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ISS Satellite Contact a Few Minutes Ago. Advice?


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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

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What radio were you using? I haven't made it successfully, but my understanding is that even with Doppler, the frequency does change throughout the contact. I doubt you had too much gain, as those I know that make those contacts do so with Yagi/Beam antennas with gain over 11dbi. I would guess you were slightly off frequency on the receive, but on the marker on transmit.

I know my IC9700 has an auto tracker than can track the received carrier and adjust as it moves with the Doppler shift, but I don't think any other radio has that. Others use the computer to adjust on the fly.

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59 minutes ago, tweiss3 said:

I know my IC9700 has an auto tracker than can track the received carrier and adjust as it moves with the Doppler shift, but I don't think any other radio has that. Others use the computer to adjust on the fly.

The long discontinued Kenwood TS-2000 SAT mode, while not automatic, did have linked Tx/Rx splits (over multiple bands) so that varying one frequency would vary the other (and with the option for inverse tracking, if the bird had an inverting transponder).

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4 hours ago, BoxCar said:

Personally I haven't worked any satellites or the ISS but some of the hams in our club have done so with tape measure yagis. 

 

I have seen those before.  Its a pretty net setup.

 

1 hour ago, tweiss3 said:

What radio were you using? I haven't made it successfully, but my understanding is that even with Doppler, the frequency does change throughout the contact. I doubt you had too much gain, as those I know that make those contacts do so with Yagi/Beam antennas with gain over 11dbi. I would guess you were slightly off frequency on the receive, but on the marker on transmit.

I know my IC9700 has an auto tracker than can track the received carrier and adjust as it moves with the Doppler shift, but I don't think any other radio has that. Others use the computer to adjust on the fly.

 

I am using a Yaesu FTM-300DR.  It only has a 5k step instead of a 1k or finer.  I wish I had a 1 Hz tuner... but the last radio that U had that feature on was my now long-gone 857D.

The reason I think there was too much gain is because of the audio characteristics.  It get louder and louder until it sounded like someone was screaming into the mic.  My S-meter was pegged, too.  I did try shifting up and down 5 KC thinking it might have been doppler, but it didn't help. 

Maybe 5k is too large of a jump and I need more fine tuning?

Just for giggles, next time the ISS is going to fly over, I my test with an HT.  LOL

 

56 minutes ago, KAF6045 said:

The long discontinued Kenwood TS-2000 SAT mode, while not automatic, did have linked Tx/Rx splits (over multiple bands) so that varying one frequency would vary the other (and with the option for inverse tracking, if the bird had an inverting transponder).

 

I tried to find one of those for 2 years and gave up.  Few are for sale and the ones that are, the owner is asking way too much.  Thankfully, the FTM-300DR has 2 seperate transmitters and receivers, which made it easy work, for the most part.

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35 minutes ago, marcspaz said:

The reason I think there was too much gain is because of the audio characteristics.  It get louder and louder until it sounded like someone was screaming into the mic.  My S-meter was pegged, too.  I did try shifting up and down 5 KC thinking it might have been doppler, but it didn't help. 

No input attenuator? or selectable pre-amp? (Well, probably not found on strictly VHF/UHF FM rigs, though the manual for the Icom ID-5100 does have an attenuator somehow linked to the squelch control dial and the ID-52 and  Kenwood TH-D74 hand-helds have switchable ones)

35 minutes ago, marcspaz said:

I tried to find one of those for 2 years and gave up.  Few are for sale and the ones that are, the owner is asking way too much.  Thankfully, the FTM-300DR has 2 seperate transmitters and receivers, which made it easy work, for the most part.

