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Author Topic: All mode receiver ?  (Read 641 times)
AA9KG
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« on: December 04, 2017, 07:06:31 PM »

I am trying to get into working FO29 and AO7 and already own a yaesu 857d. I want to be full duplex and don't think I really need a full transceiver.  Maybe something like the icom r7000 or something like that?  I am very new to working the birds but quickly found out how hard it is to work ssb or cw when you can't spot yourself.
Any/all help would be appreciated.
Brian. AA9KG
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WD9EWK
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« Reply #1 on: December 04, 2017, 07:46:47 PM »

I am trying to get into working FO29 and AO7 and already own a yaesu 857d. I want to be full duplex and don't think I really need a full transceiver.  Maybe something like the icom r7000 or something like that?  I am very new to working the birds but quickly found out how hard it is to work ssb or cw when you can't spot yourself.
Any/all help would be appreciated.
Brian. AA9KG

For FO-29, your 857 could do what an 817 does in this old AMSAT Journal article:

http://www.amsat.org/wordpress/wp-content/uploads/2014/01/FT817-Arrow-SSB_Satellites-200501.pdf

There are videos on YouTube showing this technique in action with FO-29. I have a couple on my YouTube channel:

https://youtube.com/watch?v=iy-G6rD_xl4
https://youtube.com/watch?v=QRrtYiXLq28

and one done by a friend earlier this year at the Palm Springs hamfest:

https://youtube.com/watch?v=Tqx7Beibi7M

An 817 with fried finals could serve as a downlink receiver. The all-mode receiver in the TH-D74 does well. In the past, I used an AOR AR8200 handheld wide-band receiver. Or go SDR with something like a FUNcube Dongle Pro+ or SDRplay (any model) with software on a laptop or some tablets. I wrote articles about using an SDR receiver with a Windows tablet for the publications of AMSAT and AMSAT-UK. Those can be found in the Articles folder at http://dropbox.wd9ewk.net/ (the articles reference Windows 8.1, but also apply to Windows 10).

The TH-F6A had an all-mode receiver that could be used. A drawback with this is the wide front-end of the all-mode receiver in this HT. Strong signals coming through the transponder a few kHz off your downlink frequency can make reception tough. The TH-D74's all-mode receiver more than rectifies the shortcomings in the TH-F6A's all-mode receiver.

73!
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Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/ - Twitter: @WD9EWK
AA9KG
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« Reply #2 on: December 04, 2017, 08:19:22 PM »

 Thanks Patrick, the amsat article was very helpful, I watched one of the YouTube videos as well. I am trying to do the same thing with a single antenna and the 857 much like your set up in the video.  However you are an experienced operator. I am throwing a lot of CQs out there on ssb and cw with no responses and assumed that it is because I can't find myself on the downlink.
For FO29...Transmitting on 145.970 and listening on 435.830 +5 when it is coming toward me and -5 when it is moving away. Is that right?
Thanks for all the help.
I did have a buddy in Illinois listening once and said he could hear me loud and clear on the downlink.
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WD9EWK
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« Reply #3 on: December 04, 2017, 08:33:10 PM »

Thanks Patrick, the amsat article was very helpful, I watched one of the YouTube videos as well. I am trying to do the same thing with a single antenna and the 857 much like your set up in the video.  However you are an experienced operator. I am throwing a lot of CQs out there on ssb and cw with no responses and assumed that it is because I can't find myself on the downlink.
For FO29...Transmitting on 145.970 and listening on 435.830 +5 when it is coming toward me and -5 when it is moving away. Is that right?
Thanks for all the help.
I did have a buddy in Illinois listening once and said he could hear me loud and clear on the downlink.

The Doppler shift would be more like 8 to 9 kHz +/-, not 5. When you unkey after a transmission, you'll need to look a little up and down, since not all stations will line up perfectly with you. You will be.moving the downlink frequency gradually lower as the pass progresses, but know you may have to make a small move higher at times. Just don't move your uplink frequency, or you'll be all over the place.

One of the first two YouTube links above was actually the first time I tried working FO-29 half-duplex, with a single 817 and my Elk log periodic, in 2015. I was doing a demonstration on a footbridge over a busy downtown Phoenix street complete with a light-rail train running under it.

I may be an experienced satellite operator as you wrote, but I don't do half-duplex operation on FO-29 very much. Some times, it is just easier to use one radio and antenna for FO-29, like you would do with SO-50 or other FM satellites. Otherwise, I will use a two-radio setup for full-duplex operation, sometimes using different radios for the downlink side. I have more of those videos on YouTube at http://youtube.com/va7ewk

73!
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Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/ - Twitter: @WD9EWK
N4UFO
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« Reply #4 on: December 04, 2017, 08:49:58 PM »

For FO29...Transmitting on 145.970 and listening on 435.830

That's more where CW and rare DX hangs out... try the upper part of the transponder, more like 145.930 and start the pass at 435.876 working downward with the doppler to 435.870 at TCA (time of closest approach). Then even lower towards LOS. Remember that doppler shifts quickest near TCA, especially on overhead passes. Think like a train going by... the sound frequency shifts fastest as it passes by you.

