Cushcraft MA5B Noise floor?
 

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.

Cushcraft MA5B Noise floor?
 

"David" wrote in
:

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

Cushcraft MA5B Noise floor?
 

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

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

Cushcraft MA5B Noise floor?
 

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

Cushcraft MA5B Noise floor?
 

"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

Cushcraft MA5B Noise floor?
 

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

Cushcraft MA5B Noise floor?
 

"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

Cushcraft MA5B Noise floor?
 

"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.

Cushcraft MA5B Noise floor?
 

"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

Cushcraft MA5B Noise floor?
 

"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

Cushcraft MA5B Noise floor?
 

"David" wrote in
:


"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


....
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.

These compounds are often a waterproof grease of some kind with granular
metal particles, often zinc. The concept is that the grease excludes
oxygen and water from the joint and so reduces corrosion, and the
irregular zinc particles improve conductivity by 'punching through' the
oxide layer on the aluminium.

It is conceivable that the stuff you have used may create some kind of
galvanic action which could produce some noise. The goop that I have used
has always worked without apparent problems, but it will depend on the
recipe, and different recipes exist for compatibility with different
metals.

BTW, it is my experience that marine grease does just as good a job on
clean aluminium without being nearly as messy. I use a small stainless
wire brush in a dremel tool to clean the inside of mating tubes, a
regular stainless scratch brush to do the outside, and a little marine
grease on the mating surfaces. Don't be overzealous with the wire
brushing as you embed steel in the aluminium. People often propose non-
metallic scourers, but they also embend non conductive material in the
aluminium surface.

Have you looked for other current loops that could generate noise, AC and
DC. DC loops can be 'powered' by galvanic action from things such as
mixed earth electrodes (eg copper or copper clad electrodes bonded to
galvanised iron water pipes or masts).

Owen

Cushcraft MA5B Noise floor?
 

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


"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


...
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.

These compounds are often a waterproof grease of some kind with granular
metal particles, often zinc. The concept is that the grease excludes
oxygen and water from the joint and so reduces corrosion, and the
irregular zinc particles improve conductivity by 'punching through' the
oxide layer on the aluminium.

It is conceivable that the stuff you have used may create some kind of
galvanic action which could produce some noise. The goop that I have used
has always worked without apparent problems, but it will depend on the
recipe, and different recipes exist for compatibility with different
metals.

BTW, it is my experience that marine grease does just as good a job on
clean aluminium without being nearly as messy. I use a small stainless
wire brush in a dremel tool to clean the inside of mating tubes, a
regular stainless scratch brush to do the outside, and a little marine
grease on the mating surfaces. Don't be overzealous with the wire
brushing as you embed steel in the aluminium. People often propose non-
metallic scourers, but they also embend non conductive material in the
aluminium surface.

Have you looked for other current loops that could generate noise, AC and
DC. DC loops can be 'powered' by galvanic action from things such as
mixed earth electrodes (eg copper or copper clad electrodes bonded to
galvanised iron water pipes or masts).

Owen

I still haven't found enough time to be able to bring the MA5B back down to
ground for a good look and put a good choke balun in line to see if the
noise improves.

I do know that when I purchased the grease it did say its a conductive
grease for aluminium. It didn't come with any instructions so I applied the
grease as thick as I could to prevent any corrosion. It looks like using to
much grease might be all or some of my problem. The only place I didn't put
any grease was on the elements were the matching network connects to. I used
clear silicon sealant for those.

As soon as I can find enough time I will post back with my findings.

Thanks

Cushcraft MA5B Noise floor?
 

On Tue, 30 Mar 2010 09:10:59 +0100, "David"
wrote:

I applied the
grease as thick as I could to prevent any corrosion.

Hi David,

Protection is not often a product of liberal application.

It looks like using to
much grease might be all or some of my problem.

Hard to imagine. If you are clamping things together, the notion of
"too much" takes care of itself. i.e. You cannot have "too much"
toothpaste in the tube if you squeeze hard.

If, as you say, this is "conductive" grease, then clamping down hard
also brings electrical continuity and there is no issue of having "too
much" grease.

So, what this basically devolves to is: "did you apply enough
clamping?"

The only place I didn't put
any grease was on the elements were the matching network connects to.

Why?

I used
clear silicon sealant for those.

This has an acid base (depending upon the formulation being one of the
common, garden variety sealers) that sometimes brings problems of
corrosion. Again, this depends on the formulation.

However, the noise you describe is not one ascribed to grease in any
form, nor to sealants whatever their propensity is for corrosion.

73's
Richard Clark, KB7QHC

Cushcraft MA5B Noise floor?
 

"David" wrote in
:

....
The only place I didn't put any grease was on the elements were the
matching network connects to. I used clear silicon sealant for those.

Was it a water based silcone sealant? I have observed high VSWR and noise
on an antenna feed that used such, until the stuff had thoroughly dried /
cured. It does not seem to be affected by rain since the initial cure.

If it was not a neutral cure silicone, perhaps there is something galvanic
going on?

