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[SPAM]Re: [CrossCountryWireless] Antenna Isolator install


Chris Moulding
 

The antenna and loop counterpoises are isolated from ground. The wire in the loop counterpoises is insulated and is laid directly on the ground to couple capacitively to ground.

The existing ground radial system was removed and replaced with the loop counterpoises.

If you were to use or follow the transformer design with the capacitors to counteract leakage inductance in the transformer it has an excellent match to 50 ohms so would work with the matching stub on your feeder. If you have already spent a lot of time optimising the tuning of a multiband vertical the transformer can be connected in circuit with very little difference needed to the antenna tuning. There were no changes needed on the two antennas I built to test the design.

Regards,

Chris


On 19 Sep 2020, at 11:25, Will Grocott <wjcgrocott@...> wrote:



I’ve just read the article Chris, very interesting. I have a ground mounted Butternut with a radial plate and wire radials like you describe in your article, I have tried many things to reduce the noise on 20/30/40/80m but without much success. I’m sure most of this is being coupled into my current ground system from the local houses.

I have a 10x10m garden so I might experiment with some loops of different sizes. A couple of questions:

1) Did you completely disconnect the ground radial system and replace it with the loop(s)?
2) The Butternut has a matching stub for 20m in the feedline back to the shack, I’m not sure if this would now work as it is isolated from the ground side of the antenna...

I like the isolation and protection on the ground side. I will need to give this a bit more thought as to how I could try it with my current installation. 

Thanks again for sharing your ideas. Great work
Will
2E0WCJ


Simon
 

Hi Chris..any chance of a copy?please..

Question..you say remove existing gnd system..this by disconnecting ( easy) or digging up? ( impossible.)


Chris Moulding
 

Disconnecting the existing ground system would work OK.

Regards,

Chris

On 19 Sep 2020, at 12:01, Simon <@Zen> wrote:

Hi Chris..any chance of a copy?please..

Question..you say remove existing gnd system..this by disconnecting ( easy) or digging up? ( impossible.)







Bob G3REP
 

Could the difference be a result of using isolating transformer you used as per your diagram. That is assuming you did not have it in place with the grounded vertical ?

Or did I miss something in the detail?
73s
Bob
G3REP


Chris Moulding
 

It's a combination of a few factors.

I found that using two or more loop counterpoises isolated from the ground greatly reduced capacitive coupling to nearby electrical systems compared to radials and straight counterpoises.

The isolation transformer is used to isolate the antenna and loop counterpoises from the incoming co-ax feed that will be connected to a RF noisy electrical ground at the transceiver.

Using both together reduces the noise floor dramatically as I show in the table in the article showing the measured noise levels across the HF bands.

What I couldn't add to the article is that two weeks ago we had a power cut where a digger cut the supply cable to the local substation. All power in the surrounding area had gone so I used the opportunity to use a 12 V battery to measure the HF noise levels and compare it again when the power came back on. There was only 1 or 2 dB difference in noise level between everything in the local area being off or on so it is really effective at reducing local RF noise.

A loop counterpoise can also be used to improve the performance of a static mobile installation as it increases the capacitance to ground over the vehicle body to ground capacitance. In that situation it doesn't need the isolation transformer as the vehicle is isolated from ground by the tyres.

Regards,

Chris

On 19 Sep 2020, at 18:42, Bob G3REP via groups.io <rparkes197=aol.com@groups.io> wrote:

Could the difference be a result of using isolating transformer you used as per your diagram. That is assuming you did not have it in place with the grounded vertical ?

Or did I miss something in the detail?
73s
Bob
G3REP





Simon
 

Hi Chris

What was the antenna being used on hf?

Simon

On 19 Sep 2020, at 19:41, Chris Moulding <@G4HYG> wrote:

It's a combination of a few factors.

I found that using two or more loop counterpoises isolated from the ground greatly reduced capacitive coupling to nearby electrical systems compared to radials and straight counterpoises.

The isolation transformer is used to isolate the antenna and loop counterpoises from the incoming co-ax feed that will be connected to a RF noisy electrical ground at the transceiver.

Using both together reduces the noise floor dramatically as I show in the table in the article showing the measured noise levels across the HF bands.

What I couldn't add to the article is that two weeks ago we had a power cut where a digger cut the supply cable to the local substation. All power in the surrounding area had gone so I used the opportunity to use a 12 V battery to measure the HF noise levels and compare it again when the power came back on. There was only 1 or 2 dB difference in noise level between everything in the local area being off or on so it is really effective at reducing local RF noise.

A loop counterpoise can also be used to improve the performance of a static mobile installation as it increases the capacitance to ground over the vehicle body to ground capacitance. In that situation it doesn't need the isolation transformer as the vehicle is isolated from ground by the tyres.

Regards,

Chris

On 19 Sep 2020, at 18:42, Bob G3REP via groups.io <rparkes197=aol.com@groups.io> wrote:

Could the difference be a result of using isolating transformer you used as per your diagram. That is assuming you did not have it in place with the grounded vertical ?

Or did I miss something in the detail?
73s
Bob
G3REP









Will Grocott
 

Thank you Chris.
I’ve placed my order and I look forward to seeing it installed and working. I’ll take some measurements and let you know how it goes.

Thanks
Will
2E0WCJ

On 19 Sep 2020, at 20:55, Simon <@Zen> wrote:

Hi Chris

What was the antenna being used on hf?

Simon

On 19 Sep 2020, at 19:41, Chris Moulding <@G4HYG> wrote:

It's a combination of a few factors.

I found that using two or more loop counterpoises isolated from the ground greatly reduced capacitive coupling to nearby electrical systems compared to radials and straight counterpoises.

The isolation transformer is used to isolate the antenna and loop counterpoises from the incoming co-ax feed that will be connected to a RF noisy electrical ground at the transceiver.

Using both together reduces the noise floor dramatically as I show in the table in the article showing the measured noise levels across the HF bands.

What I couldn't add to the article is that two weeks ago we had a power cut where a digger cut the supply cable to the local substation. All power in the surrounding area had gone so I used the opportunity to use a 12 V battery to measure the HF noise levels and compare it again when the power came back on. There was only 1 or 2 dB difference in noise level between everything in the local area being off or on so it is really effective at reducing local RF noise.

A loop counterpoise can also be used to improve the performance of a static mobile installation as it increases the capacitance to ground over the vehicle body to ground capacitance. In that situation it doesn't need the isolation transformer as the vehicle is isolated from ground by the tyres.

Regards,

Chris

On 19 Sep 2020, at 18:42, Bob G3REP via groups.io <rparkes197=aol.com@groups.io> wrote:
Could the difference be a result of using isolating transformer you used as per your diagram. That is assuming you did not have it in place with the grounded vertical ?

Or did I miss something in the detail?
73s
Bob
G3REP