to locate the mast (again) on Google maps and work out
bearing and distance.

As I was saying... apart from that I'm in a reasonable spot with hills
to the south and south west, but not too high.

>> Yes. In my construction I've actually cut the centre ends of the
>> elements at an angle and connected to one wall. The bolt doesn't go

> That's a good method, you could extend it a little more by cutting a
> notch and then flatten the remaining metal to form a flat to bolt
> up against..

That's effectively what I've done. Photos (to come) will show it
better than words.

>>
>> I seem to remember that. The one think I avoid, if I can, is solder
>> connections. I tend to use crimps, including crimp BNC's.

> I could relate a lot of horror stories regarding crimps.

> Generally they are NOT suitable for home built projects.

> Crimps are good, IF they are correctly made. That means you have the
> correct tooling,(Not the cheap crunch and hope stuff). You then need the
> exact connector type to match the crimp. For smaller things like the
> centre pins of BNC's the crip must be set to the correct force as
> well.

I do have what I think is the correct tooling - although the
connectors and tool are not from the same manufacturer. I've never had
a mechanical failure yet (touch wood!)

> One set of contractors I used never got another job from us when almost
> all the dataports they installed failed. Crimp tool set to hard, or
> the wrong one used. The wires fractured and the ports failed. (Old
> fashioned RS232 25 Way D-Type system) So even the "pros" get things
> wrong. That was not the only problem I came across :-)

> If you are in the business and have all these tools and connectors, then
> they will work without any problems. Not may home builders will have
> access to such things, so solder is the way to go there. I tend to stick
> to N types for antenna work. Good compression system, and big enough to
> work on. I don't think I've ever had a N-type fail on me.

I used to use N types and RG8 when transmitting (VHF/UHF), but I
haven't been on air for many years.

> With any connector system, the big killer is movement. If you ensure
> that the connector and cable cannot move, failures will be very very
> rare.

> Of course there is one type of connector that should never be used
> anywhere - PL259 / SO259. They should all be shoved in landfill never to
> sully a cable again. I only wish I could get rid of them from the Rigs
> here.

Ah yes. The "non constant impedance" connector :-)

All equipment that I own with those has a PL259-BNC adaptor on it.

Barry
--

> north, but I tend to lose enough signal to see noise on the picture
> once it drops below about 10 degrees.

I would not be too surprised at that, but the camera is a good idea, at
least you sound as if you have something to look at rather than the
frigging 60+ft block of maisonettes I have just west of north which is
what blocks the signal. No camera or maps necessary to work that one out.

> Yes. In my construction I've actually cut the centre ends of the
> elements at an angle and connected to one wall. The bolt doesn't go

That's a good method, you could extend it a little more by cutting a
notch and then flatten the remaining metal to form a flat to bolt
up against..

>
> I seem to remember that. The one think I avoid, if I can, is solder
> connections. I tend to use crimps, including crimp BNC's.

I could relate a lot of horror stories regarding crimps.

Generally they are NOT suitable for home built projects.

Crimps are good, IF they are correctly made. That means you have the
correct tooling,(Not the cheap crunch and hope stuff). You then need the
exact connector type to match the crimp. For smaller things like the
centre pins of BNC's the crip must be set to the correct force as
well.

One set of contractors I used never got another job from us when almost
all the dataports they installed failed. Crimp tool set to hard, or
the wrong one used. The wires fractured and the ports failed. (Old
fashioned RS232 25 Way D-Type system) So even the "pros" get things
wrong. That was not the only problem I came across :-)

If you are in the business and have all these tools and connectors, then
they will work without any problems. Not may home builders will have
access to such things, so solder is the way to go there. I tend to stick
to N types for antenna work. Good compression system, and big enough to
work on. I don't think I've ever had a N-type fail on me.

With any connector system, the big killer is movement. If you ensure
that the connector and cable cannot move, failures will be very very
rare.

Of course there is one type of connector that should never be used
anywhere - PL259 / SO259. They should all be shoved in landfill never to
sully a cable again. I only wish I could get rid of them from the Rigs
here.

Andy

In message <20091125170947.M89600@...>
           "Ruud Jansen" <ruud@...> wrote:

> Sorry Folks, My ^C and ^V action of the GEO-Q article was not
> sucsesful.
> The beginning text must be:

>  Hi Barry,
>  A point of consideration. If you a use antenna with a
> impedance (at 137.5 Mhz) that have NOT  the correct BALanced-
> UNbalanced matching circuit, you can get many problems. If the match
> is incorrect, a "skin" current will flow along the outside of the
> coaxial-cable. The outside braid etc....
> ---------------------------------------------------
> And remember Barry, there is a big difference between theory and
> practice (more than 40 years antenna experiments and measurments).

