dosw

I have a TinySA that has been kind of fun to figure out and test with. I received a couple of attenuators today through Amazon, and have finally been able to hook a radio directly up to the TinySA rather than just receiving through its antenna. However, I'm seeing power output levels that don't really make sense, from the radio I'm testing with. The attenuators I got are SMA 10w 40dB DC-3GHz and SMA 10w 20dB DC-3GHz (a 40dB and 20dB attenuator). The test hardware: TinySA SMA 10w 40dB DC-3GHz attenuator Baofeng AR5RM radio set to mid power (typically measures around 5w with my Surecom SW102). Whatever connectors are needed to get them connected to the TinySA. Pre-setup: I calibrated my NanoVNA, and then tested the attenuator along with the cables I'm using with my NanoVNA and measured the attenuation to actually be 41.5dB. Configuration: Radio -> 40dB attenuator -> short SMA-M to SMA-M cable -> TinySA device. TinySA: "High" mode (UHF), Level/ExtGain=-41.5dB, Frequency/Center 467.6750, Frequency/Span 18kHz (doesn't seem to matter even if I set 500kHz), Units: Watts. Radio: Mid power, GMRS repeater 20 / 462.6750+5=467.6750MHz output. Test: Key up the radio at mid power. I expect to see 5w. I see 2.304w. Key up radio at high power. I expect to see just a hair under 10w. I see 2.304w. Key up radio at low power. I expect to see 2.5w. I see 1.631w. Plug the radio into my SW102 with a 50w dummy load on it and retest (no attenuation): High: 9.7w Mid: 5.1w Low: 2.6w Connect to the TinySA again, this time with a 40dB and 20dB attenuator inline: Radio -> 40dB attenuator -> 20dB attenuator -> short SMA-M to SMA-M cable -> TinySA device TinySA: "High" mode (UHF), Level/ExtGain=-61.5dB, Frequency/Center=467.6750MHz, Frequency/Span=18kHz (also tested with 500kHz), Units: Watts. High power mode: 10.29w Mid power mode: 4.601w Low power: 1.83w I don't expect things to line up exactly with the SW102. And there's no telling which is more accurate. The old words of wisdom are "Never take two chronometers to sea, take one or take three." I've got the equivalent of "two chronometers" (no third opinion to help form consensus). But what is interesting to me is that I really do have to use both the 40dB and 20dB at the same time, and calibrate the offset to -61.5dB to get an accurate reading. The TinySA is supposed to be able to handle up to +10dB input. With only the 40dB attenuator, am I getting too close to that +10dB? As I calculate where I should be in dBm input, I 10w=40dBm, minus 40dB attenuation should bring me to 0dBm with no ext gain adjustment. And 5w is 36.99dBm. 36.99-40=-3.01dBm. In both cases, I shouldn't be approaching the danger zone for the TinySA with just the 40dB attenuator. Yet I only seem to get accurate readings if I use both the 40dB and 20dB attenuators in series. Finally, I did test the two attenuators in series, through my NanoVNA, and they came in very close to -61.5dB when connected in series.

This is exactly why I prefer not to use direct chat. The other (less common) reason is sometimes there's no end to it.

I wouldn't do direct chat. But why don't you post a few questions and we can see about knocking out answers for them? At its most basic: Get a license (which you have). Get two radios. Set the two radios to the same channel. Set no squelch tones (aka, privacy tones, ctcss tones, privacy codes, subchannels, dcs tones). None. You and your communications partner go a few hundred feet away from each other with the volume where it is comfortable. One of you pushes the button on the side states his call sign, and asks if the other can hear him. The other pushes the button on the side of his radio, states his call sign, and says yeah I hear you. You're good to go. Next step, if you start hearing lots of construction crews and kids playing walkie talkie, you both select a squelch tone and set the radios to that tone. Now you will only hear each other (everyone can still hear you though). Then you come to the realization that you can only hear each other a half-mile to a handful of miles away, and not reliably. So you come to mygmrs.com and find repeaters in your area. You submit a request to the repeater's owner to use the repeater. He or she grants the request. Then you set one of the repeater channels in your radio correctly. You'll have questions on how to do that. Ask when you're ready.

