Doppler effect on CW/SSB?!?!?

[spdfile1]

Ok as previously mentioned in an earlier thread I purchased the Kenwood TH-F6A. Love the radio!! I'm getting ready to program it with satellite frequencies and I'm not sure on one thing. Is the doppler effect the same on FM as it is on CW/SSB? For example when I want to make contacts on say AO-51 I know I need to start 10 Mhz above the center frequency and work my way down to 10 Mhz below the center frequency as the satellite moves. But that is FM (UHF) mode. Now say I want to listen to the BEESAT satellite for example which transmits a Mode U TLM Beacon of 436.000 MHz CW, do I start 10 MHz above and work my way down or is it a single MHz? I'm guessing it is the same across the board, but I don't want to program up the TH-F6A the wrong way.

 

[JeremyB]

FM is a lot more forgiving in concerns for doppler, and the FM sats are all single frequency on the uplink and downlink and the receivers bandwidth is usually wide enough so you don't have to compensate for doppler on the 2M uplink- its only about +/- 3 khz anyhow compared to the +/- 10 khz on the 70cm downlink.

For the SSB/CW linear transponders, you might be better off not programming any memory channels and just write down or memorize the downlink frequencies. You are most likely to find voice/CW near the middle of the downlink, so if the center of the downlink is 145 at AOS, I would start at 145 and move up and down from there looking for a signal. Once I find something then I use the fine tuning so I can understand. If the downlink is 435.300(like AO-51 FM) your AOS center freq would be 435.310. It can be challenging trying to listen to a QSO listening to one op on one freq and then switching up or down some to hear the other. I find more activity while listening on USB on the normal and inverting transponder sats than I do on LSB.

Have fun!

 

[spdfile1]

FM is a lot more forgiving in concerns for doppler, and the FM sats are all single frequency on the uplink and downlink and the receivers bandwidth is usually wide enough so you don't have to compensate for doppler on the 2M uplink- its only about +/- 3 khz anyhow compared to the +/- 10 khz on the 70cm downlink.

For the SSB/CW linear transponders, you might be better off not programming any memory channels and just write down or memorize the downlink frequencies. You are most likely to find voice/CW near the middle of the downlink, so if the center of the downlink is 145 at AOS, I would start at 145 and move up and down from there looking for a signal. Once I find something then I use the fine tuning so I can understand. If the downlink is 435.300(like AO-51 FM) your AOS center freq would be 435.310. It can be challenging trying to listen to a QSO listening to one op on one freq and then switching up or down some to hear the other. I find more activity while listening on USB on the normal and inverting transponder sats than I do on LSB.

Have fun!

Jeremy B,
Thanks for the info. You have been a wealth of knowledge!!!! That was my other question and I believe you already answered it!!! I noticed the frequencies on SSB mode don't differentiate weather USB or LSB on the satellite sheets, but my kenwood does. So it sounds like USB is the better mode to monitor of the two. Oh and by the way you saved me from programming probably a hundred or more channels on the kenwood!!! Thanks

 

[Token]

Ok as previously mentioned in an earlier thread I purchased the Kenwood TH-F6A. Love the radio!! I'm getting ready to program it with satellite frequencies and I'm not sure on one thing. Is the doppler effect the same on FM as it is on CW/SSB? For example when I want to make contacts on say AO-51 I know I need to start 10 Mhz above the center frequency and work my way down to 10 Mhz below the center frequency as the satellite moves. But that is FM (UHF) mode. Now say I want to listen to the BEESAT satellite for example which transmits a Mode U TLM Beacon of 436.000 MHz CW, do I start 10 MHz above and work my way down or is it a single MHz? I'm guessing it is the same across the board, but I don't want to program up the TH-F6A the wrong way.

I am fairly sure you do not mean 10 MHz of Doppler shift. 10 MHz of Doppler at 436 MHz is roughly a closing or opening relative velocity of 7,700,000 MPH (yeah, that is seven million plus).

OK, I realize it was typo or some such, just had to say.

One of the reasons that FM is more forgiving in this case is that if you are tuned 2 kHz off on FM you might loose a little clarity, maybe induce a little bit of noise, but still the signal is generally usable as long as the signal strength itself is adequate. However, if you tune off freq (or have a Doppler shift, it is the same affect) by 2 kHz with an SSB signal the audio frequencies are actually shifted up or down that 2 kHz, making the audio unusable.


For reference a Low Earth Orbit (LEO) satellite (most AMSATs are LEO) would have a maximum velocity just under 20,000 MPH, and the higher the altitude the lower the velocity will be. 20,000 MPH produces a maximum Doppler shift of 8.6 kHz at 145 MHz and 26 kHz at 436 MHz. The altitude of several popular LEO AMSATs require a velocity of under 8000 MPH, and so the maximum Doppler shift would be just over 3 kHz at 145 MHz, and about 10 kHz at 436 MHz. And that is the worst case Doppler, assuming the sat is making a pass headed directly towards you (thus the highest Doppler possible just as it comes over the horizon) and will pass directly overhead.

So, the rule is, the lower the altitude of the satellite the higher the potential Doppler shift will be, while very high orbits require less Doppler shift. For example Geosynchronous sats require no Doppler shift, because their relative velocity is very near zero to the Earth station.

T!

 

[spdfile1]

I am fairly sure you do not mean 10 MHz of Doppler shift. 10 MHz of Doppler at 436 MHz is roughly a closing or opening relative velocity of 7,700,000 MPH (yeah, that is seven million plus).

OK, I realize it was typo or some such, just had to say.

One of the reasons that FM is more forgiving in this case is that if you are tuned 2 kHz off on FM you might loose a little clarity, maybe induce a little bit of noise, but still the signal is generally usable as long as the signal strength itself is adequate. However, if you tune off freq (or have a Doppler shift, it is the same affect) by 2 kHz with an SSB signal the audio frequencies are actually shifted up or down that 2 kHz, making the audio unusable.


For reference a Low Earth Orbit (LEO) satellite (most AMSATs are LEO) would have a maximum velocity just under 20,000 MPH, and the higher the altitude the lower the velocity will be. 20,000 MPH produces a maximum Doppler shift of 8.6 kHz at 145 MHz and 26 kHz at 436 MHz. The altitude of several popular LEO AMSATs require a velocity of under 8000 MPH, and so the maximum Doppler shift would be just over 3 kHz at 145 MHz, and about 10 kHz at 436 MHz. And that is the worst case Doppler, assuming the sat is making a pass headed directly towards you (thus the highest Doppler possible just as it comes over the horizon) and will pass directly overhead.

So, the rule is, the lower the altitude of the satellite the higher the potential Doppler shift will be, while very high orbits require less Doppler shift. For example Geosynchronous sats require no Doppler shift, because their relative velocity is very near zero to the Earth station.

T!

Token,
Appreciate the info!!! Very informative. I think I did mean kHz and not MHz (lol).

 

[JeremyB]

NA2X posted a chart he uses on VO-52 as a guide: this first post has the guide flipped Re: finding yourself in the passband of an analogsatellite

Here is his corrected frequency guide: Re: finding yourself in the passband of ananalogsatellite