If you own or have used the Cushcraft MA5B in the past could you let me know
what the noise floor reading is/was and the rough height of your antenna?

I know that the noise floor will be different location to location but it
will give me some idea of what I should be looking at.

I have had mine up for a couple of years now and although the signals
increase 3-5 S points better than my Cobwebb and Dipole on receive the noise
floor has always been S7-8 on 14MHz. It is 0-1 S point on my other two
antennas. So any signal received on the MA5B less than S9+10db has a lot of
noise in there audio.
SWR is good on all 5 bands.

"David" wrote in
news
If you own or have used the Cushcraft MA5B in the past could you let
me know what the noise floor reading is/was and the rough height of
your antenna?

I know that the noise floor will be different location to location but
it will give me some idea of what I should be looking at.

I have had mine up for a couple of years now and although the signals
increase 3-5 S points better than my Cobwebb and Dipole on receive the
noise floor has always been S7-8 on 14MHz. It is 0-1 S point on my
other two antennas. So any signal received on the MA5B less than
S9+10db has a lot of noise in there audio.
SWR is good on all 5 bands.

If the noise is received equally from all directions, then the amount of
noise power received is proportional to the average gain of the antenna
system, which is essentially, the inverse of the efficiency of the
system.

Some noise sources are not very directional, eg galactic noise. Manmade
noise could me non-directional, it just depends on the physical
distribution of those noise sources at a particular instant of time at
your location.

You can of course determine if noise is non-directional, rotate the
antenna and observe the noise level. If you want to measure ambient
noise, have a look at http://www.vk1od.net/calc/anc.htm .

I calculated the expected ambient noise due to the sources discussed in
ITU P.372-8 and documented it at
http://www.vk1od.net/measurement/noi...bientNoise.htm , you may find
it interesting. Broady, if you have a receive noise level way below that
expectation, it may be sign of an inefficient antenna system.

Owen

"Owen Duffy" wrote in message
...
"David" wrote in
news
If you own or have used the Cushcraft MA5B in the past could you let
me know what the noise floor reading is/was and the rough height of
your antenna?

I know that the noise floor will be different location to location but
it will give me some idea of what I should be looking at.

I have had mine up for a couple of years now and although the signals
increase 3-5 S points better than my Cobwebb and Dipole on receive the
noise floor has always been S7-8 on 14MHz. It is 0-1 S point on my
other two antennas. So any signal received on the MA5B less than
S9+10db has a lot of noise in there audio.
SWR is good on all 5 bands.

If the noise is received equally from all directions, then the amount of
noise power received is proportional to the average gain of the antenna
system, which is essentially, the inverse of the efficiency of the
system.

Some noise sources are not very directional, eg galactic noise. Manmade
noise could me non-directional, it just depends on the physical
distribution of those noise sources at a particular instant of time at
your location.

You can of course determine if noise is non-directional, rotate the
antenna and observe the noise level. If you want to measure ambient
noise, have a look at http://www.vk1od.net/calc/anc.htm .

I calculated the expected ambient noise due to the sources discussed in
ITU P.372-8 and documented it at
http://www.vk1od.net/measurement/noi...bientNoise.htm , you may find
it interesting. Broady, if you have a receive noise level way below that
expectation, it may be sign of an inefficient antenna system.

Owen

The noise level does not change when I turn the beam 360 deg.

I have used the Cobwebb and the Cushcraft R5 in the same location and I do
not get the same noise. The noise is also present in the audio on stronger
signals.
Its the same noise you get on a weak station, where its combined in with the
audio except I get the same noise mixed with the stronger stations audio. I
do not get this on any other antenna's apart from the Cushcraft MA5B.

Does any one have any ideas to what could be the cause of this?

73 Dave

On Thu, 18 Mar 2010 16:01:13 -0000, "David"
wrote:

Does any one have any ideas to what could be the cause of this?

Hi David,

Possibly because your feed point is not choked enough.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Thu, 18 Mar 2010 16:01:13 -0000, "David"
wrote:

Does any one have any ideas to what could be the cause of this?

Hi David,

Possibly because your feed point is not choked enough.

73's
Richard Clark, KB7QHC

Hi Richard

I read on the internet, if I use 5x FT-140-43 rings stacked and then loop
the coax through 6 times it would make a good 1:1 choke balun. What do you
think about this type of choke balun for the job?

73 de David

On Thu, 18 Mar 2010 20:01:07 -0000, "David"
wrote:

Hi Richard

I read on the internet, if I use 5x FT-140-43 rings stacked and then loop
the coax through 6 times it would make a good 1:1 choke balun. What do you
think about this type of choke balun for the job?

73 de David

Hi David,

Sounds great if you are doing it.

Are you?

If you are not doing this, or some close approximation, then local
noise is backfilling your received signals (and you are degrading your
antenna's directivity by the same lack of isolation).

If you are doing this, then you may be suffering from a ground loop.
Of course, you can suffer from this by simply trying to fix a ground
loop (there is a lot of myth out there). More could be said, but I
will await to see what you have in place.

