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900mhz range question


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I have seen 5w and 8w handhelds and 30w to 100w mobile radios for Hams. The legal limit for an unlicensed operator is 800mw, but a licensed operator can go to 1,500w pep with no limit on effective radiated power. I'm unaware of anything else in the license free spectrum (outside of the Ham bands).

 

This weekend, during the VA QSO party,  a fellow club member made a contact at 75 miles. Outside of knowing he was using a mobile, I'm unaware of the rest of the working conditions for either operator. 

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Motorola DLR 1030 and 1060 give me less range than 4W Kenwood TK-3170. Not by much, though. In urban environment I'd say maybe 75% of range I'm getting from TK-3170. I still did not have a chance to compare good GMRS to DLR radios in the mountains.

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The Motorola 900 MHz digital FHSS radios are great for in-building coverage. They work pretty well outdoors in the open also. 1 watt is a little misleading when comparing them to "full power" UHF 4 or 5 watt portables.  Transmit power is only useful if it overcomes the noise floor that you're trying to transmit over.

Where those 1 watt 900 MHz FHSS radios shine, is that they have an effective receive signal level that's down in the -125 dBm range. Your typical UHF portable is lucky if it's beginning to receive anything at -119 dBm (and even if it does, then it's probably quite scratchy). So the 900 MHz radio comes in at better than a 6 dB winner in the receive category. Search that up on the dBm to Watts conversion scale, and you'll see that your UHF portable would need to transmit a decent signal at 4 watts or more just to begin achieve comparable performance - while the 900 MHz radio is hopping frequencies to avoid interference, plus pushing out a digital signal that's intelligible even at the very threshold of receive.

Forget comparing horsepower numbers. In the radio world, you need to compare receivers. That's where the magic is happening. Watts are for salespeople and marketing types.

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13 minutes ago, Radioguy7268 said:

Forget comparing horsepower numbers. In the radio world, you need to compare receivers. That's where the magic is happening. Watts are for salespeople and marketing types.

The best receiver won't do anything if there isn't enough power in the transmission to activate it. It take all three, power, sensitivity and an effective radiator.

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On 3/22/2022 at 11:58 PM, axorlov said:

Motorola DLR 1030 and 1060 give me less range than 4W Kenwood TK-3170. Not by much, though. In urban environment I'd say maybe 75% of range I'm getting from TK-3170. I still did not have a chance to compare good GMRS to DLR radios in the mountains.

What kind of range were you getting with the TK-3170 at 4 watts?

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3170vs1060.thumb.png.4d69dd4759928c667f734b6b99951ef2.png

Red lines are two DLR-1060 talking to each other, blue lines are two TK-3170 talking to each other. Test was done at the same time: I was riding bicycle with DLR and TK in my bag, while friend was sitting at the picnic table in the park. Table is located in some sort of depression, about 5", so the result on the flat ground could be better. The housing situation on the north and on the east are dense. There are small lots, 4000-6000 sq ft, not bigger. Housing is one- and two-story. Some two-story multi unit apartments.

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Another example of two TK-3170 talking to each other. Note, there is no line of sight. I was walking on the shore trail from NW toward SE. Trail is low, near the water and follows all landscape features. Friend was walking on the same trail toward NE, descended from the point on the E down to the water. We had communications broken only few times, when either me or my friend were deep in the shore canyons. There was never a direct line of sight between the radios. But thanks for the reflection and refraction of the 462MHz in mountainous terrain communications were reliable for the most part of the travel.

3170-dellvalle.PNG

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On 3/23/2022 at 4:01 PM, BoxCar said:

The best receiver won't do anything if there isn't enough power in the transmission to activate it. It take all three, power, sensitivity and an effective radiator.

Power is always limited, the antenna cannot always be changed, so, given equal power and a similar radiator, a better receiver will always beat a lesser one.

The DLR 900 vs TK UHF range similarities hints me that there might be a good 6-7 dBm difference in noise threshold between the two bands. Surprising how well these DTR/DLR radios work given the limited amount of power they have.

G.

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3 hours ago, gman1971 said:

Power is always limited, the antenna cannot always be changed, so, given equal power and a similar radiator, a better receiver will always beat a lesser one.

The DLR 900 vs TK UHF range similarities hints me that there might be a good 6-7 dBm difference in noise threshold between the two bands. Surprising how well these DTR/DLR radios work given the limited amount of power they have.

G.

That might be a good illustration of free space “path loss”, due to the capture area of the antenna at 900 being less that at 460. 

https://en.wikipedia.org/wiki/Free-space_path_loss

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