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Hi, I'm a new 900 addict...

This forum is for the discussions targeted at converting various models of Motorola equipment to operate in the 900MHz Amateur Band.

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P25Digital
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Hi, I'm a new 900 addict...

Postby P25Digital » Mon Jul 21, 2008 5:03 pm

Years ago, I was bitten by the 220 bug because we had a local repeater, and very little traffic. The 3 or 4 of us that would hang out there enjoyed that small group. 220 enjoyed a resurgence of sorts when the Alinco DJ-280 was introduced, and the DR-235 came out a little later. Some of our little group moved on to 1.2Ghz, but our little half watt Icom T-81's just weren't up to the task of covering much area, and we had no repeater. My amateur days dwindled off and I'm seldom found on an amateur repeater these days.

I've been toying with the idea of 900Mhz, a couple friends and I have talked about it for years. Well, yesterday it happened. Surfing fleabay I found an MTS2000 M3 for a good price. I hope it will arrive by the end of the week. 8)

So begins my addiction to 900Mhz... I'm sure I'll be back with alot of questions. :lol:

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MSS-Dave
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Re: Hi, I'm a new 900 addict...

Postby MSS-Dave » Tue Jul 22, 2008 4:22 am

My 2 cents..

After spending several years "experimenting" with MSF 5K, GE/Ericsson Mastr 2 and several home brew repeaters using data modules and what not, I gave up. Reason: The noise (at least in this Metro area) on 902 is astronomical! The receivers were just ate slap up. I have 7 sites that I tried, 5 of which use master receive antennas with bandpass filtering at the antenna AND at the multicoupler. The only site my RX would perform somewhat normally was 160' which really isn't much when you start at 60' ground elevation. The noise seems to be caused by combinations of consumer toys (cordless phones, video links, etc) and spread spectrum data links which even I have going in commercial applications. My noise floor at 902.5 was better than -120 dBm in 2002. I pretty much gave up when I couldn't see anything better than -85 with some peaks hitting -40 on all of my high sites. I tried tons of different filter combinations but the on-channel noise was just too much.

I have a UHF repeater at 1000' co located with a multi-channel UHF trunk system, a VHF repeater and at least 5 FM broadcast stations up the tower. I get a slight bit of desense from a TX 3 MHz away from my RX frequency and the antenna within 15 feet horizontially. If I put more effort into it, I can cure that. My RX noise floor is much better than 902 is now. I get 50 miles + out of this setup and it's nothing special at all (Read: Not /\/\ equipment but I digress...)

This is just my story. You might be in the middle of the desert or Iowa or somewhere there isn't the massive amount of ISM and Part 15 stuff running and you would be fine. Also, you could look at the 12 MHz split RX (909) and see if it is better in your area. Most of the surplus equipment will work on the 902/927 split with little modification, the lower split usually involves more work.

Sorry if this is kind of a "Debbie Downer" moment..... Good Luck whth whatever you choose to do. If you have specific questions, feel free to ask in this forum. There are LOTS of guys that have sucessfully placed a repeater at 902/927 that work fine in their area.

Dave





P25Digital wrote:Years ago, I was bitten by the 220 bug because we had a local repeater, and very little traffic. The 3 or 4 of us that would hang out there enjoyed that small group. 220 enjoyed a resurgence of sorts when the Alinco DJ-280 was introduced, and the DR-235 came out a little later. Some of our little group moved on to 1.2Ghz, but our little half watt Icom T-81's just weren't up to the task of covering much area, and we had no repeater. My amateur days dwindled off and I'm seldom found on an amateur repeater these days.

I've been toying with the idea of 900Mhz, a couple friends and I have talked about it for years. Well, yesterday it happened. Surfing fleabay I found an MTS2000 M3 for a good price. I hope it will arrive by the end of the week. 8)

So begins my addiction to 900Mhz... I'm sure I'll be back with alot of questions. :lol:

P25Digital
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Re: Hi, I'm a new 900 addict...

