The subject is about FRS/GMRS Walkie-Talkie Antenna Couplers for the sake of retransmitting the signal more efficiently (in or out).
Considering that regulations ask for not altering the certified FRS/GMRS radio unit, including the antenna per se, my question is about conceiving an antennea coupler that would fit, non-contact, on top of the existing radio antenna. For instance, in a 50 Ohm coupler, the absorbed signal could then travel in a standard 50 Ohm coax cable to transport the signal to a relevant UHF antenna.
Imaging a coupler that fits non-contact on top of of the walkie-talkie stubby antenna/ short rubber duck antenna (just the way a milking pod is used on a cow). Since the rules say that one should not modify a certified radio unit, the question is about how would a coupler be designed to fit and "match" the radio antenna as to absorb and retransmit the RF signal with minimum reflection/loss.
From there, a full signal could be passively redirected to a proper antenna that could be mounted to be more efficient and avoid environmental obstacles (mountains, buildings, etc.).
Design challange: Apparently, stubby antennas used in such hand held transceivers are short and may use a wound wire to fit the local antenna in a short space. At any rate, for a good coupling the transmitted signal from the hand held device should be fully absorbed by the coupled device in order to maximize the transmition efficiency of an extended antenna system.
I can imaging a wound wire, so many turns over a lenght covering the stub antenna. However, it is possible that the coupling would be better if designed in a toroidal way where the original antenna would fit in the center of the toroidal core if this would lend a bettern match.
At any rate, the objective is to conceive a non-intrusive coupler (ideally 50 Ohms) that would slide on top of a hand held UHF radio (462-467 MHz) in the best impedance match as possible.
Any design guide lines would be appreciated.
Many Thanks,
Syl

 

Welcome to AAC.

According to FCC regulations, any modification to the antenna invalidates the mandatory certification of the radio.

In FCC 47 CFR 15.204(c) it says:

(c) An intentional radiator may be operated only with the antenna with which it is authorized. If an antenna is marketed with the intentional radiator, it shall be of a type which is authorized with the intentional radiator. An intentional radiator may be authorized with multiple antenna types. Exceptions to the following provisions, if any, are noted in the rule section under which the transmitter operates, e.g., § 15.255(b)(1)(ii) of this part.

(1) The antenna type, as used in this paragraph, refers to antennas that have similar in-band and out-of-band radiation patterns.​

(2) Compliance testing shall be performed using the highest gain antenna for each type of antenna to be certified with the intentional radiator. During this testing, the intentional radiator shall be operated at its maximum available output power level.​

(3) Manufacturers shall supply a list of acceptable antenna types with the application for equipment authorization of the intentional radiator.​

(4) Any antenna that is of the same type and of equal or less directional gain as an antenna that is authorized with the intentional radiator may be marketed with, and used with, that intentional radiator. No retesting of this system configuration is required. The marketing or use of a system configuration that employs an antenna of a different type, or that operates at a higher gain, than the antenna authorized with the intentional radiator is not permitted unless the procedures specified in § 2.1043 of this chapter are followed.​

In 47 CFR 95.561 concerning certification of FRS radios it says:

§ 95.561 FRS transmitter certification.

(a) Each FRS unit (a transmitter that operates or is intended to operate in the FRS) must be certficated for use in the FRS in accordance with this subpart and subpart J of part 2 of this chapter.​

(b) A grant of equipment certification for the FRS will not be issued for any FRS transmitter type that fails to comply with all of the applicable rules in this subpart.​

(c) A grant of equipment certification will not be issued for hand-held portable radio units capable of operating under both this subpart (FRS) and under any other subparts of this chapter (except part 15) if the application for such grant is filed on or after December 27, 2017.​

​

Guidance from the FCC on the topic of antennas says:

Grants for Part 15 intentional radiators must be for complete transmitter systems only

– Thus external photos exhibits in filings should ALWAYS show antenna(s) [§ 2.1033(b)(7)]​

• NOT only the radio portion of a transmitter system Part 15 intentional radiators must be operated with antenna(s) and antenna type(s) identified and tested in an FCC ID record​

​

– §§ 15.204(c) [operate only with authorized antenna(s), including antenna type(s)], 15.204(c)(2) [test highest gain per antenna type, also highest output power configuration(s) across antenna type(s)], 15.204(c)(3) [explicitly identify/list allowed antenna(s) and antenna type(s)]​

​

– § 15.204(b) requires authorized transmission system (e.g., radio + antenna) to be marketed as complete system​

So the bottom line is no amount of passivity will change the fact an FRS radio may only be legally operated with the antenna(s) with which it was certified. Even the use of passive reflectors attached after-the-fact is prohibited!

