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Author Topic: Satellite Hunting  (Read 6381 times)
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ka1tdq
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« on: August 19, 2018, 01:10:08 AM »

I'm getting interested in satellites, and like anything in ham radio, the sky is the limit in terms of price. Entry level stuff is an Arrow handheld duplex antenna and a full duplex capable handheld radio. Those two alone together have a price tag of $500. 

Here's my attempt:  Two Leixan mobile radios mounted to a hip-resting homebrew antenna mount. I can aim the antennas with one hand and talk with the other. My phone has a satellite tracking app that gives every bit of information needed during the pass.  To power the radios I have a long DC cable connected to a relatively small 12 volt battery. 

Price tag thus far: $200

Jon


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« Reply #1 on: August 19, 2018, 06:13:44 PM »

That's going to be very interesting Jon. Keep us posted.

Mike KE5YTV
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Mike
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ka1tdq
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« Reply #2 on: August 19, 2018, 07:37:59 PM »

The next good pass will be at 1 o’clock tomorrow morning. I’m going to try to wake up for it. If it works, I’ll be able to hear myself on the downlink. Nobody else will because they’ll be sleeping... go figure.

Jon


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ka1tdq
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« Reply #3 on: August 20, 2018, 04:33:06 AM »

Nope. I was aiming at AO-91 and the pass numbers were about as perfect as you can get in terms of passing almost directly overhead. I guess trying to hit a repeater moving at 4 miles/sec with antennas aimed off your hip is a little more difficult than I expected. I guess not everyone is a Shooter McGavin.

Jon


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W1RKW
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« Reply #4 on: August 20, 2018, 04:24:48 PM »

yes, moving target indeed and a fast one too.  Since you were aiming overhead or perpendicular to its trajectory doppler shift should be minimal but as a sat approaches and moves away one has to compensate for doppler shift. Depending on the bird, speed, approach and retreat, doppler shift can be as much as +/- 9kHz depending if moving away or approaching. Not sure what the doppler effect would be if operating FM vs. SSB. Did you have your sub-tone or PL set correctly for AO-91?
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KA3EKH
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« Reply #5 on: August 20, 2018, 04:29:14 PM »

Mode B and J are fairly easy but just remember that the bigger the antenna the harder to aim. With stuff with a two meter uplink sometimes things like a egg beater and a 100 watt amplifier work wonders on the uplink.
Biggest problem I had years ago doing this was typical satellite pass was something like a contest QSO, you would broadcast your call and someone in the pile up would come back and say they heard so and so. Not like rag chewing. I did a lot back in the day with packet station on ISS being that’s easy to hear and hit and you can have some exchange keyboard to keyboard.
Wonder if there is any mode A stuff out there and if you can get away with A3 uplink in the passband and have that on the ten meter downlink? With SSB whatever you sent up came back on the opposite side band but with AM going to assume it would come back down AM? May also have some weird power restrictions, they use to have something that was able to identify people running too much on the uplink and knock them out.
Got me thinking I know I can come up with a couple hundred watts of AM on two now just have to find out if anything still has a mode A transponder.

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WB2EMS
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« Reply #6 on: August 20, 2018, 05:26:46 PM »

Looking at your setup, I would have expected that to work. I use the phone app also, ISS detector with the add on, and it's a pretty reliable tool for that.

As I recall, they require a PL tone to operate through - looks like 67 Hz, did you have that set? Some of them also require a second tone to start the transmit timer - if the satellite was quiet when it came over, you might have needed that also to wake it up. ISS detector doesn't seem to mention the PL tones, so if that has been your reference for frequencies, that might be the issue. They aren't that hard to hit (AO85 is a little deaf). Hopefully WD8BIL will chime in, I was hearing him on them regularly a while back, before summer got in the way of ham stuff.  :-)

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ka1tdq
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« Reply #7 on: August 20, 2018, 05:57:59 PM »

I did have 67Hz in my 70cm uplink, but my antenna has 9-elements and maybe a little too narrow of a beamwidth.  I've seen YouTube videos of guys hitting these FM satellites with 3-element measuring tape antennas, so I figured mine was overkill. 

I know the SaudiSat has a timer, but I didn't try hitting that one since it has a 2 meter uplink (although I could try). 

The problem definitely seems to be my aim.  I'm using the phone app which tells me to the n-th degree where to point, but my hip isn't calibrated. 

Jon
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ka1tdq
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« Reply #8 on: August 20, 2018, 08:08:40 PM »

I hated to do this, but it might help.

Jon


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KA3EKH
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« Reply #9 on: August 21, 2018, 10:02:31 AM »

Don’t think you will need to aim that, just put it out back sticking straight up!  When you hear the downlink that’s the time to start calling.
For years I did a fixed four element UHF antenna that I built from an old two way UHF antenna and a five element VHF that I put together from a old FM translator antenna just set at forty five degrees aimed south and with all the polar orbit birds they always at some point will appear rising in the south and setting in the north. With the fixed antennas at forty five degrees that would tend to give me around four or five minutes per pass.
Think the first thing to do is get your downlink working and be able to receive. Once you learn how to correct for Doppler you will find with broad antennas you can be wide in your aiming and you will get a feel for it. But the idea of fixed antenna aimed south will work well for at least one pass a day or so being that will be the one pass where its straight overhead and strongest downlink. Don’t waste your time on those fringe passes that last three minutes and our just on the horizon. AMSAT has obrittron or junk like that that you can download and looking at the orbital track will give a better idea of what’s going on.
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WB2EMS
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« Reply #10 on: August 21, 2018, 11:33:39 AM »

I don't know if trimming the antenna that much was needed. The arrow antenna has 7 elements on 440 and it's easy to use and point and hear. But if you have enough power to not need the gain, it will make life a bit simpler. I miss AO13 where at apogee you could move the antennas a few degrees every hour for about 4 hours. I also miss transponders instead of FM repeaters.

