Hi group,

I'm a SWL and am specially interested in Navtex DX-reception.My problem
is (was) the heavy QRM from about every TV-set, monitor, PC in the
neighbourhood.

I'm currently using a T-aerial: horizontal wire 20 meters long, ca. 10
meter above ground, vertical part ca. 10 meter down from the middle, =
1:9 "magnetic" balun = 25 meter RG58 to receiver. Receiver is located
on the first floor, and is grounded via a thick wire to the earth pin
of the house. Typical reception sounds like this:

http://users.pandora.be/dirk.claessens2/div/not_grounded.wav

....humming, hissing, hard to decode, nightmare.

In despair - and against all advise in antenna textbooks (ground
loops!) - I decided to make an additional earth point at the balun. I
drove two 1 meter 1/2 inch copperpipes into the ground, and connected
these to the shield of the RG58 at the balun. Grounding at the receiver
was unchanged. The result was stunning:

http://users.pandora.be/dirk.claessens2/div/grounded.wav

QRM totally gone!
Can anyone explain this?

Thanks for any insight - Dirk

On Fri, 21 Sep 2007 14:28:47 GMT, Navtex-Fan wrote:

I'm a SWL and am specially interested in Navtex DX-reception.My problem
is (was) the heavy QRM from about every TV-set, monitor, PC in the
neighbourhood.
....
In despair - and against all advise in antenna textbooks (ground
loops!) - I decided to make an additional earth point at the balun.
....
QRM totally gone!
Can anyone explain this?

Hi Dirk,

The coax to your antenna was suffering common mode currents. These
currents came from noise sources in your home (by coupling directly
through conduction, or over-the-air). Those currents traveled towards
the antenna along the outer surface of the coax's braided shield. When
those currents got to the antenna feed point, they reversed direction
and entered INTO the transmission line and went back to your receiver.

When you grounded the far end, those currents went to ground the easy
way instead of through your receiver's front end.

A "magnetic" BalUn is not an effective choke. Chokes are used to
decouple the transmission line from the feed point. The W2DU choke
BalUn (1:1) would also reduce noise.

You were LUCKY with ground loops. When the weather changes, you may
see your luck change.

73's
Richard Clark, KB7QHC

On 2007-09-21, Richard Clark (67.168.144.41) wrote in
message


On Fri, 21 Sep 2007 14:28:47 GMT, Navtex-Fan wrote:

I'm a SWL and am specially interested in Navtex DX-reception.My problem
is (was) the heavy QRM from about every TV-set, monitor, PC in the
neighbourhood.
...
In despair - and against all advise in antenna textbooks (ground
loops!) - I decided to make an additional earth point at the balun. ...
QRM totally gone!
Can anyone explain this?

Hi Dirk,

The coax to your antenna was suffering common mode currents. These
currents came from noise sources in your home (by coupling directly
through conduction, or over-the-air). Those currents traveled towards
the antenna along the outer surface of the coax's braided shield. When
those currents got to the antenna feed point, they reversed direction
and entered INTO the transmission line and went back to your receiver.


Thanks for the clarification Richard.
So in fact the coax shield was part of the antenna?

When you grounded the far end, those currents went to ground the easy
way instead of through your receiver's front end.

A "magnetic" BalUn is not an effective choke. Chokes are used to
decouple the transmission line from the feed point. The W2DU choke
BalUn (1:1) would also reduce noise.

Google gives many hits on this, thanks for the tip.



You were LUCKY with ground loops. When the weather changes, you may
see your luck change.


I'll keep my fingers crossed... :-)
The soil here is partly clay/ partly sand. In winter it becomes quite
moist. Would that adversely affect the situation?

On Fri, 21 Sep 2007 14:28:47 GMT, Navtex-Fan wrote:

Hi group,

I'm a SWL and am specially interested in Navtex DX-reception.My problem
is (was) the heavy QRM from about every TV-set, monitor, PC in the
neighbourhood.

I'm currently using a T-aerial: horizontal wire 20 meters long, ca. 10
meter above ground, vertical part ca. 10 meter down from the middle, =
1:9 "magnetic" balun = 25 meter RG58 to receiver. Receiver is located
on the first floor, and is grounded via a thick wire to the earth pin
of the house. Typical reception sounds like this:

http://users.pandora.be/dirk.claessens2/div/not_grounded.wav

...humming, hissing, hard to decode, nightmare.

