50 or 75ohms for MW's

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PascalD
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50 or 75ohms for MW's

Post by PascalD » 22 Jan 2017 17:40

Which cable is better for mw dx when connected for a self build active loop or can it be possible for using 75ohm cable before 50ohm ? This i hesitate for demanding because i think maybe 75 will be just good like 50ohm , is this correct and if not why ?

Good dx

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satnipper
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Re: 50 or 75ohms for MW's

Post by satnipper » 22 Jan 2017 22:36

50 ohm is conventional but it won't make any difference in practice.

daveB
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Re: 50 or 75ohms for MW's

Post by daveB » 23 Jan 2017 10:26

You can get double shielded satellite cable in 75 ohms - which I think is much better than the standard stuff. Go for the stuff with copper braiding - not aluminium - as the aluminium braiding seems to be very brittle.
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John Faulkner, Skegness
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Re: 50 or 75ohms for MW's

Post by John Faulkner, Skegness » 23 Jan 2017 11:02

I have experimented with both in the last couple of years, with a Beverage and with flags. In both cases it was a simple case of adding an extra turn on the transformer to ensure the correct match, but the difference it makes is so negligible it isn't worth worrying about.

My latest flag uses 75 ohm coax because my 50 ohm coax is of poor quality. The additional screening of the 75 ohm coax I used has made a big improvement. But my RG58 was poor quality.

At medium wave frequencies, 75 ohms or 50 ohms don't make any significant difference. If you have a choice of coax there, just use the one which has better screening.

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Re: 50 or 75ohms for MW's

Post by oldtimer » 24 Jan 2017 10:18

Yes I agree with John.
My KAZ is fed with fairly high quality 75 ohm satellite cable with two braided screens plus a foil cover. Screening is more important than impedance on MW.
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PascalD
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Joined: 29 Dec 2016 12:32
Location: l'hay les roses, Ile de France & Auray, Bretagne

Re: 50 or 75ohms for MW's

Post by PascalD » 24 Jan 2017 18:18

Thank you everyone for your input and i will now try constucting a 75ohm loop active antenne of 5m square x 2 .

Good DX

Pascal
Kenwood TS850s
Sony XDR 1FD
R820T2 SDR + software v1.0.0.1666 + plugins manager suite
Welbrook AL1530 actif loop antenna
Selmar 2-PA 320 mini VHF/UHF actif antenna
5 element FM

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