Range Testing

[Jim1348]

I may get the opportunity to do some range testing tomorrow. It will be simplex on 800 mHz with a couple of XTS5000 portables with CQPSK modulation. Anyway, what sort of range am I likely to see portable to portable with these on simplex? One will likely be in a residence and the other in a vehicle, both with rubber duck antennas. I think these are 3 watt portables, but I am not certain of the power level. We also might compare these to Nextel i315 Direct Talk range. It seems like the Nextel i315 are 500 or 600 milliwatts, but I am not certain of that. It has been a while since I have studied such things, but I seem to recall that purely from a power output standpoint that for range to be doubled, power needs to be quadrupled. In this scenario, if I do the math and use .6 watts for the i315, multiplied times 4 equals 2.4 watts. With the XTS5000 at 3 watts that it more than quadruple the i315s power, so all other things being equal I should get twice the range with the XTS5000 that I do with the i315. Might I see 1 mile with the i315 and 2 miles with the XTS5000s, or am I being way too optimistic?

[RKG]

No offense intended, but I think I'd subsitute "simplistic." The delivered audio quality between two transceivers at two distinct points on the earth will be affected by dozens of variables, of which effective radiated power is only one (and, often, not a dominant one). Most folks in the business could recount dozens of stories about a user moving 6 feet in one direction or simply turning around in place to face a different way and in the process increasing DAQ from R2 to R9. As a result, the only reliable way to assess practical coverage in a given area is to go out and do some field testing.

[dxon2m]

Like RKG said, you are over simplifying your situation. You are comparing two completely different setups, one uses CQPSK and the other uses FHSS at 900MHz ISM band. CQPSK uses 7.2kbps for voice and error control coding but operates on a single channel, while FHSS is a spread spectrum mode which occupies a wide range of bandwidth but uses a lower rate for voice encoding(clarification needed).

If you are mobile, multipath propagation will be your biggest enemy and you may benefit from FHSS because the path delay on each channel is very short, the time that the radio stays on each channel is also very short (remember, the radio is hopping on a range of frequencies), so you will have the least noticable effect on your voice. XTS3000, on the other hand, uses a single channel, so you will suffer from delay spread a lot. The effect is most noticiable if the distance between the two portables is far because it will take time for different paths of the signal to arrive. The most common way to remedy this problem is by "diversity", which is what FHSS has accomplished, utilizing several different (in directtalk case, many) channels for a single.

Plus, in a real world propagation model, your analysis can be idealized, but nothing can be ever "equal"; the car passing outside, the person walking by you can affect the propagation dramaticlly.

[Jim1348]

It was interesting doing field tests today. The XTS5000s were reliable for up to 1 mile. The Nextel had only slightly less range. Probably .9 mile.

[Dan562]

Oh, perhaps you should know while using any form of Digital communications, these modes are susceptible to interference or noise from High and Low voltage Primary power transmission lines overhead. If today's field tests appear to be okay where you tested the units, tomorrow may not bring the same results.

Dan