I have a 2 meter long RG-174 pigtail that I bought on Ebay.
This is an unmarked cable with two BNC connectors in both ends.
I wanted preparing a choke by inserting a FT114-43 in the cable (14 turns). I cut one end to facilitate the winding process. When I removed the jacket I felt the shielding wasn’t as thick as it is present on some MIL spec coaxial.
This is what I expected to find (MIL spec):
I can see the interlaced external braid but it is less dense than I expected.
Sure this is gonna reduce the maximum useable frequency, but I intend to use it for 7 - 28 MHz qrp.
Do you think this situation will perform worse compared to a proper thick shielding?
73 Ignacio
It can be a problem indeed. It seems like the quality is very variable:
When buying on Ali, it’s better to test everything properly before use. They would do everything to make it cheaper, but most of the time it has a cost (in quality). Another example with those clip leads for, where they replaced copper wire with iron:
The somewhat thinned copper shield braid of the approximately 2 m long cable would still be usable as a connecting cable, but due to the very small bending radius when winding a 1.14" ferrite core, this braid becomes distributed very unevenly, which probably has a noticeably negative effect on the properties of the 1:1 balun.
However, I find the crimped BNCs on RG316 to be not very reliable. The braid starts falling apart when twisted repeatedly. As an alternative, there are also the clamp connectors; no crimp is needed. I think they are even more reliable in the field since they also clamp the plastic sleeve. (like amphenol 000-69475)
Hello everyone, I usually check the cables headed with the nanovna for return loss. Especially on cables of dubious origin in terms of quality. 73 Luke
If it helps, Ignacio, when I put the first coaxial cable to the 10m Moxon that I have been using lately, I first used an RG174 cable that I had from a small magnetic VHF/UHF antenna… The antenna with this cable was completely deaf and had perfect SWR. I changed it to the RG174 cable that was included in my bandhopper dipole and the difference was incredible. Now there was more reasonable gain and SWR. I am talking about both cables of about 10m. The Chinese one with the magnetic antenna was completely rubbish.
Si te sirve Ignacio, cuando puse el primer coaxial a la moxon de 10m que he estado utilizando últimamente, usé en primer lugar un rg174 que tenía de una antena magnética pequeña de vhf/uhf … La antena era con este cable era completamente sorda y roe perfecta. Hice un cambio al rg174 que estaba incluido en mi dipolo bandhopper y la diferencia fue increíble. Ahora había ganancia y una roe mas razonable. Hablo de ambos cables de unos 10m. El chino de la antena magnética era basura completamente.
The professional world favours crimps now for reliability. A huge number of connectors still feature solder centre pins. If you have to prepare the cable and solder the centre then using a crimp on the braid has to show a real benefit in industry or industry would favour solder/clamp connectors as you have to soldering equipment already available for the centre pin.
But there are important things to get right if the cable will be connected/disconnected repeatedly
One is to ensure there is some flare at the end of the crimp, like this.
The other is you have to use sufficient heat shrink to add strain relief. The preferred method is to use what is known as glue-lined heatshrink* and to use a long enough length. This grabs both the crimp and enough of the outer jacket to stop the effect you describe. Typically another layer of heatshrink is added on top of the glue-lined heatshrink.
What I have seen is that the crimp ferrule on cheaper Chinese connectors is too short. The length of the crimp jaws on my average quality crimpers is about 10mm. The length of the ferrule in all my unused Greenpar and Amphenol connectors is 12.5mm. This means there is about 2.5m uncrimped to give the flare shown in the picture. All my cheap connectors have ferrules about 9.5-10mm long meaning the whole ferrule is crimped.
I have a number of crimped BNC connectors, both expensive and cheap that have been in use for SOTA antennas for many years that are still fine and dandy. Some pre-fitted and some fitted by me. Maybe I treat coax with a lot more care than others.
* You should read how heatshrink is made to understand how it works.
@EA2BD Should you choose to wind your RG-174 onto a small toroid, you will almost certainly bend parts of the cable tighter than the ‘minimum bending radius’, which is typically about 15mm.
This may or may not damage the cable on day one.
In due course, in parts of the cable, the centre may start to migrate slowly through the polythene etc centre insulation towards the braid. This risks changes in impedance, voltage-breakdown limits, loss etc.
It is quite difficult to know whether this is happening or not.
I survived the whole of my childhood travelling in the back of a car with no rear seat-belts. Back then, they weren’t required.
I was lucky, as you may be with your RG-174 cable wound onto a toroid.
However, a better plan may be to make the balun using a pair of insulated wires with solid copper conductors.
Just wind your choke and test it for outer conductor choking inductance and rf transmission power loss. If the results are OK then use it.
Ignore all the hand wringing doomsayers.
As far as transmission lines goes 7 MHz is almost DC. What would be concerning at 1.3 GHz for a weak signal operator can’t be measured at 7 MHz.
You can use steel fence wire for an antenna or transmission line at 7 MHz and it will work well enough. Someone will pop up telling their tale of using a farmers fence for an aerial.
Stainless steel is a lossy material at rf yet thousands of HF antennas are made from the stuff and millions of VHF and UHF whips are made from it and all are in daily use.
I draw attention to this to show that practical aspects can override theory. 18 carat gold whips would be as corrosion resistance, strong enough and look great but the cost of the gold is a show stopper. Anyone for a wedding ring loop yagi for microwaves?
This is the key I agree. But many of us don’t do that at all or juste put a piece of strandard heatshrink around, which is not really working since it has to make a solid “bridge” between the sheath of the coax and the metal crimp to ensure good strain relief.
They also sell versions with strain relief thingy:
