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Galvanised wire properties


paul newland
 

A little while ago I knocked up an inverted delta loop, with a 1.25Msq + aperture made from 2 mm galvanised fence-wire attached to a Loop Antenna Amplifier+. This has been highly successful (although I have been made aware that this choice, whilst good for the lower end of the shortwave spectrum, will likely drop off from upwards from 18 Mh). I suppose that I should have stopped there, but being curious, I wondered whether 7 strand  2 mm galvanised  wire rope might offer a greater galvanised surface area and whether this might enhance reception further. If anyone can answer this question, I would be grateful.
However, the net result is that using the said wire rope in the same configuration (for whatever reason), the signal strength has increased noticeably, without any obvious worsening of the SNR.
As an aside, in idle moments, I have a dabble in the NDB frequency range and this setup is so good as to be rather demanding, in that, whilst I am seeing all the same beacons as previously, that I have logged over time (with my well-respected old loop), plus one ore two more, it's taking ages to wade through them all.
I don't believe that my old setup has in any way deteriorated and it still works very well over it's full 10 Khz - 30 Mhz range.


Chris Moulding
 

Hi Paul,

I know from discussions between us that you are trying to emulate the galvanised wire loop that Mike Ladd uses with a Loop Antenna Amplifier + to great effect for his SDRPlay videos and samples.

It sounds from your description that it's working well for you.

Usually I would recommend a loop of 1m or 3ft diameter so that it covers the full HF spectrum up to 30 MHz. If your interests don't cover the higher HF bands then you can use a larger loop. Your triangular loop has sides of 1.25m and Mike's has 1.5 m sides.

The use of galvanised wire is interesting. Usually steel wire is a poor choice for antenna or loop wire due to the magnetic properties concentrating the skin effect into a very thin layer on the surface.

With galvanised wire the RF current will be concentrated into the zinc coating. The resistivity of zinc is 3.2 times that of copper so the losses will be higher.

Another point that may be significant with some receivers is that a 1m diameter loop is resonant around 100 MHz so VHF FM broadcast signals may be very strong and overload the receiver.

A triangular loop with 1.5 m sides will be resonant around 60 MHz reducing the level of VHF FM broadcast signals.

It's interesting to consider why it should work so well, if I can get some galvanised wire locally I'll try one myself.

Regards,

Chris


Simon
 

Yes. It should not work well..though is for rx only..

A thought..have you tried comparing against similar dia copper wire? Thus getting a “ bench mark” to compare against.

Mag loop simon g0zen


Chris Moulding
 

That's a good point.

I've already sourced a roll of 2mm galvanised wire online so I'll run some comparison tests when it arrives.

Regards,

Chris


Brian
 

Chris,
        I am  following the wire thread with interest.
 
For many years I used 1mm  aluminium wire for a full wave horizontal loop on 40m
erected at 10m above the back lawn and with 5 watts SSB from a Kenwood TS-130V
worked the world.
 
The wire was used at work for securing insulation  sections to pipework   before being cemented over.
 
It seems widely advertised on the Internet for floristry / jewellery work.
 
The wire came in a coil appx 0.5m dia. one thing to avoid was to let it escape ‘ captivity hi!
 
                                                      Best wishes and stay safe,
                                                                72  Brian G0NSL.
 

Sent: Wednesday, September 23, 2020 6:36 PM
Subject: Re: [CrossCountryWireless] Galvanised wire properties
 
 


paul newland
 

An apology - My schoolboy triangular area math was too long ago and I have re-calculated the aperture to be about 1.62 Msq.
In his first post concerning this build, I believe that Mike wrote that he had used about 16' of wire, so I did the same "about."
Having done my re-vamp with wire rope, I have used about 15.9' or 4.85M in the build.
I do look forward to seeing a "proper" comparison as my results speak only for my individual setup.
So far, up to the 20M band the "+" outperforms the other loop, with few exceptions. My SNR comparison is equivocal, sometimes being better, sometimes worse than the other.
Still really chuffed with it, although I understand that galvanised deteriorates over time. However, it's cheap and easy to replace,


paul newland
 

It seems only right to report what may be perceived as a downside to my experience with this antenna build.
I have found that on very strong signals, such as BBC 198 Khz and 693 Khz there is a a marked tendency to overload, However, this does not cause me a problem, as reducing gain (considerably) produces a good and clean signal.
In general I find that I can reduce gain from slightly on most signals received.to good effect.
Is this a negative feature?


Chris Moulding
 

No it's not a negative feature.

All SDR receivers such as the SDRPlay receiver you are using have a fixed maximum limit that the analog to digital converter can process.