Laird divested of its consumer antenna business, which is now TE Connectivity. At least that's what I found out dealing with their support.

dB difference = 10*log(p2/p1) 10*log(50/7.8) = 8.07dB 10*log(50/5) = 10dB At least that's how I understand it. And every 3dBi is a doubling.

The Comet GP3 is also well reviewed for use with GMRS: https://forums.radioreference.com/threads/comet-gp-3-analysis.430168/

I see no problem with these, though I would prefer an NMO-mount solution for ease of swapping antennas. Today you might want a 6dBi gain 34" whip. Tomorrow you might want a Ghost antenna so it's not as much of a big deal when you drive around town. And next week you might just want a weatherproof NMO cap so you can go through the car wash. The adapter you want, for your Baofeng UV5G Plus is SO-239 to SMA-Female. The set you linked to is a two-pack, one of them being SO-239 to SMA-Female, and the other being SO-239 to SMA-Male. You don't currently need the latter, though one can never have too many adapter options.

That sounds very sad ham-ish, indeed. And at this point, it's been 19 years. I imagine that a substantial portion of the Extra class operators who looked with fondness upon the CW requirement as a rite of passage, have already found safe passage into the pearly gates.

It's possible they misdirected my inquiry. As I dig a little deeper, the Laird TE B4505CN is now made by TE Connectivity, so it sounds like their mobile antennas spun out to TE, while their internal equipment spun out to Enzurio, which I guess is a division of Dupont now. Trying again...

https://www.ezurio.com/?utm_term=laird connectivity antennas&utm_source=google&utm_medium=cpc&utm_campaign=ezurio-rebrand-search&gad_source=1&gclid=Cj0KCQjwiuC2BhDSARIsALOVfBKIBJ0dKgXXkEyA2TgibvUWVWMHXHgOHsxggDU1lyE4CXW-g2FjPFMaAkqAEALw_wcB It looks, from the Enzurio site that Laird mobile antennas aren't even offered anymore. I found out when I emailed Laird support with a question and they responded with the following: You're looking for information on a Laird Connectivity part. LPM has since divested from Laird Connectivity. They now go by Ezurio, as a matter of fact. See link below. Good luck! Ezurio | Formerly Laird Connectivity Chuck REQUIRES IMMEDIATE ATTENTION: The Laird.com and Lairdtech.com email addresses will be retired on June 8th, 2024. This includes any direct emails to a person as well as our "DL" email format. Please note that the new dupont.com email addresses are not the exact replicas of the previous Laird.com or Lairdtech.com email addresses. Please use the email below if you are not sure of the new "DL" or direct persons email address. laird.sales-inside@dupont.com Regards, Charles Aussem Technical Service Engineer

I made the assumption that this question: "is there a gmrs mobile radio that has air frequencies to listen to" is asking for a 2-way GMRS radio, that can also listen to air frequencies. The AR-5RM is not a GMRS radio. And though it can be configured to transmit on the GMRS frequencies, it exceeds the GMRS power limit by 5x on channels 8-14. So if he's asking for a GMRS radio, that one should be out of the running unless he is ok with not using it for transmitting on those frequencies. It will, however, listen to air band, GMRS, and so on just fine. I still like the radio. But someone who wants to buy a GMRS radio that also listens to airband should know that they're getting a radio that doesn't provide a way to stay within the power requirements of GMRS.

The AR-5RM is not capable of transmitting at 0.5w, and as such, isn't appropriate for channels 8-14. Its low power is closer to 2.5w +/- 0.3w. It's also not type approved, of course. I like my two way radios, but when I need a scanner I use a scanner. Even a 25 year old Pro-92 scans faster than a modern Baofeng, at around 20-25 channels per second. I think a UV5G Plus scans around five channels per second. It takes a Baofeng just over four seconds to get through all 22 GMRS channels. It takes a 25 year old dedicated scanner a second. Let's say that at 25kHz spacing in the air band a Baofeng is 2x faster than scanning set channels, at 10 steps per second. Even a 25 year old dedicated scanner searches through frequency bands at around 50 steps per second. There are 1160 25kHz steps in the VHF air band. You get through 1160 steps in 116 seconds with the Baofeng. You get through 1160 steps in 24 seconds with an old dedicated scanner. Scanning isn't what two-way radios are optimized for.

