Re: Station not coming together - the full post (sorry for repost, reply to this)
At 08:01 PM 3/6/2007, Jonny 290 wrote:
Bruce, Gould and Les,
Sincere thanks for your thoughts so far. I'll let this topic percolate for a bit, but I had to comment on one thing:
<<<Unlike in HF, where the RF sometimes just gets through, here you're dealing with the Hard Numbers, and they will crush you into silence.>>>
THIS is why I love satellite operation. It's a huge challenge, and the ionosphere largely has NOTHING to do with it. No 'magic' involved. I know it's anathema to ye olde Amateur Radio meme of "operating in a dim room with a small transmitter", but I am finding that this satellite station is the greatest engineering challenge of my life, to date - and I'm going at it 100% solo NOBODY in my area knows anything gives a rip about the birds. Yet.
Jonny,
As you are discovering, the Amsat-bb is a great source of help for folks starting out. The others have pretty well pointed out your receiving system on 435 MHz is not working well enough. I have no experience with SO-50 so do not know if the K5OE eggbeater has enough gain. An excellent article was printed about receiving AO-51 in the latest issue of Amsat Journal. If you are not a member then this is one benefit of membership.
My impression of Hamtronics equipment is that is better for repeater use and not optimum for "weak-signal" satellite reception. The Hamtronics preamps do not have low noise figures. Gain without low noise figure will not result in bettering your reception. Preamps must be placed close to the antenna (if not directly to the antenna). The 2-dB coax loss is directly added to the noise figure of your preamp (which I estimate is no better than 1.5 dB). You want to get a 0.5 dB noise figure preamp with a minimum of 15-dB gain. The IC-208 probably does not have very low noise figure (I would guess around 10-12 dB).
Line loss is better measured using a power meter and a transmitter. Receiver S-meter indications are altered by the AGC action of the radio and not trustworthy for signal level measurements of any accuracy. But if the coax is new then 2-dB loss for 29-feet is probably close.
I would try the eggbeater on its own support mast (height is not particularly important for satellite reception if not obstructed by hills or buildings. I received AO-51 using a 2m 19-inch high mag-mount whip on a square of sheet metal and a 0.5 dB noise figure preamp with very clear signals above 10-degrees of elevation. This was very early in its history when running very low power on the satellite.
Try these ideas out and let us know how it goes.
73, Ed - KL7UW ====================================== BP40IQ 50-MHz - 10-GHz www.kl7uw.com 144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w DUBUS Magazine USA Rep dubususa@hotmail.com ======================================
At 09:07 PM 3/6/2007, Edward Cole wrote:
Jonny,
My impression of Hamtronics equipment --snip
Sorry should have written Matt. Also Ramsey instead of Hamtronics, though they are about the same in performance.
Matt, try running your preamp at the antenna as the first step and see if you improve your reception. I would also move the antenna away from the other antenna.
Then if still not good enough reception try a 2m whip. If the whip works better then you know you have a problem with the eggbeater. Does the eggbeater have a ground plane under it? If so this would favor overhead reception vs. on the horizon. The eggbeater is circular polarized for over head directions; did you make it right-hand or left-hand circular polarization? The simple whip or small yagi actually work better since polarity on LEO sats seem to shift a lot.
For much better results you might tilt your eggbeater down to 20-degrees and mount a light TV rotator to swing it in azimuth. In this position you should have the ground-plane radials to make the antenna directional. I belive that is what Jerry, K5OE, ended up doing to maximize his use of this antenna. Using an Arrow antenna mounted this way has worked very nicely for many LEO operators.
73, Ed - KL7UW ====================================== BP40IQ 50-MHz - 10-GHz www.kl7uw.com 144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w DUBUS Magazine USA Rep dubususa@hotmail.com ======================================
OK, let's take a bite out of this.
RE, the preamp: I agree that it is likely a weak point. I wanted to check it out, though, and for $22 I couldn't go wrong. It'll still prove useful at some point down the road.
If one of the mast mount preamps are what the situation requires, I"m ready to take that step.
The eggbeater is actually designed with radials to 'pull' the signal towards the horizon. It almost seems as though the radials may be working too well - I've got moderate to great copy up to a few degrees, then it falls over dead. Due to my 'beater's design, it's trivial for me to replace the loops and/or the radials without messing with the phasing harness or antenna mount, so I can try an antenna that doesn't have a by-design null at high elevations. I'd almost like to do this just as a lark, as it'd cost me a grand total of $7 to go buy another 10 foot piece of 1/4" fridge tubing.
I can also experiment with putting the 435 eggbeater on a nonconductive PVC mast. Also a cheap experiment, couple of bucks for 15 feet of PVC. That might get it up high enough with no metal above or near it, save for the feedline.
