ISS Satellite Contact a Few Minutes Ago. Advice?

[Lscott]

I’m not sure it won’t work in particular with a linear translator. The input signal is typically down converted to a base band IF frequency then up converted to the output frequency. The signal is not demodulated during the process.

Remember that digital voice is really transmitted using specially modulated analog RF such that it carry’s digital data. The pulse shape is such that it has a very narrow bandwidth. So long as the translator is linear and the bandwidth of the digital signal fits within its input and output band range it should be repeated just fine.

The one area that is difficult as you pointed out is the Doppler shift. Most of advance digital modes use some form of multi level frequency shift keying. For it to work you need very good frequency accuracy. With good orbit parameters and model a computer controlled radio readjusting the frequency on the fly might work. It works well enough for SSB on the birds up there now since as we well know an error of 10’s to 100’s of Hz results in unintelligible signals so there is a chance.

[WROZ250]

4 hours ago, Lscott said:

I’m not sure it won’t work in particular with a linear translator. The input signal is typically down converted to a base band IF frequency then up converted to the output frequency. The signal is not demodulated during the process.

Remember that digital voice is really transmitted using specially modulated analog RF such that it carry’s digital data. The pulse shape is such that it has a very narrow bandwidth. So long as the translator is linear and the bandwidth of the digital signal fits within its input and output band range it should be repeated just fine.

The one area that is difficult as you pointed out is the Doppler shift. Most of advance digital modes use some form of multi level frequency shift keying. For it to work you need very good frequency accuracy. With good orbit parameters and model a computer controlled radio readjusting the frequency on the fly might work. It works well enough for SSB on the birds up there now since as we well know an error of 10’s to 100’s of Hz results in unintelligible signals so there is a chance.

Of the current crop of (VHF, UHF, and UP) digital voice protocols, the waveform is polarized to a large extend and a linear translator such as those used on current satellites will invert whatever passes through it, both in data polarity and frequency.  The latter exacerbated by any Doppler shift.  Even a shift of a few hundred hertz is enough to send the BER soaring and so nothing gets received.  The problem, even without Doppler, is that losing or corrupting any part of the original signal will result in errors.  Dropping to baseband might pass the voice portion (might), but you would have none of the rest of the data that isn't contained in the baseband, and so the signal is unreadable by a receiving digital radio. These protocols were simply not meant to be used in this particular application.  BTW, the reason packet works is because it uses tones for mark and space rather than a pure digital waveform and,  it processes the packet before before generating and sending a new response packet.

Other 'digital protocols' like PSK and others, possibly even FT8, might actually work through an FM or LT type satellite because it is basically audio tones and, the actual received signal can be anywhere within the application pass-band (e.g.  Doppler and phase have less impact).

All that said, I'm pretty sure the regular satellite operators would be pretty miffed to hear even those signals coming through the satellite.

[Lscott]

2 hours ago, WROZ250 said:

All that said, I'm pretty sure the regular satellite operators would be pretty miffed to hear even those signals coming through the satellite. ssb signal is around 3KHz

That's likely one of the real reasons why it isn't tried. Most of the digital modes have fairly wide signals compared to side band. A SSB signal is around 3KHz, correct, while some of the digital mode signals are like the following examples:

4K00F1E – NXDN 6.25KHz digital voice (IDAS, NEXEDGE)

4K00F1E – dPMR 6.25KHz digital voice (Typically not used in North America, used in the EU)

7K60FXE – 2-slot DMR (Motorola MOTOTRBO) TDMA voice

8K10F1E – P25 Phase 1 C4FM voice

8K30F1E – NXDN 12.5KHz digital voice (Wide DAS, NEXEDGE)

9K36F7W – Yaesu System Fusion C4FM (Voice Wide) 

22K0D7E – TETRA DMO Voice 

Some of those linear translators don't have that much bandwidth to begin with. Using digital isn't going to be welcomed and very highly discouraged, not because it can't be done with the right equipment.