In despair - and against all advise in antenna textbooks (ground
loops!) -

I have never seen "ground loops" mentioned in an antenna book.
Ground loops are a main problem in audio frequency equipment,
not in HF.

In high frequency equipment GROUND EVERY POINT YOU CAN
to create a quasi-reference potential area as large as possible.

The usual way to overcome stray noise from nearby sources
a

1.) Electrostatic shielding of the antenna.
Use coax for the horizontal dipoles, and ground the coax shield
at the ends but do not create short circuited loops.
(do not confuse with "ground loops")
2. Use a noise eliminator which feeds a phase shifted signal
from a small local antenna into a combining network.
3. Improve grounding as you did.

To me it is not quite clear what happened in your case,
but antennas are and have always been much try-and-error.
w.

I decided to make an additional earth point at the balun. I
drove two 1 meter 1/2 inch copperpipes into the ground, and connected
these to the shield of the RG58 at the balun. Grounding at the receiver
was unchanged. The result was stunning:

http://users.pandora.be/dirk.claessens2/div/grounded.wav

QRM totally gone!
Can anyone explain this?

Thanks for any insight - Dirk

On Fri, 21 Sep 2007 18:40:00 GMT, Navtex-Fan wrote:

Thanks for the clarification Richard.
So in fact the coax shield was part of the antenna?

Hi Dirk,

Yes. And that "part" of the antenna was inside your home.

Please keep in mind that the same coax shield can support TWO
currents: one on the outside and one on the inside. Even though it is
the same metallic conductor, the shape creates two circuits because RF
currents on the outside cannot penetrate to the inside (that is how it
shields). Instead, those currents on the outside travel to a common
point such as the feed and gain entrance.

Also, the reverse is true as well (when we are thinking in terms of
transmission).

Put a choke somewhere along that outside circuit, and you cut off that
current. In your case, you grounded it at both ends.

The soil here is partly clay/ partly sand. In winter it becomes quite
moist. Would that adversely affect the situation?

It has happened to me (Seattle = Rain City). The "earth" connection
you use at the AC plug is NOT a shield, instead it is a safety ground.
It is in close proximity to a lot of noisy circuits. Another noise
solution is to move your plug to a different room's socket (on a
different circuit breaker). You don't have to move the radio to
experiment with this, use an extension cord. Better yet, run off
battery and unplug everything but the antenna.

Remember these last suggestions if the noise returns with rain (or
after a rain).

73's
Richard Clark, KB7QHC

On 21 Sep, 12:14, Helmut Wabnig .... .-- .- -... -. .. --.
@ .- --- -. dot .- - wrote:
On Fri, 21 Sep 2007 14:28:47 GMT, Navtex-Fan wrote:
Hi group,

I'm a SWL and am specially interested in Navtex DX-reception.My problem
is (was) the heavy QRM from about every TV-set, monitor, PC in the
neighbourhood.

I'm currently using a T-aerial: horizontal wire 20 meters long, ca. 10
meter above ground, vertical part ca. 10 meter down from the middle, =
1:9 "magnetic" balun = 25 meter RG58 to receiver. Receiver is located
on the first floor, and is grounded via a thick wire to the earth pin
of the house. Typical reception sounds like this:

http://users.pandora.be/dirk.claessens2/div/not_grounded.wav

...humming, hissing, hard to decode, nightmare.

In despair - and against all advise in antenna textbooks (ground
loops!) -

I have never seen "ground loops" mentioned in an antenna book.
Ground loops are a main problem in audio frequency equipment,
not in HF.

In high frequency equipment GROUND EVERY POINT YOU CAN
to create a quasi-reference potential area as large as possible.

The usual way to overcome stray noise from nearby sources
a

1.) Electrostatic shielding of the antenna.
Use coax for the horizontal dipoles, and ground the coax shield
at the ends but do not create short circuited loops.
(do not confuse with "ground loops")
2. Use a noise eliminator which feeds a phase shifted signal
from a small local antenna into a combining network.
3. Improve grounding as you did.

To me it is not quite clear what happened in your case,
but antennas are and have always been much try-and-error.
w.



I decided to make an additional earth point at the balun. I
drove two 1 meter 1/2 inch copperpipes into the ground, and connected
these to the shield of the RG58 at the balun. Grounding at the receiver
was unchanged. The result was stunning:

http://users.pandora.be/dirk.claessens2/div/grounded.wav

QRM totally gone!
Can anyone explain this?