The problem with antenna modification is that certification is based on EIRP (Equivalent Isotropically Radiated Power) [see: 47 CFR 2.1 “Equivalent Isotropically Radiated Power (e.i.r.p.)”] which doesn’t concern itself with how the antenna is attached, or any other reason that it is increased when operated after certification.

A Part 15 Device, such as an FRS transciever, is certified an a radio-antenna system and so your plan is simply illegal and no finessing of (what you imagine to be) the FCC rules will permit it. CFR §§ 15.204 is carefully written to make it clear that no change to the EIRP of the radio as certified is permitted no matter the method.

The only legal way I can see to do what you (appear) to want is to use a separate receiver. There is nothing prohibited about attaching a gain antenna to a receiver, and so you could effectively increase transmission range by using such an arrangement.

However, the goal of FCC EIRP limits is to ensure that channel loading for a given geographical area is maintained to maximize the number of users of the service (FRS). Given this, if such an arrangement became commonplace—and the commission began to recieve complain—it is very likely they’d engage in rule making to prohibit it.

Since you seem to need something not contemplated by the FRS service (longer range) you should probably consider a different service. Amateur Radio is an excellent possibility—so long as you are not using the radios commercially—which would mean your only choice would be an appropriate licensed land mobile service.

Sorry about that.

 

Welcome to AAC.

According to FCC regulations, any modification to the antenna invalidates the mandatory certification of the radio.

In FCC 47 CFR 15.204(c) it says:



In 47 CFR 95.561 concerning certification of FRS radios it says:

​

Guidance from the FCC on the topic of antennas says:



So the bottom line is no amount of passivity will change the fact an FRS radio may only be legally operated with the antenna(s) with which it was certified. Even the use of passive reflectors attached after-the-fact is prohibited!

The problem with antenna modification is that certification is based on EIRP (Equivalent Isotropically Radiated Power) [see: 47 CFR 2.1 “Equivalent Isotropically Radiated Power (e.i.r.p.)”] which doesn’t concern itself with how the antenna is attached, or any other reason that it is increased when operated after certification.

A Part 15 Device, such as an FRS transciever, is certified an a radio-antenna system and so your plan is simply illegal and no finessing of (what you imagine to be) the FCC rules will permit it. CFR §§ 15.204 is carefully written to make it clear that no change to the EIRP of the radio as certified is permitted no matter the method.

The only legal way I can see to do what you (appear) to want is to use a separate receiver. There is nothing prohibited about attaching a gain antenna to a receiver, and so you could effectively increase transmission range by using such an arrangement.

However, the goal of FCC EIRP limits is to ensure that channel loading for a given geographical area is maintained to maximize the number of users of the service (FRS). Given this, if such an arrangement became commonplace—and the commission began to recieve complain—it is very likely they’d engage in rule making to prohibit it.

Since you seem to need something not contemplated by the FRS service (longer range) you should probably consider a different service. Amateur Radio is an excellent possibility—so long as you are not using the radios commercially—which would mean your only choice would be an appropriate licensed land mobile service.

Sorry about that.

Thank you for the rapid reply.

I had a feeling that this would be the case. Your explaination is complete and makes sense. I am personaly a licensed ham operator and I do have equipment that works at a higher power level than FMR/GMRS. However, not every body does.

The problem that I am trying to address is about a situation that just occured, namely, regarding people that I know who went hunting recently and there was a serious accident (in the far wilderness with no cell phone coverage). They always carry their FMS/GMRS walkie talkies with them but the range is very limited. New such radios offer an emergency call feature which is somewhat helpful as long as other people can hear the call. This environment has mountains everywhere.

So, this is why I was thinking of a means of making a non-contact add-on device where a more efficient antenna could be mounted up high in a way as to provide security in the case of emergency. And, honestly, I was not intending this as a means of bypassing the spirit of the regulation.

The other case is when using this walkie-talkie while traveling in a car. The car acts somewhat as a Fraday cage where the signal is partially trapped inside the car and only a part can escape through the windows. So, mounting a roof antenna (with the equivalent gain as the originall antenna) would help in keeping the signal quality without affecting the EIRP.