OK. To mee it is like magic!

On the DCA antenna, I do not think there is a balun. Maybe it doesn't
need one? Maybe Jerry can answer that?

Barry
--

In message <20091125124326.M37267@...>
           "Ruud Jansen" <ruud@...> wrote:

> Hi Barry,
>  A point of consideration. If you a use antenna with a
> impedance (at 137.5 Mhz) that have NOT  the same impedance
> as the used coaxcable impedance and receiverinput impedance,
> you can get many problems. If the match is incorrect, a
> "skin" current will flow along the outside of the coaxial-
> cable. The outside braid of the cable will thus become part of the
> antenna, as a result of witch the antenna will exhibit an
> asymetrical radiation patern and as a perfect "pager" antenna.
> The dimensions and impedance of your antenna are verry important.
> Also DONT'T use the "normall" ferite beads (as used for computer
> cables, they are only for fastpulse damping). Use Ferite beads of
> material 43 (damping maxium between 100 and 300 MHz)

I bought some clamp-on ferrites. I don't know the specification. I
will have to look back at the information when I bought them.

> In my article about "developing the PADAT137 in Geo Quarterly no.9
> page 6-11, you van find more information. Also on my website (see
> under).
> N.b. I have no idea about your DCA-antenna impedance.

>  http://www.jendela.nl/diversen/PADAT137LES_web.pdf

I have downloaded that and will study it.

> Here a part of my article in GEO Quarterly 9:

snip

Thanks for your suggestions.

Barry
--

In message <FDBD0FF4037F4B78AED1DE9AD3DE74E9@narvik>
           "David J Taylor" <gm8arv@...> wrote:

>> A few years ago a bought a filter off ebay. Exactly like the one shown
>> at http://www.wxsat.org/filter%20001.jpg
>>
>> It doesn't seem to make a lot of difference, but maybe it's not at its
>> optimum adjustment for my/our application and without a spectrum
>> analyser I have no way of checking it.
>>
>> Barry

> Barry, that it made little difference is not surprising because what you
> need is /not/ a band-pass filter, but more a sharp notch on the pager
> frequencies.  You might want to build and try the one I described, but it
> /will/ need aligning onto the pager frequencies.

>   http://www.satsignal.eu/wxsat/filters/HelicalNotch.htm

Ah! That makes sense and is something I had missed reading and/or
understanding when I glanced at the web page.

I'll take another look and get the bits together to build one.

And without sophisticated test equipment, the notch will be easier to
align than a bandpass, because the pagers radiate a constant power
(almost) 24/7 whereas the APT signals vary in strength and are only
available for, at most, a couple of hours/day.

Barry
--

Hi all.



Due to health problems I am having to sell all my WX Equipment.



It is Brand New & Unused.  I Bought it from GEO some time ago but not had
the time to set it up.



Here is what is for sale.



DVB World DVB-S USB2102

A superior 'free-to-air' DVB satellite TV and data receiver recommended for
trouble free EUMETCast reception with Windows XP or Vista. Supplied with
comprehensive installation instructions and drivers on CD. Similar to the
Dexatek unit reviewed by David Taylor in GEO Quarterly No 17. A power supply
for UK or EU is included. Note that this unit requires a USB2 port.



80 cm dish and Universal 0.2 dB LNB

A quality dish and LNB with an AZ/EL mount to fit onto a vertical pole.
(Wall or patio mounts are available from local satellite TV dealers)

RRP: £143

Fully boxed as it was when i had it delivered.

SELLING FOR £70 PLUS £30 FOR COURIER UNLESS YOU CAN COLLECT OR ARRANGE A
CHEEPER COURIER..

THANKS

Tony (Rotherham)





[Non-text portions of this message have been removed]

In message <20091125004526.7e47ee01@...>
           Andy Eskelson <andyyahoo@...> wrote:

> Barry,

> Talking about the Rig/Dartcom preamp here
> BF981 etc...

> Contact me off list if you need the Dartcom preamp instructions.

Will do. Thanks.


> To add to the confusion John said that Geo also sold this preamp.

> GEO now sell a DIFFERENT preamp, the John Silver unit.

I have one of those as well!

Barry
--

In message <hej158+hkhk@eGroups.com>
           "Simon L" <simon@...> wrote:

> Barry

> my dipoles are taken from Jerrys article

> They are 980mm overall length.

> with a gap of 15mm in the centres

OK. Then maybe mine need shortening a bit more. I was careful not to
cut them too short. I can cut more off, but you can't add back on if
you've already cut them too short!

