[amsat-bb] Re: Station not coming together - the full post (sorry for repost, reply to this)
jonny290 at gmail.com
Tue Mar 6 21:01:02 PST 2007
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
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.
On 3/6/07, Bruce Robertson <broberts at mta.ca> wrote:
> Quoting Jonny 290 <jonny290 at gmail.com>:
> > LONG LONG LONG post ahead.
> > OK, the situation is: I'm building up a satellite station to get
> > familiar
> > with LEO sats and to get ready for the phase 3E fun to start soon.
> > Here's my
> > station, and I'll post my thoughts after that.
> > The "too long, didn't read" version: I've built good antennas, fed them
> > with
> > good feedlines and into a supposedly good receiver, but I just can't
> > keep
> > solid copy on LEO birds, and cannot get a QSO. I am jealous of the
> > "Satellites worked with HT and 5/8 wave" articles, and want to figure
> > out
> > what the weak link in my station is.
> > RX path:
> > Eggbeater II antenna mounted at 15 feet. This is built to the K5OE
> > Eggbeater
> > II spec (http://members.aol.com/k5oejerry/eggbeater2.htm) using RHCP
> > but
> > uses a 100 ohm phasing line using two 50 ohm coax lines done in
> > parallel,
> > used in a balanced configuration, instead of 93 ohm RG-62. Antenna was
> > 'redesigned' in MMANA-GAL to match exactly 100 ohms and to use 6mm
> > diameter
> > copper tubing instead of AWG 12 house wire. It is peaked for SWR < 1.1
> > at
> > 436 MHz, and is less than 1.5 at 435.0 and 437.0.
> > Our lot is lightly treed, but there is no wood (natural or otherwise)
> > within
> > six feet of this antenna. A good chunk of the sky, mainly northwesterly
> > looking, is partially obscured by a large tree, but right now the leaves
> > are
> > off and it shouldn't kill the signal that much...should it?
> > This antenna is the secondary antenna on this mast and is mounted on a
> > 3
> > foot PVC stand-off pipe. The primary antenna is a Diamond F22A mounted
> > at
> > approximately 18 feet. It has a 10 foot vertical element and three 1/4
> > wave
> > horizontal radials. It is not used in the satellite station but I wanted
> > to
> > describe it, in case it is interfering (I suspect it is.)
> > Eggbeater is fed through29 feet of 213 spec coax (5.1 dB loss/500 MHZ)
> > terminated in well done PL-259 connectors. I have verified this
> > particular
> > cable's loss at less than 2 dB at 432 MHz, using my Icom PCR-100's
> > accurate
> > S-meter and a known signal source.
> > My latest upgrade: RX chain goes into a homebrew bypass relay / Ramsey
> > preamp box (the relay is DPDT and switches the preamp in or out of the
> > RX
> > signal path). The preamp provides approximately 18 dB of gain when
> > inserted
> > and using a test signal around 432 MHz. It has proven somewhat
> > beneficial,
> > giving me 2-3 S-units advantage at certain points from the LO-19 CW
> > beacon
> > (Which I recently received at up to S9 with the preamp on a ~60 degree
> > pass,
> > a new record so far).
> Thanks for submitting your antenna system to the scrutiny of this list.
> many of us, planning and organizing these systems are good fun. I have
> direct experience that pertains to some part of your system; I hope those
> with other experiences will concur or debate.
> As you probably already know, it is considered a requirement of satellite
> work that a low noise preamp. be placed before your receiver, especially
> 70cm. One measurement that indicates the quality of this is its gain, and
> you have indicated the Ramsey unit's declared value in this dimension.
> However, an equally important measurement of quality is the noise figure.
> believe most advise that this be below 1 dB, and the lower the better. The
> math on this issue is really very revealing, and I'll leave it to you, if
> you're interested, to pursue it with Davidoff, _The Radio Amateur's
> Satellite Handbook_. However, it's important to note that a high-gain
> preamp with an inappropriate noise figure likely will do nothing to
> your reception of satellite signals.
> In hopes of getting an inexpensive preamp for my satellite work, I built
> the 2m version of the Ramsey preamp you described. I quickly concluded
> it didn't do what I wanted. Now that I own a mast-mounted ARR preamp., I
> certain that the unit I built doesn't have the appropriate noise figure.
> Now 2m is way less touchy in all this than 70cm, so I have to say that I
> suspect your preamp. is simply not up to the task. I highly recommend you
> buy a known quantity for this part of your system: Advanced Receiver
> Research and SSB USA are both well-liked. Once you know what one of these
> can do, homebrew to your heart's content until you get something that
> performs as well or better. Then sell your commercial preamp on this list!