This ^ My AR-5RM (max 10w) is set to 5w so that I don't drain the battery. If I need extra power, I know where the menu option is for that. My Retevis RA-87 (max 40w) is set to its Mid mode, which is about 25w because it sounds fine that way when I hit repeaters. And again, if I find that I need more power, I know where the menu option is. The frequency that we use for family simplex while skiing/camping/etc. I have programmed into my radios at a low, mid, and high setting so that I can just switch the channel quickly to step up the power if needed.

As you saw in my writeup on the radio, I did test it at its various power levels, and at various regions within the RF spectrum. It's not exactly 10w; usually a few percent low, occasionally a percent or two high. But it is so close it doesn't matter. I can hit a repeater 64 miles away with the 771 and this radio. I think I've hit that same repeater with the UV-5G (old <5w model), with a 771 antenna. Your amazement should really be about the repeater you're hitting's quality setup. I don't know what hardware they're using for some of the repeaters in my area, but if I'm hitting one 64 miles away, and coming through legibly, it's because the repeater is amazing, and the radio is good enough. Not hitting the broadside of a barn, so to speak, is all about line of sight, and path loss (through trees in your case).

I recently picked up a Baofeng AR-5RM. The kit included the radio with battery, a standard "701 clone" antenna tuned to FM (broadcast radio) / 136-174MHz / 400-520MHz, an Abbree AR-771 VHF/UHF antenna, a desktop charger, wrist strap, belt clip, and a manual which turned out to be better written than the manual for my old UV-5R radios. For those who are unfamiliar with this radio, it is pretty much identical to the UV-5G Plus, the UV-5RM Plus, and possibly other Baofeng radios. It's marketed as pushing up to 10w transmit power. The radio is quite a bit larger than the older UV-5G (UV-5R sibling). The screen is much nicer, though I've seen complaints that it's hard to read in bright sunlight. I suspect that's true, though it's still legible to me. The menus seem better laid out, but maybe that's because the display has more characters, so it's easier to understand what the menu is saying. Compared to the UV-5R's 128 memory locations, this radio has 999. Just about the first thing I did was use my old Baofeng UV-5R USB cable to program it with Chirp. This process went smoothly, and the data upload/download is about twice the speed of data transfers with the older UV-5G. Chirp is going to be Chirp -- if you know how to use it with one radio, it works just about the same for any compatible radio, with the addition or subtraction of a few field columns depending on the radio you're programming. I noticed that this radio allows up to 12 characters in the channel name field. And it offers three power levels, low, medium, and high. Through some testing I determined that these equate to about 2.5w, 5w, and 10w. Spurious emissions.... When transmitting with my older UV-5G and looking at the spectrum waterfall on my RTL-SDRv4 I would see a sharp peak at the frequency center, with two short peaks a few kilohertz away in either direction. This isn't terribly surprising, as my SDR's antenna is only six feet away when I test. But when I transmit with the AR-5RM and observe the waterfall, I don't see those secondary peaks on either side of the frequency center. I also used some software to do a wider scan with the SDR to see if there were other significant emissions across a broader portion of the UHF spectrum, and really didn't see much, in my unscientific test. Next I hooked up the Surecom SW-102 along with a dummy load, and tested power output at 2m, MURS, Marine VHF, 1.25m, 70cm, and GMRS frequencies. At low power, the output was usually in the 2.3-2.7w range, with a bit of a dip, closer to 1.9w in the 1.25m band. At medium power, there was another dip down to just over four watts at 1.25m, but in other VHF and UHF portions of the RF spectrum power was very close on either side of 5w -- sometimes a little over, other times a little under, but just barely. At full power it came in around 8.2w in the 1.25m band, but everywhere else was between 9.4w and 10.2w. It's worth noting that as a GMRS radio (for which it isn't type approved), it would be inappropriate to set it up to transmit on GMRS channels 8-14, since they're supposed to be 0.5w channels, and this radio really doesn't go below about 2.5w. For MURS (for which it is also not type approved) you're also pushing it a little, since MURS is supposed to be <2w. But 2.5w is only 25% too powerful, versus 5x more power than it should be putting out, which is the situation for GMRS 8-14. The antennas: I did sweeps with a NanoVNA within each of the ranges mentioned above; 2m, MURS, Marine VHF, 1.25m, 70cm, and GMRS. The included antennas perform fairly well. The shorter one had an SWR of <2.5:1 throughout all the ranges except 1.25m, where it was something like 3.5:1 -- not appropriate for use in that band. The longer antenna scored consistently better in all of the ranges I tested. Still not really appropriate for 1.25m. With both antennas, they tended to see a bit too much rise near the top of the Marine VHF spectrum. If this spectrum is important you would probably want an antenna better tuned to that set of frequencies. But they both did pretty good at 2m, MURS, 70cm, and GMRS. I compared a Nagoya NA-771G, and it did even better at GMRS frequencies, at the expense of slightly higher SWR in the lower parts of the 70cm band. The 771G did okay in the upper portions of the 2m band, and MURS as well, though it's not designed to be a dual band antenna. Testing with the long antenna (the Abbree 771) at 5w (medium power) I hit the Ogden repeater (43 miles away) and the Promontory repeater (64 miles away). It helps that I have line of sight to those repeaters. Over Simplex I tested at about 3 miles and 5 miles from my home at each power level using both the shorter and longer antenna. The 5-mile test was more interesting, so I'll rank the results of that test from best configuration to worst. First, though; I did manage to get through to my home, with where I had a VOX recorder set up, using each of the