902 MHz band

[jhooten]

My point remains the same, most public service are using 450 MHz and lower for a reason. The 700/800 that is used in your area are neither 900 nor 400 MHz as the OP was about.

You yourself pointed out you said 450 and lower. 7/800 may not be 900 but it is still way above 450.

I am curious, does GATRRS use VHF at all with their system? If so, how many VHF frequencies are allotted versus 700/800.

I already said GATRRS uses some VHF sites out west. Look for your self:

Greater Austin/Travis Regional Radio System (GATRRS) Trunking System, Austin, Texas

Greater Austin/Travis Regional Radio System (GATRRS) Trunking System Profile

www.radioreference.com

Now it is getting to the point this discussion is going around in circles and nits are being picked. I'm done.

 

[AK9R]

Folks, since this thread is in the Amateur Radio General Discussion forum, one would assume that the topic was the 902 MHz band for amateur radio use, not public safety.

 

[xmo]

Exactly. BTW, there are no 900 MHz public safety frequencies, however, there is a 900 band for commercial and utility use that has resulted in surplus gear which hams have used in the ham 900 band.

The original questions were: " How does 900 MHz compare to 440 Mhz for local reliable range? Does antenna gain and lower noise floor make up for greater path loss? "

Each band has different propagation characteristics. There have been several good responses from people who have compared the two bands. I have also had repeaters on both440 and 902. We got the 902 off to a good start with surplus equipment from Nextel as well as MSF repeaters and high gain base antennas from defunct paging operations.

In the metro and suburban areas, the 900 band is so infested with wireless widgets that the "noise floor" was aweful and repeater talk-in coverage was severely degraded. At its best, the 900 was fun and something different to play with but 440 coverage was always better from the same sites.

I understand that some amateur systems have been successful in avoiding the high noise floor by using the repeater receive frequency closest to the band edge. Pretty much all of the wireless devices are cheap and not equipped with accurate frequency determination so they intentionally stay away from the edge to insure that they don't go outside the band.

This spectrum analyzer view of the "noise floor" at one of our sites shows the lower noise near the band edge.

This is a screen capture from an Agilent ESA-E analyzer preceded by a high gain LNA and a 900 preselector filter. The yellow trace is the 'live' trace and the blue trace is a peak hold.

The noise function marker at 902.5 MHz is showing a current value that is more than 14 dB higher than the thermal noise. By comparison, the "noise floor" at many 800 MHz public safety sites does not exceed the thermal noise.

 

[kinglou0]

I believe if any future for 900 lies in digital modes.

You know, I thought that as well.

I’ve been piecing together the equipment needed for a low level 900 MMDVM repeater for a few months now. Everything I need is stashed away in the garage.

My motivation stalled out. Why? Because I couldn’t get past the likelihood that I would be the only user. It seems at the moment to be a lot of expended effort and future costs to have a repeater that gets 1 user with an occasional passerby.

The biggest problem facing 900 is not the noise floor or propagation characteristics but the lack of equipment that could be picked up at HRO or Amazon.

Amateur radio has lost much of the individual drive to experiment and venture into areas where your knowledge level makes you uncomfortable. If it can’t be bought on Amazon and learned quickly via a flashy YouTube video, there’s no interest in it.

900 is going to remain the domain of very dedicated and small groups of hams. Just wish the Chinese would make a hotspot that actually works on 900 because despite advertising 900 capabilities, they’ve all come-up short so far.

 

[N4KVE]

Remember the days when hams would buy surplus HT200’s to get on VHF ham repeaters? They had to recrystal, & align the radios to work on ham repeaters. Well 900 users are in the same boat, but it’s much easier. If you can figure out how to hex edit the CPS, you’re good to go. So it still takes some knowledge. Compare that to new DMR users who buy a CCR on Amazon, but are too lazy to learn how to build a proper code plug, & go begging on social media for an unproven, untested code plug from a total stranger. And when they can’t get it, they send the radio back.

 

[Project25_MASTR]

900 MHz use can differ greatly depending on where you are at. Some have posted about Texas 900 MHz; 33cm is very difficult to use in areas like Midland/Odessa, Lubbock and other areas that have heavy oilfield presence due to the use of 900 MHz FHSS SCADA equipment such as the GE TransNET and GE iNET 900 radios (when I worked for one of those big energy companies in Midland, TX I had roughly 10,000 900 MHz devices that I backhauled between Grand Junction, CO and the southern portion of the Permian Basin. In Lubbock, just as an example, there is a single 33cm pair with a fairly low noise floor...everything else is elevated 10-20 dB.

Makes 900 MHz use a little difficult. Another thing to think about (going back to GATRRS) is 900 MHz can run into some extreme attenuation issues when pine needles become involved. That was one of the primary reasons behind Bastrop abandoning the LCRA 900 MHz system they were using and joining GATRRS with 700 MHz simulcast. As to VHF and 7/800 MHz use on the GATRRS system...there are pluses and minuses to both bands but what it really comes down to is VHF is often the solution when fewer sites are desired (remember, since the merger of the Permian Basin system GATRRS became the largest P25 system in the state in terms of coverage due to the heavy use of VHF in the rural areas of coverage).

 

[KN4EHX]

900 in East Tennessee (Smoky Mountains) is pretty much hit and miss. We have a few analog 900 repeaters around here and when it works they aren’t too bad. 900 on digital is another story. I’ve been throughly impressed by both DMR and P25 on digital simplex.

One very unusual thing about 900 is vegetation will indeed consume your outgoing signal. It is also unusually bouncy. Using a 15 watt mobile and high gain antenna I can’t hit my local repeater if I pull forward from my house. Although if I happen to have anything parked around me or a low flying airplane happens to come by I can hit the repeater.

It would be nice if someone would actually make some 900 radios that are easy to program and don’t sound tiny on analog. Talking bout you Motorola GTX with your tiny audio.

If you can get a 900 MHz spectra would be ideal for analog but if you happen to have 900 DMR or P25 around you definitely go that way.

If you don’t have any repeaters around I wouldn’t bother because you’ll have a desk Queen that doesn’t do anything.

On the flip side simplex 900 is a good way to chat if you don’t want everyone under the sun listening to you. In East Tennessee I would say the distance is probably 50% or less than 440. VHF is king of the mountains and valleys. Urban or open range 900 is probably ideal.