Bias T and active mini-whip

Useful information regarding antennas for SDR products.
sdrplay
Posts: 575
Joined: Wed Jan 07, 2015 7:58 am

Re: Bias T and active mini-whip

Postby sdrplay » Tue Jul 04, 2017 5:38 am

There is a bug with the Bias T setting in SDRuno and it will be fixed in the next release.

Best regards,

SDRplay Support

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Paul
Posts: 77
Joined: Fri Feb 17, 2017 9:52 am

Re: Bias T and active mini-whip

Postby Paul » Tue Jul 04, 2017 8:50 pm

For Heinrich and Andy
Thanks for the support and advice with regard to my active mini-whip antenna problems.
I have isolated the problem to an intermittent short (I think) in the RG58 cable (an old run).
I have replaced this in part and the problem appears to have gone away.
All power supplies and antenna checked out OK, so my problem is (hopefully) solved.
For info only - the RA0SMS mini-whip is now mounted on an 8M non-conductive mast with the coax grounded (instead of atop a base pate on an alloy pole) and working well.

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DanubeBCL
Posts: 168
Joined: Sat Jul 02, 2016 12:39 pm

Re: Bias T and active mini-whip

Postby DanubeBCL » Wed Jul 05, 2017 6:50 am

Paul wrote:the RA0SMS mini-whip is now mounted on an 8M non-conductive mast with the coax grounded
Hi Paul,
that's how it is recommended. Quote of PA3FWM (the creator of the famous Twente WebSDR) on "Grounding of MiniWhip and other active whip antennas":
What can be done to improve the situation? Firstly of course, improving the grounding of the mast, or if the mast is non-conductive, making a connection between the cable's shielding braid and a ground electrode...
http://www.pa3fwm.nl/technotes/tn09d.html

And shorts on a coax cable (or plug/socket) happen more often than one might think, especially when you are tinkering a lot. Yesterday I managed to shorten my 24 V feed for my active antennas. Fortunately there was only a big spark when a 6800 µF capacitor was discharged, but all components survived. Such things happen :cry: .
73, Heinrich

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Paul
Posts: 77
Joined: Fri Feb 17, 2017 9:52 am

Re: Bias T and active mini-whip

Postby Paul » Wed Jul 05, 2017 7:39 am

And one very last thing Heinrich (if you have the time)
Now that all is hopefully in order, would you consider that there is any advantage from moving from my serviceable (switched) 12v/1200ma half-brick to the 13.8V/5-7Amp more sophisticated unit?
It does seem like a no-brainer, but what you said about "tinkering" certainly applies to me.
Best Wishes
Paul

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DanubeBCL
Posts: 168
Joined: Sat Jul 02, 2016 12:39 pm

Re: Bias T and active mini-whip

Postby DanubeBCL » Wed Jul 05, 2017 10:43 am

Paul wrote:from my serviceable (switched) 12v/1200ma half-brick to the 13.8V/5-7Amp more sophisticated unit?
Generally switched PS are not very much loved by radio amateurs. They cause high RF noise which is spreading all over the power lines in the house and beyond. I have several neighbours in appr. 80 m distance and I can receive the harmonics of their switched PS of their tellys and other "modern" devices in my antennas. As soon as TV primetime begins they are coming up one after the other.
But not all switched PS are bad by design. Some manufacturers equip them with filters, but often the manufacturers save every penny for a coil or capacitor. I would suggest that you try out. When you receive strange buzzing noise patterns repeating every 50...200 kHz especially on the lower bands (but I have seen them up to 25 MHz as well), your switched PS is not suitable. When you see no difference you can keep it and save the 7 A brick for other purposes.
73, Heinrich

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Paul
Posts: 77
Joined: Fri Feb 17, 2017 9:52 am

Re: Bias T and active mini-whip

Postby Paul » Thu Jul 06, 2017 1:33 pm

Thanks again for your time and interest Heinrich - I will do just that. And just by the way, the mini-whip now compares very favourably with my 20M simple longwire .
I'm beginning to think that antennae can become an addictive obsession.
Best Wishes
Paul

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