> The dipoles should be spaced 550mm centre to centre across the axis

I can't remember the spacing I've used. I'll have to measure it again
when I take it down (and put the crossed dipoles back up)

> Phasing harness can be any convenient length .... just extend it by
> 360mm on two dipoles as per the article ie qtr wave inc dielectric
> calcs

Yes. I did that. I'm sure I was within 1/4 inch (6mm) of 14.25 inches.

> My dipole centres are wooden dowel ...purists would say bad as wood
> gets damp but needs must!

> I drilled and self tapped into 10mm tube with the 8mm dowel up the centres

> I used 40mm water pipe fittings .. T pieces and end caps plus short
> sections (uncritical) to stabilise the dipoles ends

> centre joint is a small ABS box hole cut in the sides to accept 40mm
> threaded adapters from pipe to a wall

> vertical mast is 40mm pipe with another adapter in the base, all the
> coax goes in the box and down the tube

> I have clip on ferrites ... one at the dipole centres on each then two
> at where the cable enters the box

I've use one at each dipole and one where the four lengths start.

> I found nothing that didnt work and my only issue is that it is now
> too low against my metal roof on the garage and needs to get about 2m
> higher .... which I shall do in the next days .... as I occasionally
> on some passes get an odd reflection that causes a drop out ... but
> never appears in the same place so not antenna related!

I'll take some photos of my installation soon and put them on my
website.

Barry
--

In message <20091125141731.3c1ce821@...>
           Andy Eskelson <andyyahoo@...> wrote:

> I START to get an image at about 3 degrees to the south, toally useless
> and only when the pass is not blocked. The image cleans up somewhat at
> about 6 degrees, then gets better all the time. However that only takes a
> few seconds. so the loss of a few degrees is not too bad. In my situation
> I am quite badly screened to the North, if the pass is through a hole in
> the path, then I get down to about 10 degrees before the signal starts to
> drop, it the pass swings to the west slightly, I only get down to about 20
> degrees, so have a very careful look at your takeoff and see what the
> min elevation is in various directions. There is no point in chasing a
> few extra degrees if something is in the way.

I'm planning to put a camera on the mast when it's dry and not windy
and take some pictures and stitch them together as a panorama. I know
there's a hill to the south. A few degrees elevation. Not much to the
north, but I tend to lose enough signal to see noise on the picture
once it drops below about 10 degrees.

> I also find that N18 is the worst for pagers, I have a 30db+ signal to
> contend with. It is just the separation, if the pagers were another meg
> higher things would be fine.

I agree.

> With the antenna connections, what you need is a well bonded connection
> between the antenna elements and the cables. You also need something
> that will provide a good conduction. For most situations steel
> and brass will work as well as each other, brass having the advantage that
> you can solder to it and that it will not rust.

> What is critical is how well the connection bonds to the antenna. If the
> joint is first cleaned and then made gas-tight the contact point will
> stay good. Gas tight does NOT mean wrapping things in tape, (however I am
> a great believer in self-amalgamating tape) Gas tight means that there
> are points of contact between the two parts that any oxygen or other gas
> cannot get to. When you use a self tapper for the first time, as it cuts
> the thread , that will form a gas tight joint, however undo the screw a
> couple of times and you can end up with a poor connection.

> If you have ever seen wire-wrapped circuits, the wire is wrapped tightly
> around a square pin, and at each of the 4 corners the wire cold-welds
> itself to the corner of the pin, forming a gas tight joint. With several
> turns and 4 contact points per turn wire wrap provides a very reliable
> joint.

Yes, I once built some logic boards with wire wrap.

> To achieve the same thing in antennas means using things such as star
> washers that bite into the metal on each side to make the contact.

Good suggestion!

> The
> problem is that with tube it is easy to deform and also as it is a curved
> surface getting something to fit that will bite can be a bit of a
> challenge. If you have seen a range of commercial antennas, you may have
> seen a short curved plate used as a washer, that looks as if it was cut
> from a short length of scrap tube. Very often the underside of this is
> ribbed to provide something that will bite into the elements.

Yes. In my construction I've actually cut the centre ends of the
elements at an angle and connected to one wall. The bolt doesn't go
all the way through. My pictures (when I get round to putting them on
my website) will show how I've done it.

> There is no one way to make the connections especially with home brewed
> antennas, they just have to be good, and stay that way.

> One very poor example was with a Tonna 12 (I think) XY for 70cms the
> connections of the cable were made with PUSH ON Lucar type spade
> connections. You can imagine that fitting H100 coax to that was not the
> most successful type of joint. That was very soon modified to have a
> N-Type sockets mounted on the antenna.

