What is 33cm good for?

[KF5YDR]

FIrst, let me say the topic question isn't meant disparagingly. Everyone has their favourite bands to operate on, but I think our amateur spectrum is a "use it or lose it" proposition, so I want to use as much of it as I can.

I've never used 33cm (900Mhz band) for anything, but it's right there, available to use. I have a good grasp on the utility of the other VHF/UHF bands, propagation-wise. In a forest environment I'd use 6m, in open terrain I'd use 2m, in an urban environment I use 70cm for its better penetration of structures and its tendency to reflect off many structures. 1.25m has an advantage in a lower noise floor and is a good compromise between 2m and 70cm. (these are mostly with regards to FM voice; I know 440 is also used for ATV and higher-speed data because of the available bandwidth)

But what about 33cm? At 900MHz, foliage absorption begins to be a factor, and my body more readily absorbs RF energy. This is countered somewhat by the smaller physical dimensions of higher-gain antennas; I can have a 5/8 wave on my HT and a 3dB gain colinear on my car without taking up any more space than a lower-frequency quarter-wave or helical antenna.
Most public safety systems seem to have moved to 700/800/900MHz, and I always assumed that was due to greater channel availablity on those bands, but is there a task or situation that high-UHF wavelengths are particularly suited to?

 

[jaspence]

33cm

First of all, I do not know of any public safety using 900 mhz. although it is a possibility I'm not sure how you would use 6 meters in a forest. A decent antenna is just too long for easy deployment, especially on a handheld. 900 mhz, along with other high frequencies, is a way for amateurs to experiment and learn. In my area, we have two 900 mhz machines connected through IRLP. This frees the 440, 2 meter and 222 repeaters for local use and still gives us easy access to the network. Used 900 mhz equipment is fairly inexpensive, and the Kenwood and EF Johnson radios are very easy to program compared to other commercial brands.

 

[ko6jw_2]

What's 900Mhz good for?

First of all, one of the purposes of ham radio is to experiment. Having been given a 900 Mhz allocation, we need to find out what it's good for. Our concerns are not necessarily the same as commercial and public safety users.

One of the problems with 900Mhz is the lack of equipment from the usual ham radio manufacturers. I think Alinco is only company to offer an HT for this band. However, there is plenty of commercial gear that can be adapted easily. It is common on the microwave bands to use converters that multiply signals on a lower band and output in the microwave region. This allows the use of all modes available on an HF radio on higher bands.

I think also that we need to look at a different model to use this band. The traditional approach is to put repeaters on high mountains or buildings to give good coverage. Commercial users have gone to a model where there are a larger number of linked low power repeaters to provide coverage. Obviously, cellular telephones are a prime example. This is not very common in ham radio, but it may become more common to utilize higher frequencies.

I see 900Mhz as being very useful in urban environments where it will be reflected off buildings and fill in coverage better than lower frequencies. It will not be as good in rough terrain without many more sites than would be needed for lower frequencies. There is a good reason why, here in California, the CHP has stuck to 42Mhz frequencies. Ironically the rush to 700-900Mhz has left that band available for expansion.

We should not overlook the uses of 900Mhz and higher bands for propagation experiments, EME and the like. We don't have to talk through repeaters or use FM all the time. By the way, 900Mhz is not "high UHF." The UHF spectrum is defined as being 300Mhz to 3Ghz, so its really at the low end of the band.

As was pointed out, another advantage of UHF frequencies is the ability to get very small high gain antennas. Antennas that would be physically very large on 6 meters or 2 meters are very practical on 900 Mhz.

So, what's it good for? That's for us to find out.

 

[KF5YDR]

Good responses.

jaspence, Moto and several others make low-band VHF helicals that will cover 6m. They're about two feet long, they work about as well as a 6" 2m duck or a 3" 70cm stubby. The main thing is that 40-70MHz signals punch through trees like they aren't there, whereas at higher frequencies you start to get serious attenuation.
An inefficient antenna is less of an impediment than all your signals being absorbed!

KO6JW, I say "high UHF" because even though the spectral definition goes up to 3GHz, the characteristics of propagation, absorption, feedline and antenna design change in such a way that things which work from 50-500MHz don't work at all above 1GHz. Coax starts to become extremely lossy, connectors become RF reflectors, antennas get detuned by rain, microstripline construction becomes feasible, etc. Where the main difference in dealing with a 50MHz system and a 220MHz system is just tuning, the difference between 440MHz and 1.2GHz is different equipment.