You aren't getting mine -- even though it currently only shares a 4-band OCFD with a newer TS-590. If the cancer doesn't get me I may eventually put up the 2m/70cm 1/4wave ground plane antenna. It wasn't exactly cheap even back in 2010 when new ($1700) [the 590 was $1750 in 2015

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37 minutes ago, KAF6045 said:

No input attenuator? or selectable pre-amp? (Well, probably not found on strictly VHF/UHF FM rigs, though the manual for the Icom ID-5100 does have an attenuator somehow linked to the squelch control dial and the ID-52 and  Kenwood TH-D74 hand-helds have switchable ones)

You aren't getting mine -- even though it currently only shares a 4-band OCFD with a newer TS-590. If the cancer doesn't get me I may eventually put up the 2m/70cm 1/4wave ground plane antenna. It wasn't exactly cheap even back in 2010 when new ($1700) [the 590 was $1750 in 2015

 

There is no attenuation function on my radio.  It's a mobile VHF/UHF radio.  I do have an Icom 746 Pro which has an attenuator, but there is no UHF, so it wasn't an option.  I may look at a Yaesu 991a, if that has an attenuator and 1 Hz tuning.

 

Sucks to hear about the cancer... but it sounds like you have a nice setup with the radio.

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The distortion is due to Doppler and, it's an FM repeater. 

I've tracked the ISS on my SDR, and depending on the pass (relative to my location), the Doppler can be as much as +/- 10KHz from the down link center frequency.  So if your radio has a tight bandwidth, there will be distortion for all except the closest part of the pass.  I use my FT-818 because my tuning rate isn't fixed at 5KHz.  You leave your transmit signal alone and simply tune the receiver as the pass progresses.

The FT-818 isn't a 'Satellite" rig, but it's better than using an FM HT.  Sadly, rigs that offer full cross-band duplex can get expensive. That said, the Alinco DR-735 and my Yaesu FTM-400 will do cross band duplex and more refined tuning steps than simply 5 KHz, so at least for the FM satellites they are an option.  Basically, any dual band radio that can do/work as a cross band repeater is usable for FM satellite.

As far as power, don't ever use more than about 10W.  Not because it will cause distortion, but rather you overload the repeater.  It doesn't take a lot of power to access any of the satellites.

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@WROZ250 I appreciate the advice. 

 

I have used other people's gear before and had a great time, which is why I tried my own equipment yesterday. It was pretty fun using one person's radio at 800mw and another at 5w.

 

I had an FTM-400. I don't know if it was a firmware issue compared to your experience, bit the lowest mine went was 5kc steps.  I replaced it with the FTM-300DR. 

 

I'm currently thinking about an FT-991a, IC-9700 or an IC 705.  I just don't know if I like the idea of being QRP unless I buy a bunch of amps, or I would have already purchased the 705.

 

Anyway... thanks again. I guess a new radio is in my future.

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@marcspazI just reread your earlier comment.  It would be a very (very) odd event for the ISS repeater to overload your receiver and/or peg the S-meter.  I'm wondering if perhaps a newbie might have been transmitting on the down link frequency (i.e. they got the split wrong/reversed).

We have a small group out here who work the sats somewhat often and even one guy with an 11 element yagi on the down link (into an HT) who has never experienced anything near an overload on the down link.

Food for thought

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16 hours ago, marcspaz said:

@WROZ250 I appreciate the advice. 

 

I have used other people's gear before and had a great time, which is why I tried my own equipment yesterday. It was pretty fun using one person's radio at 800mw and another at 5w.

 

I had an FTM-400. I don't know if it was a firmware issue compared to your experience, bit the lowest mine went was 5kc steps.  I replaced it with the FTM-300DR. 

 

I'm currently thinking about an FT-991a, IC-9700 or an IC 705.  I just don't know if I like the idea of being QRP unless I buy a bunch of amps, or I would have already purchased the 705.

 

Anyway... thanks again. I guess a new radio is in my future.

As far as rigs go, keep in mind there are rigs that transmit cross-band, but cannot actually receive while transmitting (Like my FT-818).  Most rigs that can be configured to be a cross-band repeater can listen on one band while transmitting on the other 'duplex', so watch the specifications closely.  Just because a rig is dual band doesn't mean it does duplex. I know the IC-9700 can do this (it better given the price tag! LOL!) and, you also get the option of working the SSB/CW satellites. 

Duplex isn't strictly necessary, but it helps to be able to hear yourself in the down link, because that is likely where others hearing your signal will answer you!