Postby P25Digital » Tue Jul 22, 2008 1:35 pm

I don't know that I'm ready to put up a repeater, yet. :lol: Interferance is an issue I thought might crop up. For now I'm probably just going to look for a second handheld, or maybe a mobile to experiment with and have some fun.

There are a few repeaters in other cities a couple hours away from me, so the MTS2K should at least get a little bit of a workout occasionally.

Thanks for the "heads up", I want to learn the pitfalls of 902 just as much as anything else.

Sorry if this is kind of a "Debbie Downer" moment..... Good Luck whth whatever you choose to do. If you have specific questions, feel free to ask in this forum. There are LOTS of guys that have sucessfully placed a repeater at 902/927 that work fine in their area.

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Jim2121
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Re: Hi, I'm a new 900 addict...

Postby Jim2121 » Tue Jul 22, 2008 8:38 pm

get a GTX -- do a Search query for: GTX 900 here! look at posts, you should be able to pick 1 up at a fair price... Its a good place to start before you put up a repeater....Jim
Messages can't be intercepted if they aren't sent, can they?
Erwin Rommel

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MTS2000des
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Re: Hi, I'm a new 900 addict...

Postby MTS2000des » Tue Jul 22, 2008 9:44 pm

we've had 927 ham stuff in Atlanta since the summer of 2002. The 927.575 machine has been on Sweat Mountain since then, it is an MSF5000 with a DB products vertical. We have noticed an increase in the noise floor and some type of rhythmic clicking noise on the input which others have reported around the country. At first we thought it was craptel QRM (which now pollutes the 935 band as well as 800) but it is something else. There are other 927 repeaters out in Gwinnett county on the NE side of the Atlanta suburbs that don't seem to have this issue (though they are located on lower RF saturated sites). The biggest issue is coverage, Atlanta metro is a hilly area and 900 plain sucks compared to UHF. The Sweat Mountain UHF ham repeaters (three of them on three different sides of the mountain) blow away the 900 with the same type of antenna.

As far as the MTS2000, hopefully you'll get one that works on both 927 repeat and simplex. I've owned about half a dozen 900 Jedis over the years and my experience is either they work great or they don't, sometimes they work on repeaters but not 927 simplex. I have a model II MTS2000 right now that was a depot rebuild in 2001, new RF board and controller, and it works great on 927 RX and TX's just fine on 902, but unlocks on 927 simplex. It's hit or miss hopefully you'll get one that works well on both simplex and repeat.

The GTX's seem to be less cantankerous but they have their hangups as well. Kenwood also makes some radios that can be made to do 900 as well.
The views here are my own and do not represent those of anyone else or the company, the boss, his wife, his dog or distant relatives.

mike m
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Re: Hi, I'm a new 900 addict...

Postby mike m » Wed Jul 23, 2008 1:31 pm

Ditto on the 900 MHz noise problem.

I had a 900 repeater with a frequency agile 6 meter remote base that I just took down a month ago because of all the analog and digital non certified part 15 junk that Customs and the FCC let the Chinese sell in this country.

The 900 MHz band was good around 8 to 10 years ago when I started in it but it is useless now in my opinion.

Why waste your money and put up a repeater that has the capability of hearing down to -122 dBm on the bench only to have the usefull sensitivity reduced to -50 to -80 dBm when you factor in the site noise reduction, and this is with a good Band Pass band reject duplexer and notch filters on the receiver.

All of which doesn't help one bit when the part 15, 1 watt unlicensed garbage transmitters fall right on your input frequency.

It's was frustrating listening to great 6 meter band openings on my remote from several miles out with a 22 watt maxtrac 900 radio unable to get back in.

It used to be that you could get away from the noise problem by moving your repeaters input frequency to the extreme low end of the 902 band to reduce the noise but not anymore, it seems that in the last year or so even the low end of the band is getting nailed by all the spread spectrum transmitters.

Oh and I'm out in the country in Northern AZ where the noise is just as bad as down in the big city.


Mike

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Tom in D.C.
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Re: Hi, I'm a new 900 addict...

