reception problems

prpr said:
If that were true, then why would it not jump an inch if you pulled the connector out completely? An inch is still much less than several miles.
It obviously isn't true
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Dunno. Isn't it highly directional when it exits the cable? I have held two ends of coax well papart and the signal jumps. I was just asking the experts. So how far will it jump?

Edit: Just did a little experiment. The signal does jump over a small gap but strength and quality decrease rapidly with distance. I would assume there is high dispersion at the end of the wire. However, I am still not convinced that it is necessary to have a physical connection for the lead to work. I don't have any way of measuring the difference though so must still rely on experts to do that. How much difference is there between a coax that is/isn't soldered? My rough experiment indicates that even with a few mm gap there is little difference in signal.
 
It's hard to say that the signal actually "jumps". The efficient transmission of EM radiation through a non-conducting medium relies on perpendicular electric and magnetic fields, and the transmission and reception antennae are designed to convert the oscillating movement of electrons in the conductor into the EM radiation or vice versa, at the particular frequency of interest - none of which is true of the bare end of a piece of coax separated by even a few mm from another piece of coax.

The effect you are talking about is purely the capacitance between the conductors separated by an insulator (proportional to the inverse of distance). At UHF frequency you don't need very much capacitance to get some kind of signal coupling (the electric field on the one conductor induces a voltage on the other). However, it will be inefficient compared with a direct connection and is going to reduce the signal substantially. Also, as I mentioned before, there is transmission line theory to take into account: the impedance discontinuity at the break will act like a partial reflector sending some of the signal power back to the antenna (and into the ether).

In short, it's not good (especially if there is a phantom powered amp somewhere up the line!).
 
Mike0001 said:
However, I am still not convinced that it is necessary to have a physical connection for the lead to work.
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It depends what you mean by work. The bigger the gap, the bigger the loss. Whether it matters depends on how much you have to start with and how much you need at the end (certainly with the way digital modulation works). How long is that piece of string?

How much difference is there between a coax that is/isn't soldered? My rough experiment indicates that even with a few mm gap there is little difference in signal.
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It depends. Where it can make a difference is if moisture starts getting in and you get corrosion, as that can make it act as a diode junction. This can introduce all sorts of weird and wonderful effects due to the non-linearity of such a thing. It was much easier to see on analogue as you would perhaps get patterning caused by intermodulation. On digital you will still get intermod. of course, but you will just get random dropouts as it approaches threshold due to the worsening of the BER and be none the wiser as to the cause.
Not soldering is just sloppy and it's so cheap and easy to do that you might as well do it. So-called professionals (those who charge) will never do it because it costs them time, but it may save the real professionals (those who solder) from having to call them out to fix a simple fault. The former group like callouts and the fees they can charge to cure 'simple' faults.
Ironically, the 'putting a kink in the inner conductor' is more likely to cause point contact between the connector and the cable and make the 'diode' formation more likely.
 
I disagree, solder isn't good. For one thing, it makes copper brittle and more likely to fracture under repeated mechanical strain. Even worse if you have to use the modern non-lead stuff. It also makes rework a pain.

I have never had any trouble from non-soldered, non-screwed, decent metal UHF plugs properly terminated to the braid (and with a kink in the core). Whenever there has been a problem it has been with a nasty plastic plug and/or horrid thin coax.
 
It's incredibly bad practice not to make a good mechanical joint, hence soldering. Please don't try that sort of stuff with the mains:byebye: You don't need moisture for copper to oxidise either (but it helps it along quicker). No self respecting RF engineer would 'stuff a bit of wire into a hole' and expect it to work properly for the reasons ppr said above and BH said in 124. I suspect BH is winding someone up in his post above. Most unlike him to preach appallingly bad practice (although I do agree about this lead free solder cr@p)
 
Are you serious - particularly about the mains bit?