> Secondarily, it is very important that the preamp be as close to the
> antenna as possible. That 2 dB of loss on the cable is killing you. You
> effectively negate it by putting the preamp before it; but you never get
> back if you put the preamp after it. Again, I recommend playing with the
> simple formulae and seeing for yourself how the configurations of
> are very important.
> I know mast-mounted preamps are a big pain; and I know bias tees are not
> fun. But given your cable and your antenna, you don't have a choice, you
> really don't.
> Finally, your antenna. This is one I would very much like to build myself;
> it seems very carefully designed. However, due to its slightly complex
> construction I have my doubts about using it as a first satellite antenna.
> I have advocated elsewhere that everyone have on hand a simple 1/4 wave
> vertical to use as a known-good antenna. Outside, tilted and in the clear,
> it may well only pick up very little intelligible audio of an FM bird's
> pass with an FM-only radio (a CW one will get the warbling tone quite
> nicely), but it should quiet the radio a bit and give some general
> indications of life. You should then expect your egg-beaters to be better.
> By using fixed antennas, you are, of course, limiting your gain. That
> everything after your antenna has to be spotless: no 2 dB here, 2 dB
> Unlike in HF, where the RF sometimes just gets through, here you're
> with the Hard Numbers, and they will crush you into silence.
> > Receivers:
> > IC-208H dual band radio, rated at <0.18 uV for 12dB SINAD
> > OR
> > PCR-100 computer controlled receiver, rated at <0.34 uV for 12dB SINAD
> > The TX setup is currently an IC-271 pushing from about 4 to 38 verified
> > FM
> > watts into a simple RHCP turnstile, recently built. It is mounted on a
> > slightly shorter PVC mast about 10 feet away from the "big mast". It is
> > the
> > only antenna on this pole, and is fed through 27 feet of 213 spec coax.
> > Peaked at 145.8 MHz with SWR less than 1.1 . I know the turnstile
> > pattern
> > has most gain directly overhead and has some shortages towards the
> > horizon,
> > but I have plenty of theoretical EIRP to get on the LEO sats, I believe,
> > and
> > I'm not worried about the TX path right now.
> Don't worry about the uplink. You're fine there.
> > I'm just not getting the signal strength and intelligibility that I
> > expect
> > from this setup. For example, there was a theoretically perfect SO-50
> > ascending pass today at about 5:15 PM Central, 15 minutes plus duration
> > and
> > it peaked at almost 80 degrees elevation. I received the signal
> > faintly
> > starting at 2 degrees, and it steadily improved to a 'fluttering S3" at
> > about 8-10 degrees. I attempted to come back to a station that finished
> > a
> > QSO, because I thought it cleared - turns out,the signal DIED. I could
> > just
> > barely track it for the rest of the pass, even when it was almost
> > directly
> > overhead at less than 900 miles altitude. Gave up when it was five
> > minutes
> > before LOS, with no contact made.
> > So, given my station description, what am I facing? Is my Eggbeater's
> > 'overhead 10dB null' design killing it? I would think that, as designed,
> > the
> > greatly decreased path loss as the bird comes overhead should compensate
> > for
> > this shortage, and then some.
> > As mentioned earlier, I'm also concerned that the Diamond F22's radials
> > are
> > destroying the radiation pattern of this antenna. I'm in a rent house
> > and
> > have to conserve masts as much as possible, but if it's killing me, I
> > can
> > move the satellite antennas to a ~12 foot PVC mast instead of trying to
> > piggyback them on my metal vertical mast.I've copied beacons and
> > various
> > carriers from birds as low as 0.5 degrees, so I know the antenna 'gets
> > out'
> > okay at lower elevations. It's the high elevation periods that are
> > disappointing me.
> I honestly don't think this is your first worry. It's all about the
> mate :-)
> > How does my IC-208H compare to more refined receivers? Is it too deaf?
> > I've
> > considered feeding my IC-735 HF radio with a 435 MHz receive converter.
> > This
> > would allow all mode 70cm reception with a very good radio (comments on
> > the
> > Hamtronics converter boxes would be great). I'd love any comments on
> > the
> > Hamtronics receive converters from those who have tried them out.
> This is super-great fun. I bought one of these when I started out and used
> it with my IC-728. FO-29 is an amazing bird. Worth the price of admission.
> One warning, though. Be sure the converter can do 435 MHz. Mine was 432
> only, and I had to buy a new crystal for it. Alas, I sold it this summer
> the Great Kenwood Purchase of 2006.
> > I'd appreciate any comments and advice from the great minds on this
> > list.
> > Thanks for taking the time to read up and give any advice or comments.
> No great mind; just a fellow-traveler.
> 73, Bruce
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