configurations. I'm going to mix my RA-87 (40w radio) with MXTA-26 for comparison: Best to Worst: Retevis at 40w: Full quieting, no static at all. Crisp sound. Retevis at 25w (M): Nearly full quieting, no static. Crisp sound. The noise floor was just very slightly higher. AR-5RM at High with long antenna: Obviously it's going to sound a little noisier at 10w with a 771 clone antenna than the Retevis, but still very good. Retevis at 5w (L): slightly higher noise floor than AR-5RM at 10w. AR-5RM at Medium power, long antenna: noise floor was just a little higher than before. AR-5RM at High power, short antenna: I had to listen several times to hear the difference between high/short and medium/long. But medium/long won by a hair. AR-5RM at Medium power, short antenna: Still pretty good, but high/short was a little less hiss. AR-5RM at low power, long antenna: Noise floor was quite a bit higher, and some static coming through. AR-5RM at low power, short antenna: Considerable hiss and static, but my voice was still very clear, easy to make out. I should have tested against my older UV-5G but I ran out of time. At higher powers, the difference between the long and short antenna wasn't as important. At lower powers, the antenna length mattered a lot more. Overall, though, antenna length seemed to make more difference than power level. Configuration: I don't see much point in draining the battery and singing my eyeballs by transmitting at 10w all the time. The sound quality at 5w from 5-miles away was pretty good, particularly with the longer antenna. And I was able to hit those distant repeaters at 5w. Therefore, as I configured the radio with Chirp, I set channels 1-7, 15-22, and repeater inputs to medium - 5w. I set MURS to Low, 2+w. Marine VHF/16 and the 68,71, etc working channels are set to Low (2+w). I haven't tested it with an antenna -- only with dummy load -- at 2m, 1.25m, and 70cm, and currently have it configured to not be able to transmit on any frequencies. And I've set GMRS channels 8-14 to not transmit, since its minimum power level is way too high compared to the requirement of staying below 0.5w on those channels. To configure it to not be able to transmit on a frequency that you have programmed into its memory slots, you set the "offset" to "off." At that point, when you hit PTT, nothing happens. In Chirp there are four possible offset modes: (blank) which is no offset/simplex; off which is no transmitting possible, + (positive) offset, and - (negative) offset. Air band: I've listened to air band with this radio. When you set it into the airband (108.0000 - 135.99875MHz) it automatically switches to AM, and will not transmit (tested with a dummy load). It does pick up ATC just fine. Battery life: I've never run it all the way down, so I don't know. But I do like that you can charge it either from the desktop base, OR with a USB-C plug. In the spirit of avoiding surprises: This radio, at least in the package I bought, doesn't come with a USB data cable. But it works with the same data cable used with the UV-5R or UV-5G. And within Chirp you chose the Baofeng 5RM profile (my UV-5G uses the Radiodity UV-5R profile). The green button (search): Hold the green button for a few seconds. The phone will say "Search." Now hold the PTT on another radio. In a few seconds this radio will show the frequency, and a second or so later, will show the DCS or CTCSS tone. Then it will let you save it into a memory bank. I can't remember for the life of me how to delete it (other than with Chirp) but that's in the manual, for sure. The point is that you can pair it up to another radio that is already set to a frequency and tone quickly and easily. I tend to be the one setting up my radios and handing them out to family members when we go skiing or hiking, so it's probably not a feature I'll need much. But if you find yourself bringing a radio to an event where you know others will be using GMRS or FRS to keep in touch, you can get paired up to their radios easily. I'm well aware this isn't a $50, $80, $100, or $150 two-way radio; it's a $35 (with extra antenna) multi-band two way radio; it should, by all rights, be a much worse radio. But its power levels are quite close to what's advertised, within about 5-6% of advertised across most of the bands I tested. 1.25cm is kind of the exception, being more like 10% off. But still, this radio is better than it should be. It feels pretty solid. Its sound quality is quite good. Listening to my recordings, it sounds like it transmits clearly. Scanning is pretty slow -- scanning is always slow on 2-way radios I've used. Squelch isn't perfect -- scanning 2m repeaters I keep getting hung up on one that must have another more distant one on the same frequency, too far to hear, but powerful enough to break squelch even when I have it set high. When people review equipment there's often some level of confirmation bias. I'm probably looking for reasons to like the radio, and to defend my purchasing decision. If I were looking for negatives, things not to like, I would come up with a few: It's quite a lot bigger than the UV-5G / UV-5R. It doesnt' fit into a pocket as easily. The included ABBREE 771 knockoff antenna feels cheaper than my Nagoya 771G, and the 701 knockoff is even cheaper than that. The scan button requires a long press, and an accidental short press puts you into a DTMF transmit mode that you can't seem to get out of except by hitting the "monitor" button once, which is an undocumented path. The antenna jack is SMA-M, whereas the UV-5G was SMA-F, so I had to order different adapters to be able to use an external antenna. The dust cover over the mic/speaker/data ports feels like it could wear out if you're opening and closing it a lot. Unlike the UV-5R/G you can't alter the levels associated with the squelch settings. That was a common customization people made with the UV-5R series. The USB-C charging light on the back of the battery shows a dim green when fully charged -- too dim to see in outdoor daylight. You can't set the power level low enough to meet power requirements for GMRS 8-14, but I don't really care about using those channels anyway; my mobile radios can't use 8-14 either. In the overall picture, those are minor things, for a $30-35 radio.

