Tag Archives: Coax

Comparing Coaxial Loss in RG-58 and RG-316

by Eric, WD8RIF

I recently decided that I would operate portable during the upcoming ARRL 10 Meter Contest and would combine this operation with a pair of Parks on the Air (POTA) activations, one on the Saturday of the contest and one on Sunday. While putting together my field station for this, I realized I wanted to see how lossy my RG-58 and RG-316 feedline cables were on 10m. Yes, I could have resorted to online charts of feedline losses, and I know that the RG-316 is lossier than the RG-58, but I thought it would be fun and more enlightening to make actual measurements, to empirically determine the losses in my particular coaxial cables.

The two coaxial cables in question are both 25′ in length and both are equipped with BNC male connectors on each end. The RG-58 cable is a high-quality cable that was originally manufactured to be a 10Base2 ethernet cable, but it’s probably now over twenty years old. The RG-316 cable was recently purchased from Tufteln (link) and includes an RF choke near one end.

To make my measurements, I used my Elecraft KX2 (link) to generate RF into an Elecraft DL1 dummy load with RF detector (link), using a digital multimeter to measure the voltage at the DL1’s measurement points. I used the formula that came with my DL1 assembly instructions to calculate the measured wattage:
P = (((V x 1.414) + 0.15))^2)/50

I made measurements in the CW portion of the 10, 15, 20, 40, and 80m bands, with the KX2 set at 5 Watts output.

My first set of measurements was made with the DL1 connected directly to the KX2’s antenna jack using a BNC union:

Direct (no feedline)
Band Volts Watts
10 11.62 5.498
15 11.59 5.470
20 11.61 5.489
40 11.63 5.508
80 11.63 5.508

My immediate observation was that the KX2 appears to be generating more than 5w when it is set to be producing 5w but also that the KX2 output is essentially same from 10m through 80m.

My second set of measurements was made with the DL1 connected to the KX2 through the RG-58 cable:

Direct RG-58
Band Watts Watts
10 5.498 4.809
15 5.470 4.844
20 5.489 5.004
40 5.508 5.184
80 5.508 5.276

My third set of measurements was made with the DL1 connected to the KX2 through the RG-316 cable:

Direct RG-316
Band Watts Watts
10 5.498 4.190
15 5.470 4.322
20 5.489 4.507
40 5.508 4.774
80 5.508 4.959

I was pleased to see to see that both the RG-58 and RG-316 behaved as I expected them to: the loss increased with increasing frequency.

Using the magic of MS-Excel, I created a table of Loss in Watts for both cables, relative to direct connection and to each other:

Direct Difference (Loss) (Watts)
Band Watts RG-58 vs
RG-316 vs
RG-316 vs
10 5.498 0.690 1.309 0.619
15 5.470 0.626 1.148 0.522
20 5.489 0.485 0.982 0.497
40 5.508 0.324 0.734 0.410
80 5.508 0.232 0.549 0.317

In looking at this table, it was immediately obvious that RG-316 is much lossier than the RG-58, particularly on 10m. By looking at the row for 10m, one can see that I am losing nearly 0.7 watts in the RG-58 but I am losing over 1.3 watts in the RG-316.

For completeness, I added columns for Loss in dB to the spreadsheet:

Difference (Loss) (dB)
Band RG-58 vs direct RG-316 vs direct RG-316 vs RG-58
10 0.582 1.180 0.598
15 0.528 1.023 0.495
20 0.402 0.856 0.454
40 0.263 0.621 0.358
80 0.187 0.456 0.269

This exercise showed me that for my upcoming ARRL 10 Meter Contest POTA outings, I would do best by connecting my antenna directly to my transceiver, if possible, without using either coaxial feedline. If conditions at the operating site require me to use feedline, I will chose the RG-58 over the RG-316.

The tables also tell me that RG-316 is pretty lossy regardless of the band; for my regular field operating, unless I’m planning to do bicycle- or pedestrian-portable operations where weight and bulk is a consideration, I’ll carry RG-58 instead of RG-316. (I purchased the RG-316 specifically for bicycle- and pedestrian-portable operations, and I plan to continue to use the RG-316 for those applications.)