Ironically, one of the widest coverage sats is AO-7 which is back from the dead and, only when it is full sunlight (Batteries croaked).  It isn't an FM satellite though, only SSB/CW, but even with it's 40 year old decaying orbit, you can work half to 3/4 of the country during a pass.

Have fun!

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@WROZ250 Good info!  You know, you may be onto something with someone having the uplink and downlink flopped.  One of the really heavily distorted/load stations I heard was calling from FM19 and I am FM18.  I can 100% full quiet to a station in FM19 from my house.

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1 minute ago, marcspaz said:

@WROZ250 Good info!  You know, you may be onto something with someone having the uplink and downlink flopped.  One of the really heavily distorted/load stations I heard was calling from FM19 and I am FM18.  I can 100% full quiet to a station in FM19 from my house.

Yeah, and as I mentioned, another newbie mistake is thinking you need QRO to get a satellite.

BTW, When I mentioned less distortion on the closest part of the pass (due to Doppler), I meant when it is moving the least, relative to your position.  That is usually at the apex of a pass for near overhead passes, or it can be when a sat is just over the horizon and/or nor coming or going away from your location.  I hope that makes sense, kind of difficult to explain how and when Doppler becomes a PIA for FM satellites. 

The bottom line is Doppler is at it's worst when the sat is coming directly towards you and as it moves away.  Higher frequency coming at you and lower as it moves away.

The real bitch IMHO, is that you really only have a few minutes, on most sats, to tune and make contacts.  It is, however, pretty cool!

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@marcspaz One last thing...

With a vertical antenna, your best signal would be when a satellite is near the edge of your coverage and so the signal will likely will drop in strength when directly overhead. 

Short of a pair of small yagis (and the ability to aim them) the best antennas for sat work are Turnstiles and Eggbeater types.  Both are relatively easy to make, but not really a beginner project, at least the eggbeater (phasing issues).  If I were to suggest a DIY, it would likely be the Turnstile type.  Eggbeater antennas are available from MFJ and M2, but getting a pair of them would be as much as a new radio. :(

We did have one guy in our club use a single DIY Log Periodic antenna for satellite work.  That however, is a somewhat complicated antenna for DIY.

 

FWIW

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17 minutes ago, WROZ250 said:

The bottom line is Doppler is at it's worst when the sat is coming directly towards you and as it moves away. 

Ah!  That makes a lot of sense.

 

18 minutes ago, WROZ250 said:

The real bitch IMHO, is that you really only have a few minutes, on most sats, to tune and make contacts.  It is, however, pretty cool!

Agreed!

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I got on the repeater again tonight and didn't have any issues.  I couldn't hear myself in the downlink but a new acquaintance sent me a recording of me talking and I was staying right on frequency, even with the gross adjustments I'm limited to.

 

I think I can't here myself in the downlink because the uplink and downlink are almost perfect harmonics.  The satellite is 437.800 down and 145.990 up.  If at the beginning of the pass, I noticed that if I listen on 437.810 and transmit on 145.980... I get a faint sound like a station nearby, but not on the same frequency.  Since I didn't hear myself in the downlink, I started dropping my transmit frequency thinking I didn't adjust enough for doppler.  When I got to 145.940, I could hear myself 100% perfect, full quiet and zero distortion on the receive side.  Flawless talk back.

 

I guess from now on, I am just going to start at 10kc+/- and assume that if I heard the repeater at +10kc, then my transmit needs to be -10kc.  As I move the receive down, I'll increment transmit up the same amount.  That seemed to work well last night.  I may look for some other satellites to work and see how it goes.

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My only experience with ISS was to use their APRS digipeater, and I do not have any other experience with satellites. I've been told or read somewhere, that Doppler effect on VHF is small for LEO sats, and you should not need to adjust the VHF frequency. As opposed to UHF, where people normally program 5 adjacent frequencies and go through them during the satellite pass. Is my impression right or wrong?

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14 minutes ago, axorlov said:

Is my impression wright or wrong?

 

Honestly, I don't know.  The stuff I deal with at work is all geostationary for data and I just manage the servers that control them... The few AMSAT contacts I made prior to a few days ago was all on other peoples gear, with SDR's and everything was computer controlled there, too.  This is my first time doing AMSAT or any other type of satellite work 100% on my own, with my own gear and manually. 

