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Author Topic: 1.2Ghz/23cm/1296 advice  (Read 11223 times)
WM3M
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Posts: 6




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« on: September 24, 2011, 10:13:31 AM »

Looking for some advice for getting on 23 cm.  I have never been on 1.2 Ghz.  I will soon have a IC-910H with the 1.2 Ghz module but no antenna yet.  I am not sure if there is any activity even on 1.2 Ghz in my area, about 20 miles west of Baltimore?  I believe there is some SSB activity during VHF/UHF contests.  And there are a couple FM repeaters listed in the directory near Baltimore.  Looking for advice on a small beam for SSB.  Also, I have done some searching for a mast mount preamp, but only one I could find was from SSB, for $500, out of my price range, are there any others available?  Thanks for the time and help. 73
Emory  WM3M
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W8JX
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Posts: 12088




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« Reply #1 on: September 24, 2011, 11:33:02 AM »

I played with 1296 in early 90's and technology was not quite up with it. It is making a come back and even in some HT's now. Three major things here. One is height, what ever antenna you use get it as high as possible. Very important on this band.  Second, you really want to use 1/2 or bigger hardline here (3/4 would be good). Third forget PL259's and only use N's (or BNC for jumpers.)
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KA4POL
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Posts: 2409




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« Reply #2 on: September 24, 2011, 12:24:23 PM »

I used a homebrew loop yagi like this one: http://www.directivesystems.com/PDF/2424LYRMK.PDF
You probably have to find partners on 2m or 70cm to get them to contact you on 23cm. As you are working on line of sight everything in the path will be reducing your chances. Working through reflections ((buildings or mountains) is helpful. Good cable and definitely N connectors are a must. As a preamp you might consider http://www.tgn-technology.com/shop/index.php?cat=c11_23cm-Band---L-Band.html&XTCsid=nohmobooozkzub I can't tell if they ship to the US. I'd try it first without a preamp. I never used one. SSB got pharmacy prices  Tongue
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W7AIT
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Posts: 501




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« Reply #3 on: September 24, 2011, 03:35:33 PM »



I been on 1.2 ghz for about 6 years now.  Here are some important points:

1.   Low Loss Coax:  Use low loss coax and the correct fittings.  The wrong coax will kill your signal.  Use the lowest loss coax you can and the shortest run as possible.  Use the best fitting possible – mine are all N and some SMA.  Don't skimp on connectors – bad ones will kill your signal.  Mine is 1318 coax with N fittings and a run of 125 feet. 
2.   Antenna:  FM vertical - You can build your own simple ground plane on a N connector and brass welding rod in about one hour.  Mounted high, that will get you on the air (FM).  SSB horizontal - For SSB use a horizontal beam.  I use NGC/ Comet CYA-1216E.  It has 16 elements and about 16 db gain.  I have two of them, one mounted vertically and one mounted horizontal.  SSB beam is at 30 feet high and same with the FM beam 30 feet high – each has its own mast and rotor, settable to 1 degree.
3.   For repeaters:  NOT recommended using a beam.  Use a vertical collinear such as the GP-21 (14 db vertical collinear gain) so you won't get accused of rotten signal reports from not having the beam antenna exactly pointed at the repeater.  Beamwidth is extremely narrow on 1.2 in the order of ±7 degrees which is darn tight and if you miss, your signal seriously degrades and everyone complains.
4.   Hams to work:  You might find one or two repeaters or linked repeaters in a major metro area like yours.  I have one big linked system here in the central valley of CA and there are several others but almost out of range.  I have some 1.2 friends that are 40 – 60 miles away and we carry on regular SSB simplex QSO’s every night with no problem, once everything is set.
5.   Mast preamps:  Use you rig by itself to start, work the antenna improvements and have fun.  Add the expensive preamps/ test equipment later.
6.   Tree leaves, rain and fog:  Weather, tree leaves, rain, fog, temperature hugely affect 1.2.  It makes it fun.  When it rains, no 1.2.  When it's a cool temperature inversion night, loud CW beacon signals in here S4 to S5 from 100+ miles away.  Day time and night time make a huge difference – night is best.
7.   Test Equipment:  Get some test equipment to tell if everything is working but look out for inaccurate power/ SWR meters!  I had a SX1100 that was way off.  I finally spent serious bucks and bought a spectrum analyzer (INSTEK GSP-830) a set of 40 db directional couplers, a 2.4ghz counter, and some pads, then I stated making accurate frequency, power, return loss (SWR) measurements and could get everything working properly.   
8.   FUN:  LOTS OF FUN!  Real challenge to get things working up there, but TONS OF FUN!
9.   Rig and Test Equipment (Add at your leisure):  2 each TS2000X, INSTEK GSP-830 SA, BK1823A counter, HP and NARDA, Mini Circuits directional couplers, and a bunch of 3 db pads.  Also lots of N, SMA, UHF, BNC, TNC between series connectors, cable assemblies.

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KA1MDA
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Posts: 548




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« Reply #4 on: September 24, 2011, 09:03:55 PM »

"When it rains, no 1.2"

I've always wondered where this "rule of thumb" originated. I have made contacts of 40-60 miles on 1.2Ghz in rain and heavy snow using an extremely lossy setup, including 50 feet of RG-213 for feedline and a badly mis-shaped loop yagi. As far as I can tell, the published atmospheric attenuation at 3 Ghz during a tropical downpour is less than .05 dB/km, as posted here:

http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/rf_absor.pdf

Tom
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WB2WIK
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Posts: 21754




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« Reply #5 on: September 26, 2011, 03:44:12 PM »

I've been on 23cm since about 1968 and at times have had a pretty big station for weak signal work on the band.  NEVER with a masthead preamp, as they're just too prone to lightning static damage and I get tired enough climbing towers without having to do more of it.

As such, I always used the biggest, fattest  (and shortest!) transmission lines possible to keep line loss low enough that a masthead preamp just wasn't required.

At my last "big" station in NJ, that was 1-5/8" Heliax from rig to rotator shelf in the tower, then semi-flex line like LMR400 above that for a short distance.

Loop yagis work well on 23cm and are less effected by rain since the water just runs down the loops and falls off, where it's a zero-voltage point anyway.  Linear element yagis are much more easily detuned by rain.

Very heavy rain (cloudburst) can impact propagation for a while, but ordinary rain doesn't do much that I've ever seen or found.

We routinely work 200+ miles on 23cm SSB with about 10W from "rover" to "rover" when "mobiling" around during VHF-UHF contests.  And that's not with either station being parked on a mountain or anything, just parked in fairly "open" areas not severely blocked by mountains in the path.  The distances are greatly extended when one party is on a mountaintop with a very clear and long horizon.  In those cases, our "rover" stations have the transverters and PAs on the vehicle roofs, rotating along with the antennas, so the feedlines are very short: typically 18" to 24" long per band.

Interesting observation is that when you catch a tropo duct (which are really common, you just need "timing"), the higher you operate in frequency, the better the propagation is -- very commonly.  During "normal" condx we work each other from 50 MHz up to 10.3 GHz, jumping band by band until all contacts are completed (or not); but when there's a duct, we start at 10.3 GHz and work our way "down" the bands -- it's more fruitful, since the ducts rarely support 50 MHz at all, and even 144 MHz may be very weak...compared with 23cm which is STRONG, and by the time we get up to 5.7 and 10.3 GHz, it's STRONGER.

Very interesting band.

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