33cm Experiances

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by W6LDK, Dec 1, 2019.

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  1. W6LDK

    W6LDK Ham Member QRZ Page

    Would anyone care to share their experiences with 33cm band? What kind of antenna do you use... elevation, gain, omni-vs-directional, etc.? What radio and type of emission are you using?

    I recently acquired a used Kenwood TK-981 and a used Aston 918-6. I'm waiting for a length of ½-inch hardline to be made up and a hardline grounding kit, then I have to install it. I also considered building a multi-element vertical co-linear. Tuning will be the tricky part as most affordable SWR meters and analyzers do not reach these frequencies.

    Just curious.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'm not on 33 cm FM at all, and really never was, but am set up for 33 cm SSB/CW.

    20W output to a 33 element horizontally polarized loop yagi, rotatable of course. "Range" isn't much different from 70cm or 23cm, and often it's the "same stations" heard/worked as those two bands.

    One fun thing about these higher UHF and even SHF bands is when there's a tropo duct they often work much better, stronger signals over longer distances, than VHF. But unfortunately we can't "make" a duct, you just have to wait for one to happen and hope you'll be near your equipment (and others will be also) when it happens.
     
  3. KE4VNC

    KE4VNC Ham Member QRZ Page

  4. W6KCS

    W6KCS Ham Member QRZ Page

    When I added 900 to my repeater system, I found that the mobile coverage was about 2/3 that of 450, with about the same ERP. It was also hard to get rid of the Part 15 device noise on the repeater receiver. You'll probably want to use receive PL, too, if you experience a lot of momentary squelch-openings. All of the 900 repeaters that I know of transmit PL so you can do this at the receive end.

    I ended up using 300 watts on the repeater (about 150W into a 9 dBd omni paging antenna) and three-receiver voting on directional RX antennas to equal the 450 coverage, but luckily 900 surplus equipment is cheap and plentiful, at least around here.

    There are a lot of 902-928 antennas to choose from since the band is also used for unlicensed equipment. Omnis, Yagis, grids, etc. are cheap and easy to come by. Just google "902-928 antenna" to see what I mean. I wouldn't bother making an antenna unless you are really determined.

    Lots of mobiles and portables are available. The Motorola MTX9250 is my favorite portable, but there are some others.
     
  5. N1RIK

    N1RIK Ham Member QRZ Page

    I've been experimenting with 900 MHz repeaters for a couple years now. I have been having good success, however I have higher ERP on my 927.1375 repeater than my 442.250 repeater at the same site. Coverage is about the same, however the signal on the 927.1375 is a little bit stronger. I'm using a Ma/Com - Lucent Cellular 40db preamp and fortunately have a pretty low noise floor at the site 900.

    Here's how the two repeaters stack up (McCain, NC site) :

    900 setup:

    927.1375 / 902.1375 - PL 131.8 hz (Made of 2 900 MHz Maxtracs)
    Preamp: Lucent - Ma/Com 40 db gain
    Power Amp - MSF5000 DPA and FPA - output set for 150-watts
    Feedline: 110 ft. of 7/8" Heliax & 35 ft. of 1/2" Superflex
    DB Products Pass/Reject 4-cavity duplexer
    Antenna: Comet KP-20 9.2 dbi gain

    440 setup:

    442.250 / 447.250 - PL 107.2 hz (Made of GE Mastr Exec II set for 55-watts output)
    Preamp: Advanced Receiver Research GaAsFET 17 db gain
    Feedline: 140 ft. of 7/8" Heliax
    Sinclair Q3220E 4 cavity Pass/Reject Duplexer
    Antenna: Andrews DB-420 16-bay dipole array 11.4 dbi gain

    Mobile coverage on the 900 MHz repeater is quite well, with over 50 miles in some directions with a HAAT of 361 ft.


    The other project we have is a repeater on 927.025 / 902.025 in Sparta, NC @ 3900' ASL. Coverage is up to 85 miles in certain directions. It's output is 25-watts, but have recently purchased a MSF5000 DPA that will be able to boost power levels up to about 80-watts to a 10 dbd 900 MHz paging antenna. Results have been decent without a preamp. Last time we tried a preamp, we were having overload issues due to all the other transmitters on the mountain top... but will try again with more filtering and see if we can make things even better. Currently coverage is about the same as the 442.600 repeater at the same site, which does have some losses due to being combined with a commercial UHF system on the same TX and RX antennas.