It is dangerous to use solder in mains plugs unless they are specifically designed to be soldered. The typical scenario is that the multi-stranded ends of the cable are "helpfully'" soldered to stop them fraying, then clamped into screw terminals on the plug pins. The solder causes the cable to lose its resilience, so that over a long period of time the compression from the screw makes it creep away from the pressure, and become loose. This results in a bad contact and a hot spot from the current passing through the high resistance, and a potential fire. This is now outlawed, you will not see it in any mains plug assembly on sale today and it would not meet the CE requirements.

The same applies to other types of compression termination. A tight bare-copper joint is better than solder, as long as there is a mechanical restraint to hold the joint firm and take any strain away from it.

UHF doesn't care much about an oxide layer, the capacitance is sufficient, but in other situations an oxide layer is prevented by what is known as a "gas tight" joint - for example sharp edges which cut into the surface of the copper (and are held physically stable by other means).

I should also point out that the standard all-metal UHF plug has a hole down which to stuff the wire, and is regarded as perfectly adequate (and indeed it is). My "kink" method creates a firmer contact, which breaks the oxide layer as it is forced down the hole and makes an attempt at a gas-tight contact.

Solder does provide a convenient way to make a low-resistance electrical path between two conductors when the mechanical loading is low, and it has good long-term reliability in the right situation, but it must not be exposed to flexing, and the mechanical properties of copper are made worse by adding solder.
 
Are you serious - particularly about the mains bit?
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No, of course I wasn't. I was warning against the 'kink the wire and push it into the hole' method when wiring a mains socket. I fully appreciate that a straight metal to metal contact is perfectly acceptible as long as there is enough contact, taking wire wrap connections where there are multiple turns of the wire around a square 'post'. I suppose 'poking it is' is OK because 'F' connectors use this principle, but it is a specially designed hole. I used to work for a radar company and their OA would have been aghast at the 'push it into the hole' method of connecting RF connectors.
Shirley there is not much flexing on a TV plug unless you consistently pull it out by the cable?
 
Trev said:
I used to work for a radar company and their OA would have been aghast at the 'push it into the hole' method of connecting RF connectors.
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I don't think the situation with radar, where the transmitter is sending significant power to the antenna and cannot tolerate even the slightest impedance mismatch in the line, and the receiver is trying to pick up incredibly small signal powers, is a reasonable comparison with domestic TV reception.
 
Black Hole said:
I disagree, solder isn't good. For one thing, it makes copper brittle and more likely to fracture under repeated mechanical strain.
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I disagree with your disagreement. It adds electrical and mechanical stability which are both good. Repeated mechanical strain is highly unlikely in the given use case. Have you ever had a Belling-Lee connector break in this way? No, of course not. You are just arguing for the sake of it and to make a point (I don't know or care what point, but it's non-sensical).

Even worse if you have to use the modern non-lead stuff. It also makes rework a pain.
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You can still buy normal tin/lead and it's perfectly acceptable to use in the miniscule amounts needed for domestic work. You never need to rework it. If you do, you cut the end off and put a new one on.
 
I just can't believe how flimsy F-connectors are. Twist onto the end of the cable and hope it all holds together? And that is where you definitely need a physical connection!
 
prpr said:
I disagree with your disagreement. It adds electrical and mechanical stability which are both good
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In the case of a metal UHF plug, unnecessary and overkill. The rest of my commentary is about the effects of solder and its appropriate and inappropriate use in general, from the perspective of electrical safety engineering (which of course you have lots of professional experience in).
 
Mike0001 said:
I just can't believe how flimsy F-connectors are. Twist onto the end of the cable and hope it all holds together? And that is where you definitely need a physical connection!
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They are designed like that, and designed to work. In the States (with a lower mains voltage), even joints in mains cables are made by twisting together the cables and then twisting on a threaded plastic cap.
 
Mike0001 said:
I just can't believe how flimsy F-connectors are. Twist onto the end of the cable and hope it all holds together? And that is where you definitely need a physical connection!
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You need to use the correct size to match the diameter of your cable. I've never had any trouble.
 
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