Thank you again for your help.

 

The problem that I am trying to address is about a situation that just occured, namely, regarding people that I know who went hunting recently and there was a serious accident (in the far wilderness with no cell phone coverage)

Ah, well in this case, if the device was only used in emergencies presenting a risk to life, the law would almost certainly allow it. But, I am not sure one would be allowed to market it.

In the car situation, a passive repeater arrangement might be permitted because I know they were previously sold for handheld cellphones in the analog days. It this case, I believe the EIRP (outside the vehicle) would be reduced from the permitted maximum,

But, for your emergency, I would suggest looking into the various satellite-based devices now on the market. They are text message only but offer affordable subscriptions, emergency locater functionality, excellent coverage, and non-emergency messaging. Some also include live (private) tracking.

 

Ah, well in this case, if the device was only used in emergencies presenting a risk to life, the law would almost certainly allow it. But, I am not sure one would be allowed to market it.

In the car situation, a passive repeater arrangement might be permitted because I know they were previously sold for handheld cellphones in the analog days. It this case, I believe the EIRP (outside the vehicle) would be reduced from the permitted maximum,

But, for your emergency, I would suggest looking into the various satellite-based devices now on the market. They are text message only but offer affordable subscriptions, emergency locater functionality, excellent coverage, and non-emergency messaging. Some also include live (private) tracking.

Thank you Ya'akov for the suggestions.

The satellite based device is a good idea indeed. Something to look into.

As for the antenna coupler, this is not for a commercial intent but simply to help people as previously described (emergency) and for personal use only. Do you have any design suggestions as to achieving a good match with the integral antenna, namely absorbing all of the transmitted RF signal and not causing internal reflections back into the walkie talkie during a transmission. The impedance of the coax coming out of the coupler would likely be 50 Ohms. It is assumed that the SWR in the remainder of the system would be as near to 1:1 as possible. I am thinking of a generic solution but the unit that I plan to use this with is a Motorola T473.

Thanks.
Syl

 

Beyond the idea of a resonant coil, I’m sorry to say I don’t. Generally, I don’t think you should expect very high efficiency. It is likely that the existing antenna is not a particularly good match since it has to one fairly broadband.

I think I would a coil with a diameter that allows it to fit snuggly over the antenna, and making it resonant on a particular channel so get the best Q rather than try to cover the band. A variable match would help get it right, though I’d expect it to be very sensitive to the operator’s body (touching. &c) and its own load—the gain antenna.

Do you have an NanoVNA? I think it might be an investment in mental health if you don’t already have one.

One more thing I just thought of: a lightweight collapsable pole (tent poles that nest?) and a remote speaker mic, allowing the user to raise the radio (and it’s antenna) high above average terrain might be a solution...

 

Beyond the idea of a resonant coil, I’m sorry to say I don’t. Generally, I don’t think you should expect very high efficiency. It is likely that the existing antenna is not a particularly good match since it has to one fairly broadband.

I think I would a coil with a diameter that allows it to fit snuggly over the antenna, and making it resonant on a particular channel so get the best Q rather than try to cover the band. A variable match would help get it right, though I’d expect it to be very sensitive to the operator’s body (touching. &c) and its own load—the gain antenna.

Do you have an NanoVNA? I think it might be an investment in mental health if you don’t already have one.

One more thing I just thought of: a lightweight collapsable pole (tent poles that nest?) and a remote speaker mic, allowing the user to raise the radio (and it’s antenna) high above average terrain might be a solution...

Hello Ya'akov,

Thank you for the interesting ideas.

As for the nanoVNA I do not own one for now but I was consirering it. I have seen many Youtube videos where people use it and it looks like the tool to have.

Tuning a resonant circuit might be a good solution indeed. Moreover, while the FRS/GMRS occupies 462/467 MHz, the most popular channels are on 462 MHz (Ch 1-7, 15-22) as the power limit is more restricted on 467 MHz (Ch 8-14). So, tuning for 462 MHz would likely be optimal when looking for help over a large territory. Consequently, this choice narrows the bandwidth considerably.

The idea of mounting the walkie talkie up high on a pole with a remote mic/speaker is also a good idea. One drawback is if one needs to change channels while trying to get attention.

All in all, I think that I have many possibilities to explore.

Again, many thanks for your ideas Ya'akov.

Syl