As I said before any signal that's transmitted is always an analog type regardless of what information is being sent. The main difference is how the signal is shaped. Simple rectangular pulses are not sent because the bandwidth required is stupid wide. Various types of pulse shaping is used. One such shape is GMSK. There are others with different properties.

https://www.oscium.com/sites/default/files/WhitePaper_Simple_Signal_Shaper_GFSK.pdf

http://www.sss-mag.com/pdf/gmsk_tut.pdf

https://www.researchgate.net/profile/Thierry-Turletti/publication/2575678_GMSK_in_a_nutshell/links/0deec517e72247f39d000000/GMSK-in-a-nutshell.pdf?origin=publication_detail

I get the point about possible signal inversion occurring in a linear translator. However that would depend on the design. I would guess not all of then do so. That how the convention between using upper or lower side band on HF originated, selecting the high or low side mixing product of the VFO with the local oscillator depending on the band.

Also likely the reason why simply connecting the output from a receiver's discriminator to a transmitter's modulator might not work has to do with the frequency accuracy. With 4FSK it's critical the frequency shifts are right. Being off too much the RX radio can't decode the data. That means the level being fed into the transmitter's modulator has to be very carefully controlled to achieve the expected frequency shifts. That's also assuming the frequency shift is a linear function of the modulation voltage, which it might not be.

[Lscott]

Just for my info I went looking to see if there are in fact any digital voice capable digital voice satellites. I found one for D-Star.

http://www.d-star.one

[KAF6045]

A (short-term) store&forward system, with the bird regenerating packets between receive and transmit... {Just commenting -- no analysis intended)

Figuring out how to program it into a radio might be interesting (it likely won't be of use in the repeater-list of units with a "nearest repeaters" function unless one is mid-ocean ). I've not configured any D-STAR contacts into the regular channels of my systems.

[WROZ250]

5 hours ago, KAF6045 said:

A (short-term) store&forward system, with the bird regenerating packets between receive and transmit... {Just commenting -- no analysis intended)

Figuring out how to program it into a radio might be interesting (it likely won't be of use in the repeater-list of units with a "nearest repeaters" function unless one is mid-ocean ). I've not configured any D-STAR contacts into the regular channels of my systems.

https://www.n2yo.com/satellite/?s=43881

[WROZ250]

Should be interesting! the orbital data shows the passes that at some point will cover pretty much anyplace on earth.

BTW, I found this one on the Heavens Above site by searching for the NORAD ID (43881).

https://www.heavens-above.com

[deerhunter1972]

On 7/6/2022 at 1:54 AM, marcspaz said:

Hey folks,  I have a quick question.  Tonight I made a 1,700+ mile contact from Virginia to Mexico using the ISS cross-band repeater (VHF/UHF).  I was running my Diamond X300 vertical which has 7 dBd gain (9 dBi) on UHF and my frontend was getting overloaded to the point where a lot of audio was distorted.  I was watching the tracker and I could only hear well when I was on the edges of the coverage area, near the horizons.  However, one person sent me an email saying he could hear me very well in Mississippi... so I know the take-off angle and the doppler effect is accounted for.

 

 

Does anyone here do satellite work?  I'm thinking I have too much gain.  I am considering building an omni-directional horizontal loop and trying again soon.  With the exception of buying a beam on a tripod, do any of you have any advice on what to do for antenna design?  What has worked well for you?

 

Thank! 

Spaz

You really do need a directional antenna to track satellites and adjust for Doppler. I use an Arrow II antenna with built in duplexer(https://www.arrowantennas.com/arrowii/146-437.html) paired with a Yaesu FT530 for FM satellites, and the Arrow II antenna paired with 2 Yaesu FT817's for Linear satellites. Don't use more than 5W to transmit. I typically easily get in to the satellites using only 1 watt. As far as doppler, only adjust the UHF frequency during the pass for FM birds, and really only very minimally.

I do believe FTM300 should be able to work FM satellites in Full Duplex, so it's just a matter of programming the FTM300 with the correct uplink and downlink frequencies for the pass of the satellite adjusting for Doppler.

