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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Sat Jul 13, 2019 6:00 pm
by sdrom33
Hi Phil & Gianfranco, it seems to me that this thread, that had to be closed, because it had become "toxic" according to some guys, is by contrast showing a lot of useful information on small antennas. This is a lesson to us all that a good discussion on technical problems and data is only "toxic" for some egos, but can be very useful for most of us. Pse keep up the good work!

Thomas

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Sat Jul 13, 2019 6:42 pm
by glovisol
More reception examples with non-optimized original cross pallet loop antenna.

The peculiar thing, that comes to attention at once, is the low level of backgrund noise: under these conditions, signals at levels of -115 to -120 dBm are easily copied witout problems, even if the S meter shows S1 to S3.

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Sat Jul 13, 2019 6:47 pm
by glovisol
And this evening at 18:45 GMT with good propagation......

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Sun Jul 14, 2019 5:09 pm
by glovisol
Hi Phil,

You have really convinced me and surely I am going to put up a big loop antenna once I get home in August. Here at the sea side I did not have any antenna at all and fortunately followed your suggestion and started experimenting with small loops. The results are incredible, because I see plenty of signals in the ham bands from 3.65 to 14.3 Mhz, while I have seldom experienced such remarkably low noise levels. The result is that I start copying a signal and then I jump on the chair when I realise I am copying quietly and peacefully a signal at a level of -120 dBm!!

Before the discovery of the loop, I used to set up a "long wire" about 15 m long and tie the return to a water pipe. Then thru the low noise transformer to the HI Z input of the SDRduo. It goes without saying I could copy shortwave broadcast stations, but nothing else. It was a great evening when I could get a ham on 40 m. Signals were weak and noise levels in the order of -100 / -110 dBm. Now with the loop we are below -120 dBm and better, depending on the frequency.

Today I have "optimized" the efficiency of the "space taken" by the antenna (plenty of pallet wood on my hands): I have built a square around the cross, so the side has gone from 88 cm to 129 cm and I shall see the improvement this evening.

Hope to get the toroids tomorrow.

Kind regards,

Gianfranco

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Sun Jul 14, 2019 7:27 pm
by glovisol
Hi Thomas.

I agree with you, even if we should understand that words perhaps written in anger are not really meant and should be quickly forgotten. But you are right in observing that this thread, born under such unhappy auspices, has turned to the better. Now, thanks to Phil's suggestions and help, I know from my own experience, and perhaps a lot of people reading this thread do too, that if one lives in a small apartment, like I am doing these days, he can, in a short time and with little effort, cook up an antenna that will allow him to operate an RSP Processor with reasonable results, spending a few cents of insulated electrical wire and wood self tapping screws (provided he can safely steal a pallet). I have now modified the antenna obtaining a significantly larger aperture area and shall post results next.

I intend to more deeply investigate this small antenna solution in the next few days and seriously test the wideband matching method later on, when I get back and have my lab facilities in hand.

Kind regards,

Gianfranco

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Mon Jul 15, 2019 10:13 am
by vk7jj
Let's get back to antennas, wonderful things that they are.

Yes, I bet you can't wait to have a play with longer lengths of wire at home.

Even if we all lived in a perfect noise free environment there is clearly a point where the desired signal voltage from a small antenna falls below the level where whatever RF gain one has is still not enough to raise the wanted signal above the noise floor of the receiver.

Put another way, it's clear that many people have limited space but do they really *have* to go out and buy the ubiquitous physically small loop or mini-whip?

I absolutely love trying to give people a bit of understanding of the issues and encourage them to have a go at building something for themselves, as large as their living space will permit. At the end of the day, if it is to be a small loop then try the hula hoop!

https://www.sdrplay.com/community/searc ... words=hula

Large or small, these loops are simple antennas with simple feed systems that are very inexpensive and can so easily be whizzed up if people feel it is worthwhile. That's why I value your efforts so much, what you are doing empowers people.

Phil

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Mon Jul 15, 2019 2:41 pm
by glovisol
Hi Phil, it is exactly that. You pushed me and I am now going full blast.

Yesterday I increased the side of the square from 88 cm to 1.29 cm. The practical footprint space actually taken by the antenna is the same, but the capture surface has more than doubled, from 0.77 sq. metres to 1.66 sq. metres. Using the original "small" antenna in the last few days, it was evident that performance became better and better going up from 3.65 MHz to 14.3 MHz.

Now, with increased dimensions, performance improved slightly at 14.3 MHz, but had a very significant improvement at 3.65 MHz, as proven by the screen enclosed below. No toroids yet, but I keep looking forward to them.

Rather than hula hops, I am thinking of an all stainless steel (or copper) square made with tube shafts tapped at the ends and screwed into machined corner ends. This would be the perfect portable antenna: you carry it in a golf bag and you deploy it anywhere, or you keep it at home and assemble it when needed. I think we are making quite a progress with respect to whips (!) or amplified printed circuit boards. If the new wideband matching works as well, then we shall have a bomb. Please advise me on possible flaws in this scheme.

Of coure we are covered down to 3.65 MHz only, and at the limit there, but lower than that we come into the domain of "large" ferrite antennas and this is a new world to explore. Luckily a fantastic amount of information is available here, even though large ferrite sticks are quite expensive.


Kind regards,

Gianfranco

Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Posted: Tue Jul 16, 2019 12:39 am
by vk7jj
glovisol wrote:I am thinking of an all stainless steel (or copper) square
A quick note on stainless, here is a pic of a full size 160m delta using copper, aluminium and steel wire.
Copper is line 1, aluminium line 2 and steel line 3. Wire radius is 0.8mm in all cases.
Screen Shot 2019-07-16 at 10.36.29 am.png
Screen Shot 2019-07-16 at 10.36.29 am.png (50.89 KiB) Viewed 2145 times
Look at the R (ohms) and weep! Unless you want a great SWR on transmit and don't mind keeping the sparrows feet warm!

Best regards, Phil

Edit:

To clarify, R (Ohms) is the sum of the antenna's radiation resistance and the wire's inherent resistive loss.
The figures given are at the fundamental frequency of the loop which is 1.8MHz, chosen because it provides a low radiation resistance and thus makes the wire loss all the more obvious as it is a larger percentage of the total resistance, ie. 163 ohms of resistive loss in the wire compared with a radiation resistance of around 20 ohms.

Small loop R as we know is a fraction of an ohm at or below their fundamental frequencies and lots of efforts goes into making the resistive losses of so called magnetic loops as low as possible.