73's
Richard Clark, KB7QHC

"David" wrote in
:


The noise level does not change when I turn the beam 360 deg.

You did give S meter readings, but with respect, they are meaningless in
the context you have given. Radios are not iniversally well calibrated,
and most hams could not tell us what radio setting (eg PREAMP ON/OFF) put
the radio in the calibrated mode.

Remember that a directive antenna does not reduce noise that is non-
directional, for all that it reduces noise picked up off the main lobe,
it increases noise picked up on the main lobe.

Ok, we hear that the noise is not strongly directional. You didn't care
to share how you worked that out. If you had an extremely high noise
level, it would quite likely be local, that is the way of things. It it
appears to not be directional, it is probably very close (ie under the
antenna). It could be in your own home, it could be some kind of fault
with the installation.

If it is within your own home, resolution is somewhat simplified. To
clear away your own home as a source, turn EVERYTHING off and run a
receiver on battery. No prizes for missing something, turn things off at
the main switchboard.

Does the noise vary by hour, day? Is it the same level when all the TVs
and Inverter Air Conditioners should be off.

If the noise is excessive, and it is real local, you have the choice of
dealing with the source, and/or reducing your pickup (eg minimising the
effects of feedline common mode current... good coax, effective
connectors, an effecive balun, system grounding).

Owen

"Owen Duffy" wrote in message
...
"David" wrote in
:


The noise level does not change when I turn the beam 360 deg.

You did give S meter readings, but with respect, they are meaningless in
the context you have given. Radios are not iniversally well calibrated,
and most hams could not tell us what radio setting (eg PREAMP ON/OFF) put
the radio in the calibrated mode.

Remember that a directive antenna does not reduce noise that is non-
directional, for all that it reduces noise picked up off the main lobe,
it increases noise picked up on the main lobe.

Ok, we hear that the noise is not strongly directional. You didn't care
to share how you worked that out. If you had an extremely high noise
level, it would quite likely be local, that is the way of things. It it
appears to not be directional, it is probably very close (ie under the
antenna). It could be in your own home, it could be some kind of fault
with the installation.

If it is within your own home, resolution is somewhat simplified. To
clear away your own home as a source, turn EVERYTHING off and run a
receiver on battery. No prizes for missing something, turn things off at
the main switchboard.

Does the noise vary by hour, day? Is it the same level when all the TVs
and Inverter Air Conditioners should be off.

If the noise is excessive, and it is real local, you have the choice of
dealing with the source, and/or reducing your pickup (eg minimising the
effects of feedline common mode current... good coax, effective
connectors, an effecive balun, system grounding).

Owen


If I can here a weak station on any of my other antennas that is fully
readable but weak and I then switch over to the beam the station gets lost
in the noise.
On stations that are a bit stronger but under a S9 after switching to the
beam then there is a noticeable amount of noise in with there audio. Of
course the beam brings the whole signal in a lot stronger as it should do
with but with this large increase of hiss/background noise that is some how
mixed in with there audio that wasn't there before.

I do not get the same noise on any of my other antennas even when they are
positioned in the same spot as the beam and connected to the same coax line.
I have tried the Cushcraft R4 and the R5 the Cobwebb and several mobile
whips and I do not pick the same noise up..

I have had the MA5B down and I cannot see any thing wrong with the
installation.

I have ordered some Ferrite and I will make a coke balun up and see if it
improves.

I will let you know what happens.

"David" wrote in
:

David,

If your tests are not exposed to temporal effects (eg comparing the R4 last
year with the MA5B now), then the reduction in S/N with the MA5B on
boresight is telling. Something is wrong somewhere. (A prophetic statement
I know!)

Some of the earlier suggestions remain relevant. Does the noise in a
battery powered receiver reduce significantly when you turn the power off
to everything in your own premises?

Owen

"Owen Duffy" wrote in message
...
"David" wrote in
:

David,

If your tests are not exposed to temporal effects (eg comparing the R4
last
year with the MA5B now), then the reduction in S/N with the MA5B on
boresight is telling. Something is wrong somewhere. (A prophetic statement
I know!)

Some of the earlier suggestions remain relevant. Does the noise in a
battery powered receiver reduce significantly when you turn the power off
to everything in your own premises?

Owen


Sorry Owen. I forgot to put this in.
I have turned all power off to the house and ran it from a battery. There
wasn't a lot of difference.

Maybe its coming from a neighbours house close by or the overhead power
lines on poles that feed all the homes along this road. I noticed today
there are also some that feed power to the homes over the back as well. But
that doesn't explain the fact that I do not get the same noise from any
other antenna. All antenna tests were all done in the last couple of days.

If the choke doesn't work then I will bring the antenna back down and take
it apart and start a fresh rebuild.
The only thing I can think of that is different is that I used some special
grease from Vine Antennas on all the joints that was advertised for antenna
joints.

David