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WRNA236

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  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. Testing is an open-ended question depending on what parameter or characteristic you're validating and how rigorous it has to be done. This is just one example test setup from FCC submitted test data by Harris. Sometimes it's done inside an RF chamber, sometimes in a lab that happens to be quiet enough or even outside like this (to get away from sources inside, like computers). I've seen this set-up in other Harris reports so it must work fine for them. It doesn't necessarily have to be absolutely radio silent as long as you can characterize the baseline with high confidence. Edit To Add: It occurs to me that this won't have answered your question because the fundamental question is still open. "What are they actually testing?" The radio itself was analyzed in simulation so the real article tests are validating those analysis. You don't necessarily have to re-test SWR at every level because if all the analysis was correct you can tell by the field strength and pattern that it radiates like you predicted. If they were interested in SWR they'd probably measure at test points on the circuit board. Whether they test the antenna as a stand-alone item depends. Most of the basics are well understood so you don't have to keep reinventing the wheel. But a novel antenna they would test using a mock-up of the device, like for highly integrated devices like cell phones because they have antennas folded within antennas integrated into the enclosure.
  8. 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.
  9. 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.
  10. I have a mix of DMR radios - Vertex-Standard VXD-720 UHF and VHF portables, a VXD-7200 UHF mobile, a Connect Systems CS800D. I'd run the VXD-7200 in my truck but it's monoband UHF, which is fine for most ham DMR but I still use plenty of analog VHF. Plus the remote mount kit would cost as much as I paid for the radio! In those respects the CS800D is a big winner, dual band VHF/UHF and remote mounting the face was limited to the cost of an Ethernet cable. The CS800D has a few bugs but mostly it's been fine, worth the price IMO. It's not a super cheap radio with a true decent superheterodyne receiver, Mitsubishi power amps, well shielded, periodic firmware updates. I think the key with the Chinese radios is having domestic support. So my $0.02 is to go with what Connect Systems, Bridgecom, Powerwerx, etc. sell. So you'll have a real person within a couple of time zones of you to deal with.
  11. 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.
  12. That's the key. I adopted DMR a few years ago because that was what everyone was experimenting with here. A couple of local repeaters grew into a small network with a C-Bridge that grew with a DMR-MARC and Brandmeister connection and now there's a multi-state linked system that's part of the state ARES emcomm plan that runs up and down the Rockies built around DMR with several smaller sub groups by region. It's actually a robust microwave-linked IP network that's completely stand-alone from the Internet. The last year or so another system has developed that's mostly Fusion-based. It uses public Internet and isn't from what I see nearly as robust. It's got some interesting bridges going on to analog repeaters, a couple of dedicated DMR and NXDN and a Brandmeister talkgroup for push-to-talk repeaters and hotspots. What it lacks in strict architecture it gains in experimentation and lighting up a lot of previously lightly used repeaters now having activity. I stick with DMR because that's what I have available primarily. At this point it's DMR or Fusion going forward it seems to me. D-STAR isn't growing much but does have dedicated users. Icom and Kenwood don't really push it. NXDN and P25 seem local and sporadic. It really comes down to Yaesu aggressively pushing their Fusion with new radios and the Chinese radios adopting DMR. I wish hams would have adopted P25 personally and Yaesu had the opportunity with Fusion C4FM (it's vaguely similar to P25) to do it but they didn't and here we are. Honestly if it wasn't for CCRs adding ham-friendly features I think DMR would have withered. Motorola couldn't care less if hams adopted it or not. As the database grew it was the likes of Anytone who did things like increasing the memory in their radios to allow 50k then 100k then 130k and so on IDs to be stored. They added promiscuous mode (e.g. essentially open squelch for digital, as long as the signal is valid it decodes regardless of time slot, talkgroup and color code). There's been some CCR duds that give fits to repeater owners, radios that don't adhere to timeslots. But most of the CCR DMR radios do fine, it's not really a big problem.
  13. 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!
  14. That's a really slick way to do it. Very inventive! Just a general FWIW statement, don't neglect the benefits of vertical separation. Antennas don't radiate necessarily in perfect 180° spheres and the more gain they have the more flattened their patterns become. There's a zone where the two might interact (which is the principle behind collinear elements) but it may not take much vertical distance to fairly effectively decouple them. Just ferrites chokes I wouldn't think will be enough to filter 70cm ham from GMRS. They are effective for gross filtering, e.g. keeping a feedline from becoming an antenna or preventing a 20m station from affecting your 70cm. They might be enough to keep VHF and UHF from interfering with each other, maybe. Ferrite chokes are several tens up to even hundreds of MHz in bandwidth. So they can't substitute for true in-band notch and pass filters or at very close frequencies, cavity filters. The good thing is it's doesn't have to be difficult or expensive to build and test. Even simple coax 1/4λ stubs might be sufficient. You might find this approach interesting since it only requires coax to test: http://www.radagast.org/~dplatt/hamradio/K6OIK-filters.pdf The fallback is to pull out some caps and get to winding coils. It shouldn't be necessary to use cavity filters, although at 50 watts you might be looking at needing pretty hefty attenuation just the same.
  15. I've read that the T800 has X-Pand but the fella who started the RadioReference thread says it seems less offensive. I wonder too about the T400, which was what I was considering as hand-out radios since high power on them is 1.7 watts according to the FCC test data in their grant. The T600 and T800 are listed as 0.75 watts in the FCC grant.
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