Something thats bugging me..

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bigbassman
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Something thats bugging me..

Post by bigbassman » 11 Jan 2018, 20:38

I wonder if someone can clear something up for me once and for all? I'm setting up a 50' random wire for SWL only,no TX.Will a 9:1 balun,or should it be Unun,make the slightest bit of difference? What is the difference,if any between a 9:1 Balun and a 9:1 Unun and what exactly do they do? I can never find a definitive answer.Thanx.
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Buick Mackane
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Re: Something thats bugging me..

Post by Buick Mackane » 11 Jan 2018, 20:57

9:1 is a ratio, Say a long wire has an impedance of 450 ohms, The unun will transform it to 50 ohms, Or there abouts, 450/50 = 9, Which is closer to the impedance required by most transceivers/receivers, Unun stands for Un/balanced to Un/balanced, They're Normally used on long wires, Baluns are used to join coax which is unbalanced to balanced antennas such as dipoles, Balun stands for Balanced to unbalanced,

Hope this helps :)
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bigbassman
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Re: Something thats bugging me..

Post by bigbassman » 11 Jan 2018, 21:13

:D OK Buick thanx.Thats pretty concise and clear.When you say 'Say a long wire has an impedance of 450 ohms',what if it doesn't? How do I know? I'm using a short length of coax attached to the wire for connection to the radio purposes (DX-394).Do I mount the balun at that join? See? Im lost. :D
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Buick Mackane
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Re: Something thats bugging me..

Post by Buick Mackane » 11 Jan 2018, 21:22

bigbassman wrote:
11 Jan 2018, 21:13
:D OK Buick thanx.Thats pretty concise and clear.When you say 'Say a long wire has an impedance of 450 ohms',what if it doesn't? How do I know? I'm using a short length of coax attached to the wire for connection to the radio purposes (DX-394).Do I mount the balun at that join? See? Im lost. :D
Well first up, A balun is used on a balanced antenna such as a dipole to isolate it from the coax, Which stops TX RF returning to the transceiver, Not applicable in your case as you wont be transmitting or using a balanced antenna,

The device in your case is called a unun, They're normally enclosed in a plastic waterproof case, With a connection point for the long wire and a connection point for the coax,

You would normally use an antenna tuner, To bring the impedance down to 50 ohms, The unun transforms the impedance down to a level where the tuner can do its job
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Re: Something thats bugging me..

Post by bigbassman » 11 Jan 2018, 21:25

All good mate.I've got all that.Fancy building an Unun myself so we'll see how that goes.Thanx for your input.Much appreciated.
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Re: Something thats bugging me..

Post by Buick Mackane » 11 Jan 2018, 21:28

bigbassman wrote:
11 Jan 2018, 21:25
All good mate.I've got all that.Fancy building an Unun myself so we'll see how that goes.Thanx for your input.Much appreciated.
No hassle, Good luck with it :thumbup:
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Re: Something thats bugging me..

Post by Buick Mackane » 11 Jan 2018, 22:07

Just remembered, I used to have a DX-394, its got a high impedance input phono socket next to the S0-239 Socket, Think its marked ''HI-Z'' Just plug your long wire into the HI-Z Socket, No unun required,
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Re: Something thats bugging me..

Post by bigbassman » 12 Jan 2018, 09:49

Ok then so I dont need an Unun at all.If I did build one though would I notice any difference at all noise wise? Or is it just a waste of time.Its just that the Hi-Z socket is the one I'm using and I'm getting a lot of noise.I thought an Unun would help.Youve been really helpful.Thanx.
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rogerbeep
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Re: Something thats bugging me..

Post by rogerbeep » 12 Jan 2018, 11:46

Impedance of a wire antenna is not constant, it varies with the RX frequency.

Depending on the RX frequency the antenna is closer or further away from it's natural resonance frequency. If the antenna is far away from its resonance, i.e the impedance is higher (increased SWR ratio) and antenna becomes more deaf.
Just check with your current setup; At some bands you probably have excellent RX, at others it is almost quiet or significantly lower signal.

The wire antenna has "always" (much) higher impedance at most frequencues than RX equipment and common coax cable for radio or TV.
In general the impedance in a single wire antenna is too high.
To lower the impedance at the radio side you need an impedance transformator to lower impedance value. This is the UNUN.
A 9:1 ratio is one of the best compromise if you use one single wire antenna for a larger bandwidth.

Example: If the impedance of the wire is 450 ohm at a frequency your SWR is only 1:1 with the UNUN (instead of 1:9). If the impedance is 2000 ohm at a frequency still the impedance at RX side is only 1:4,5 (instead of 1:40).

I have used random wire antenna for SWLing for some years.
After I built and connected 9:1 UNUN to antenna and earth rod, I got a noticable better signal/noise ratio. At that time I was using an RTL SDR dongle and an upconverter for SWL. The waterfall at my computer screen came alive and I was able to receive more signals than before.

When that is said, the 9:1 might worsen the S/N ratio at some frequencies since the impdance after transformation is less favorable at the coax side. Solution for that is to add (or remove) some lenght at your antenna.
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Re: Something thats bugging me..

Post by bigbassman » 12 Jan 2018, 21:11

Wow.Pretty thorough there rogerbeep,thanx.Actually its the signal/noise ratio thats my biggest problem.My main interest is HF airband,and sometimes reception is ziltch or very faint with a lot of noise on top and other times Im copying Gander radio and New York volmet no problem at all.
I'm going to give the Unun a go and see what happens.Cheers!
1 X PRO 2006 1 X DX-394 1 X GRE PSR 282 1 X UBC780XLT with ProScan 1 X Pro43 2 X Uniden UBC9000XLT Tristar777 LCL 2740.

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