I seem to remember that. The one think I avoid, if I can, is solder
connections. I tend to use crimps, including crimp BNC's.

Barry
--

Hi John, Thanks
Also best wishes, ruud.
N.B. If you need some "43" ferite beads, mail me off line.

Ruud Jansen
Saeftinge 102
2036 GC Haarlem
Nederland

website ruud:
http://www.jendela.nl

website adri:
http://www.kookadri.nl


---------- Original Message -----------
From: geojohnt@...
To: GEO-Subscribers@yahoogroups.com
Sent: Wed, 25 Nov 2009 12:59:10 EST
Subject: Re: [GEO-Subscribers] GEO preamp - variable/reduced gain?

> In a message dated 25/11/2009 17:35:32 GMT Standard Time,
>  ruud@...  writes:
>
> Hi  Barry,
> A point of consideration. If you a use antenna with a
> impedance  (at 137.5 Mhz) that have NOT the correct BALanced-
> UNbalanced matching  circuit, you can get many problems. If
> the match is incorrect, a "skin"  current will flow along
> the outside of the coaxial-cable. The outside  braid  etc....
> ---------------------------------------------------
> And  remember Barry, there is a big difference between
> theory and practice  (more than 40 years antenna experiments
> and measurments)pra
>
> Hi Ruud,
>
> You beat me to it!
>
> Thanks for a proper technical answer.
> And yes, my down-lead was of course - vertical!
>
> Best wishes,
> John.
>

In a message dated 25/11/2009 17:35:32 GMT Standard Time, ruud@...
writes:

Hi  Barry,
A point of consideration. If you a use antenna with a
impedance  (at 137.5 Mhz) that have NOT the correct BALanced-
UNbalanced matching  circuit, you can get many problems. If the match
is incorrect, a "skin"  current will flow along the outside of the
coaxial-cable. The outside  braid  etc....
---------------------------------------------------
And  remember Barry, there is a big difference between theory and
practice  (more than 40 years antenna experiments and measurments)pra


Hi Ruud,

You beat me to it!

Thanks for a proper technical answer.
And yes, my down-lead was of course - vertical!

Best wishes,
John.






[Non-text portions of this message have been removed]

All,

Regarding pager interference in the UK I've just remembered that  whilst
undertaking some APT receiver comparison tests at my location [SW London]  in
2006 I was surprised when using a bog standard turnstile antenna to be able
to reduce pager interference considerably on some receivers by slowly
rotating the antenna.

I wrote an article about this effect in GEO Quarterly # 11 September  2006.
The antenna was mounted in the centre of my garden on a pole 'in the
clear.'

As I said, the antenna was a bog standard turnstile with the down cable
connected directly to the phasing harness.
Speaking to Ruud Jansen at the September meeting of the Dutch group later
he took me to task saying that if I wanted to try and reduce pager
interference  in my location my antenna must have a balun before the down-lead.
I never got around to this but Ruud proved to me the theory of this via
diagrams and maths.

Regards,
John.






[Non-text portions of this message have been removed]

Sorry Folks, My ^C and ^V action of the GEO-Q article was not
sucsesful.
The beginning text must be:

  Hi Barry,
  A point of consideration. If you a use antenna with a
impedance (at 137.5 Mhz) that have NOT  the correct BALanced-
UNbalanced matching circuit, you can get many problems. If the match
is incorrect, a "skin" current will flow along the outside of the
coaxial-cable. The outside braid etc....
---------------------------------------------------
And remember Barry, there is a big difference between theory and
practice (more than 40 years antenna experiments and measurments).

A peaceful Ruud Jansen PA0ROJ
Saeftinge 102
2036 GC Haarlem
Nederland

website ruud:
http://www.jendela.nl

website adri:
http://www.kookadri.nl


---------- Original Message -----------
From: jerry@...
To: GEO-Subscribers@yahoogroups.com
Sent: Wed, 25 Nov 2009 18:38:29 +0200 (EET)
Subject: Re: [GEO-Subscribers] GEO preamp - variable/reduced gain?