The technical aspects are worth considering. For the main channels (15-22, and repeater inputs) in the 462 and 467MHz range, you may configure your radio for wideband or narrowband. The channel spacing is 25kHz. Wideband is 16kHz with a transmitter deviation of +/- 5kHz. You may optionally configure narrowband. Same channel spacing. Bandwidth is 11kHz with transmitter deviation of +/- 2.5kHz. On the mains, you may use power levels up to 50w, though handhelds are rarely more than 5-10w, usually less. For the 462MHz interstitials (1-7), the same rules as above apply, though you are limited to output of 5w. For the 467MHz interstitials (8-14) you should be using narrowband (11kHz with deviation of +/- 2.5kHz), and no more than 0.5w. This additional power and bandwidth limitation is designed to prevent the interstitials from interfering with the repeater inputs. The 467MHz interstitials also are handheld only. The reason I mention all this is because some handheld radios won't transmit as low as 0.5w. My AR-5RM, on low, transmits at 2.5w, which would be 5x the limit for the 467MHz interstitials. If I were to use that radio for GMRS I would not set up those channels (8-14) for transmit at all, so that I'm not risking causing interference with repeater inputs. Keep in mind that in the actual frequency chronology GMRS is laid out like this: 462.xxxx MHz: 15 01 16 02 17 03 18 04 19 05 20 06 21 07 22 Max Power(w): 50 5 50 5 50 5 50 5 50 5 50 5 50 5 50 Bandwidth: W W W W W W W W W W W W W W W 467.xxxx MHz: R1in 08 R2in 09 R3in 10 R4in 11 R5in 12 R6in 13 R7in 14 R8in Max Power(w): 50 0.5 50 0.5 50 0.5 50 0.5 50 0.5 50 0.5 50 0.5 50 Bandwidth: W N W N W N W N W N W N W N W You can see that the channels are interleaved. 15-22 and R1-R8 inputs are considered the "main" channels, and 1-7 / 8-14 are the interstitials -- the ones that are scaled back a bit in power to reduce interference with the mains. If the radio can be set up like this, then it would be working identically to how a type approved GMRS radio would transmit, though it would still be non-compliant in terms of type approval itself. If it can't be set up for <=0.5w on channel 8, for example, it probably shouldn't be transmitting on 8-14 at all. I like the old USPS mail commercial slogan, "If it fits, it ships." I can make channels 1-7, 15-22, and the repeater inputs fit within the permissible limits for power output and bandwidth. With one of my handheld radios, I can't make the radio scale back on power enough to fit in the 8-14 channels. So it gets used on 1-7, 15-22, and repeaters, but does not get used to transmit on 8-14. And I really don't miss being able to transmit on those frequencies, with their 0.5w max.