    In conclusion, you can get about the same performance on 900 as you can with a UHF system if you don't have much interference issues and compensate with more gain, and better receive sensitivity.

    73s,
    Bill, N1RIK
     
  6. N1RIK

    N1RIK Ham Member QRZ Page

    And elevations of sites:

    927.1375 McCain NC repeater (watertank site) - 132 ft. AGL ... 660 ft. AMSL... HAAT 361 ft.

    927.025 Sparta NC repeater - 20 ft. AGL ... apx. 3900 ft. AMSL... HAAT just over 1,500 ft. (Sponsored by WA4PXV)

    73
    Bill, N1RIK
     
  7. N1RIK

    N1RIK Ham Member QRZ Page

    Another note... MSF5000 900 MHz Driver Power Amps and Final Power Amps are something to look for. The TTF-1242 (DPA) and TTF-1212 (FPA) don't need to be modified to transmit on 927 mhz. You can directly power them by 14vdc. With the DPA, you can run them up to 80 - 100 watts with about 3 to 4 watts drive. They are turn-key!

    You can drive the TTF-1212 FPA easily in the 150 - 200 watt power range. They will do higher and may be ok running a little over 200-watts continuously with proper ventilation, however I'm sticking to 150-watts to not burn up my light duty Comet 900 mhz antenna.

    You can find these PAs rather cheap on the 900 MHz email forums. Also you'll see them on ebay too ! I saw both of these PAs today on ebay for $119 each.

    73
    Bill, N1RIK
     
    K3RW likes this.
  8. W4EAE

    W4EAE Premium Subscriber QRZ Page

    I have never used 33cm, but I have used 23cm.

    There was a full stack of colocated Icom D-Star Repeaters in my city (up until a few weeks ago) 2m, 70cm, and 23cm.

    Performance--usable distance and signal strength--was pretty much identical with 70cm and 23cm while driving around mobile.
     
  9. K3RW

    K3RW Ham Member QRZ Page

    The NanoVNA, a real one and not a knockoff copy, has the ability to 900 MHz now. It may just need an extra thingee depending if you get one that already goes that high or an old one that needs that thingee. I don't recall what that thingee is! Its advertised 'to 900' so I don't know that it can squeeze out 927. But I understand a newer version will be out soon that goes beyond 1296, and it will cover 927.

    A vertical collinear is tough to build because the elements are so short already. I've done okay with using repurposed wifi or cell network antennas. But these aren't adjustable.

    You may not want forward gain if the intended setup is omni. But the band does much better to overcome trees and obstacles.

    Many ops make a yagi with a tight spacing and lots of elements. My Elmer built a looper basically identical to the Directive Systems 33cm antenna. Big booom length, lots of elements, and it works. But the tradeoff is very tight beamwidth. That works since we can point it up I-5 from his QTH and hit all of Puget Sound without a rotator. But thats a 927 FM one and to run 902 we'd have to roll it 90deg over for horizontal. Though there are so few 902 ops here.

    We know all the contestors who have 900 at all that we could reasonably work here. 95% of them are on FM and the other 5% have all-mode. The FMers are almost all using Kenwood 981s, 941s, or Motorola converts. One has the rare Alinco 900 HT. A few have transverters for 927 FM and a few have a transverter for 902.

    Good practice here was to program the repeaters, the simplex 927.5, but also the lower 903.2 (depends on your regional calling frequency) for nBFM. A few guys have that capability.

    A good filter would elininate some of the 915 trash. I'd like one that gives me good 927 reception and a LNA would be nice to have.

    Only for mobile would I use an omni antenna, since 900 boom lengths don't have to be super long for decent gain. If I had a repeater up 4000ft I'd consider an omni, but if I knew most of my traffic was funneled in due to geography, I'd do a sector antenna.

    Elevation of a vertically polarized yagi... as high up as you can get it. If you mean 'what angle' then that depends on your prevailing terrain. In some cases it might make sense to angle it slightly down rather than flat.

    On a collinear, same deal. Depends on geography. In some cases it makes sense to even invert a collinear. WB2WIK suggested that to me, and he's right!
     

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