Here's my main issue with the TV rotator, and you'll think this is silly and trivial, but it's a major sticking point, and why I've been going at this with omni antennas so far. My main mast sits _directly_ outside my roommate's window, due to overhead power line and tree location. It's the only place where I can safely have a structure above 10 feet, that is less than 75 'coax feet' from my shack window.
I'm concerned that spinning the rotator at night will bother him. If the mast is solidly mounted to the house just a few feet away, how much will one of these inexpensive TV rotators conduct into the building? Could I cut that down by putting some rubber between the mast and clamp, something of that nature?
The next step, and I'm ready to move to this point if I can address the noise issue to my satisfaction, is to build a small cross yagi, 4 to 7 elements, and mount it at fixed elevation on a small TV rotator. I believe that an antenna in this size range will prove a big advantage over the omnis, should have a wide enough beamwidth such that I will get away with fixed elevation, and should only have to crank the rotator every 60 to 90 seconds, except for the extremely high angle passes.
If that works on receive, but I'm having uplink problems, I can put a 2 or 3 element CP yagi for 2 meters on the same boom, which should let me hit most of the satellites with 10-15 watts of power, max.
I'm very eager and willing to design and play with antennas - love homebrew in general, I just can't design a circuit to save my life - and know how to model and build good quality antennas. I'm fairly certain that I can get crafty enough to get around what restrictions this environment does have.
So, here's what I'm looking at, I think.
1: Mast mount preamp 2: Beam with rotator 3: Hamtronics downconverter (435.5 - 437.5 MHz, somebody tell me if I'm getting the wrong frequency range choice - my HF radio stops at exactly 30.000.000 so I want to make sure I can hit the 437+ frequencies)
The beam will require design and construction time (I don't believe in buying antennas except in rare circumstances); I can throw green paper at the preamp and get it out of the way, since store-bought is the best option for that at this time. In addition, I don't want to have to install the beam and rotator and preamp all at once; it'd be nice to have the preamp ready to go by the time I put up the beam and rotator.
I'll be honest, I'm generally an impatient person, and I'm busting my chops and treating this station in a rent house as a challenge. I was serious about hitting the Phase 3E sats when they go up, but I do _not_ expect to do it at my current QTH. If all comes together, I move into a house this fall, at which I hopefully will have clear space and the ability to put up a "real" antenna support. Once that happens, either a roof mount or small tower, I'll build a long yagi array and get it under computer control. But I'm not at that phase yet, and I want to get experienced at this level before I think about trying to work the high orbit satellites.
I actually grew up a ham in my early teen years back in the early 90's, and remember poring endlessly over AO-13 articles. It seemed like the zenith of technical accomplishment in our hobby. I came back to ham radio last year and was disappointed to find that we had no high orbit satellites currently, but the LEO satellite 'scene' seemed active and I figured I could get my feet wet with them before I tackle the big ones when they go up.
Google on Jerry's "Texas Potato Masher II". His changes to the original are worth the effort. I built one each and worked AO51 with them using 5 watts and an HT. Progressed to M2 beams and UHF preamp and retired the IIs for possible field day use. They are easy to make with PVC and #12 house wire. A length of 12/2 with ground or 12/3 will get you the wire if the junk box is empty.
73, Jim
Edward Cole wrote:
At 09:07 PM 3/6/2007, Edward Cole wrote:
Jonny,
My impression of Hamtronics equipment --snip
Sorry should have written Matt. Also Ramsey instead of Hamtronics, though they are about the same in performance.
Matt, try running your preamp at the antenna as the first step and see if you improve your reception. I would also move the antenna away from the other antenna.
Then if still not good enough reception try a 2m whip. If the whip works better then you know you have a problem with the eggbeater. Does the eggbeater have a ground plane under it? If so this would favor overhead reception vs. on the horizon. The eggbeater is circular polarized for over head directions; did you make it right-hand or left-hand circular polarization? The simple whip or small yagi actually work better since polarity on LEO sats seem to shift a lot.
For much better results you might tilt your eggbeater down to 20-degrees and mount a light TV rotator to swing it in azimuth. In this position you should have the ground-plane radials to make the antenna directional. I belive that is what Jerry, K5OE, ended up doing to maximize his use of this antenna. Using an Arrow antenna mounted this way has worked very nicely for many LEO operators.
73, Ed - KL7UW ====================================== BP40IQ 50-MHz - 10-GHz www.kl7uw.com 144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w DUBUS Magazine USA Rep dubususa@hotmail.com ======================================
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participants (3)
-
Edward Cole -
Jim Wright -
Jonny 290