10

A transformer can help and could also make things worse. I have some bad experience with this. The way that a radio is damaged by static is simple: Something charges up to a high voltage, and then there's a sudden breakdown resulting in a high voltage on the first transistor of the receiver. This can happen in a few ways: A long-wire or monopole type ...


8

To help identify a mystery ferrite core mix, the most common method is to take some measurements to determine the initial permeability (µi). Then compare your results to a table of µi for common core materials. This will put you in the ballpark and likely more than close enough to make an educated guess about the application(s) the ferrite core would be ...


6

It can be done! Remember that a transmission line consists of some self-inductance per unit length, and some capacitance per unit length, and the ratio of these determines the line's characteristic impedance: $$ Z_0=\sqrt{\frac{R+j\omega L}{G+j\omega C}} $$ Intuitively then, a lumped element implementation might look like some series inductance and some ...


5

Assuming that power losses in the transformer are acceptable, and that it's placed after 1:1 current balun (which eliminates common-mode current), is there any reason why it might be a poor solution? Well, the assumption about loss may not be a great assumption to make. It takes a substantial core to avoid saturation and overheating even at modest transmit ...


5

This is a magnetic flux transformer, not a transmission line transformer. It works by flux coupling just like a mains power transformer. So the bifilar part isn't too special, nothing like a transmission line transformer. In a regular flux transformer, the position of the winding doesn't really matter, only the number of turns. At RF though there is the ...


5

The problem is most likely the type 43 core material. It is quite lossy at 21 MHz and is a poor choice for the auto-transformer. Unlike a transmission line transformer, the auto-transformer relies on the coupling of the two coils to partially occur by passing flux through the core. The complex permeability of type 43 material indicates high losses for this ...


3

VHF transmission line baluns are very difficult to construct due to interwinding capacitance. As a result, the balun will have an undesirable self resonant point and will not typically reach the desired transformation ratio. Note that a balun does not consist of simple primary and secondary turns but rather primary and secondary transmission lines (2 ...


3

The answer is no. The best way to protect against static build-up would be to have both antenna elements DC-connected to ground. This would be automatically ensured with a 1:1 voltage balun. With a 1:1 current balun, only one element would be DC-connected to ground. Hence a resistor would be required to be connected between the two elements. With the 1:1 ...


3

The transformer is most probably a part of a critical tuned circuit. If the ferrite is broken then the radio keeps working but the filtering is worse. There a a number of ways to find a replacement for the transformer. 1: Try to get the technical manual and find the partnumber and supplier (manufacturer) 2: Look for the information on the pcb and try to ...


3

Interesting. Assume half-wave resonant antenna. The feed point in the middle (just a series source, or a transformer) results in 70 Ohm real impedance. When the antenna height is lower a match to 50 Ohm is sometimes possible. When moving the source insertion point in the direction of one of the ends the impedance grows up to beyond 1500 Ohm (depending on the ...


3

For illustration, here's a 9:1 unun construction using 3 wires from M0UKD: Since the A and B windings are connected together in series, there's no compelling reason you couldn't replace them with one longer wire that has the same number of turns. For an ideal transformer only the number of turns would matter, and how those turns are arranged would be ...


3

It may help to consider that this: is equivalent to this: The lines above the transmission line indicate it is wound on a ferrite. Because only the common mode affects the electromagnetic fields outside the coax, the ferrite increases the common mode impedance but does not affect the differential mode. To simplify analysis we can assume the common-mode ...


2

The voltage doubles because the two coaxial cables are connected in parallel on the input side, but in series on the right hand side. In the diagram, there shouldn't be a little i in the middle of the upper coax, no common-mode current can flow there. This trick doesn't work with batteries at DC, it just shorts out the supply, but at RF the choke, shown as ...


2

I am still of the opinion that it is “unclear what you are asking”. But I will try to answer the two questions that you actually wrote: Q. How does the carrier telophone system works on the conext of radio and most important how does this circuit work in establishing a connection between the receiver and the transmitter. [sic] A. It doesn’t. There is no ...


1

I thought I'd come back to this having discovered the real reason why I wasn't developing the expected voltage across the 50 ohm load. Glenn's answer was good and is still very relevant, but I made a silly and simple mistake and I'd like to post it up as an answer in case someone else has the same issue. Basically, I had reversed the windings on the toroid....


1

Chances are you can find what you need here. http://www.digikey.com/product-search/en/inductors-coils-chokes/adjustable-inductors/196629?k=toko Could be you broke the slot without moving the coil core. If that's the case you might be better off to leave it alone. If you can solder and want to replace it you need a voltmeter and a schematic. Put the ...


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