On this page is an invaluable cheat sheet for all the FM and Linear birds... https://ke0pbr.wordpress.com/2018/12/31/my-frequency-cheat-sheet/    

Here is also a link to a spreadsheet that will show current and past radios capable of Full Duplex  https://www.dropbox.com/sh/v3byggtuqw33fkk/AAAamatWbd9657AQfXhM6-wPa/Articles/Full-duplex_radios_for_satellites.xlsx?dl=1

A live satellite tracking app such as GoSatWatch for iOS or Heavens Above for Android will help you track the birds with ease.

Hope this info is useful! Satellites are very addicting and fun and are pretty reliable no matter what the propagation is.

Also watch these short videos on FM satellites

 

 

[Lscott]

You can use directional antennas, or a bit more power with an “eggbeater” type for TX and RX. The way they are designed is the radiation pattern is circularly polarized and directed up and out to the horizon, thus no tracking required.

http://146970.com/PDFs/Antenna Eggbeater-Revisited-English.pdf

[Lscott]

Here is some more info on eggbeater antennas.

 

Antenne Eggbeater-Engl-Part2-Full.pdf Antenne Eggbeater-Engl-Part1-Full.pdf

[Andyigor]

I have made over 1000 Sat QSO's with my ELK 5 Ele. Hand Held Beam....

 

ANDY

[AdmiralCochrane]

On a nice high angle pass I have no trouble hearing the ISS with a regular HT.  I do compensate for doppler and I do try to keep antenna polarization in mind. I encourage everyone to give it a try.

[WRQG411]

21 hours ago, AdmiralCochrane said:

On a nice high angle pass I have no trouble hearing the ISS with a regular HT.  I do compensate for doppler and I do try to keep antenna polarization in mind. I encourage everyone to give it a try.

Are you listening on 145.8 +/- for doppler effect, or on the cross-band repeater 437.800 +/- for DE?

[WRQC527]

On 7/5/2022 at 11:54 PM, marcspaz said:

What has worked well for you?

I have an Arrow beam antenna that works well. I use it with my FT-60 and an MFJ diplexer. (They call it a duplexer.) I've got several memory channels set with different UHF downlink frequencies to account for the Doppler shift. All my satellite contacts have been through the SO-50 AMSAT satellite. I have yet to make one through the ISS. 

[dugcyn]

this has been a cool side show for me as only GMRS license only. listening has been an experience and enlightening to how dopler shift, horizon event works with this and the radio and antenna. I pick it up with a verticle antenna and or HT. found holding HT side ways works a bit better as it not normally running directly above, horizon in and out. cheers to them that have made contact. that there is a challenge.    again no TX for meh at this point. 

[WRQC527]

1 hour ago, dugcyn said:

this has been a cool side show for me as only GMRS license only. listening has been an experience and enlightening to how dopler shift, horizon event works with this and the radio and antenna. I pick it up with a verticle antenna and or HT. found holding HT side ways works a bit better as it not normally running directly above, horizon in and out. cheers to them that have made contact. that there is a challenge.    again no TX for meh at this point. 

Check oout the AMSAT website. It has everything you need to know about listening to and communicating through Amateur Radio satellites. Somewhere buried in this site are instructions on how to make a satellite antenna using literally hardware store parts. I built one and made my first contact through a satellite with a Baofeng UV-5R. There's also a pass prediction section where you can specify your location and pick a satellite to see when it will be passing your location high enough above the horizon to hear. Heavens Above has a similar feature.

https://www.amsat.org/

https://www.heavens-above.com/

[tweiss3]

I did try to get to the ISS again a few weeks back. Using my 9700 and this application https://www.microsoft.com/store/productId/9WZDNCRDNDF7, I was able to hear it and other satellites, but the time frame is so short, and its such a mess trying to get in, it takes some patience. I also realized I need to upgrade feedline to get better reception on UHF, as the 75' of 400MAX is not excellent.