Thanks for any insight - Dirk- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

Hi, let me clarify your problem. The most efficient radiator is one
wave length long where it is considered to be in equilibrium with a
parallel electrical cuircuit
instead of the usual series circuit. For most efficient radiation both
the capacitance and the inductance
must act as a energy storage such that when the terminals are shorted
the energy is released in a burst such that radiation can begin,
the electrical circuit by the way is often called a TANK cuircuit. In
the case of a fractional wave length radiator the pendulum type
radiation is not available for radiation and thus it travels up the
outside of the coax where it can radiate or become part of the "real
resistance" of the radiator in a similar way a vertical 1/2 wave
antenna would do when half of the applied energy is absorbed by the
ground.
Per the replies you will see what these currents are named when one
has an antenna that wants to work as a full wave length long even tho
a 1/2 wave length of the radiator is missing for max efficiency.
Hope that helps
Regards
Art KB9MZ

On 2007-09-21, Richard Clark (67.168.144.41) wrote in
message

Please keep in mind that the same coax shield can support TWO
currents: one on the outside and one on the inside. Even though it is
the same metallic conductor, the shape creates two circuits because RF
currents on the outside cannot penetrate to the inside (that is how it
shields). Instead, those currents on the outside travel to a common
point such as the feed and gain entrance.


This is complicated, but I now (begin to) understand the true source of
the problems I had in the past. I'm not going to post a list here of
antennas I've been experimenting with to get rid of the QRM...

[..]

The soil here is partly clay/ partly sand. In winter it becomes quite
moist. Would that adversely affect the situation?

It has happened to me (Seattle = Rain City). The "earth" connection
you use at the AC plug is NOT a shield, instead it is a safety ground.
It is in close proximity to a lot of noisy circuits.
[..]

So the safety ground is a bad RF ground in most situations.

Thanks again for the clarification Richard!

--
Dirk.
No trees were killed in the creation of this message;
however, many electrons were terribly inconvenienced.
http://users.pandora.be/dirk.claessens2

On 2007-09-22, art (74.133.197.189) wrote in
message .com

In the case of a fractional wave length radiator the pendulum type
radiation is not available for radiation and thus it travels up the
outside of the coax where it can radiate or become part of the "real
resistance" of the radiator in a similar way a vertical 1/2 wave
antenna would do when half of the applied energy is absorbed by the
ground.

Sure, Navtex is broadcasted on 518/490 KHz. Even a 1/4 wavelength
antenna is beyond my real estate capabilities. :-(


Per the replies you will see what these currents are named when one
has an antenna that wants to work as a full wave length long even tho
a 1/2 wave length of the radiator is missing for max efficiency.
Hope that helps
Regards
Art KB9MZ

Thanks for the info Art, it is appreciated.

73 - Dirk

--
Dirk.
No trees were killed in the creation of this message;
however, many electrons were terribly inconvenienced.
http://users.pandora.be/dirk.claessens2

In article ,
Dirk Claessens wrote:

On 2007-09-21, Richard Clark (67.168.144.41) wrote in
message

Please keep in mind that the same coax shield can support TWO
currents: one on the outside and one on the inside. Even though it is
the same metallic conductor, the shape creates two circuits because RF
currents on the outside cannot penetrate to the inside (that is how it
shields). Instead, those currents on the outside travel to a common
point such as the feed and gain entrance.


This is complicated, but I now (begin to) understand the true source of
the problems I had in the past. I'm not going to post a list here of
antennas I've been experimenting with to get rid of the QRM...

[..]

The soil here is partly clay/ partly sand. In winter it becomes quite
moist. Would that adversely affect the situation?

It has happened to me (Seattle = Rain City). The "earth" connection
you use at the AC plug is NOT a shield, instead it is a safety ground.
It is in close proximity to a lot of noisy circuits.
[..]

So the safety ground is a bad RF ground in most situations.

Thanks again for the clarification Richard!

i know this is prob a dumb question reading the last part i agree
but i say how come ? they say all points are to be tied together at
enterance of house so what is the diff between any two proper grounds
connect points then?

On 2007-09-22, ml (151.205.97.125) wrote in
message


i know this is prob a dumb question reading the last part i agree
but i say how come ? they say all points are to be tied together at
enterance of house so what is the diff between any two proper grounds
connect points then?

From a safety viewpoint all ground points are equal.
For _RF_ however, one ground point _may_ be better then another,
depending on how the wiring goes through the house, and where the
ground wire is picking up QRM, hence Richard's suggestion to feed the
receiver from a wall outlet in another room.