Noise susceptibility of a 2m yagi
 

On Tuesday, November 12, 2013 11:28:19 AM UTC-6, Richard Ferryman wrote:
Thanks David. The problem is susceptibility to noise from domestic

equipment including TVs (or at least their PSUs), low energy lamps.

transients from various switches such as lights or central heating and hash

from 'digital devices' such as computers and routers. Fortunately this is

only a problem on 2m but not on 23cm and above where other factors are

predominant. Two antennae of similar gain and diectivity but different

driven element types can have as much as 15 dB difference in noise floor

near the house. The same antennas on a 20' pole in the middle of the

adjacent field have near identical noise floor. It seems a folded dipole or

quad driven element is less susceptible to locally generated noise than the

simple centre fed dipole driven element. The gamma match uses capacitive

coupling to a one piece dipole so is likely to be somewhere between loop and

simple two section dipole with regards to noise floor. In all cases my

tests so far have also had VHF ferrite blocks clipped onto the feeder at the

antenna and receiver ends to help reduce noise on the sheath of some LMR200

coax..

Unfortunately I have to locate the antenna close to the houses where the

noise is worst!

Dick G4BBH

It's my opinion that as mentioned, only element static buildup
might be reduced. And in most cases, that is usually only a problem
in dry areas, sometimes in the winter during snow storms, etc..
Also at high altitudes, one example being HCJB using loop elements.
Or they used to anyway.
As far as any local noise that is received by the antenna, they should
be the same as far as s/n. No difference at all. I'd almost be willing
to bet that your case of lower received local noise is due to that
antenna having better decoupling from the feed line than the one that
seems noisier. Good decoupling is critical. If using coax, poor
decoupling will allow noise that is picked up on the outer shield
of the coax, to be piped back down to the receiver on the inside
of the shield.
I'd be willing to bet there is some problem with the decoupling
from the feed line on the noisier antenna and it's not as well
decoupled as it should be.

Noise susceptibility of a 2m yagi
 

It's my opinion that as mentioned, only element static buildup
might be reduced. And in most cases, that is usually only a problem
in dry areas, sometimes in the winter during snow storms, etc..
Also at high altitudes, one example being HCJB using loop elements.
Or they used to anyway.

As far as any local noise that is received by the antenna, they should
be the same as far as s/n. No difference at all. I'd almost be willing
to bet that your case of lower received local noise is due to that
antenna having better decoupling from the feed line than the one that
seems noisier. Good decoupling is critical. If using coax, poor
decoupling will allow noise that is picked up on the outer shield
of the coax, to be piped back down to the receiver on the inside
of the shield.

That's pretty much the conclusion that I had stumbled my way to, after
thinking about the question over the past few days.

It's possible that the length of the feedline might be an issue. The
impedance seen "looking down" the outside of the feedline coax could
vary a lot depending on whether it happened to be closer to an odd or
even number of electrical quarter-wavelengths. This could
significantly affect the antenna system's overall pattern (a low Z
along the braid would result in greater current flow and more RF
radiation/pickup from the feedline).

Adding some ferrites to the end of the feedline, just below the point
of connection to the (noisy) dipole, might bring this antenna "to par"
with the others.

Noise susceptibility of a 2m yagi
 

On Friday, November 15, 2013 3:17:48 PM UTC-6, David Platt wrote:


That's pretty much the conclusion that I had stumbled my way to, after

thinking about the question over the past few days.



It's possible that the length of the feedline might be an issue. The

impedance seen "looking down" the outside of the feedline coax could

vary a lot depending on whether it happened to be closer to an odd or

even number of electrical quarter-wavelengths. This could

significantly affect the antenna system's overall pattern (a low Z

along the braid would result in greater current flow and more RF

radiation/pickup from the feedline).



Adding some ferrites to the end of the feedline, just below the point

of connection to the (noisy) dipole, might bring this antenna "to par"

with the others.

He said that the beads on the line helped, which pretty much
confirms the problem is common mode. I bet if he switched from
the simple gamma match to say a T match, or whatever that is more
balanced, and then added beads to the line about 1/4 wave down
from the feed, that would probably help a good bit.
The gamma match usually works OK, and I've used it quite a bit.
But it's not the best matching scheme out there.

Why not just raise the antenna higher?

Most ambient noise is vertically polarized.

This is the reason why television is horizontally polarized.

Use a poly phaser and ground to dc.

Noise susceptibility of a 2m yagi
 

On Sun, 17 Nov 2013 22:26:53 +0000, Channel Jumper
wrote:

Why not just raise the antenna higher?

Because that will pickup more noise by reducing the number of
obstruction between the noise sources and the antenna (and coax
cable).

Most ambient noise is vertically polarized.

Most man made noise is horizontally polarized because it is
re-radiated by power lines, which are horizontal. A good example is
electric motor noise. By the time you get to VHF frequencies, noise
sources are random, mostly due to multiple reflections.

Incidentally, "ambient" noise is usually used in reference to audio
notice levels, not RF.
http://en.wikipedia.org/wiki/Ambient_noise_level
I suspect you meant atmospheric noise and/or man-made noise.

This is the reason why television is horizontally polarized.

TV is horizontally polarized because the first FM operated in the
42-50 MHz region, where horizontally polarized antennas were more
common. A vertically polarized 30 MHz Yagi would be quite
impractical. The first TV stations were 44-50 MHz, and later moved to
50-56 MHz. Same problem... a vertical Yagi would be too big. There
are some other reasons if you want more detail.

