RA0SMS Miniwhip bad performance on SDRPlay

Useful information regarding antennas for SDR products.
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Re: RA0SMS Miniwhip bad performance on SDRPlay

Postby Paul » Wed Sep 13, 2017 2:19 pm

I am strictly non-technical, but this is my experience -I also have one of these antennas feeding my RSP2.
As this receiver has a choice of three ports, it is attached to Port A.
Port B is a H/V/UHF discone and an end-fed longwire (with a 9:1 balun) is attached via the HI-Z Port.
In summation, with experience, I have found that the mini-whip is noisier than the longwire, but may equal or exceed it's signal strength on occasion, under certain conditions and with LNA adjustment.
It is mounted, duct-taped to the top of an 8M non-conductive pole, with the RG-58 coax shield grounded to an earth spike, it's power unit is supplied via a good quality 12V supply with well over the minimum milliamps necessary and earthed to a copper cold-water rising main pipe.

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Re: RA0SMS Miniwhip bad performance on SDRPlay

Postby DanubeBCL » Wed Sep 13, 2017 3:47 pm

ha4006swl wrote:I had very clear reception until may, when the ventillation system of the building is modernized, and added inverters to the fan engines. The result is S6-S9 noise around from 8 to 17 MHz.
Yes, noise generators are becoming more and more. Photovoltic inverters, lawn mowing robots, switched power supplies, DSL leaks, charging docks for pedelecs and electric cars ... and here in Europe above all those evil powerlan modems (PLC). This is our fate. And no authority cares, no market supervision takes action. It's a hazardous game to purchase a VLF...SW receiver and equipment nowadays.
73, Heinrich

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Re: RA0SMS Miniwhip bad performance on SDRPlay

Postby ToryGlenn » Sat Jun 02, 2018 2:22 pm

I bought one of these antennas and am also very disappointed by its performance with my RSP1A. I was truly hoping this antenna would help capture those weak signals. Instead, all it does it generate a ton of noise and overload. I also hear annoying buzzing on commercial shortwave broadcasts.

The thing that puzzles me is the 'weight' (or lack of) that makes me wonder what is in the tube. I made a different PA0RDT antenna, and the circuit board alone seems like it weighs more than the PAORDT. I'm almost tempted to cut open the tube to see what's inside. Or more like, what isn't inside.

My inverted V dipole does a better job than the mini-whip as far as tuning in commercial shortwave broadcasts, and I don't have to worry about distortion or noise accompanying the signal.
Last edited by ToryGlenn on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Re: RA0SMS Miniwhip bad performance on SDRPlay

Postby ToryGlenn » Sat Jun 02, 2018 5:56 pm

I was able to pry off the bottom 'cap' of the RAOSMS mini-whip (the end with the BNC) and I found a 'wedge' of foam (like styrofoam) coming in contact with the pc board, but acting as a spacer for the 'wire' antenna inside the tube. Is it possible this piece of foam could be causing more problems than it solves? I would think putting a piece of styrofoam inside the tube with the pc board could create static, which would interfere with the performance of the antenna.

The piece of wire attached to the pc board is stiff enough to stand up on its own without the styrofoam chunk. So, I'm not sure what purpose it serves.
Last edited by ToryGlenn on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Re: RA0SMS Miniwhip bad performance on SDRPlay

Postby vk7jj » Sun Jun 03, 2018 1:05 am

Anyone in a noisy environment interested in low noise HF antennas should surely avoid short whips and end fed wires. It's hard to imagine anything less efficient on HF than a short length vertical whip and putting a preamp on the end of one is worse.

There are great solutions that cost almost nothing all over the internet, here is one whose second paragraph could possibly have been written by Heinrich as per his excellent comments above, both are a sad testimony to our deteriorating RF environment.

You can tell immediately this author is a dedicated radio enthusiast by his garden, and the roof on the clothesline is surely testimony to his inventiveness.

~ apologies for my warped sense of humour, but it's an article that really does make a good case.

http://users.monash.edu.au/~ralphk/shie ... tenna.html

Cheers, Phil VK7JJ

----- eg. modelling a short vertical on HF:

length of vertical = 0.5m
end fed against perfect ground, on a frequency of 1MHz it has a feed point impedance of 0.0095 ohms and a reactance of -31622 ohms producing a 50ohm SWR of 1999999 : 1

And that's without any consideration of the non-merit of being a vertically polarised antenna which is best designed to pick up low angle man made noise rather than with any idea of the vertical angle of propagation of the frequency of interest, eg. local HF is going to be NVIS and distant HF is determined by wavelength and distance, with thousands of articles on the internet discussing those sorts of things.

Antenna researching, designing, building and modelling with free software, (eg. try MMANA) is one of the few fantastic, inexpensive and exciting facets of the hobby!

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