Lscott

Just for the record this is the FCC rule part covering public safety frequencies. https://www.law.cornell.edu/cfr/text/47/90.20

So a fiber link would be more reliable than a cable link? I would agree if we're talking about a cheap DSL connection to the local telco. Just for information purposes what is the typical link speed you think, or based on experience, makes a high quality link for VOIP traffic between linked repeaters?

Well what about all the old boat anchor equipment out there using analog VFO's? Those radios can very easily run outside of the official band limits. As a Ham it's YOUR responsibility to ensure station operation occurs within the service's band limits. In fact crystal calibrators were popular projects at the time to check RX and TX dial calibration. Some radios had them built in. Hams have gotten spoiled by the firmware in modern radios that prevent out of band operation. So would the section referenced in a prior post now make owning one of those old radios illegal?

Wouldn't that also be true with other digital voice modes using Internet linked repeaters? That would be independent of whose equipment was used at the end points for the RF part.

The few I got were between $50 and $100 each.

http://www.w3pga.org/Antenna Books/Reflections III.pdf

I’m going to look into that a bit more. It would be nice to have some cheap hardware that does digital modes that would be costly buying commercial radios to do. Might be more fun than screwing around with a hot spot.

It's a cheap way to experiment. If the radio gets bricked with funky firmware won't cry much. Better than bricking a $500 radio.

https://www.law.cornell.edu/cfr/text/47/90.407 https://www.law.cornell.edu/cfr/text/47/97.403 https://www.law.cornell.edu/cfr/text/47/97.405

That would be a very interesting test. I would like to see just how much adjacent channel rejection the radios really have. The transmit bandwidth can be controlled through careful pulse shaping while in digital mode. That's why you see mention of such things as GMSK modulation for some digital modes. https://en.wikipedia.org/wiki/Gaussian_filter https://www.electronics-notes.com/articles/radio/modulation/what-is-gmsk-gaussian-minimum-shift-keying.php https://urgentcomm.com/2001/04/01/does-the-digital-radio-standard-come-up-short/

My question about using two adjacent 6.25KHz channels, or even 12.5KHz channels, is how steep are the filter skirts in the radio's IF section. They typically use cheap ceramic resonator type filters. If they're not extremely steep the attenuation of the adjacent channels will be noticeably degraded because the IF filter pass response would still be fairly high as it overlaps the adjacent channel's bandwidth boundary. For example you might see a selectivity specification of negative 60db at 30KHz using a 16KHz wide signal, 5KHz deviation with 3KHz audio. That would imply the filter skirt's roll offs are 14KHz total for both sides. Reducing the signal bandwidth to 11KHz, 2.5KHz deviation with 3KHz audio, and adding in the same filter skirt bandwidth, roll off is the same but pass band is narrower, results in a possible performance of negative 60 db at 25KHz. The total bandwidth is less but it's not as narrow as you would first assume. For mobile/base radios there is enough room to put in better analog filters with steeper roll offs. However in portable radios' HT's, PCB area is limited. Perhaps replacing the analog filters with a high order DSP based one at a lower IF frequency might work. You can design a DSP filter in hardware using an FPGA which would give better performance than a DSP type micro could provide. Any claims that going to a bandwidth of half of the former value the number of channels can be doubled I'm very skeptical about it without some major improvement in the filter technology IMHO.

I think the FCC, and other agencies in other countries, will move most users to 6.25KHz, most likely digital, when the technology is easy and cheap enough. There was a post somewhere I read where the FCC considers 12.5KHz as an intermediate step before moving to the narrower 6.25KHz bandwidth. If you don't have a radio that can do 6.25KHz now I would start looking for one. That's why you see mention of the TDMA method used for DMR as being 6.25KHz "equivalent" bandwidth even though the channel bandwidth is 12.5KHz. NXDN uses FDMA and can do 12.5KHz and 6.25KHz bandwidth, both in digital mode, depending on the VOCODER data rate used so it's already when the ultra narrow bandwidth is mandated by the FCC. https://en.wikipedia.org/wiki/NXDN

Ok. Those are the newer models.

A lot of companies don’t understand how their customers use their software. The Internet connection required to run it, license servers, dongles and all the rest of the crap really keeps me using older software that isn’t shackled 10 different ways. Some companies have legally purchased the software then go out and find a crack for it to avoid the hassles the licensing forces on users.

