The discussion below is truly unique. It was put together out of the author’s frustration with not being able to find adequate discussions combining the purposes, place, application, and uniqueness of coax in general as opposed to hookup wire. Only with a proper understanding of these distinctions can we move on to an understanding of what distinguishes the effectual natures of RG-214 and RG-213 coax.
The obvious differences relate to cost. RG-213, at the time of this writing in Chelsea, Michigan, is priced at a little less than $2 per foot while RG-214 is priced at almost $8 per foot. That alone tells us that there must be some very important differences between the two. If your objective was to optimize every aspect of your amateur radio activities and the cost was no limitation, RG-214 (even at $8 per foot) would be the optimal choice. WRONG! You would be shooting yourself in the foot.
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HOOKUP WIRE DISTINGUISHED FROM COAX
Hookup wire is a conductor (stranded or solid-core) with an insulation covering. Coax cable is like hookup wire in that it also has a center conductor with an insulating covering. But coax cable has more.
The major “more” that coax cable has relative to hookup wire is a known characteristic impedance, Zo. Hookup wire also has a characteristic impedance, but it cannot be known since it is typically routed all over the place with a never-ending change of the distance to its ground plane.
For a fuller discussion of characteristic impedance, please see another web page of the Chelsea Amateur Radio club where one of our members gave a nice presentation.
The major “more” that coax cable has relative to hookup wire is effectual rather than physical.
Coax has a known characteristic impedance, Zo. While everyday hookup wire has a characteristic impedance as well, it cannot be known since Zo is dependent on a known and consistent distance to the ground plane. The effective characteristic impedance of hookup wire depends on where it is placed and where the ground plane may be in that application. Further, for a given run of hookup wire, that distance to the ground plane will not be consistent.
Thus, where the rubber meets the road regarding distinctions between the two is that one has a known and consistent characteristic impedance and the other does not.
The reader is no doubt asking, “But what about shielding?” It’s not relevant to the discussion thus far. But it’s coming. At this point in the presentation, all we are doing is placing dots. The reader will be able to connect those dots later on.
WHEN CAN YOU GET AWAY WITH USING HOOKUP WIRE?
An application requires the use of coax (or a matched impedance) as opposed to hookup wire when the transmission signal’s wavelength is less than one-tenth of the wire’s length to the destination. The reader might now be asking if that includes DC or signals so slow that they are like DC. Let’s consider 60 Hz. What is the wavelength of a 60 Hz signal? Let’s see: 299.79e6/60 = 5e6 meters or 5,000,000 meters or 5,000km. What is one-tenth of 5,000km? It is 500km. Therefore, to transmit a 60 Hz signal a distance greater than 500km, you must be using coax or at least have a matched impedance. Next question: What is the distance from New York to Los Angeles: is 3,935km but let’s call it 4km. The distance from LA to New York is 1/125th of the maximum cable length at 60 Hz so it’s a go.
But a tenth is an absolute limit if you want to circumvent frequency doubling. We have not yet talked about fidelity. A twentieth is a safer bet but a hundredth will probably get you there. In other words, the wire is too long given the frequency of the transmission signal. You have to address impedance matching for excess lengths.
A fuller discussion of this is offered on another Chelsea Amateur Radio Club web page. But that means impedances must be matched for a minimal distortion signal transmission.
The illustration at the right reveals the electrical specifications of RG-213 and RG-214 cables. One would think that if anything were different between the two that it would be in the electrical specifications. Think again.
When we look at the aspects of construction, we can see a difference between the two. We see differences in weight and overall diameter. These, however, are ancillary and not significant for this discussion except for requiring a lot of elbow grease when it comes to stripping.
What is of effectual significance is the conductor material and shield nature. We can see that the RG-214 core conductor is silver-plated. Silver has a lower resistivity than copper so RG-214 should have less dB loss per 100 feet than RG-213. Well…you would think so. But if you think so, then (amazingly) you are wrong.
If the application is to minimize signal loss, then our silver-plated RG-214 would be a very poor choice for amateur radio. At 50 MHz, it has a loss of 1.7 dB per 100 feet while RG-213 only has a loss of 1.2 dB. Even better yet is LMR-400!
CONNECTION CABLING FOR REPEATER DUPLEXERS
One very important use for RG-214 cables is for the interconnectivity of repeater duplexer cavities. At VHF frequencies, repeater input and output frequencies are only separated by 600 kHz. Even with all of our 21st-century technology advances, we in Chelsea, Michigan still have to rely on the ancient 1950s vintage duplexer cavity technology to avoid an intermodulation distortion (IMD) that would result from not sufficiently splitting those two frequencies when using only one antenna.
The duplexer principle receives one input from the antenna. It then splits that input into two paths. In the case of the Chelsea repeater, the four cavities of its duplexer are custom tuned from the factory to only allow signals of 144.850 MHz to reach the repeater’s receive port (and blocked from the TX port) and to only allow signals of 145.450 MHz to be sent to the antenna and blocked from doubling back into the receive port. If there were to be some escape of these signals (or mixing), this would represent an intermodulation distortion and degrade the repeater performance.
One path for the escape of these signals is through the duplexer’s four cavities interconnecting cables. Each cable is less than one or two feet (at 2 meters). To minimize this risk, we utilize the silver-plated double-shielding aspect of RG-214 coax cables. Yes, the cost per foot is astronomical even for us rich Chelsea folks, but we are only talking about a few feet of cabling.
SUPPOSE WE ARE CHEAP
There is nothing wrong with being a spend-thrift. But we don’t want to save a dime and be a dollar short. Some people will say, “No way I am spending $75 on coax when $10 will do.”
Suppose that having installed a total of 3 feet and 5 inches of RG-213 coax in a system of five cables, the repeater experiences a noticeable modulation distortion and or desensitization. What can you do? Our presumptive spend-thrift amateur has agreed to make the RG-214 switch to rid the repeater of its IMD but what can you do right now, today? It may take a week to get into the water tower with the new cabling. You have a net coming up day-after-tomorrow.
What you can try is to turn down the repeater’s output power. RG-213 or LMR-400 is very good cabling and it is certainly fighting the IMD, but it can only do so much. If you put less power into the duplexer, there is less power to escape through the shielding.