by Thomas (DM1TBE)
I think every portable operator thinks about their coax cables and how to use more light and flexible types. During the last few activations, I have switched from my rigid Aircell 5 to the lightweight and flexible RG316. I have bought a couple of different lengths, mainly from Chinese online sellers at AliExpress.
However, I had some hard to define issues like the vague feeling that I am not getting out as good as I should, or a changing SWR during an activation. So I thought I should check my cables before looking at other parts of my equipment.
My professional and educational background does not have anything to do with electronics, and I don’t have the equipment to measure the cable loss directly. But my goal was to check if the cables were faulty, not to measure the exact attenuation.
I have an SWR and Power meter from DJ9PK as per image below. It can measure PEP and has, according to the seller, an accuracy of +/-4 percent. You can find more details about it here in German or here in English (Google / auto translated).
My KX3 with a CW paddle served as signal source. As large differences are easier to spot than smaller, I switched to the 10-meter band as the HF band with the highest attenuation.
I then measured a short cable with a very low loss, a 1 m / 3.3 ft RG213, which should have an attenuation of less than 0.1dB (excluding plugs).
I simply checked how much power came out at the other end of the cable. That value I have used as reference. This cable (and all others) was plugged directly between the KX3 and the power meter, no ATU involved anywhere. The power meter was set to measure PEP.
I repeated all measurements, but the results were very consistent, with only small deviations.
The results were a nightmare. Two RG316 cables out of 3 from AliExpress had an attenuation of more than 4dB, i.e. less than half of the power came out at the other end.
The other cables were fine, with the losses broadly in range with the cable specifications.
I can not say, if it is a loose connection, a faulty plug or if my handling was too rough. It could be that all cables arrived fine, and I damaged the cables during my usage. But to be honest, I don’t care. If a coax fails after some weeks, then it is not an option for me.
I have briefly discussed the findings with local ham radio club members and then decided to go for a Hyperflex 5 cable until I found a reliable source for RG316 cables.
Why Hyperflex 5 you may ask? It is very flexible, as opposed to Aircell 5, and has a much lower attenuation when compared to RG58.
Appendix
Cable 1: RG316 / 5 m / 16.4 ft
Cable 2: RG316 / 10 m / 32.8 ft
Cable 3: RG 316 / 3 m / 9.8 ft
Cable 4: Aircell 5 / 5 m / 16.4 ft
Cable 5: RG316 / 1 m / 3.3 ft
Thomas-
Thanks for an interesting report!
I’m always a bit skeptical of items I purchase on e-Bay. The prices are usually very low for a reason. It has to do reliability issues with electronics production, and the items that fail may go to the surplus market. The best-known of these was the AD9850 modules. A small board with a wonderful sine-wave output in the HF bands. There was a design error that made them useless at still-higher frequencies, and thousands of them were scrapped as surplus.
I used to use a 50-foot/15M length of RG-174 for portable operation. It came with BNC connectors at both ends, which made it very convenient. It’s fairly lossy, though- about 2 dB on 20 Meters. It was worth it in terms of putting up a high dipole, and a tradeoff I was willing to accept. It worked well for me.
My point- it pays to be a bit skeptical of low-price surplus electronics stuff from AliExpress or e-Bay. There’s often a reason why the prices are so attractive. ‘Caveat emptor’.
73- K1SWL
I guess coming from an electrical engineering background it was ingrained into me at a very early age that all things aren’t equal when it comes to coax and connectors. I always by from a known good supplier. I don’t buy from auction sites. This article is so useful to those who may think all connectors are equal. Thanks for posting. Regards Mike
” I don’t buy from auction sites”
Some reputable vendors have their storefronts on auction sites like Ebay. To broadly refuse from buying on them is short sighted.
I forget what it was, but I once bought something on eBay hoping it was o.k. Free shipping included, and it turned out it came from GigaParts. Whodathunk?
Thanks Thomas.
I hadn’t given it much thought but now I think I will do some testing too.
I usually run RG174 to the antenna and use the 316 for jumpers. I carry a small QRP dummy load ($15 from Amazon) for field testing issues.
I’m going to look into how I can loss test with the equipment I have on hand.
One Question: have you considered that it could be your coax connector on the K2?
W4MKH
https://w4mkh.com/
Hi Marshall!
I have repeated the measurements and the good cables were still good and the bad cables were bad again. I think it would be a big coincidence that the coax connector at the KX3 shows a loose connection only for specific cables. But I will keep an eye on it how it goes with the Hyperflex 5.
Hi Thomas. I’ve had the same question. What did you use for a load? I may be reading your meter incorrectly but it seems to be showing an SWR greater than 2 in the pics? Thanks.
Hi Scott,
it is an antenna as load
Cheers
Thomas
For a good test you need a 50 Ohm resistive load, like a good dummy load. An antenna would be a poor load for dont know what it will be doing. It can affect coax measurements.
I too have bought some short 1ft RG316 coax jumpers with BNCs from AliExpress. They do look good visual wise. But now I might consider some testing. I just use to connect my rigs to my tuners. I use an assortment of longer cables with RG58 and RG8x and BNCs for the antennas.
73, ron, n9ee
Hello Ron,
I just ordered the QRP Guys Digital Power/SWR Meter w/Dummy Load recommended by Steve in another comment. The test was not supposed to be an excat measurement, more like a functional test. The QPR Guys tools should allow me more precise measurements.
