Batboard

As usual, suddenly I have to get up to speed on a product I've never seen, touched, or bled on. The railroad industry apparently had a convention recently, and they are convinced 6.25 will happen sooner than later. They urged their members to leapfrog 12.5 and go straight to 6.25 in their system migrations. Motorola has abandoned the RR market leaving Kenwood Nexedge and Icom iDAS. Reading up on the technology, it looks like they developed this together, and are doing something similar to Mototrbo. Rather than real 6.25 channelization, they are doing 6.25 "equivalent" with two subchannels in a 12.5 split.

Can someone discuss this?

Thanks.

It's actually a true 6.25KHz carrier, FDMA modulated. Appears you are conflating IDAS/NXDN with MotoTRBO, which is a 12.5KHz carrier modulated into 2 timeslots, giving 6.25KHz equivalency.

Not sure what else there is to be said here, their marketing collateral explains everything pretty clearly.

The current photos don't show any IDAS units that are "railroad service" packaged, which leads me to wonder
of the AAR has thought the whole matter through carefully. Current LMR cabinetry wouldn't be suitable for
RR service, IMHO.

Technically, the Icom writeup reads very nicely:

http://www.icomamerica.com/en/products/ ... fault.aspx

Icom explains their 6.25 with this graphic -

Tom in D.C. wrote:The current photos don't show any IDAS units that are "railroad service" packaged, which leads me to wonder
of the AAR has thought the whole matter through carefully. Current LMR cabinetry wouldn't be suitable for
RR service, IMHO.

Technically, the Icom writeup reads very nicely:

http://www.icomamerica.com/en/products/ ... fault.aspx

Well Icom does not have a Clean Cab radio, there are vendors who make Clean Cab interface for the Icom, and Kenwood (TK-7180's, or NX-700's) as well as Ritron who makes a nice looking CC radio
http://www.ritron.com/rccr.pdf . Kenwood also released a new HT the NX-210 with railroad use in mind.

The RR's have been using Kenwood HT's for years (BNSF TK-290's, UP TK-2180's) I understand that CSX has used a lot of Icom units.

Jim

Bill_G wrote:Icom explains their 6.25 with this graphic -

IDAS takes the idea of radio spectrum efficiency one step further. It surpasses the FCC current mandate to go to narrow band voice channels by leapfrogging the 12.5kHz target and going directly to 6.25 kHz channels. This aligns with the FCC's vision of getting the 6.25 kHz in the near future.

http://www.idas625.com/

n7maq wrote:Well Icom does not have a Clean Cab radio, there are vendors who make Clean Cab interface for the Icom, and Kenwood (TK-7180's, or NX-700's) as well as Ritron who makes a nice looking CC radio
http://www.ritron.com/rccr.pdf . Kenwood also released a new HT the NX-210 with railroad use in mind.

The RR's have been using Kenwood HT's for years (BNSF TK-290's, UP TK-2180's) I understand that CSX has used a lot of Icom units.

Jim

The Ritron unit is pretty impressive, and the price isn't bad compared to prior Motorola product. Slides right in and you're good to go.

escomm wrote:

IDAS takes the idea of radio spectrum efficiency one step further. It surpasses the FCC current mandate to go to narrow band voice channels by leapfrogging the 12.5kHz target and going directly to 6.25 kHz channels. This aligns with the FCC's vision of getting the 6.25 kHz in the near future.

http://www.idas625.com/

Yeah. I found that site, saw that quote. They use the same graphic I posted above in their color glossy pdf download handout, but with a corrected 6.25 where it says 12.5 above the twin sub-channels strongly suggesting they need a 12.5 split to accomplish their method. I'll keep reading. Could be the sales dept has it wrong.

Kenwood's Nexedge/NXDN and Icom's IDAS are identical and interoperable. The system is 6.25KHz FDMA.
MotoTRBO is 12.5KHz, 2-slot TDMA.

Both will meet the FCC's 6.25 mandate, since it requires a 6.25 "equivalent". 2-slot TDMA in 12.5KHz complies.

The big knock I've heard against NXDN's approach is that the adjacent channel rejection is significantly worse compared to TRBO infrastructure, due to the 6.25KHz channels. Also, the infrastructure is fairly pricey (primarily due to the controllers).

Interesting. So, several are saying the illustration is incorrect. I'll keep studying.