Owen

Cushcraft MA5B Noise floor?
 

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

...
The only place I didn't put any grease was on the elements were the
matching network connects to. I used clear silicon sealant for those.

Was it a water based silcone sealant? I have observed high VSWR and noise
on an antenna feed that used such, until the stuff had thoroughly dried /
cured. It does not seem to be affected by rain since the initial cure.

If it was not a neutral cure silicone, perhaps there is something galvanic
going on?

Owen

It was normal sealant silicone from a diy store.

Cushcraft MA5B Noise floor?
 

"David" wrote in
:


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

...
The only place I didn't put any grease was on the elements were the
matching network connects to. I used clear silicon sealant for
those.

Was it a water based silcone sealant? I have observed high VSWR and
noise on an antenna feed that used such, until the stuff had
thoroughly dried / cured. It does not seem to be affected by rain
since the initial cure.

If it was not a neutral cure silicone, perhaps there is something
galvanic going on?

Owen

It was normal sealant silicone from a diy store.

What is "normal".

There are two kinds commonly available, neutral cure and acetic acid
cure. Some of the neutral cure ones are water based (ie water washup of
un-cured material).

If you use acetic acid cured silicone on metals, it corrodes them.
Silicone sealants intended for roofing will have a neutral cure.

Do you know what you used?

Owen

Cushcraft MA5B Noise floor?
 

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


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

...
The only place I didn't put any grease was on the elements were the
matching network connects to. I used clear silicon sealant for
those.

Was it a water based silcone sealant? I have observed high VSWR and
noise on an antenna feed that used such, until the stuff had
thoroughly dried / cured. It does not seem to be affected by rain
since the initial cure.

If it was not a neutral cure silicone, perhaps there is something
galvanic going on?

Owen

It was normal sealant silicone from a diy store.

What is "normal".

There are two kinds commonly available, neutral cure and acetic acid
cure. Some of the neutral cure ones are water based (ie water washup of
un-cured material).

If you use acetic acid cured silicone on metals, it corrodes them.
Silicone sealants intended for roofing will have a neutral cure.

Do you know what you used?

Owen

Thanks for the explanation. I didn't know that the did a neutral (water
based silicone).

The one that I have used is the acetic acid cured silicone.

Cushcraft MA5B Noise floor?
 

"David" wrote in news:Wpitn.580013$DL1.346763
@newsfe25.ams2:

The one that I have used is the acetic acid cured silicone.

Then it is corrosive on aluminium. The galvanic currents created may be
causing or contributing to your noise problem.

I would be removing the stuff, difficult as it is to do, but if it is in
contact with metal, it is not suited to your application.

Owen

Cushcraft MA5B Noise floor?
 

"Owen Duffy" wrote in message
...
"David" wrote in news:Wpitn.580013$DL1.346763
@newsfe25.ams2:

The one that I have used is the acetic acid cured silicone.

Then it is corrosive on aluminium. The galvanic currents created may be
causing or contributing to your noise problem.

I would be removing the stuff, difficult as it is to do, but if it is in
contact with metal, it is not suited to your application.

Owen

Ok Owen. I will remove it as soon as I get the time to bring it back down to
ground level.

Thanks

Cushcraft MA5B Noise floor?
 

Hi all

I took down the antenna and I could not find any fault with it. I decided to
move the antenna down the bottom of my garden @ 20ft off the ground and hay
presto. Every thing is working 100%. All my hiss is gone. I can only think
that it must have been caused by some thing very near to my house.

Thanks all

I'm now a happy chappy.

73
"David" wrote in message
...

"Owen Duffy" wrote in message
...
"David" wrote in news:Wpitn.580013$DL1.346763
@newsfe25.ams2:

The one that I have used is the acetic acid cured silicone.

Then it is corrosive on aluminium. The galvanic currents created may be
causing or contributing to your noise problem.

I would be removing the stuff, difficult as it is to do, but if it is in
contact with metal, it is not suited to your application.

Owen

Ok Owen. I will remove it as soon as I get the time to bring it back down
to ground level.

Thanks

Cushcraft MA5B Noise floor?
 

David Inscribed thus:

Hi all

I took down the antenna and I could not find any fault with it. I
decided to move the antenna down the bottom of my garden @ 20ft off
the ground and hay presto. Every thing is working 100%. All my hiss is
gone. I can only think that it must have been caused by some thing
very near to my house.

Thanks all

I'm now a happy chappy.

73
"David" wrote in message
...

"Owen Duffy" wrote in message
...
"David" wrote in
news:Wpitn.580013$DL1.346763 @newsfe25.ams2:

The one that I have used is the acetic acid cured silicone.

Then it is corrosive on aluminium. The galvanic currents created may
be causing or contributing to your noise problem.

I would be removing the stuff, difficult as it is to do, but if it
is in contact with metal, it is not suited to your application.

Owen

Ok Owen. I will remove it as soon as I get the time to bring it back
down to ground level.

Thanks

Its surprising how much noise and interference is generated by or in our
own home.

--
Best Regards:
Baron.