Cheers
Tom
If you can, it would be interesting to borrow a VNA and a decent dummy load and repeat the tests to characterize the cables, that being said, M&P makes pretty good cables, I know that since Dad (R.I.P. ) bought cables there for a nearby AirForce base, and the factory is about 30Km by car from my location
https://messi.it/en/comparison-chart-50-ohm-cables.htm
notice that another decent pick could be the airborne cable, somewhat higher attenuation, sure, but it’s quite robust 😉
Thank you, Andrew. I just bought the Hyperflex cable, and hopefully it will last awhile. But Airborne looks interesting too. Thank you
I know eBay is not necessarily a great place to buy coax. But, I’ve had very good experiences with wifi-expert. They put their coax together in southern California. It seems to be very good quality. If you contact them, they’ll make whatever you want. The prices are reasonable and they deliver quickly.
It’d be great to hear if anyone else has tested the wifi_expert coax.
Thanks, Rus! I will check out wifi-experts if I don’t find a reliable manufacturer in Europe.
Cheers
Nice work Thomas and thanks for taking the time to share this. I recently performed the same test on a 15Ft RG-316 jumper I purchased off of Amazon. I used a QRP Guys Digital Power/SWR Meter w/Dummy Load to perform the measurement and found similar results and I promptly returned the cable. I have used a Nano VNA in the past to confirm coax impedance values on new cables and have found issues that way as well. Investing in and learning to use basic testing tools is a part of the hobby more of us should do which can be fun and educational.
Thanks for sharing your experience., Steve. I found the QRP Guys Digital Power/SWR Meter w/Dummy Load very interesting and just ordered it. Thanks for the advice 🙂
Timely article Tom! When I have issues, it’s usually with jumpers. I have gotten a bunch of RG316 jumpers from eBay, and will be looking at all of them closely, in fact, all my cables I’m using. Again, great article to get us thinking!!
Good side-by-side comparison of real versus China cables.
Too often, I have been disappointed with their (China-CCP) products (ham radio, appliances, electronics, tools)…so I try to spend my money elsewhere.
73
https://kv5r.com/ham-radio/coax-loss-calculator/
Does not include 316 . Otherwise a great tool.
100′ of RG58 will eat half of your power .
A very reasonable thing to test for. Down here everything gets an extra ham markup so I’m even more inclined to find cheaper sources.
A nanovna can test for loss, and I used it on every single cable I’ve purchased to make sure the loss is acceptable, about 90% of them were acceptable
Hey Tom,
If you could include a new column with “measured attenuation per 1 meter” I think it could be make it easier to understand the behavior of different cable types and suppliers .
Thomas, your post is timely because I’m currently in the process of building a few new RG-316 cables for various field kits. I’m hoping the RG-316 cable I ordered is up to spec–I assume it will be because it came via a recommendation from a friend who tests cables.
Thank you so much for sharing this!
Cheers,
Thomas
How about using no coax at all — just an end-fed resonator and a counterpoise attached to the transceiver via a BNC-to-dual-post adapter?
73,
Bruce Prior N7RR
The SparkPlug antenna is an EFHW designed like that and there are a few other commercial antennas like that.
And a binding post to BNC connector with some wire opens up a whole lot of possibilities.
But they usually require a built in tuner. My IC-705 doesn’t have an AT so I still have to use a short jumper to the tuner then I hook the antenna directly to the tuner.
W4MKH
https://w4mkh.com
I have used RG 316 a lot from AliExpress without any problems. Each time it’s the connectors. They are usually for SMA. With BNC crim connectors, you can have problems in the field especially with corrosion.
A NanoVNA can be used to measure coax loss and is very inexpensive. For example,
Thank you, Jack. I am using a Rigexpert Stick as my favorite Analyzer, but a NanoVNA is something that I already thought could be useful.
Thanks. That was a great video on the VNA.
I subscribed and I will be watching the other 94 VNA videos you have up on the channel. I have a VNA and a Mini1300 that I would like to utilize more as well as understand better.
W4MKH
https://w4mkh.com
I love the make-do approach to actually testing something most people probably just assume. Many of us could do this with our cross-needle tuners or whatever power meter we might have. It won’t measure 0.1db or whatever, but it certainly will let us see 4db!
I’ve thought about that aliexpress rg316 before for portable antenna kits, but I guess I’ll stroke that off.
Interestingly, one could use open wire without a tuner (any impedance) for extremely low loss if the wire length is electrically a 1/2 wavelength or a multiple. So, approximately 10.7m of feedline for 20m. Interestingly, the exact length (and thus frequency) isn’t super critical https://www.wolframcloud.com/obj/9bfedd3b-a970-44ad-beb9-0be632df0abb
A frugal ham could build a set of dipoles with built-in 1/2w open-wire feedlines that weigh, and cost, next to nothing each.
Hi Jason. Thank you. That sounds fascinating. Not so much for SOTA as I am already carrying way too much stuff with me. But
for “near-car” activations such as POTA or WWFF, this is definitely worth a look, especially when sending QRP. Thanks again
I like RG-58C/U for portable ops. This is like RG-58A except the center conductor is stranded instead of solid, so I think it handles the coiling and uncoiling that is associated with field radio work.
It is certainly heavier than the -174 or -316, but it is also much more rugged and I have tools to install crimp connectors myself. I have 20- and 10-foot lengths terminated in BNC connectors in my portable kit.