Which NX model radios did you test?

My Kenwood P25's and NXDN radios use AMBE+2. I believe it is backwards compatible with the older IMBE VOCODERS. If there is any audio differences I suspect that's due to different bits rates and compression used on the data stream. Some radios, codecs, don't do well in a noisy environment. The codecs are highly optimized for human voice only and in a noisy environment the audio gets distorted. Those radios have some kind of noise filter to process the audio before going to the VOCODER. In fact one complaint I've read is with the NXDN radios used by railroads. A lot of the equipment is controlled by tone sequences which works poorly over digital NXDN voice channels. They revert to analog FM when necessary when tone control is required.

That's too bad. I would have taken a couple of the XTS-5000's you trashed for free. A buddy got a used one for 800 MHz which he's using as a scanner for the local PD. I have some Kenwood NX-200's and NX-300's for NXDN. They use the same VOCODER chip as the Kenwood P25 radios I've got. https://purcellradio.com/Downloads/Radio/Kenwood/nx-200-300_brochure_nx-200-300-brochure.pdf The sound quality should be about the same I would assume between the P25 and NXDN radios.

If I understand things correctly P25 Phase 2 is for trunking operation only. I would assume for basic P25 repeater and simplex Phase 1 should be good enough, at least for Ham Radio use. Maybe as various agencies switch to Phase 2 radios more Phase 1 units will show up on the used market for reasonable prices. I did some haggling with an eBay seller the other week and picked up a used TK-5220 VHF P25 radio for $175. That pairs up with the UHF TK-5320, 400-470 band split, so I have both bands covered. https://pdfs.kenwoodproducts.com/18/TK-5220&5320Brochure.pdf

I picked up a nice clean XPR-6580 too for 900MHz. The guy selling it already has a code plug built for the Ham band. I did get a second one but for various reasons the calibration got screwed when I tried to revert it to analog/DMR from the trunking version of the software. That radio is sort of a junk one I’ll use to experiment on before mucking around with the good one. The in memory software hack to get the CPS to accept frequencies down to 902MHz does work well. You just have to remember to do the hack each time you load the CPS and then the code plug you hopefully saved to disk. You can’t read the one in the radio out. The CPS will trash the out of range frequencies.

A quick estimate is take the square root of the antenna height in feet and multiply by 1.4 to get the line-on-sight distance to the radio horizon in miles. In your case that works out to about 6.3 miles. If you assume the other station is an HT held at 5 feet it’s distance to the radio horizon is about 3.1 miles. With trees and other obstructions between the two radios your real range might be a lot less.

Yup. Keep playing “twist the dragon’s tail” game sooner or later one wins and gets the flame prize.

Looks interesting.

Yeah, the fold over spring is shot. At highway speeds the darn thing lifts out of the socket base and flips over, I had to use several layers of electrical tape to hold it in place. Whenever I need to go to some place with low clearance I have to unscrew it from the base and stow it inside the Jeep. Sort of a pain. The antenna is about 20 years old. I hate to give it up since the match is fairly good on the Ham bands, MURS and GMRS and is ground independent too. Comet doesn't make this model any more. The closest they have is the CA-2x4SR. However it's a 5/8 wave design on the 2M band and requires a GOOD ground plane to work. I have one but the match sucks using the current mount I have for the old antenna. How often would I use a motorized mount? Whenever I want to park the Jeep in my garage, go through a drive through, need to park in a parking structure etc. I've even taken it off to get an old change. The tip of the antenna even drags across the glass on the huge roll up doors at the quick oil change place when the door is up all the way. Yeah it will see some use. Antenna Scan Results (CA-2x4MB FRS_GMRS Jeep).pdf Antenna Scan Results (CA-2x4MB MURS Jeep).pdf Antenna Scan Results (CA-2x4MB UHF Jeep).pdf Antenna Scan Results (CA-2x4MB VHF Jeep).pdf CA-2x4MB Manual.pdf

I thought about adding in some micro switches for the up and down position. I would think adding them internally by Diamond would be the better solution. External position sense switches are likely to get buggered up after a while being exposed to the weather.