Any experiences with NXDN coverage? Trbo has turned out to have great improvements over equivalent analog systems. Every single local customer has found new coverage in building areas that used to be dark, or poorly served before. We haven't put in any wide area systems yet, and do not know if the horizon moves out, or if we just get better fill.

The graphic is showing the possibility of having two users in a 12.5KHz channel. "2 offset 6.25KHz channels available". All it's showing is the possibility of having two users, on two separate 6.25KHz channels, in the same space as one 12.5KHz channel.

I have Nexedge gear, I've programmed Nexedge radios, etc. I can assure you the format is 6.25KHz FDMA.

Nexedge will provide better coverage than analog due to increased power density, all else being equal. Again, the problem will be RF conditioning... with significantly reduced adjacent channel rejection due to the 6.25KHz nature, can you provide good enough filtering to keep the receiver from desense?

Thanks tvsjr. The illustration is for illustration only.

On rejection - Yes, in lieu of careful coordination, cavities with tight skirts will be necessary. I've already experienced digital output clobbering analog input 30kc away. A crystal filter helped, but some rumble can still be heard when the input is near threashold. Without good rejection, channel spacing will still need to be spread out. Not a new problem, but kinda negates the rationale for splitting channels.

Icom claims their repeater can do dual mode for easy system migration - it will repeat both analog and digital. That is, if an analog signal is present, it will pass analog, and if digital is present, it will pass digital. Does anyone know if the mobiles and portables are mixed mode as well? IOW on a given channel will they demod analog or decode digital correctly depending on the input without the user having to change settings?

The ICOM portables and mobiles will do mixed mode, however you need to determine which will tx. I had to set ours up with 2 channels, 1 for analog and one for digital

Thanks jsikora. For clarification, you mean you have an analog mode channel and a digital mode channel programmed on the same freq. On the analog channel, it will transmit analog, but receive both analog and digital. On the digital channel, it will transmit digital, but it will receive digital and analog.

Or is it strictly analog for analog, and digital for digital, and the users need to know which mode a particular freq is operating to communicate correctly?

Bill_G wrote:Interesting. So, several are saying the illustration is incorrect. I'll keep studying.

Any experiences with NXDN coverage? Trbo has turned out to have great improvements over equivalent analog systems. Every single local customer has found new coverage in building areas that used to be dark, or poorly served before. We haven't put in any wide area systems yet, and do not know if the horizon moves out, or if we just get better fill.

Ehh, I can see what they tried to say with that graphic but I can see where they went wrong trying to say it. Ignore it.

NXDN puts two smaller carriers within the larger space of a single 12.5 kHz channel. Mmk?

You mention new coverage... Since RF is RF, just modulated differently for digital, I suspect your new coverage is just the fact it's a new repeater and field units. Just sayin'... In a fringe area, digital drops out faster where analog main drag on as static for a while longer or less. This is highly subjective in my opinion.

Someone else mentions adjacent channel desense... I don't see this as a problem... I think the graphic is trying to explain it more from a universal perspective rather than a single SMR perspective. Something like, "you can have another license next to you" and not that your up and down links are a single channel and are going to be zero spacing... although you could, we tried that too without any problems, unless you count the very expensive isolators required, but the field units couldn't have cared less no matter how close they got to each other. In TRBO your up and down are the same channel because it's alternating data packets between the two within the 12.5 channel. Do you see the difference and how the graphic only sort of applies?

We've abused these radios heartily, mostly iDAS and they haven't suffered from any desense except for blatant and abusive, in it's face receiver overload... which it recovered from. Competitor fear mongering I say.

jsikora wrote:The ICOM portables and mobiles will do mixed mode, however you need to determine which will tx. I had to set ours up with 2 channels, 1 for analog and one for digital

Mixed mode with same made talk-back, within a programmable time frame.

Hasty example... I TX Digital, but I received and unmuted to an analog call. Since I programmed a 10 second talk-back window I have until the beep that goes off in 10 seconds to respond in the same mode I just received.

BIll, if you are looking at this equipment - stay with a true DMR solution. Yes, it is 12.5 actual bandwidth, but is 6.25e spectrally. You are completely covered. The 6.25 equipment is real hookey. Double the infrastructure cost and a real pain to coordinate channels in congested areas. Just my 2 cents.