Amateur Equipment Standards

There is an article floating around the internet that appeared in our club newsletter last month on the topic of what radios may and may not be used in Amateur service. It makes the case that Amateurs may use any type-accepted radio for any service, and that non-type-accepted radios for other services are not usable by Amateurs on Amateur bands. Both of these statements are untrue, or at least not the entire truth. I’d like to clear things up a bit.

Type acceptance

Type acceptance of radios is a term used to specify a model of radio that has been demonstrated to meet the requirements of a particular FCC role (e.g., public service use on the VHF high band from 148 to 174 MHz). A type accepted radio gets an FCC ID and may then be sold for the purpose for which it was type accepted. The aforementioned public service radio, for example, would be type accepted for “Part 90”, or the portion of the FCC regulations relating to privately-licensed land mobile radios. Business band radios would have a similar license, while Citizens Band radios would be type accepted under Part 95, Personal Radio Services.

Each part of the FCC regulations specifies requirements for radios that may be type accepted for that service. This includes things like spurious emissions, the type of RF modulation used, maximum power output, how radios must be marked to indicate their compliance, and other technical requirements that vary by service. Some of these requirements are very strict, and some are more lax, but all are specific to the particular radio services they regulate.

Amateur service

Amateur radios do not require type acceptance. Likewise, type acceptance for another service does not indicate that a radio is appropriate for amateur service. In lieu of type acceptance, the FCC lists a number of requirements for Amateur station operation in Part 97, our part of the FCC regulations. In particular, Part 97 Subpart D specifies the “Technical Standards“ that must be met by an Amateur station, including, as for type accepted radios, allowable emission types, spurious emissions, power levels, etc.

The big difference here is that the requirements for Amateur service are not for the radio itself, but for the station in operation, and thus the onus of correct operation is not on the radio manufacturer — it is on the individual Amateur! This is a lot of responsibility, but along with it comes a privilege that no other licensed service is granted: the ability to build our own equipment. Licensed amateurs are the only FCC licensees authorized to homebrew radio equipment and transmit with it on the air without testing and acceptance from the FCC. Likewise, we are the only service permitted to use radios type accepted for a different purpose for our own use. This is why a radio Amateur may purchase a Part 90 certified business band radio, for example, and use it on the 2 meter Amateur band.

Impedance mismatch

As we have just seen, the regulations for commercial and Amateur service are significantly different. This creates a bit of a mismatch when discussing radios taken from another service and used in Amateur service. To continue with the above example of a VHF high band Part 90 accepted radio, such a radio is not automatically allowable on the Amateur bands! It is allowable on the Amateur bands if its emissions satisfy the requirements of Part 97, independent of its Part 90 acceptance. Furthermore, it is the responsibility of the Amateur operating the radio to ensure this!

It is entirely plausible for such a radio to achieve Part 90 acceptance but not be suitable for Amateur service. Playing fast and loose with the regulations and terminology for brevity, suppose that the radio has a fixed frequency of 170 MHz and a 50 W final amplifier topology that produces a second harmonic of 50 dB below the primary emission, and that it meets its Part 90 requirement of 70 dB below the primary emission for this spurious emission by way of a low-pass filter that reduces the 340 MHz second harmonic by exactly 20 dB.

An ideal low-pass filter does not attenuate low frequencies at all, and eliminates all energy above a stated frequency entirely. However, in the real world, low-pass filters attenuate low frequencies a tiny amount, and above some frequency by (steeply) increasing amounts. An LPF with -20 dB attenuation at 370 MHz and approximately 0 dB attenuation at 170 MHz might, for example, attenuate frequencies near 350 MHz by only 10 dB, and frequencies below about 250 MHz not at all.

Consider that this radio, used on the 2 meter Amateur band, will be operating below 148 MHz. The second harmonic of 148 MHz is only 296 MHz. The low-pass filter designed for 370 MHz is far below its design spec at this point! If it attenuates by only -5 dB at this point, and the second harmonic remains 50 dB below the primary emission, this is only 55 dB of attenuation. However, Part 97 states that an Amateur station must have no spurious emissions stronger than -60 dBc at this frequency and power level!

This scenario is hypothetical, and these precise numbers are unlikely, but there are certainly circumstances where commercial equipment does not meet Amateur spec when used out of its intended frequency range.

The saving grace

The flexibility of Amateur abilities under Part 97 gives us a lot of power to fix scenarios like the above. For example, if a commercial transmitter does not have satisfactory harmonic suppression at a particular desirable Amateur frequency but otherwise operates satisfactorily, we can put a low pass filter on the output to bring spurious suppression within spec and then use it anyway! This also allows us to use devices in ways that are not allowable in their original service; for example, Part 15 (unlicensed transmissions) regulations are used to certify most household electronics (this is the regulation that causes devices to have a statement on them to the effect of “This device must accept any harmful interference and may not cause any harmful interference’ and an FCC ID), including electronics that use the unlicensed bands such as 2.4 GHz — like Wi-Fi access points. Amateurs can legally open these up and raise their power levels much higher than allowable Part 15 limits, then use them to create wide-area mesh networks … and many Amateurs do just that!

Likewise, if a commercial radio does happen to meet Amateur requirements, an Amateur may use it on the ham bands without any sort of specific type acceptance or formal verification of suitability. The individual Amateur is simply responsible for ensuring that it meets spec.

Part 15

The other, related argument in this vein is that commercial equipment imported from abroad without Part 15 type approval cannot be used by Amateurs in Amateur service. Similar to the argument that all Part 90 type accepted units are immediately usable by the Amateur, I find this specious. Homebrew equipment is not Part 15 type approved. Neither are many of the boat anchor radios we use. While I agree that the sale and distribution of such radios is of dubious legality, I see no reason that the radio Amateur, having verified that the radio meets the requirements of Part 97, cannot use it.

Note that while this specific scenario is not discussed in Part 97, the construction and sale of amplifiers is. Its requirements are all placed on manufacturers and importers, and it even allows non-certified amplifiers to be sold — but only to Amateurs! The intent here is clearly that the radio Amateur should have the equipment available, should the individual wish to verify (or correct) its compliance before use. (See Part 97, Subpart D, section 315.)

Conclusions

In conclusion, we find that the Amateur Radio operator in the US has a lot of flexibility to use a wide variety of equipment — including homebrew — regardless of its origin or stated purpose. However, each individual Amateur is responsible for making sure that his or her equipment meets the requirements of FCC Part 97, including spectral purity and allowable emission types. Radios marketed to radio Amateurs are typically designed (now, but this has not always been true!) to ensure that their emissions are within spec at all times. Radios marketed to other services, or imported from abroad, may require verification by the individual operator.

So go forth and acquire radios from other services to be repurposed for Amateur use, just make sure they’re suitable! If they’re not, fix them, document the fixes, and increase the pool of available radios for your fellow hams!

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