Fortunately I only bloviate in forums, not over the airwaves.

Broadcasting is over the air. This is really just listening in, and providing a feed to the listening device. Two way traffic, be it simplex or duplex carries on as it always has. But a radio happens to be listening and putting a feed online. I don't think this violates any rules, and therefore could be a nice feature in the absence of this site carrying interconnected repeater networks.

So if GMRS frequencies are permissible, this may fall into a category of site feature request: Allow repeater listings to provide a feed link. Let the feed software that the site has been using for linked networks instead just provide audio access to the feeds people voluntarily list for their repeater listings.

I'm not saying your use case isn't legitimate. I'm aying there's a lot that can be learned by investigating what others have already learned as they work the 10m, 2m and 70cm bands. I think that you're asserting that you need to know for your specific situation which will work better; CB, MURS, GMRS, at an equivalent power. For that, sure. You're going to have to set a GMRS radio to 2w, and set a MURS radio to high power of 2w, set a CB to 2w if possible, and do your comparisons. But in a broader sense you're asking questions that may be answered by looking at the body of knowledge developed over decades of amateur experimentation with 10m and 2m and 70cm. So I'm not suggesting "Go get your amateur license and be a ham." ...you may already be there, but that's not relevant. I'm just suggesting that the findings of others in those bands would apply to answering your question in general ways, though probably not specific to your neck of the woods.

SDR software allows SDR owners to set up an SDR server that can either be the back end of a web page (websdr.org, for example) or can be connected to by SDR++ itself. I could connect SDR++ to any SDR server on the web that allows me to access it. And sites like websdr.org aggregate sites that provide web interfaces to networked SDRs. Similarly, there are websites online that allow users to listen to radio scanners in varioius geographical regions. Is there now a problem with this paradigm with respect to GMRS? If a website wanted to expose SDR or scanner feeds in various regions, is that now against the rules? Maybe it always has been. Let's say, for a moment, that it is permissible to expose an SDR feed or a radio scanner feed over the Internet. If an SDR feed from Atlanta is set to GMRS 462.7000 with PL 127.3 and that is available to be listened to over the Internet, it's not repeater linking -- people can't respond, they can just passively listen. And if that is okay, a feature of *this* site (or some site) could be to allow repeater owners to provide a link on their repeater's information page, to an SDR, scanner, or radio that is passively listening to that frequency in their area and feeding it through the link. Is the FCC saying, now, that is against the rules? Because if it is, it's the one radio service where that's suddenly a problem. OR all online SDR and scanner websites are in violation, across all radio services they feed, except for amateur bands. I'm just trying to think through the ramifications, and figure out what is allowed, and what isn't.