Use a poly phaser and ground to dc.

Polyphaser makes lightning arrestors, which are of no use in
eliminating or reducing noise pickup.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Noise susceptibility of a 2m yagi
 

On Sunday, November 17, 2013 4:26:53 PM UTC-6, Channel Jumper wrote:
Why not just raise the antenna higher?

What good will that do if the noise received is a decoupling/
common mode issue?



Most ambient noise is vertically polarized.

Doesn't really matter much. He's picking it up on the outer
shield of his coax.




This is the reason why television is horizontally polarized.

So? We are not really talking about noise that is received
from the antenna itself. We are talking more about house noise
that is picked up on the outer shield of the coax, which then
pipes it right back to the receiver on the inner side of the
shield. You can have this problem with any antenna, horizontal
or vertically polarized. It is due to poor decoupling.




Use a poly phaser and ground to dc.

Huh? When did lightning protection become an issue?
Besides moving the antenna, there is little one can do to
negate noise that is actually picked up by the antenna itself.

The main reason I even talk of all this is to refute the claim
that the folded driven elements receive less noise than a
regular dipole driven element. It's not the type of element.
It's the decoupling differences between the antennas, and it
was pretty much verified when he added beads to the feed line,
and the noise was reduced.

Noise is RF same as any other signal. It follows all the same
rules. If an antenna element actually received less noise than
another, it would receive less intentional RF also.
But I'd be willing to bet he notices no lack of performance
for it's number of elements and boom length when listening to
other hams.

Noise susceptibility of a 2m yagi
 

On Monday, November 18, 2013 12:44:51 AM UTC-6, wrote:

But I'd be willing to bet he notices no lack of performance

for it's number of elements and boom length when listening to

other hams.

One other note though... If he is showing signs of a decoupling
problem when receiving, that means conditions are ripe for mayhem
when transmitting. He may well have skewing of his pattern.
It can skew upwards off the horizon, and you will see less gain
at the lower angles you want, and it could probably skew the
pattern as far as the heading in some cases.
So improving the decoupling will help greatly both transmitting
and receiving.
With the old Ringo Ranger verticals, the difference between
the original antenna with no decoupling, and the Ringo Ranger 2,
which had a lower decoupling section, was several S units when
tested on local signals at my QTH. Of course, the amount of
skewing can be all over the map depending on the length of the
un-decoupled feed line.
The difference in performance is reciprocal between transmit
and receive. IE: if I saw 3 db less signal on a particular
station with no decoupling vs decoupled, they would see the same
3 db less signal from me on their receiver.

I don't think he gets it - if there is noise in his neighborhood - why blame it on the antenna?

The purpose of the YAGI antenna is to improve in one direction while causing rejection in another direction.

If noise is your problem - MOVE!

No one said you had to put up a antenna there.

I had power line noise, actually BBOP, which I solved after some discussion with the electric company, followed by a complaint to the PUC, followed by a complaint to the FCC.

In the end, it cost me $500.00 - because the electric company made me replace my service entrance - bad cable jacket.

The bottom line is - if you are intelligent enough to find the source of the noise and can eliminate that source, you shouldn't have noise anymore.

Most vertical antenna's are to DC ground.

Because they do not provide any rejection, they cannot physically have any gain. Although they might have characteristics like a antenna that does have gain.

I have proven a dozen times that I will talk just as far with a simple vertical antenna as many people will with a beam antenna. It is more about the location of the antenna then it is of the actual power level or the amount of gain of the antenna. I just happen to be in a better situation then most people when it comes to antenna's and two way communications.

Noise susceptibility of a 2m yagi
 

On Monday, November 18, 2013 9:55:55 PM UTC-6, Channel Jumper wrote:
I don't think he gets it - if there is noise in his neighborhood - why

blame it on the antenna?

I don't think you get it. As usual.. :/

His tests with the beads on the feed line indicate that the
noise is not from his neighborhood. It's from his own house.

The rest of your unrelated and largely incorrect writings,
I will have printed out, so I can feed it to the possum that
prowls my backyard at night.

I imagine it won't crap right for a week.. :+
I hope they don't call PETA on me.. :|

Noise susceptibility of a 2m yagi
 

In message , Jeff Liebermann
writes
On Sun, 17 Nov 2013 22:26:53 +0000, Channel Jumper



This is the reason why television is horizontally polarized.

TV is horizontally polarized because the first FM operated in the
42-50 MHz region, where horizontally polarized antennas were more
common. A vertically polarized 30 MHz Yagi would be quite
impractical. The first TV stations were 44-50 MHz, and later moved to
50-56 MHz. Same problem... a vertical Yagi would be too big. There
are some other reasons if you want more detail.

In the UK, we longer use VHF (low-band and high-band) for TV (it's all
now on UHF). However, when we did, around 50% was vertical and (of
course) 50% was horizontal. The very first BBC transmitter (in London,
opened in 1936) was actually vertical, on 45MHz (they were rather big,
especially at ground level!), and remained so until VHF closed in the
late 80s. With only one or two exceptions, all high-power UHF is
horizontal, but quite a few lower-power fill-in transmitters are
vertical (to minimise mutual interference).
--
Ian