New Sdrplay and antenna creation

[Kenh2os3]

Hi All, my 1st post here,

I have been tinkering with SDR for a while and I really didn't have a lot of room before.

But I just moved to Garland TX, and I bought 3 days ago the SDRplay, I had a SDR-RTL which was marginal at best, but soon I will play with it some more.

So, I wanted to start simple, and after reading this article https://www.sdrplay.com/wp-content/uplo ... DRplay.pdf , I was enlightened. Well, shall we say my light bulb came on to what I forgot.


ALWAYS, ALWAYS, ALWAYS - ground the antenna.

I ran about 100 ft, of what I had available. I had a metal wire from Micheals that looks a lot like wire used for hanging pictires or tieing down nic nac creations. I stung it up along the house to a fence. Using tacks to secure it and redirect it. It's almost a "U" shape. Then I grounded to a nearby water pipe. Attached the ground to the shield of the skinning coax that has the SMA on it, about 10' long, Attached my main U shaped wire one the fence line to the center conductor. All of this was done as just a test. The fence line is about 6' high.

I went to the SDRplaydou software and wow, it worked really well.

Without a ground, all you get is noise unless the stations are really close by.

Sometimes at my age, I feel I have forgotten more then I learned, but hey, what can we say.

Now what I am really after is a dipole that I can put in the back yard, it's about 65' x 50', or a broadband stick that I can mount. I do like the 80m band listening, but it seems so many antennas start at 25 Mhz and go up. I would like to listen from 3.5mhz - 54mhz, but always ready for more listening adventure. Just something simple to make, or cheap to buy. relatively.

Thanks for any links or suggestions,

Oh, and to the great people at https://www.hamradio.com/ Ham radio outlet in Plano, what a great bunch there.

Kenh2os3 - Ken Waters

[M0RON]

Hi Ken,
I'm quite new to sdr as well, if I may make a suggestion, I've just bought a PA0RDT mini whip antenna, good for very low frequency to around 30mhz. It can be built with minimal tools, easily found components and is tiny for a HF antenna, around 3 1/2 inches tall.
I also have a dipole and random wire antenna, which is my Wspr antenna but the mini whip outperforms them both.
Have a listen to the websdr at Twente on the web, one is used for their receive antenna. If you can't or don't want to build it yourself the designer will build for you.
Andy
M0RON

[ON5HB]

Hi Ken,

You do not need to ground the antenna, it's just one way of doing it.
The antenna described in the article is just a wire, as such it doesn't have a counter length.
Grounding can provide that but also adding some length of counter-wire or a fence.

Grounding can attract lightning and as such I'm not a huge fan of doing so, better use a counter-wire, as such you actually create a sort of a dipole.

@Andy, sorry the Mini-Whip does not outperform a dipole, it's not even on par. It's a good antenna when you don't have enough room but it surely doesn't work better then a dipole. Compare it to Hackgreen websdr, that is a double-full-size G5RV (70m long!). http://hackgreensdr.org:8901/
Or you can compare mine, ON5HB websdr that is a full-size G5RV (35m long). http://heppen.be:8091/

Trust me, your mini-whip will not match that.
It's a nice antenna when you lack space.
But if you have space, the full length it better.

[M0RON]

Hi Bas,

At my house the PA0RDT definitely outperforms a dipole I had, linked dipole for 20 and 40m. Noise here is S7 on a good day and S9+ on a bad day. Lots of man made noise here, I live 50 yards from a big school.
I had given up operating from home due to noise and operate portable with S1-s3 noise.
I've recently started wspr and have no problem transmitting and being heard all over the world with 0.2w, on a random wire around 23m long against a good ground system. Receive however was awful.
I installed the mini whip, 4.5m high, lmr400 coax grounded at base of non conductive pole, 10m of lmr400 to a common mode choke and another ground rod, then a small length of lmr400 to the duo. Leo bodnar frequency source attached. Now with SDRuno and WSJT-X I am able to receive more than the dipole gave me.
So in my paticular situation, Yes the mini whip outperforms a dipole.
73
Andy

[Mike2459]

Bas, I took your advice - compared the two G5RV's (yours and Hackgreens) and the Twente sdr : http://websdr.ewi.utwente.nl:8901/ which uses a miniwhip. I'm not going to make any further comments. Make the comparison for yourself and report back.