There's a wealth of information available on 10m propagation, and on 2m propagation, since they are both amateur, ham bands. Probably a lot more you can read up on than if you search for CB vs MURS propagation. I'd start there. CB is 11 meter, ham has 10 meter. They're close enough to be very similar. And with ham 10m, you'll find a lot of information about SSB, FM, and AM: SSB is usually at 28.3MHz to 29.3MHz. AM is usually 29MHz to 29.2MHz. And FM is usually at 29.6MHz, all within the 10m band. And in 2m, you can find allocations for SSB and FM, including weak-signal work. Each of those categories is a world of pet projects for some people (this time I'm using "some people" in a good way, I hope). Consider MURS approximately equivalent in propagation characteristics to FM simplex over 2m. And consider CB approximately equivalent to AM and SSB in the 10m band.

It would do fine at 5w, just like a 2m ham does at 5w. There's plenty of dialogue online about 2m ham at 5w. But it's an unlicensed set of channels intended for short range use. Increasing power would potentially interfere with adjacent frequencies in the MURS neighborhood. There's not enough difference in propagation between VHF and UHF for the FCC to carve out a new set of frequencies to do pretty much exactly what is being done with GMRS, and charge for a $35 license, when we already have GMRS. The VHF spectrum is crowded, so it's an uphill battle to make it happen in a GMRS similar fashion. Amateurs get to leverage the difference in propagation because they jumped through the test hoops and paid their fees. I don't think MURS will or can go to higher power as an unlicensed service because of the impact to paid license neighboring frequencies. And there's just no room for repeaters with only five channels at funky offsets from each other with some allowing wideband and some allowing only narrowband.

I've done some research into ground planes, and it's entirely possible I've got some of this wrong, but here's what I understand: A good ground plane will provide a radius that is at least a quarter wavelength. So for GMRS, that would be at least 6.4" radius. Ground planes should extend in all directions along the horizontal plane, or at a downward diagonal, depending on the antenna / design. If the ground plane isn't a contiguous surface it is often set up as a series of rods. Two opposed rods would have better propagation lobes along the plane of those two rods, and worse at 90 degrees. Three rods is fairly common. Four is also very common. There are diminishing returns for ground plane rods beyond four, though there's always a non-zero positive impact to adding more symmetrical rods. There's also a diminishing return for making the rods longer than a quarter wavelength. But at less than a quarter, the lobe tries to curve around the end of the rods. Asymmetrical ground planes may have a somewhat truncated propagation lobe in the shorter directions. In your case, the propagation lobes may try to curve around the rack's pipe, for example. The point being, I don't think a roof rack's beam is ideal as a ground plane. But ideal may be the enemy of good enough. However, given that there are pretty good "no ground plane" antennas out there, you may be able to at least select one that doesn't force as much compromise. For my RV I use a Laird TE B4505CN ("N" means no ground plane). I had to trim its bottom whip element for GMRS, but product literature helps by suggesting where that sweet spot is. And as I mentioned in another post here recently, it's very easy if you have a VNA instrument (NanoVNA). Someone who doesn't want to buy measurement equipment could probably find someone on a local GMRS repeater willing to spend a half hour helping measure and cut. But for the B4505CN the manual recommends the appropriate length for GMRS. It's a 5.1dbi antenna.