 

It does seem like I was doing okay both days.  The first day I only adjusted the UHF downlink and the second day I adjusted both the VHF uplink and the UHF downlink.  I had equal success both days, but the recording I received from day 2 sounded great.  So I am prone to think it depends.  LOL

 

Based on what I am reading, the experienced doppler it is mostly based on the speed of the satellite and its trajectory in relation to your station.  For example, if you have a direct overhead pass, horizon to horizon, you would have the most noticable doppler effect.  If the satellite comes into view off in the distance and traces the horizon, you may experience no doppler effect.  Again, I am new to this, but I think that is correct.

 

 

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5 hours ago, marcspaz said:

I got on the repeater again tonight and didn't have any issues.  I couldn't hear myself in the downlink but a new acquaintance sent me a recording of me talking and I was staying right on frequency, even with the gross adjustments I'm limited to.

I think I can't here myself in the downlink because the uplink and downlink are almost perfect harmonics.  The satellite is 437.800 down and 145.990 up.  If at the beginning of the pass, I noticed that if I listen on 437.810 and transmit on 145.980... I get a faint sound like a station nearby, but not on the same frequency.  Since I didn't hear myself in the downlink, I started dropping my transmit frequency thinking I didn't adjust enough for doppler.  When I got to 145.940, I could hear myself 100% perfect, full quiet and zero distortion on the receive side.  Flawless talk back.

Does the FTM-300 actually /receive/ and produce audio for one band while the other band is transmitting? The only units I've seen that can do that have not only dual receivers, but separate antenna connections for each (and are usually things like HF/6m on one antenna, 2m/70cm on a separate (my TS-2000 does have two HF/6m connectors [only one can be selected at a time] and separate 2m & 70cm connectors -- being fed to a diplexer for a dual-band antenna to be installed; I still think one can not do V/U without having transmit cut out the other band). Normally the radio will cut out the receive circuit when PTT, to avoid feeding the "massive" signal into the sensitive receiver inputs.

 

5 hours ago, marcspaz said:

I guess from now on, I am just going to start at 10kc+/- and assume that if I heard the repeater at +10kc, then my transmit needs to be -10kc.  As I move the receive down, I'll increment transmit up the same amount.  That seemed to work well last night.  I may look for some other satellites to work and see how it goes.

https://www.amsat.org/tag/doppler/

A bit old, and partly involved with the HF birds though VHF/UHF does get lightly mentioned.

 

3 hours ago, marcspaz said:

Based on what I am reading, the experienced doppler it is mostly based on the speed of the satellite and its trajectory in relation to your station.  For example, if you have a direct overhead pass, horizon to horizon, you would have the most noticable doppler effect.  If the satellite comes into view off in the distance and traces the horizon, you may experience no doppler effect.  Again, I am new to this, but I think that is correct.

 

 

Doppler is dependent upon the rate of change in distance between transmitter and receiver and is, I believe, proportional to the frequency.

So, relatively speaking, if the bird is moving directly toward/away from you, doppler will be greatest (standing on the station platform as an express zooms through the station). Minimal change in distance, minimal doppler effect (standing on a roof in the center of the village while the express is taking a rail line that arcs around the perimeter). The speed of the express is the same in both cases <G>

 

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46 minutes ago, KAF6045 said:

Does the FTM-300 actually /receive/ and produce audio for one band while the other band is transmitting?

 

Yes, it does. It has a built-in repeater.  So it has to be able to transmit and receive at the same time. There are two radios in one package that function independently of each other.

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12 hours ago, marcspaz said:

 

Yes, it does. It has a built-in repeater.  So it has to be able to transmit and receive at the same time. There are two radios in one package that function independently of each other.

This website has a list of recent radios that offer cross-band repeat functionality:

http://www.ssiarc.ca/cross-band-repeat.php

 

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On 7/6/2022 at 2:54 AM, marcspaz said:

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 xception 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?