[glovisol]

My grandfather, a doctor, used to tell his patients, enthousiastic about some medicament, herb or other remedies: "yes, you swear this thing healed you, but perhaps you would have recovered even without taking it....." meaning by this: (1) that no technical solution is generally valid if not resting on solid theory and (2) that comparison is the key to proof.

This tale of the great performance of a small piece of PC board cum MOSFET amplifier, able to outperform medium aperture antennas, like dipoles or other wide band derivates makes me very skeptical, because I have yet to see a convincing theory supporting the operation of this device. All I have seen (perhaps through my ignorance and would be very glad and hope to be contradicted) is that the "small PC board intercepts the "E" field". The shape and the size of the surface of the antenna PC board seem to be "magic " in the sense that, as soon as you alter these dimensions, the antenna does not work any more: perhaps these dimensions are related to the Planck's constant or to the speed of light...

As far as I can see, the PC board antenna is simply a very high impedance capacitive probe suspended in space. The "E" field signals are captured by a very high impedance MOSFET and its output is translated to a low impedance fit for coax (50 to 75 Ohm). This composite amplifier setup, in ancient times, was called "a cascode", nothing new under the sun.

If the above is the theory of the workings of this antenna, then a bigger capacitor will have a bigger aperture and couple more "E" field, thus more signal to the receiver.....but this does not seem to be the case in practice. Another mysterious, but equally unproven theory, is that the coaxial line to the receiver also acts as an antenna, contradicting the "E" field story. If this is the case, then make it very long, guys....

[Mike2459]

If the above is the theory of the workings of this antenna, then a bigger capacitor will have a bigger aperture and couple more "E" field, thus more signal to the receiver.....

You would then need an SDR that could handle the increased dynamic range, the SDRPlay class cannot.

[glovisol]

You would then need an SDR that could handle the increased dynamic range, the SDRPlay class cannot.

Hi Mike,

This would mean that the potential output of this antenna is so big that, as soon as we increase the size of PCB, the RSP Processor would be overloaded. This really seems very unlikely, both in theory and in practice. Considering that the RSP is protected by its built-in input attenuator and band limiting filters, it is more likely to have the capacitive antenna wide band MOSFET amplifier circuit overload first, probably because of strong FM signals, or strong local MW Broadcasting, and not on increased PCB surface, but on the existing, original PCB.

The overload potential of the RSP processors is really much higher than you appear to think and it is easy to compute and compare the overload thresholds of the MOSFET amplifier and of the RSP, based on the SDRplay intercept point published data.

Apart from the above, if what you describe is the case with the PA0RDT antenna, then the RSP connected to my Beverage would simply blow up....

[Kenh2os3]

Accidental Discovery...

Last Night I was using my portable Tecsun PL-660 Outside, I was trying to get a feel for an upcoming thunderstorm. I had the antenna extended and it bumped into the Metal roof of my Carport. I was surprised at the increase in signal level. I was pulling in signal from all over the world, and strong. My favorite 80m band was alive right there on my portable, I had to turn down the AGC on the radio to local,

I never considered this roof, as it is grounded by the metal supports.

I am going to experiment with the SDRplay.

Thoughts, or theories?

Kenh2os

[ON5HB]

What you have "build" is an antenna with grounding at the end.
It's not uncommon and it does work.

Basically you probably made this beverage without knowing:



Funny thing is, the longer the wire is below 80m (especially the very low bands) often the better it works.
You wouldn't believe what is out there, and yes, it works.

When I was young I connected my radio to the central-heating-pipes and it worked very well.