GL! 73, Kevin N4UFO
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AA9KG
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« Reply #5 on: December 04, 2017, 09:01:40 PM »

Thanks a bunch Patrick!  I will keep trying...I like the AMSAT article that says the CQ should say something like "half duplex, long calls please".  I guess when I am starting out, I am relying on you experienced guys to find me...but then my next question is when they find me on say 435.838, where would they transmit?  Are they assuming +8khz as well (so really 435.830 downlink), so they would transmit on 145.970 ?
The reason I ask is because I heard a guy calling CQ at 435.845...I assumed the real downlink was 435.840, so I tried answering on 145.960, but he never answered so I assumed I was way off or something.
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AA9KG
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« Reply #6 on: December 04, 2017, 09:09:57 PM »

Thanks for the advice, Kevin!
This is challenging...but fun!
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N4UFO
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« Reply #7 on: December 04, 2017, 09:57:50 PM »

Thanks a bunch Patrick!  I will keep trying...I like the AMSAT article that says the CQ should say something like "half duplex, long calls please".  I guess when I am starting out, I am relying on you experienced guys to find me...but then my next question is when they find me on say 435.838, where would they transmit?  Are they assuming +8khz as well (so really 435.830 downlink), so they would transmit on 145.970 ?
The reason I ask is because I heard a guy calling CQ at 435.845...I assumed the real downlink was 435.840, so I tried answering on 145.960, but he never answered so I assumed I was way off or something.

Someones uplink vs downlink is going to depend on where they are in the footprint. If the bird is coming towards me, my doppler is going to be higher than someone who the bird is going away from. If you knew his uplink frequency, then you'd match it... but you can't tell that just from where you are hearing him on the downlink. If he is calling on 435.845, then all you can do is try to figure out how to get your signal to downlink on 435.845 as well. Which would be ~145.962 at AOS, ~145.955 at TCA and then ~145.948 towards LOS. (I could be off 1-2 on each of those...)

OR, maybe an easier way to grasp it... if you heard him CQing on 435.850... you'd be 145.957 at AOS, 145.950 at TCA and 145.943 at LOS.

Which is 'backwards' than if you were CQing at 145.950... you would hear yourself at 435.857 at AOS, 435.850 at TCA and 435.843 at LOS. I say your would hear YOURSELF. Just because you hear yourself at a frequency, doesn't mean that's the frequency that other people will hear you at... it all depends on where they are in the footprint, where their doppler shift is. - That's why when a rover wants to tell people where he will be for an upcoming pass, he will tell folks his UPLINK frequency and then you find him from that according to where you are in relation to the bird.

I know, I know, it's like thinking upside down and backwards... but after a while it starts to gel.  Wink Just keep practicing...

73, Kevin N4UFO
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AA9KG
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« Reply #8 on: December 04, 2017, 10:38:22 PM »

Awesome...thanks Kevin!  That is just what I needed to know.

Just one more quick one...after you both establish that you can hear each other, you keep the TX fixed, right?...and just adjust the RX to follow the shift?  This is what the amsat article said.
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AA9KG
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« Reply #9 on: December 04, 2017, 10:58:55 PM »

I guess now my original post doesn't make any sense...it doesn't make sense for me to use a second receiver/antenna to "find myself" on the downlink because whoever I am talking to is going to hear it on a different frequency anyway depending on whether they are close to AOS or LOS.  Thank you Patrick and Kevin for answering my newbie questions patiently Wink
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N4UFO
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« Reply #10 on: December 05, 2017, 04:31:59 AM »

Just one more quick one...after you both establish that you can hear each other, you keep the TX fixed, right?...and just adjust the RX to follow the shift?

Normally you shift the higher frequency... UHF in this case. Because doppler will affect it a whole lot more than 2m, whether that is uplink or downlink.

I guess now my original post doesn't make any sense...it doesn't make sense for me to use a second receiver/antenna to "find myself" on the downlink because whoever I am talking to is going to hear it on a different frequency anyway depending on whether they are close to AOS or LOS. 

A second radio/receiver is actually VERY USEFUL and operating full duplex is the norm...  because what you are trying to achieve is having it where you can hear the other station AND yourself on the same downlink frequency. In short... you tune the other guy in, then you adjust your uplink until you also hear yourself clearly on the same frequency. Then once you are both on the same downlink frequency, BOTH of you can hear yourselves AND each other and after that you adjust for doppler. The difference is, you will not necessarily have the same uplink frequency. I know that kind of seems to clash with what I said before about rovers advertising their uplink, but it's not the same situation... one is finding someone on air, the other is adjusting to start a conversation. There also tends to be a lot of wiggle room as most stations are willing to 'tune off' their own frequency a little in order to hear 'the other guy'.

Just get in some practice, make a few QSOs and it should be more clear... then come back with the next set of questions.  Cheesy

73, Kevin
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