Since I'm a gadget addict I got a NanoVNA a few days ago, for about $59 through Amazon. It came with two SMA-Male to SMA-Male cables, an SMA Female to SMC Female adapter, and three "standards" (open, short, and 50 ohm load), as well as a little stylus, and a lanyard with a guitar pick on it (presumably to use in place of the stylus). I wasn't expecting a lot, but I have to say, this thing is pretty cool, for the price. It's not professional-quality analysis gear, but for a hobbiest it's great. The first thing you should do when putting it to use is to calibrate it for the band you wish to analyze. You use the "standards" that it comes with to perform the calibration. I followed that up by putting an antenna on it, and on my RTL-SDRv4, and verifying its signal generation was accurate. It was close enough without any tweaking. Next, I used it to test some antennas. At first I just confirmed that the MXTA26 is very well tuned, out of the box, centered on 465MHz. And then I put the NA771G on it: In that graph, you can see that I have it configured to scan the range from 420MHz to 480MHz. I've set a marker at 462.2MHz just by dragging it into place with the stylus. I could have set it more precisely through the menu. The S11 LOGMAG represents return loss. The lower the dip on the graph, the better (less reflection/return means more signal is radiating, which is what an antenna is supposed to do). The blue line here indicates SWR. And as you can see for the NA771G, it is 1.055:1 at 460.2MHz. At 480MHz (I don't have a marker set there), it was about 1.27:1. The green curve is the Smith diagram. And the purplse is the |Z|, coming in at 52.2 ohms at 460.2MHz. There are many graph views, I selected four of them. But they include logmag, phase, delay, smith, swr, resistance, reactance, |Z|, polar, linear, real, imaginary, Q factor, conductivity, susceptivity, |Y|, series C, series L, Parallel R, Parallel X, Parallel C, Parallel L ... most of which I don't comprehend. One thing that I learned was how great it is to be able to look in realtime at the various curves. It made it really easy to observe changes as I added and removed the ground plane rods from my Nagoya GPK-01 (Ground plane kit) when the antennas were mounted on a camera tripod where there's no good inherent ground plane. And it was really useful to be able to observe what happens when I take a half centimeter off of an antenna. In the case of the NA771G, if one were wanting to tune it (which you can't), you might decide to subtract a fraction of a centimeter from its length, and you can see that on the chart. I used the SWR and Logmag curves to tune my Laird TE B4505CN antenna, for example, as I recognized its SWR dipped a little further to the left of the GMRS band. By trimming its base element down to about 10" (taking about 2cm off), I moved the dip to 465MHz. And knowing which direction to go was really only possible by looking at these curves and observing what they do as I move the element in and out a little with its set screws. I also tested the pass-through mode using a VHF/UHF diplexer, verifying the cutoff ranges for each of the diplexer's ports. A good feature is the ability to plug it into a computer and command the device, and observe its graphs, right on the larger screen of a computer. On my Linux laptop the NanoVNASaver application was already available for Ubuntu install through the apt and apt-get package manager tools without having to compile from source (one dot-release behind the Git repository). With the free NanoVNASaver software I can specify a scan range and set up multi-pass averaging. And the software can step through a scan range to achieve much finer resolution than the device natively supports. For example, if I use the native 101 data points the device supports to scan from 144-480MHz, that's one sample every 324kHz. Not very good resolution. But if I tell the external software to take 3240 samples, it will step through the range 100 samples at a time, and get me resolution finer than I can reasonably use on a full size monitor. Another interesting option, through the NanoVNCSaver software, I'm able to see feed line length and attenuation. I can test a 50 foot run of LMR400, and a 50 foot run of RG58, and see loss per frequency. That's really interesting information for a hobbiest. Some negatives: If you're completely in standalone mode (no computer), it's only got 100 sample points in a given scan. So if you're trying to optimize a dual-band antenna, you would want to concentrate on 2m, and then on 70cm, going back and forth one at a time, rather than trying to show both on the screen while tuning an antenna. This is where using a computer with a much higher sampling rate is important. Its screen it pretty tiny, too. Having spent the $59, I kind of am on the fence as to whether I should have spent $89 to get the larger screen. On the other hand, adding a computer to the mix, even an inexpensive low-powered laptop, the screen becomes irrelevant, and sample-points become virtually infinite. Another negative is the lack of instructions. It comes with a single page showing where to find the various menu options, but no other explanation. It took some youtube videos and online reading to figure it out. And without a microSD card you're missing out on being able to save screenshots (though you can take a screenshot through the computer's software), and limited on number of calibration configurations you can store. But most of those shortcomings can be overcome with an external computer and/or a cheap microSD card. For my purposes this device is fantastic. With the Surecom SR102, I could see the SWR of a given antenna setup. With this device, I can see which direction things need to go in tuning antenna setups. And I can verify a diplexer is working as intended.