At some point, I will repeat this exercise with RG-8X, a feedline that is very close in size to RG-58, is less lossy, but is also heavier and stiffer.

Coax cables I used for SOTA/POTA – A horror story

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. Continue reading Coax cables I used for SOTA/POTA – A horror story

The importance of quality cable and connectors

Note that this post was originally published on the SWLing Post, but I feel like quality cable is especially important for those of us who are into field activities like Parks On The Air (POTA) and Summits On The Air (SOTA) where our gear gets a lot of handling and outdoor time.

Two radio accessories I often forget to mention in my posts and reviews are cable and connectors. When a cable functions well, it’s taken for granted and easily overlooked.

You’ll hear me say that a radio is only as good as its antenna and while that’s true, the important link in the system is your antenna cable and connectors. If you have a fabulous antenna and a benchmark radio, but you connect the two with substandard cables, it will create unnecessary losses and even shorts if you’re not careful.

But let’s be honest: it’s easy to cheap out on cables.

When I first started using tabletop receivers and transceivers in my youth, I had a tight budget. When I would go to a local hamfest where I’d find excellent prices on cable assemblies from those accessory retailers who sell a little bit of everything.  You know…the tables with everything from $10 multimeters to $5 blinking lights–? I’d find their prices for cable assemblies too attractive and would grab them.

No more.

Back when I owned my original Yaesu FT-817, I used one of these cables on Field Day and blew my finals due to a small short ono a connector end (if memory serves, braiding was touching the conductor). From that point forward, I decided I’d invest in quality cables.

ABR Industries

At the Hamvention in 2010, I found ABR Industries’ table. The only thing they had on display were cable assemblies and a handful of cable accessories. I picked one cable up and inspected it–I could tell it was good quality. Although I know how to make my own cable assemblies (with PL-259s, at least) I appreciate professionally-built assemblies.

I spoke with the representative that day and learned about their company and how they go about making standard and custom cable assemblies in the USA for the consumer, commercial, and government markets.

Although the price was at least double what I would have paid at one of the discount retailers, I never looked back.

From that point forward, I’ve only purchased ABR cables typically at Hamvention, Universal Radio, or even directly from ABR’s website (when I ordered custom assemblies).

The quality of ABR cables is second to none. I have never had one fail at home or (especially) in the field.

For my QRP POTA activations, I started investing in ABR316 and ABR100 BNC to BNC assemblies. I’m especially fond of the ABR316 assemblies (above) because they’re so resistant to memory when I coil them.

You pay for what you get

I suppose this is on my mind because I’m about to do an assessment and make another ABR order so that my new field radio kits have their own dedicated cable assemblies with correct ends (so I’m also not forced to use BNC or PL adapters for matching).

I’m also replacing some of my 3 foot cable assemblies with SMA connectors to PL-259 for my bank of SDRs. This is a part of achieving one of my goals for 2021. I’ll know then that each receiver will have a quality link to my antenna splitter and antenna.

My point here is don’t skimp on your cable, adapters, or cable assemblies.

If you have the skill to build your own, buy quality components and take your time building them.

If you prefer purchasing pre-made cable assemblies, talk with your local ham radio retailer, or seek out cable assembly houses like ABR Industries. I’d avoid purchasing cheap cables you may find on eBay or Amazon.com, for example. That’s not to say that there aren’t quality discount assemblies out there, I just prefer buying from a company that takes pride in their work and stands behind the quality.

Click here to check out ABR Industries. 

ABR Industries isn’t a sponsor of the QRPer (although I’d love to add them!)–I’m just a long-time customer who is happy to plug their products. I can recommend them without reservation.

I’ve also bought numerous long cable runs, wire, DC cable, ladder line, paracord, and sealant from The Wireman. I also highly recommend them.

ABR isn’t the only quality cable assembly house–there are many others throughout the world. Who do you recommend? Please leave a comment and links to your picks!