Its virtually impossible to tin polyethylene coax braid without softening the dielectric. It will re-solidify. PTFE (Teflon) is better in that respect.
If you think the braid is steel, try it with a magnet.
From a quick look at Belden specs, they, at least, don't make any RG6 types with steel braid. There are some versions with aluminum braid.
If it's aluminum, you can't. Either get some cable with tinned or silver plated copper braid, or put a BNC socket on the PCB, and a crimp BNC on the cable. (I don't trust crimping to aluminum, BTW, there's a metallurgical creep problem)
100% of the RF connectors I use for mountain top radio sites that I deal with are crimped, not soldered. Well, maybe a few soldered abominations such as PL-259 connectors.
The losses per connector are quite low. For example, here's a string of random adapters: That's about 15 assorted adapters (30 connections) showing 2dB loss at
2.4 GHz or: 2dB / 30 = 0.07 dB loss per connection. Unless you're working with high power levels, the connector loss is not a problem.
Unless you're working with microwave frequencies, mismatch loss is also not much of a problem. For example, if you insert a section of
75 ohm coaxial cable into your system, a TDR would certainly show an impedance bump far larger than what might be produced by a solder blob. However, the losses are fairly trivial. Much depends on the frequency of operation. If you're doing microwave, then precision is required. If you're doing lower frequencies, you can be fairly sloppy and things will still work quite well.
Cut-n-pasted from my previous rant on the topic from rec.radio.amateur.antenna.
Let's pretend that I mix in a 75 ohm coax connector into a
50 ohm system. Depending on the location of this "impedance bump", the VSWR is no more than 1.5:1 which is generally considered marginal. That's 0.18dB of mismatch loss. If you're doing satellite or microwave DX work, then 0.18dB might be important. However, for most other applications, it's a trivial amount.
You might be amused to know that most of my rooftop antennas are fed with 75 ohm coax and that my favored antenna designs are also 75 ohm. There are various reasons, but the main one is that coax cable losses are less at 75 ohms, than at 50 ohms. 50 ohms can handle more power, but 75 ohms has less loss. The only problems I have with 75 ohms is finding the proper connectors and dealing with the pads needed to make my 50 ohm test equipment look like 75 ohms. (Actually the real reason is that the 75 ohm stuff is mostly CATV surplus, which tends to be really cheap).
This is where the original short length of RG6 was soldered to the pcb antenna. It's an inexpensive broadcast TV antenna for home.
Rather than make a male crimp plus a barrel to join the 2 mailes, just solder the long run directly to the pcb. Or so I thought...
I crimped 1/2" of center solid conductor to the braid and soldered the solid to the pcb. It seems to work but I have no way to measure any loss. I plan to replace this when I find some REAL copper RG6.
get some phosphoric acid and brush it on when the surfaces are as hot as you can get them... the solder will flow and wet like a dream. you would not believe it! (BTW it's the same acid that's in coca cola). hope this helps,
Thank you for disclosing what you're trying to accomplish. Context is always important.
You're going to have corrosion problems. Note that all the aforementioned crimped connectors have the crimped area sealed inside the connector. In addition, they are usually wrapped in some form of waterproofing (i.e. PTFE tape and electrical tape) to keep out the water. Even if you solder the connections, the capillary action is going to force the water up the braid and under the jacket. Depending on the outer jacket slop, corrosion will rot up to several inches of braid. You can try to seal the braid and solder connections with RTV silicon rubber that doesn't contain acetic acid but I haven't had much luck with that.
Using bare wires from the end of a coax cable is about as bad an impedance bump as you can possibly create. However, it won't matter for a TV antenna, that has wide bandwidth, but relatively little gain. PCB TV antennas tend to be rather small, and therefore have even less gain. Impedance discontinuities will not have a huge effect on overall performance. Therefore, you can probably just attach some spade lugs onto the ends of the RG-6/u coax, and use ordinary brass screws and nuts to make the connection.
If you have a PCB, why not use a PCB mounted F connector?
I tried to find such a coax cable from my distant past. It had a copper clad steel center conductor, aluminum foil shield, and a very loose braid of flash galvanized steel wire braid over the shield. The braid was only for strength and not for shielding. The zinc plating was for galvanic compatibility with the aluminum shield. Such a cable was not intended to be soldered, only crimped. I saw it at STV (subscription TV) in Smog Angeles in the 1960's. However, I couldn't find it which suggests that it's either uncommon, not in current production, or my memory is faulty.
It would be helpful if you could provide any markings on your cable so that it can be identified.
It was my call (based on almost no RF expertise) that any solder connection was much better than the best crimp and that crimps are used strictly for convenience. I'm beginning to doubt these presumptions...
Thanks.
PS, a police helicopter just flew over the neighborhood at a few hundred feet. The digital channel I was watching blanked out completely. This at about 50 miles from the broadcast site, as the crow files (Sutro Tower).
Ok. You won't need to deal with anti-corrosion precautions.
I consider crimping better than soldering mostly because soldering requires some skill, but crimping can be learned by almost anyone. With ratcheting crimpers, it is possible to guarantee that the degree of compression is both sufficient and uniform. Crimp and compression connectors also will survive the SCTE IPS-TP-401 40 lb pull test, while soldered connectors often fail this test. In general, crimp and compression connectors are much better at keeping water out. I've seen much better reliability after switching to crimp type connectors. They're also cheaper. I can't think of a single advantage to soldered RF connectors.
Bingo. Aluminum braid over aluminum foil shield. You can't solder to the aluminum. Find a different cable with a copper braid (or use a connector as I previously suggested).
Can I guess(tm)? I don't think the helicopter is large enough to complete block out the signal unless the TV station signal strength from Mt Sutro to your PCB antenna is rather weak. That's about what I would expect at 50 miles with a small PCB TV indoor antenna. Digital is ummm... digital and tends to deliver either a very good picture, or nothing. At 50 miles, I would have recommended a bigger, better and possibly amplified (to compensate for the coax cable losses) antenna. You might want to check your location with: to see if the indoor PCB antenna is adequate, and if a bigger antenna will be of any benefit. Otherwise, the police helicopter might have been transmitting video on some frequency to the ground which overloaded your TV receiver front end.
Just like a nearby metal structure causing "ghost" images, they produce strong reflections of the transmitted signal so your antenna gets two similar strength signals, one of them delayed by a few microseconds.
This is often enough to seriously corrupt the wanted signal so large amounts of data are lost.
End result, the pic freezes or pixellates crazily.
Bad luck if you live near a major airport and rely on an off air signal.
Of course I agree re. connectors. In my situation the original (short) coax was soldered to the pcb. I thought that duplicating this connection when replacing with a longer run of coax was better (re. loss) than introducing connectors. Soldering F (or other) connectors vs. crimps, I agree: a nightmare.
The loss is horrible in copper braided coax at TV frequencies. The cost is excessive, as well. 'Headend cable' used to be silver plated copper braided coax, but that was abandoned for foil & drain when headends passed 216 MHz. That silver plated coax was over a dollar a foot, in the '70s.
Ok, I'll bite. What's wrong with F-connectors? There are zillions installed on indoor and outdoor CATV installations with no failures or issues. Certainly there are connectors with better specifications, but for the intended purpose and cost ($0.30/ea), F-connectors are more than adequate. The only real problem I've found is the wide variety of cables claiming to be RG-6/u. Making a connector that will fit all these RG-6/u mutations is tricky, but T&B has done a decent job with their "red" SNS1P6U Snap-N-Seal connectors:
So, what's wrong with F-connectors and what would you recommend the CATV industry use instead?
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