TK-5720 Not Usable for Public Safety

[jbaker6953]

The TK-5720 is advertised as a public safety radio, but the brochure says the TK-5720 can only do 12.5 kHz channel steps (not 7.5 kHz). I thought surely this was an error, but a call to Kenwood's land mobile support confirmed. Is there something I'm missing? The FCC has been assigning interstitial frequencies in the public safety band since 2005, and there have been several well-documented cases where radios incompatible with 7.5 kHz spacing became a safety hazard on a fire incident. Why would Kenwood be selling a public safety radio that can't even tune to any of the interstitial frequencies?

 

[mmckenna]

I think you've been given some bad information.
The Function Programming Manual (FPROG) for the TK-5720 shows that they will do 3.125KHZ and 2.5KHZ steps.

The terminology can get confused in translation. Could be the guy at Kenwood was quoting you the channel spacing. They will do the 12.5KHz narrow band FM, as required.

 

[jbaker6953]

I think you've been given some bad information.
The Function Programming Manual (FPROG) for the TK-5720 shows that they will do 3.125KHZ and 2.5KHZ steps.

The terminology can get confused in translation. Could be the guy at Kenwood was quoting you the channel spacing. They will do the 12.5KHz narrow band FM, as required.

Thank you for that information. The manual isn't available on Kenwood's site that I can see.

I think Kenwood is using misleading terminology in the product brochure. Channel spacing not the same as bandwidth (as I'm sure you know). Narrowband analog FM has an 11 kHz bandwidth. The assigned channel spacing in the NTIA band (162 - 174 MHz) is 12.5 kHz to allow for slightly out of spec radios (e.g., 163.700 and 163.7125). When Kenwood says the channel spacing on the radio is 12.5 kHz, that's telling me that the smallest separation in frequencies supported by the radio is 12.5 kHz.

 

[mmckenna]

I don't see it as misleading, but that's just my opinion. Most of us know that 12.5kHz narrow band uses an 11kHz signal, hence the emission designator starting with 11K0. I've never seen a company use anything different.

The channel spacing and the channel steps are two different things and shouldn't be confused. One has to do with channel width, the other has to do with where the center of that channel can be.

This is the sort of stuff where a knowledgeable radio shop, sales guy, consultant, etc can save a lot of headaches. Getting terminology confused can cost a lot of money.

 

[jbaker6953]

The channel spacing and the channel steps are two different things and shouldn't be confused. One has to do with channel width, the other has to do with where the center of that channel can be.

The channel width is 7.5 kHz in the public safety band. I don't see where 12.5 kHz is related at all to anything in the public safety band - it's not the bandwidth and it's not where the center of the channel can be.

 

[mmckenna]

The channel width is 7.5 kHz in the public safety band.

Show me.

I really think you are getting some things confused here. Don't take that the wrong way, I just think you are missing something here.

 

[jbaker6953]

Band Plan (150-174 MHz) - Channels are generally spaced every 7.5 kHz. Authorized Bandwidth is 20 kHz, 11.25 kHz or 6 kHz.

And this NIFC memo outlines some cases where the 7.5 kHz spacing has been an issue.

 

[northzone]

The channel width is 7.5 kHz in the public safety band. I don't see where 12.5 kHz is related at all to anything in the public safety band - it's not the bandwidth and it's not where the center of the channel can be.

WRONG, read above. The channel WIDTH is 12.5 khz, the channel spacing is 7.5 khz . Lots of people do not understand this.

 

[jbaker6953]

WRONG, read above. The channel WIDTH is 12.5 khz, the channel spacing is 7.5 khz . Lots of people do not understand this.

What definition of channel WIDTH are you using if it's not the width between channel centers and it's not the signal width? What other width is there?

 

[northzone]

It is the channel signal width, peak modulation plus a small guard band on each side.

 

[jbaker6953]

It is the channel signal width, peak modulation plus a small guard band on each side.

What does it mean, then, to say that "this radio's channel width is 12.5 kHz" if it DOESN'T mean the channel signal width is 12.5 kHz and it doesn't mean the spacing between channels is 12.5 kHz?

 

[mmckenna]

I think you are assuming that the channel centers and the channel bandwidth are set up so nothing ever overlaps. This isn't the case.

 

[AK9R]

The channel WIDTH is 12.5 khz...

The FCC mandated that the bandwidth of the transmitted signal be no wider than 12.5 kHz. However, if you apply Carson's Rule, you get a slightly different number.

Carson's Rule says that the bandwidth of an FM signal is 2 times the deviation plus the maximum audio frequency used to modulate the signal. That is:

BW = 2 x ( Deviation + Maximum Frequency)

In two-way radio communications, the maximum audio frequency is generally 3 kHz. In the case of +/- 5 kHz deviation, which is the old "wide-band" standard, the formula works out to BW = 2 ( 5 + 3 ) = 16 kHz. In the case of +/- 2.5 kHz deviation, which is the new narrow-band standard, BW = 2 ( 2.5 + 3 ) = 11 kHz.

This is why the narrow-band emission designator is 11K0F3E. "11K" is the bandwidth.

All that said, the bandwidth of the signal has nothing to do with the channel spacing. Bandwidth of an FM signal is a function of the way the signal is generated in the transmitter. Channel spacing is an arbitrary number determined by spectrum managers which is then translated into the programming software of synthesized transmitters.

 

[jbaker6953]

I think you are assuming that the channel centers and the channel bandwidth are set up so nothing ever overlaps. This isn't the case.

Not at all. That's bandwidth, which is separate from channel spacing. I'm saying that there's no third measurement involving channel width that I'm aware of, but some people disagree. There's this "channel width" that ISN'T bandwidth or spacing between frequency assignments. I'm trying to figure out what they're measuring.