Postby Tom in D.C. » Wed Jul 23, 2008 4:06 pm

Two additional points of comment, or interest maybe:

1. I've found the GTX mobile radio doesn't have enough power in most situations to cut
it on 900. A 40-watt Spectra is a better choice. The GTXs put out only about
13 watts in most cases.

2. You will want to run PL on both receive and transmit to help alleviate the noise/
background junk problems. Around the DC area it seems to come and go but it's always
there in some form or other. Fortunately the capture effect of a good, fairly strong,
FM signal can usually overcome it.

3. If you can, put a 9db gain vertical on your house and keep the feedline as short as
possible, using N connectors on the terminations. You'll lose a lot of signal no matter
what you do but starting out with 40 watts instead of 13 means you'll still have more
ERP at the antenna which is what really counts.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.

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motorola_otaku
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Re: Hi, I'm a new 900 addict...

Postby motorola_otaku » Thu Jul 24, 2008 2:07 pm

I was a big user of 900 base/mobile simplex a few years back with a group of local chuckleheads. Luckily, we had a licensed 936 MHz frequency to play on, but I'm getting back into it in the 902-928 band.

-Simplex range in this band, as well as 700/800, is going to be very short compared to UHF and VHF no matter what you do and very susceptible to building and foliage attenuation. This can play out to your advantage, however, as most consumer-grade scanners have terrible receive sensitivity up at 900 making it difficult for scannerheads to pin you down. 8)
-Don't go cheap on coax. Use white Teflon RG58 or LMR195 for your mobile installs and no less than LMR600 for base installs.
-Use the highest-gain antenna you can reasonably accommodate. Low-profile "beercans" and 1/4-wave spikes don't cut it mobile.. use center-loads, "pigtails", or dual-coil trilinear antennas. My personal favorites are this one and this one.
-You can do real good point-point with Yagis up high. For a while, I had a 9-element Yagi on a rotor up at 50' in my backyard that I could work mobiles with up to around 12 miles out.. with both of us using 12-watt radios.
-On that point, get high-power mobiles if at all possible, but don't completely write off the 12-watt radios. GTXes have the big added bonus of not needing any hardware modification to do 902-928; just bandsplit-hack the RSS and away you go. Ditto for the MCSes.
-Don't worry about whether antennas are spec'd for 902-928 or 896-902/935-941. The SWR curve is so broad it's irrelevant.
When exposed to Rapid Fire Growth or Thermal Emergency, two things are lost:
1. Ability to use fine motor skills
2. Presence of mind

P25Digital
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Re: Hi, I'm a new 900 addict...

Postby P25Digital » Sat Jul 26, 2008 3:02 pm

I was hoping to have my MTS2000 by this weekend, maybe Monday. I may be in the Atlanta area in a few weeks, and I'd like to try working the 902 machines as I cruise through.

RWhite
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Re: Hi, I'm a new 900 addict...

Postby RWhite » Sun Jul 27, 2008 3:09 pm

I have had a repeater (927.1125) on 900 for over 18 months in Dallas and the activity on it has not increased substantially. I have (had) for sale a number of GTX mobiles at a substantially lower price than what I pad for them (all programmed with the known repeaters in the DFW area) and most of them still sit in my shack. The few I have sold have been to hams out of State. Most likely, I paid too much for them last year. I guess I could give them away if anyone wanted them :o . The repeater works real well, although it does hear the clicking sound (like a clock) on occasion. It has never covered up or affected a signal, so I live with it and since there are so few users, I have not looked into it at the site.

My antenna, a 900 MHz paging antenna, is up over 350 ft. side mounted on a large faced tower. It does get out pretty well and sometimes is heard as well or better than the 2 meter and 220 repeaters that are about at the same height on the tower. Like an earlier poster said, the 30 watt rigs fare much better into the repeater than the 10 watt rigs and mobile handhelds are not much use unless you are within a few miles of the repeater.

