WRNA236

Yes, 50 watts is one limit (that for VHF). On 70cm UHF the limit is 70 watts. Those are absolute limits where analysis is mandatory for hams (I'd also have to read Bulletin 65 to see what it says about other services to be honest). But under those limits you may have to do an analysis depending on the situation, such as distance your antenna is from perhaps a fence that limits access or how high up on a roof of your car or on a tower. There are criteria for permanent vs temporary, too. It's not a simple "50 is go/no-go" though.

You're right that the consumer shouldn't be expected to necessarily know everything. Unless they are. The FCC recently changed their stance regarding RF exposure and no longer is there a blanket exception that hams, GMRS, business and other two-way users have enjoyed forever. Now everyone is expected to know the OET Bulletin 65 rules and do exposure analysis if it applies. In the case of legitimately tested portables (in this case Midland seems to follow the rules IMO) the reason you see in FCC documents that some GMRS radios aren't actually 5W is that for uncontrolled exposure you'd exceed the SAR limits. So unless you know for yourself or can warn people you manage radios for about exposure (make it controlled) you have to assume worst case uncontrolled. With a unity gain antenna it works out to about 3 watts when held up to your face. You can use more power it's just that you have to know to potentially limit the exposure intensity and duration, which is what the manufacturers assume. You're handing radios to people who are given some instruction on how to use them or is often the case they have hand mics to move the antenna to arm's length or into a belt holster, for example.

Did there happen to be any weather in the area, perhaps thunderstorms? Investigate what's called tropospheric ducting, that's probably what happened to give you the favorable path. It's hard to predict and ducts form and fall apart quickly. Another phenomenon is sporadic E-layer skip, but this is usually lower in frequency (from about 28 MHz up to 150 MHz if you're really lucky) and often much longer distances. This occurs in the ionosphere and is more predicable as the solar cycle rises and falls.

Looks fine to me for Mk.1. If you use solid 12 or 14 AWG electrical wire like that one I showed you can work it to be straight-ish but for more permanent antennas you might experiment with welding filler rod, coat hangers, metal rods you find at a hardware or hobby shop. Oh, also, you should test it with insulation on and off, you might see if it makes any difference (it should).

Depends on how bad it's pinched. Removing the pinch will help but it's not going to really fix it either. I should also admit that it's not a situation where any damage is automatically bad necessarily. Ideally you have perfect coax but that's also not realistic and a little damage isn't going to take your SWR from perfect to terrible. So if you can test you should but unless you've completely flattened the coax I'd probably not worry too much. I would not notch my sheet metal personally, that's not necessary. I'd just run it until the jacket abrades or the UV takes it toll and be more careful next time. BTW there exist mounts with a short length of tiny coax (RG-174 or RG-316) that transitions to RG-58 after about a foot. This is the slick way to get through gaps.

[deleted]

Someone DID ask the FCC OET and that was their response. The debate is never ending because it wasn't the desired answer to the question.

[deleted]

The U.S. military, for one, is a customer who might want such features. The Fed government operates under a whole different separate set of rules (they are administered by the NTIA, not the FCC) and the DoD is a segment of that. So they aren't bound necessarily to rules that prohibit front panel programming, for example. Also hams can modify radios to our heart's desire without needing to adhere to Type rules (we essentially self certify our radios). Kenwood has historically been ham-friendly (or at least not agnostic) so they're not averse to letting us do that.

[deleted]

[deleted]

This is a fixed station. It's similar to a base or repeater station in that it's in a fixed location. But key distinctions are that it's normally unmanned (like a repeater but mainly different than a base). Fixed stations also usually talk only to other fixed stations (e.g. a remote sensing site talks back to a central site collecting data), which means they usually have Yagis and don't have wide, general coverage. They also may operate on a predictable schedule on predetermined frequencies. BTW, this isn't a GMRS fixed station, but rather a weather station in Rocky Mountain National Park that sends data from the Loch Vale watershed for the USGS and NOAA.