> Hi Ruud
>
>   It is possible that *have misread your text below.   You wrote
>
> "If the match is incorrect, a
> > "skin" current will flow along the outside of the coaxial-
> > cable."
>
>   That is an incorrect statement.   Mismatching of coax
> impedance does not cause current to flow on the outside of
> the coax.
>
>   What is it that you really meant to communicate??
>
>   You also wrote
>
>   "I have no idea about your DCA-antenna impedance."
>
>   The input impedance of the DCA is 50 ohms.   The DCA is
> very easy to model so you can check the DCA impedance easily.
>
>              Jerry   KD6JDJ
>
> > Hi Barry,
> >  A point of consideration. If you a use antenna with a
> > impedance (at 137.5 Mhz) that have NOT  the same impedance
> > as the used coaxcable impedance and receiverinput impedance,
> > you can get many problems. If the match is incorrect, a
> > "skin" current will flow along the outside of the coaxial-
> > cable. The outside braid of the cable will thus become part of
the
> > antenna, as a result of witch the antenna will exhibit an
> > asymetrical radiation patern and as a perfect "pager" antenna.
> > The dimensions and impedance of your antenna are verry important.
> > Also DONT'T use the "normall" ferite beads (as used for computer
> > cables, they are only for fastpulse damping). Use Ferite beads of
> > material 43 (damping maxium between 100 and 300 MHz)
> >
> > In my article about "developing the PADAT137 in Geo Quarterly
no.9
> > page 6-11, you van find more information. Also on my website (see
> > under).
> > N.b. I have no idea about your DCA-antenna impedance.
> >
> >  http://www.jendela.nl/diversen/PADAT137LES_web.pdf
> >
> > Here a part of my article in GEO Quarterly 9:
> >
> > Matching an aerial.
> > There are two issues, which have a negative influence on the
> > properties of an aerial.
> > 1. The absence of a matching system to achieve a good match
between
> > a symmetrical RQHA and an asymmetrical coaxial cable by means of
a
> > so-called “Balun”. (Balanced-unbalanced) circuit.
> > 2. The (miss) matching of the aerial impedance to the receiver
> > impedance.
> >
> > Matching of a symmetrical aerial to an asymmetrical coaxial cable
> >
> > Why is matching a symmetrical aerial to an asymmetrical coaxial
> > cable so important?  If the match is absent or incorrect a “skin”
> > current i3 will flow along the outside of the coaxial cable (Fig.
> > 14). The outside part of the cable will thus become a part of the
> > aerial, as a result of which the aerial will exhibit an
asymmetrical
> > radiation pattern.   shows the resultant effect.  The first
> > observation is that when a signal is transmitted via an
incorrectly
> > (Balanced-Unbalanced) match; the transmitted signal will not be
> > distributed through the ether in a symmetrical fashion.  This
aerial
> > would exhibit rather “cross-eyed” behaviour and in the case of a
> > RQHA it would be directional.  .Furthermore, part of the
transmitted
> > signal will be transmitted through the outside of the coaxial
cable
> > shield.  Since in most cases the aerial coax cable runs from the
top
> > to the bottom, part of this signal will be transmitted through
the
> > cable in a vertically polarized fashion.  When a horizontally
> > polarized signal is received, the receiver input will not only
> > contain the dipole signal, but additionally it will contain the
> > signal received from the vertically acting component in the
coaxial
> > cable.
> > In practice this means that a good, but incorrectly connected
aerial
> > will be subject to considerable interference (usually these are
> > vertically polarized and what about PAGERS?), which will disturb
the
> > desired signal and result in unwanted noise bands.
> >
> >
> >
> >
> > Ruud Jansen
> > Saeftinge 102
> > 2036 GC Haarlem
> > Nederland
> >
> > website ruud:
> > http://www.jendela.nl
> >
> > website adri:
> > http://www.kookadri.nl
> >
> >
> >
>

All,

I hope I wasn't the only one looking skyward around 17:12 GMT this  evening?

The ISS went over SW London [30 deg. elv. to the S] with the Shuttle very
close behind.
I hadn't realised they were undocking today or else I would have warned
'viewers' about the close dual pass.

Regards,
John.




[Non-text portions of this message have been removed]

>  Hi David
>
>  Aparently, my standards are different from yours regarding noise in APT
> images.   I consider it worthless to lessen the pager interference if
> the interference remains.   For me, elimination is the objective.
> Amelioration is good for education, even when it only demonstrates that
> further investigation using passive filters is impractical.
>
>        Jerry   KD6JDJ

Jerry, I can assure you that I am after the highest possible quality of
reception of APT satellites, and my SatSignal software was written with a
view to extracting the maximum possible image quality from the available
data:

   http://www.satsignal.eu/software/satsignal.htm

However, I do not like to promise more that I can deliver, so while in
some circumstances it may be possible to completely eliminate the
interference, I don't like to set expectations too high - hence I prefer
the term interference reduction rather than removal.  With the analogue
signals used in APT today, there will always be some residual
imperfection, that's one reason why the professionals have now moved to
digital transmission.

73,
David
--
SatSignal software - quality software written to your requirements
Web:  www.satsignal.eu
Email:  davidtaylor@...