In any case, it sits there listening quietly, waiting for a user. About the same happened to the first repeater I built in 1978 (its been on 224.18 on the same tower for the last almost 30 years) and its useage is somewhat greater but has a steady number of regular users. At least it gets kerchunked a number of times a day! :lol:
Roger, W5RDW
Murphy, Texas

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Re: Hi, I'm a new 900 addict...

Postby topramen » Wed May 22, 2013 4:42 pm

Jim2121 wrote:get a GTX -- do a Search query for: GTX 900 here! look at posts, you should be able to pick 1 up at a fair price... Its a good place to start before you put up a repeater....Jim


Just thought I'd echo this comment. I recently (this past weekend) got a GTX Portable at a hamswap for $40(!) with a rapid charger. I've got a few buddies who "hide out" on 900 and since the WiSPs in this area have pretty much disappeared off 900, this area of Northern California is perfect for 900. It seems to be pretty popular here with the PavePaws killing 440. I've only been using my GTX HT for a few days but I love it. I wish that the Alphatags worked on it (Hacked codeplug to get more channels) but I can't complain for 40 bucks! It's a great radio and it's very durable. I could beat the everloving $%!& out of a mugger with it, on the street if I ever got into a sticky situation.

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Jim2121
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Re: Hi, I'm a new 900 addict...

Postby Jim2121 » Thu May 23, 2013 5:53 pm

$40. not bad with charger....

topramen
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Re: Hi, I'm a new 900 addict...

Postby topramen » Tue Jun 11, 2013 2:37 pm

no kidding. It sounds like the old equipment from the 900 LTR systems in my area that dissolved around 2005-2006 are starting to make their way into the ham market around here. There were several GTX mobiles (which by the way 15 watts around here does just fine) that were going for around 50 bucks. I just wish there was a p25 900 repeater around here. Or any p25 repeater around here for that matter.

AEC
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Re: Hi, I'm a new 900 addict...

Postby AEC » Wed Jun 12, 2013 9:15 pm

Good deal on the GTX portable, just don't 'lose' the SMA adaptor that is screwed into the radio.
If anybody does lose one, I have a couple of spares from previous service duds I squirrelled away.

jhooten
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Re: Hi, I'm a new 900 addict...

Postby jhooten » Thu Jun 13, 2013 3:45 pm

I put my call out a few times a week when I'm in range of the Austin machines and get no answer. Few minutes later a conversation starts up. I'm getting to the point of believing there is nothing but clicish turds on 900.

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MTS2000des
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Re: Hi, I'm a new 900 addict...

Postby MTS2000des » Fri Jun 14, 2013 11:34 am

jhooten wrote:I put my call out a few times a week when I'm in range of the Austin machines and get no answer. Few minutes later a conversation starts up. I'm getting to the point of believing there is nothing but clicish turds on 900.


The repeaters like that aren't just on 900MHz
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John G
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Re: Hi, I'm a new 900 addict...

Postby John G » Sun Jun 01, 2014 8:47 am

900 is the only band I have any interest in. I've had a repeater on for several years now and it is almost never used. 900 does have issues, that's for sure. Not the least of which is that it, or portions of it have been licensed. My frequency, 927.7500 has been licensed to a vehicle location concern. They missed their construction deadline but got it extended. I have no idea when, or if, they will be operational. I am sure I will hear from someone when that happens. Then I will take it off the air. The site I am on does get some data type interference but so for, it hasn't been too bad. I actually have a complete MSF5K ready to put on if only I could find a suitable site. I thought I retired this year and thought I would have time for more ham radio experimenting. I was asked to continue to work part time, which has turned into pretty much full time. I plan on continuing to be on 900 even if with no repeater. I know this topic is old but I don't check here very often and found it interesting.

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d119
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Re: Hi, I'm a new 900 addict...

Postby d119 » Wed Jun 11, 2014 9:56 am

I think the real winner on 900MHz with regard to amateur applications is going to be either P25 or DMR.

It's really the only thing that stands a remote chance against all the crap and noise on the band, even though that crap and noise is sure to affect usable range on any digital system.


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