Most people probably do what I did and take the Radio Reference combined chart and set repeater 1 to 8 in sequence. https://wiki.radioreference.com/index.php/FRS/GMRS_combined_channel_chart And indeed when setting up a radio for an unknown person I usually follow the Midland channel scheme.

According to the FCC grant the radio is rated 5 watts. https://fccid.io/2ASNSRT97 As far as filters, doesn't the RT97 already have a cavity duplexer in it? Have you verified that it's tuned? Being off center could be giving you several tens of dB of attenuation and cavity filters aren't wide bandwidths. Just temperature fluctuations can cause them to drift. You shouldn't need a preselector with a cavity filter unless you have a very strong source interfering. It's possible but you need to verify that overload is actually your problem. It's not likely to be out of band with cavity filters, which are going to give you 80, 90, 100dB of notch. You do sometimes see sensitivity issues when the transmitter isn't clean enough and the radios are interfering with each other despite the filters. It's possible and easy to test. Disconnect the transmitter from the duplexer and connect to it either a dummy load or another antenna and see if the reception improves. If this helps then it's not really easy to filter without incurring a lot of insertion loss that negates the steeper notch. Usually means you need a better transmit radio when this happens. When additional bandpass filters are used in repeaters there's usually an accompanying amplifier to offset and the preselectors are also cavities and not discretes. I'd really make sure the duplexer is tuned before anything else.

I think every ham should at least try building a 1/4λ ground plane like this and cut some dipoles. GMRS users are obviously not in the hobby to experiment but I think being able to use stand alone antennas there seems value in understanding how they work and see first hand what impacts performance and issues.

It doesn't get much more reasonably priced than a panel mount SO239 and some old copper wire. Not withstanding the "this isn't ham radio" aspect in a couple of ham radio classes I've taught we built these 5/8λ mobile antennas in a morning as a group. The attendees got a kick out it and most of them ended up being put into actual service on trucks, this being members of my 4WD club, with good results. They aren't quite Larsen or Laird commercial but they're not bad and there's pride in being able to say "I built that" kicking tires around a campfire. http://www.arrl.org/files/file/Technology/tis/info/pdf/8009022.pdf Although for a home installation a J-pole makes more sense IMO. If you can find - and afford - enough copper pipe anyway.

Speaking of Kenwood APRS, I also haven't seen anyone mention Mic-E APRS packets, which seems compatible. Both Kenwood and Yaesu ham radios use Mic-E encoding, although it's application has drifted from the original intent. Mic-E stands for microphone-encode and it pares down packets to be very short so that they could be burst when you release your PTT. Sort of like a roger beep that's actually useful. The very minimum location plus indentifier Mic-E packet is 25 bytes but even if you add your call sign and some telemetry or status (such as voice frequency) to end up with the largest defined packet it'll still be about 300 ms on the air. It's pretty similar to MDC data, for comparisons. It dodges the busy channel issue but it's also not automatic nor independent of the PTT.

The antenna is almost always not supposed to use the coax shield, that would not make it not a shield anymore. You go to great lengths to prevent this in fact with chokes. Coax as feedline should not be radiating and the length should have no significant effect on SWR. There are intentional exceptions to this, such as using coax stubs as impedance matching and there are designed coax antennas. Usually when this will happens it's due to an issue such as the mount location not providing a sufficient ground plane (counterpoise). The RF wants to complete the circuit and will find whatever return it can back to the radio. This would be my guess as to your issue. The mount isn't well grounded to the vehicle or you're using an antenna that needs a plane and you don't have one. You might make it work but it's not optimal. For one the coax shield radiating will create local EMI. This causes anything from irritating noise to potentially problems. You might just get buzzing on your mic or you might reset your computers. On the flip side if the shield is part of the antenna you open yourself to conducting radiation from the environment, you'll get bad alternator noise or cross talk from other radios or your cell phone. Shields work both way, to keep transmitted energy contained within the coax and to keep external noise out. So in a vehicle having coax radiating is almost always bad. BTW, regards to soldering PL259, it's kind of an art because heat will definitely melt the dielectric so it's about speed. You want a good soldering iron with lots of mass. You want the heat put into the outer shell fast, get the braid soldered in a second or two and get out. If you have to sit there and hold your iron for tens of seconds then you're probably ruining the dielectric. I have an old 100 watt leaded glass soldering iron I use for this although honestly I prefer crimp connectors much more. In the case of PL259, though, I use solder center, crimp outer types. I find the crimp/crimp have too long of a nose to always fit SO239s. But any other type - BNC, N, SMA - I always crimp.

