Onderwerp: Welke SDR?

Voor de lage frequenties heb je bij een RTL-SDR een upconverter nodig.

Neem nou maar gewoon een SDRplay 1A, krijg je echt geen spijt van.

WADnWIND schreef :
Waarom niet meteen de SDRplay RSPdx?

In contrast to cheap copies, the MLB is not just a simple 1:9 transmission line transformer (unun). This original Magnetic Longwire Balun, invented by RF Systems, is based on an impedance matching transformer with completely separated antenna- and receiver circuits sharing a common ground. The transformer makes use of a special ferrite, developed at RF Systems. This makes It possible to transfer signals with extremely low loss from the antenna to the receiver, only by using a magnetic field. There is no direct connection between the antenna and the receiver. This magnetic transfer technology reduces the overall background noise, caused by statics.

The “VMR version” MLB was made from scrap. 3 core 2 amp lighting flex and an old ferrite rod. The results are just the same as the posh version!

We can also get rid of the “magnetic” and give the balun its true name of voltage balun. My interest in the MLB was started after a friend went out and paid ?30 for one and started to tell me how this little device will produce a 50 ohm match at all frequencies. Any aerial will have differing values of impeadence depending on what band it is used, a 66 foot wire on 80m is about 30 ohms and on 40m the impeadence is about 1000 ohms.

For any sort of balun to be able to match different impeadences to 50 ohms you need to be able to vary one or more of its components. And when you can do this, the balun will match most things to 50 ohms, but you would call this type of balun an ATU. An ATU is a variable balun.

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The first balun was made “by the book” using the correct wire SWG and ferrite ring with a type 63 core for 1 to 30 MHz. I used a friend’s MFJ analyser for the tests and a 35 foot wire aerial.

The balun did improve the match to the receiver. Only near the resonant frequency of the aerial was any match close to 50 ohms or a VSWR of 1 to 1, as you would expect. On all other frequencies the match varied from 3 to 1, to 5 to 1 VSWR. Without the balun the match was horrible!

In the real world this means I had some thing like a increase of signal from 1 to 4 “S points” on the receiver from 1 MHz to 30 MHz.

The “VMR version” MLB was made from scrap. 3 core 2 amp lighting flex and an old ferrite rod. The results are just the same as the posh version!

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So is a MLB worth having? They do produce a “better” match to the receiver but you could get an ATU kit for about the same price, which will always produce the right match. If you buy surplus VC’s you can make an ATU for under ?10. Find a couple of broken tranny radios and you can make one for free.

The main advantage of the MLB is you can use COAX to the feed point of the aerial out side and get a reduction in noise pick up from TV’s etc in your home. I would not spend money on one, but a home made MLB in a box is worth having. Because it is a pain to keep peaking the ATU as you tune up the SW bands and anything that helps to give a better match is better than having nothing at all.

Die RF Systems MLB is ooit met de Loper meeverkocht, ik heb nu nog niets. Ik twijfel over zelf maken of deze: www.svb24.nl/nl/marine-balun-m...-longwire-balun.html

Indien zelfbouwen: is die RF Systems MLB inderdaad een “ordinaire” 1:9 balun met nog uit te zoeken ringkern (welke?). Of maar gewoon kopen en zeker weten dat die MLB geen beperkende factor meer is?