RSP2 with ALA1530 Antenna

Useful information regarding antennas for SDR products.
kjdahlen2
Posts: 5
Joined: Thu Dec 14, 2017 10:42 pm

RSP2 with ALA1530 Antenna

Postby kjdahlen2 » Tue May 29, 2018 11:22 pm

What is the best way to connect an RSP2 with a Wellbrook ALA1530 ?
The ALA1530 has a BNC Connector [ 50 ohm with RG58C ].
Last edited by kjdahlen2 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Thanks in Advance for your help and comments.
kjdahlen2 ....

g1hbe
Posts: 354
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: RSP2 with ALA1530 Antenna

Postby g1hbe » Wed May 30, 2018 1:37 pm

Hi. I have had a 1530 and then the 1530LN for years and I swear by them, but connecting the 50-ohm coax output from the interface box to the green connection block causes much confusion among enthusiasts.
The first thing to realise is that a mismatch of 50r to 1k is not that serious and any loss incurred is small. You can insert a matching transformer if you wish, but these can introduce frequency restrictions of their own, especially if you like to listen below 500 KHz. Generally, the ferrite they use for the transformer is usually type 43, which does not couple well at low freq's.

For my first attempt I made a BNC to pigtail connector and connected it straight to the P and G terminals (coax inner to P, outer to N and a link between G and N. This works fine, but if you have a lot of noise in the house from psu's etc, you may find it gets into your system by way of earth loops because you are not taking advantage of the balanced feature of the Hi-z input.
To use the input in truly balanced mode, you WILL need a transformer. You can use a 1:1 and ignore the mismatch or you can use of of the popular 9:1 balun transformers available from you-know-where. I settled for a home-made 1:1 transformer using type 73 ferrite as I am a LF fan and need a ferrite which works well below 500 KHz.
To connect up, the coax from the Wellbrook interface goes across the primary (50r) side and the secondary winding connects across the P & N of the Hi-z block. No links or earth connection needed, and there must be no connection between the primary and the secondary or you will undo all your good work.
This method reduced my noise level by 10dB and I could see signals that I could not see before as they had been buried in the ground-loop clutter.
I've just looked back at what I've written and I see I've gone on long enough. Good luck, and don't forget there is a very busy and helpful Facebook page.

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Andy


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