Are you hearing the satellites? Got easy frequency control for doppler correction?



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73 de Kevin, WB2EMS
ka1tdq
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« Reply #11 on: August 21, 2018, 02:19:33 PM »

My only compensation for Doppler shift right now is running fast in the other direction. 

Seriously though, not really.  I can just make my call when the pass is at its peak and there's little shift at that point. 

Come to think of it now, I'm going to pull the radio template to make sure the 67Hz is programmed in. I know I put the number in, I'm just not sure I checked the box for subaudible tones. 

Jon
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ka1tdq
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« Reply #12 on: August 22, 2018, 06:08:39 AM »

AO-85 just passed directly overhead, but still nothing. The radio template looked fine, but I did have the power set to low before (1/2 watt).  I put it on high (10 watts) for this pass. 

At one point in the pass, it should've worked when it was literally directly overhead.  No doppler shift, no difficult aiming (just straight up). 

Now I'm suspecting the equipment.  Either the antennas or the radios. 

Jon
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« Reply #13 on: August 22, 2018, 05:13:23 PM »

I have a bunch of adjacent memories in my rigs programmed for the doppler shift over the pass from AOS to TCA to LOS. About 5 memories.

Most of those birds are pretty well populated during the daylight hours - if you are not hearing anything, then I would look for a rig or antenna issue. AO-85 is a bit harder to get into than the others, has some desense issues as I recall. But driving around with a mobile whip on the car, I hear them all the time if they are above the horizon and I'm listening. And that doesn't have as much gain as even  your abbreviated antennas.





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73 de Kevin, WB2EMS
ka1tdq
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« Reply #14 on: August 22, 2018, 05:50:48 PM »

Ah, I never thought about using memory channels for Doppler.  What's your spacing if channel 3 is the center? And AOS would be the high side frequency, correct? I'm trying to think of the train analogy.   

I've never heard any of the satellites during my daytime practice sessions.  It's probably my high quality Chinese radio.  I even have the squelch on minimum (but not open).  

I have another Vegas trip shortly.  At the end, we always stop by the Gigaparts store.  Maybe if I'm good I can get a full duplex portable.

Jon
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W2ZE
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« Reply #15 on: August 23, 2018, 09:53:09 AM »

You gotta have the squelch open, the satellites are not strong enough to break the squelch. AO-85 is particularly hard to operate because the receive antenna was accidentally damaged before launch. You need to run about 30-40 watts to hit AO-85. AO-91 and SO-50 are much easier and can be operated with about 5 watts.
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WB2EMS
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« Reply #16 on: August 24, 2018, 01:23:59 AM »

I agree, squelch off. And make sure you don't have pl squelch on. I don't think there's any tone on downlink

My memory steps are 5khz. Aos at +10, +5, TCA 0, -5, Los at -10.

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« Reply #17 on: August 26, 2018, 02:07:31 PM »

Hunted dozens of them! Great sport!


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« Reply #18 on: August 26, 2018, 05:05:13 PM »

ok Kevin, I'll chime in.Smiley AS you guessed, summer activities and a new job have lessoned my sat work lately.

1) Aim - With the +/- 15 degree beam spread on most antennas aiming isn't as precisely needed as one might expect. At 300 miles up that's a pretty wide window. Polarity, on the other hand, is far more important. Because of the sats rotation (spin) you need to be able to go vert/horz quickly. If you are hand holding your ants, something like the Arrow or home brew WA5RCN Cheap yagis, spinning it become an art. After a while you'll get the hang of it.


2) Power - yes, as Mike said, 30 watts and modest gain ants should work just fine. I've worked the FM birds from the truck at hunting camp with 45 watts and a mag mount 1/4 wave! Most problems occur in the receive systems. Work on getting the receive setup to the point where it is dependable. Last summer i started with the antennas you see on my QRZ page and a pair of Baofangs 8 watters.  


3) Mode - consider expanding to the linear birds. The XW series and CAS 4B satellites are extremely easy to work. They have very good receivers and usually put down excellent signals. If you are going to stick with the FM birds use all the power you have to medium gain antennas. As with all FM systems capture is gonna depend on who's strongest at the input.


I'm presently building a pair of 5 element 2 meter quagis and 7 element 70cm quagis for my setup. They'll be mounted cross polarized 180 outta phase. This has proven, to me anyways, to give great results without having to come up with a switching arrangment for polarity.

Good luck and have fun.

de WD8BIL EN91 Ohio
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ka1tdq
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« Reply #19 on: August 26, 2018, 05:32:48 PM »

All this is great advice. One thing I learned is that my initial attempt setup was modest at best. By the way, you cannot completely turn squelch off with Leixen mobiles.

I’m going to shelve this idea for a bit. I’m going to focus current efforts back on my 40 meter class E rig. By the way, is that cabinet finished yet? I need to ask him.

BUT, right now I’m in Vegas and other priorities come first.

Jon
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