RE: LF: F6CNI to night testing a tuned loop TX on MF

[VIGILANT Luis Fernández <luis@vigilant.es>]

Thank you for the spreadsheet Andy

 

I have set the parameters of my loop. As I know the total lenght and capacitor used to tune it

have adjusted diameter to a theoretical circular loop. Don't know the exact resistivity. I'm using

RG58 cable (braid + inner shorted) for the loop. But the 1000pF is close to what I'm using to tune it

8x100pF fixed caps plus about half 490pF variable

 

Resuls can be seen here on this screenshot

https://dl.dropboxusercontent.com/u/7162072/Fotos%20varias/MF/70m%20MF%20Loop%20at%20100W%20.png

 

The voltage and currents figures explain why I can not use it when sun is heating the matching capacitors and feed transformer

And also why I burned out my RF current sensing system

 

Anyway the calculated ERP looks quite high. Not sure if there is something wrong with the provided data

 

Unfortunately, the loop is horizontal. No way to turn it vertical :(

 

73 de Luis

EA5DOM

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De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de Andy Talbot
Enviado el: martes, 28 de julio de 2015 11:13
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: F6CNI to night testing a tuned loop TX on MF

That is interesting, and encouraging.  I inserted your loop parameters into a spreadsheet I wrote many years ago in the early days of LF to calculate the properties of loop antennas.   As the spreadsheet is designed to work with circular l loops I used a diameter of 9.45m to give the same area as your 7m x 10m rectangular loop.

The results come out very close to the values you give from measurement.

and for your loop, the spreadsheet figures can be seen below:

The ERP for 1W of RF shows as -22.5dBW which is so close to your 6mW as to be almost impressive!

The spreadsheet (with different values inserted) can be found at http://www.g4jnt.com/DownLoad/MagLoop.xls

Andy  G4JNT

Frequency	0.475	MHz		Loop area	70.14	m^2
Loop Diameter	9.45	m		Radiation res	9.64E-04	Ohm
Conductor dia	10	mm		Tot Cond Length	29.69	m
No. Conds. (Litz)	1			Winding Length	29.69	m
No. of turns	1			Inductance	41.16	uH
Resistivity	1.7E-08	Ohm/m		Skin depth	9.52E-05	m
rel Permeability	1			RF Resistance	0.169	Ohm
				Xl	123	Ohm
Tx Power	1	W		Q	724
				Bandwidth	656	Hz
				Efficiency	0.0057
				"	-22.5	dB
				Resonate Cap	2.7	nF
				Current	2.4	A
				Voltage	298	V
				ERP	-22.5	dBW

On 28 July 2015 at 09:54, F6CNI - Andy - JN19QB <f6cni@orange.fr> wrote:

Yes Alan.

 

I just compute the loop antenna using the new EZNEC Pro V 6.0

 

As you predicted the front to side is sharp and deep only at very low angles, that means for ground waves on day light.

 

About the DK7FC night reports : his location is at 45° azimuth outside my loop plane, and 390 km of distance means a site wave of about 55/60° for an usual F1 + F2 layer at a night altitude of 350 km. In that case, the signal is only 0.8 dB lower than a signal coming at same distance and in the plane of the loop.

 

For long distance, as 2° site angle for 3500 km, the front to side is not 0.8 dB but 20 dB….

 

On the way, I just made very accurates measurements on this transmitting loop antenna. In accordance with the EZNEC, I found for 1 Watt TX, 6 milli watt EIRP. This is an average value for 20° to 80° site waves. With 6 mW EIRP, a night report of -16 dB at 390 km is normal when the MF band is very quiet as last night.

 

Andy.

 

 

From: Alan Melia

Sent: Tuesday, July 28, 2015 12:29 AM

To: rsgb_lf_group@blacksheep.org

Subject: Re: LF: F6CNI to night testing a tuned loop TX on MF

 

I think there is quite a lot of high angle off the side......the "null"is only at zero degrees elevation.??

 

Alan

G3NYK

----- Original Message -----

From: DK7FC

To: rsgb_lf_group@blacksheep.org

Sent: Monday, July 27, 2015 11:03 PM

Subject: Re: LF: F6CNI to night testing a tuned loop TX on MF

 

Hello Andy,

How is this possible? Your Loop points to SE, my loop also points to SE. But we are not in one line. Actually it would be best for us if our loops would point to NE.
But i can receive you at -16 dB SNR in WSPR with 1 mW ERP ??

73, Stefan