I did at one time.

https://www.g0mrf.com/ao-40.htm

I had a portable setup for AO-40, 70cm SSB uplink working with an 11 element M Squared Yagi,

https://www.m2inc.com/FG4205011

and the down-link was on 2.4GHz with a UEK-3000 down converter to the 2 meter band working with a 24db dish antenna.

http://websites.umich.edu/~umarc/files/misc/UEK-3000.pdf

https://www.radiolabs.com/wireless/wifi-antennas/directional-wifi-antennas/parabolic-grid-wifi-dish-antenna-24db-2-4-ghz/

The radio I used at the time was a Yaesu FT-847 with an optional after market IRAD RX IF crystal filter for SSB.  I made a couple of contacts through it. The down-link signal wasn't that strong.

https://www.hamradio.co.uk/userfiles/file/FT-847.pdf

https://w6aer.com/ft847-inrad-filter-modifications-upgrade/

Because of some screw up the satellite ended up in a very highly eccentric orbit. At the farthest point the distance was around 40K miles. The delay in the down-link in the head phones was about a 1/2 of a second, very noticeable and hard to adjust to hear one self with a delay. The advantage at that distance is the satellite hardly moved for about 10 to 15 minutes making manual static pointing of the antennas practical and almost no Doppler shift. 

I lived in a ground floor apartment at the time so I needed to to drag the whole antenna setup outside every time. That was done late at night to attract far less attention. The last thing I wanted were the other tenets calling the local PD thinking I was some kind of spy or terrorist. The van had enough strange looking antennas on it as it was and I got a few people driving circles around it at shopping centers staring at them while giving me weird looks. Oh well. 8-/

I made a few contacts on FM through a low earth orbit satellite, mode U/V, from a mobile using an Icom IC-706MKII I had with some simple vertical antennas on the roof. Those  satellites tend to get very busy since they are far easier to work. 

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@Lscott Great post.  Sounds like you had some nice gear.  The FT-847 looks awesome.

 

I know what you mean about the weird looks, too.  Especially with my Jeep, which is 6 inches higher than stock with 37" offroad tires and 3 86"+ antenna's hanging off the bed.  It's a convo starter almost everywhere I go.

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10 hours ago, Lscott said:

I guess if you really want a challenge try running a digital voice mode through one of the satellites. I remotely remember reading about a Ham that claimed it was accomplished with DMR. 

Impossible to do through an FM or an SSB (linear translator) satellite, given the nature of digital voice technology (DV).   The latter, (Linear translator) might actually result in a DV stream on the down-link, but all of the data would be inverted and/or distorted (not to mention the Doppler impact), resulting in gibberish that could not be decoded.

Early on in DV, a lot of people thought you could hack a mobile and simply feed the discriminator out on a DV receiver and feed it into the modulator of another DV radio's transmitter, which doesn't work.  Actual DV repeaters do not simply send base-band from the RX to the TX as with an analog FM repeater.  Even if one were to take the raw speaker audio and feed it to the microphone of another radio, it would not work.  Yes, something that sounds like digital would be transmitted, but it would not contain the information from the sending radio.  DV is not analog.  At best, a simplex repeater device connected to a DV radio would perhaps parrot the voice information, but all other signalling would be lost.

Indeed, virtually all of the mainstream digital voice technologies, DMR, D-Star, P25, etc... essentially decode the digitized information from the receiver, process it, and then re-encode it for the transmitter, hence the slight audio delay on digital systems (in the case of repeaters).  Because of that, in the very early days of DV, many of the D-Star advocates argued that their repeater wasn't actually a repeater at all, but rather a 'store and forward' technology, in an effort to bypass repeater coordination and frequency restrictions.  One such advocate, convinced the idea was valid,  posed the question to the FCC to 'settle the debate', which resulted in a all of systems that had subscribed to the (not a repeater) idea and, had constructed systems outside the legal repeater sub-bands, were ordered to shut down.

In any event, unless a satellite was specifically equipped with a DV repeater, which today is not out of the question technically, none of the current crop of digital voice technologies would be retransmitted (repeated) by any of the currently active satellites. 

All transmitting into a current satellite using DV technology would do, is jam the other users.

:-|

BTW, a perfect example of why DV through a satellite can't work... try using DV through an analog FM repeater.

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