The RF gain control is used to wind the gain down to keep the maximum signal below this point.

It allows you to get the maximum dynamic range from the receiver. You should now be able to hear signals way down in the noise while still having BBC 198kHz on your SDR display.

All the old timers among us who started with what are now vintage valve or tube short wave receivers soon learned that the RF gain control was the most used control on the receiver next to the tuning knob. Being able to control the level of very strong signals while listening to the faint ones was a skill that was soon picked up!

Regards,

Chris


Simon
 

To illustrate what Chris said.

I always wanted a yaesu ft707 since I was 14. Just a few weeks ago bought one now silly cheap.( 40 plus years later.)

Wow the rx was rubbish ..far too much rf gain..s9 plus 20 back ground noise plugged into the dipole on 40m (7mhz.)totally overloading the rx.

No real rf gain control, it does have one but just attacks the agc line and makes it “ deaf”.

So modded it to leave the agc just controlling the if stages and not the rf preamp fet..wired the rf preamp fet to the rf gain control.so now i have full control of front end gain and the agc is working on the if stages..

This means I have -60 to + 20db (or so ) gain on the preamp.

It now is a pleasure to use! Infact (apart from the if filters not as brick wall as the sdr ) nicer to use than the elad duo..just as sensitive and fun..

Rf gain control = ability to weed out weak signals ( along with good aerial!) and now days here in urban city a noise phaser canceller..

Re 909khz etc..if a major issue it can be notched out with a very simple circuit inline with your antenna.
Of course you could try nulling it out with the loop..

Mag loop Simon


Paul Newland
 

Thanks Simon
Very kind of you to point that out.
However, it isn't actually a problem as I do have good control over gain which is all that is neede (I think).
Best Wishes
Paul



Virus-free. www.avg.com


On Fri, 25 Sep 2020 at 10:49, Simon <ohhellnotagain@...> wrote:
To illustrate what Chris said.

I always wanted a yaesu ft707 since I was 14. Just a few weeks ago bought one now silly  cheap.( 40 plus years later.)

Wow the rx was rubbish ..far too much rf gain..s9 plus 20 back ground noise plugged into the dipole on 40m (7mhz.)totally overloading the rx.

No real rf gain control, it does have one but just attacks the agc line and makes it “ deaf”.

So modded it to leave the agc just controlling the if stages and not the rf preamp fet..wired the rf preamp fet to the rf gain control.so now i have full control of front end gain and the agc is working on the if stages..

This means I have -60 to + 20db (or so ) gain on the preamp.

It now is a pleasure to use! Infact (apart from the if filters not as brick wall as the sdr ) nicer to use than the elad duo..just as sensitive and fun..

Rf gain control = ability to weed out weak signals ( along with good aerial!) and now days here in urban city a noise phaser canceller..

Re 909khz etc..if a major issue it can be notched out with a very simple circuit inline with your antenna.
Of course you could try nulling it out with the loop..

Mag loop Simon





Simon
 

Yes sure you have it in hand..
Was more aimed at others who reading..you be surprised how many “readers” there are.




On 25 Sep 2020, at 13:48, Paul Newland <newland.newland@...> wrote:


Thanks Simon
Very kind of you to point that out.
However, it isn't actually a problem as I do have good control over gain which is all that is neede (I think).
Best Wishes
Paul



Virus-free. www.avg.com

On Fri, 25 Sep 2020 at 10:49, Simon <ohhellnotagain@...> wrote:
To illustrate what Chris said.

I always wanted a yaesu ft707 since I was 14. Just a few weeks ago bought one now silly  cheap.( 40 plus years later.)

Wow the rx was rubbish ..far too much rf gain..s9 plus 20 back ground noise plugged into the dipole on 40m (7mhz.)totally overloading the rx.

No real rf gain control, it does have one but just attacks the agc line and makes it “ deaf”.

So modded it to leave the agc just controlling the if stages and not the rf preamp fet..wired the rf preamp fet to the rf gain control.so now i have full control of front end gain and the agc is working on the if stages..

This means I have -60 to + 20db (or so ) gain on the preamp.

It now is a pleasure to use! Infact (apart from the if filters not as brick wall as the sdr ) nicer to use than the elad duo..just as sensitive and fun..

Rf gain control = ability to weed out weak signals ( along with good aerial!) and now days here in urban city a noise phaser canceller..

Re 909khz etc..if a major issue it can be notched out with a very simple circuit inline with your antenna.
Of course you could try nulling it out with the loop..

Mag loop Simon