[deleted]

I'm surprised Nine Mile Station didn't have a procedure that had to be followed clearing stuff for surplus. Maybe they were leasing their radios.

If you're interested in going down the rabbit hole you can read about antenna isolation with respect to repeaters. The general rule of thumb is the safe separation for same-band unity gain antennas using 50 watts is four wavelengths. How you arrive at that this is 50 watts = +47 dBm and you get about 34 dB of path loss at 4λ. So +47 dBm - 34 dB = +13 dBm, which is right around the absolute max signal strength most radios can safely tolerate. Most tests limit max signal strength at the antenna port to +10 dBm. This is just to protect against damage. You will desensitize the receiving radio, just probably won't blow the front end. But this is impossible to achieve on a tower shared with other repeaters. So they've done all kinds of study and experiments with how to best optimize physical separation because cavity filters are physically large and expensive, have insertion loss and keeping them tuned is a pain. That's why vertical separation and radiation patterns are so important to repeaters. You want to get one antenna physically located in the null of the other.

[deleted]

The impedance of coax relies upon the inner and outer diameters being constant. It's best not to pinch any coax but especially if it's used to transmit or reception is critical it really needs to stay round. More technical stuff. In this the diagram the 'εr' stands for the dielectric constant, which varies depending on the material used. Take a typical coax, RG-58/U. This has an inner conductor O.D. of 0.036", which is the same as the dielectric I.D. (Di), and the dielectric O.D. (Do) is 0.116". With a solid polyethylene dielectric constant of 2.25 this gives your characteristic impedance of roughly 50Ω (calculates to 46.8Ω). With the shield and outer insulation thicknesses the overall O.D. will be 0.195". For the sake of argument say you pinch the coax so it's outside is 5/32" (0.15625"). The inner conductor and shield are unlikely to compress being copper and tin. So it'll be a little bit of the outer jacket but mostly the dielectric that distorts. So say the dielectric becomes 0.07725" in O.D. now. The impedance at that pinch be calculated and will be about 30.5Ω. With that a lot of other stuff can be found. Reflection coefficient can then be calculated, that will be 0.25. With this you can estimate VSWR, that's going to be 1.67. Other things can be estimated, mismatch loss for a reflection coefficient of 0.25 is 0.28 dB. Return loss will be 12 dB, which means about 6.25% of the transmitter power is reflected back due to this example pinch. If you need coax to go through narrow spots you can use a smaller in diameter coax, such as RG-316. There's a downside in distributed loss, meaning to avoid a mismatch in impedance (it'll remain a constant 50Ω) the cable has higher loss (at UHF this is substantial). So you'd want to especially keep it short. There are some antenna mounts that mix coax types, a short length of RG-316 at the end to get behind a seal that then transitions to RG-58 or RG-8X for the length inside the vehicle.

[deleted]

It is interesting how people grow accustomed to full duplex conversations. I'm kind of the opposite since I talk on two-ways as much as anything. I find I don't say much in Zoom meetings. My habit is to hesitate a couple of seconds to make sure the speaker is complete (e.g. subconsciously i'm waiting for the repeater tail or squelch drop). During which time someone invariably jumps in and starts speaking!