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