It's more of a subjective difference in utility than physics, sure. Like how HF by definition stops at 30MHz, but you get HF-like propagation all the way to 50-60MHz, or how NVIS doesn't really work above 10MHz.
The boundaries of how radio waves behave on earth as used by humans aren't the same as the boundaries the ITU has assigned, I guess is what I'm saying. ^_^

 

[jaspence]

900 mhz

I have a 2 meter/440 antenna that is two inches long, but the efficiency is poor.

In a rural situation, a friend and I with 6 meter handhelds using stock antennas about three feet long could barely make contact at a distance of a mile, with no trees or hills in between. We did far better with a pair of $50.00 FRS radios. A two foot long antenna would still be a pain in a wooded area.

 

[ko6jw_2]

Sorry, didn't mean to suggest that you were ignorant of the definition of UHF. However, not all OPs on RR have a high degree of technical knowledge.

 

[mikepdx]

What is 33cm good for?

Around here we have several 900 repeaters on 3500-4500 ft
mountaintops with unobstructed views over the valley which is
around 100-350 ft elevation.

One of the guys has three of them linked for very wide area operation.

 

[KF5YDR]

A two foot long antenna would still be a pain in a wooded area.

Oh, I'm not saying it would be great. I'm saying you'd still get that barely a mile, and with FRS you'd get about a hundred feet.

We're arguing different things here. I'm saying 50MHz RF penetrates trees better, and you're saying a physically long antenna would be annoying to carry. Both true, but not the same topic.

 

[zz0468]

First of all, one of the purposes of ham radio is to experiment. Having been given a 900 Mhz allocation, we need to find out what it's good for. Our concerns are not necessarily the same as commercial and public safety users.

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This!

There's been a lot of guys on this forum and others saying they want to build a repeater just to learn how they work. Invariably, they decide to try it on 440, which in many areas is saturated, and garage experimenting can't be done without bothering someone. Invariably, the discussion deteriorates around coordination and band plans, and going with the flow.

900 MHz is PERFECT for this experimentation. Surplus radios are available for CHEAP on eBay, virtually everywhere has available channels without bothering anyone, and the band could use a whole lot more activity before you can expect more ham grade radios offered to the market.

 

[KF5YDR]

Hmm...after I started this thread, I looked at RepeaterBook and the Houston doesn't have a 33cm repeater at all. Maybe I should see about putting one up...

 

[AK9R]

The ARRL recommended band plan for the 902 MHz band calls for repeater inputs from 902.125 to 903 MHz. The guys in Central Indiana who are running a 902 MHz repeater system have found significant interference problems from other users on the band. Remember that amateur radio is secondary on the 902 band and there are other users under Part 15 as well as instrumentation users that amateur radio has to contend with. The local guys found that the high end of the recommended repeater input segment is all but useless in the Indianapolis area. They've concentrated their input frequencies at the low end of the repeater input segment.

I post this not to scare anyone away from trying the 902 MHz band. Just be aware that you may have some unexpected problems from other users on the band.

 

[rapidcharger]

It seemed like 900 was really picking up steam in my area. there was a group that had a high site repeater and it was one of the most active repeaters in our city (pop. 6 million). Some clubs set up 900mhz repeaters and did a group buy on surplus radios and gave them to members. I know at least one of the repeaters was eventually linked to 440.
I think the primary cause to the slowing of growth of 900 aside from the dwindling (yes it's dwindling) supply of surplus radios, is the recent popularity and growth of digital voice modes. A lot of the same folks that were into adapting commercial gear to the ham band such as myself) wanted to do the same thing on 900 but got sidetracked by the lure of all the digital offerings on 146 and 440.

There is a case to be made for "use it or lose it" however I think we are at even greater risk of losing 440, and being more versatile for more people, I've been focusing my efforts there.

 

[k9rzz]

902Mhz is more points in the VHF/UHF contests! Show this subject to the guys who have worked more than 25 grid squares and have VUCC for 902 and they'll give you what for! It's not all done just on FM. :^]