SATELLITE MODE

VK3KYY
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Re: SATELLITE MODE

Post by VK3KYY » Tue Sep 21, 2021 9:39 am

r2dze wrote:
Tue Sep 21, 2021 8:37 am
VK3KYY wrote:
Tue Sep 21, 2021 1:08 am

Did you try without the duplexer

If you have separte feeds to the 2 driven elements of the 2m and 70cm yagi's, then you may not need the duplexer, and it may improve the performance of the antenna if you don't have the duplexer.
My antenna is single cable fed by design, so no way to work in duplex two station cross-band without duplexer. However I am pretty sure when one station would TX full power and another is RX at different band using the same antenna setup separately fed, the receiving one would be almost completely blocked by the strong signal of another, even though they are on different bands. Just tried it with two stations in proximity - and yes, receiving one getting signal readings and noise becomes lower, when another is TX on a different band. So that having duplexer which is isolating 2m and 70cm bands by additional 60+db is a benefit. In band through losses of the duplexer are quite low.
OK

I asked about the duplexer, because they are not cheap and people with 2 compatible radios e.g. RD5R could make a cheap satellite antenna by using separate radios with no duplexer.

I use a dual band yagi (Chinese) , which has the duplexer as part of the antenna construction, and it only has 1 coax to the antenna, so its not possible for me to listen to the response from the satellite while I'm transmitting.

I normally get much stronger signals that you seem to receive in your video, and contacting AO-91, AO-92 and ISS is not difficult

r2dze
Posts: 8
Joined: Tue Sep 14, 2021 2:20 pm

Re: SATELLITE MODE

Post by r2dze » Tue Sep 21, 2021 11:17 am

VK3KYY wrote:
Tue Sep 21, 2021 9:39 am
I normally get much stronger signals that you seem to receive in your video, and contacting AO-91, AO-92 and ISS is not difficult
I can confirm the same observation indeed, usually when I worked satellites before geared by Yaesu FT-857 for TX and RPS1A SDR for RX via the same duplexer and antenna, or even single 857 in simplex mode i was getting 9+ signals. However on Baofengs that was not the case the time shown on video, don't know why though. Also sometimes as i recall it sounded like the radio was not completely on frequency of satellite transponder. Need to test more, maybe something went wrong with time settings. But in general, agree - signal level on my video is not what anyone would expect from those satellites. Will test more and post here in case of any additional data.

VK3KYY
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Re: SATELLITE MODE

Post by VK3KYY » Tue Sep 21, 2021 11:40 am

OK

You can check the Rx and Tx freqs against some other program

And if you have a freqency counter you can check its actually transmitting on the frequency on the display

For Rx its more dificult to check the freq, perhaps transmit a 1mW signal from your other DM1801 and see how far off frequency you can be before there is no Rx.

r2dze
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Joined: Tue Sep 14, 2021 2:20 pm

Re: SATELLITE MODE

Post by r2dze » Tue Sep 21, 2021 11:57 am

Just finished a quick check, no issues found so far with either RX or TX frequencies set on the radio, or any significant frequency calculation difference with Orbitron as reference.

Used NanoVNA for a signal generator and TinySA as a spectrum analyzer, both are calibrated frequency wise. So no issues - both radios receive and transmit exactly at the frequency displayed.

However the FW installed right now is Sep 14 version, the video was on Sep 10, don't know if something could already be fixed in between. Need to have one more field test with Sep 14 version on board :)

Image

VK3KYY
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Re: SATELLITE MODE

Post by VK3KYY » Tue Sep 21, 2021 9:07 pm

The only bug I remember wax incorrect Tx freq in an older version, where the Tx freq could be 1499Hz off freq under some conditions

This is because the TRx chip is only set to a new Rx freq of its freq is > 500Hz from the correct freq

I can not constantly update the TRx chip freq, because the freq can not be changed while it is receiving or transmitting. The chip has to be set to No Rx and No Tx to change the frequently, and this causes loss of signal for around 50ms, And the AGC is reset.

So during Rx the freq is updated when abs(freq_satellite - freq_rx_chip) > 500

Initially I updated the Rx freq once per second, but there was a click on the audio every second and also if the squelch was opened, there was a distinctive "woosh" sound every time the frequency was changed, as the AGC takes up to 200ms to fully recover.

In Tx it is set at the start of the transmission and not changed during transmission, because it can't be changed during Tx

So for long transmissions the Tx freq would eventually be incorrect.


I did consider pulling the master VCO to achieve the frequency correction, but this is not practical because the voltage / frequency response of the VCO varies from radio to radio.

And in practical operation this method seems to give usabe results for most people

VK3KYY
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Re: SATELLITE MODE

Post by VK3KYY » Fri Oct 01, 2021 10:07 pm

For anyone using Satellite mode, the should update to the latest public beta, because it has multiple bug fixes to this feature

https://www.opengd77.com/downloads/Publ ... /firmware/

There was a bug with the Rx freq not updating as intended.

i.e it was updating, but not as often as it should have been, and the main predictions list and also the individual satellite passes list, the Rx freq was not updating at all.

So leaving the radio on the main predictions list screen, while listening to a satellite would not have worked very well.

OK3SN
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Joined: Fri Dec 17, 2021 8:37 pm

Re: SATELLITE MODE

Post by OK3SN » Fri Dec 17, 2021 8:43 pm

Hello, would it be possible to add ability to change the bandwidth in the satellite mode?
I sometimes hear the birds better with narrow FM.

VK3KYY
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Re: SATELLITE MODE

Post by VK3KYY » Fri Dec 17, 2021 8:51 pm

camelopardalis wrote:
Fri Dec 17, 2021 8:43 pm
Hello, would it be possible to add ability to change the bandwidth in the satellite mode?
I sometimes hear the birds better with narrow FM.
Not currently. It would require a change to the CPS and firmware

Which satellites are yoiu listening to


Edit.

The Star key could possibly be assigned to change bandwidth

OK3SN
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Joined: Fri Dec 17, 2021 8:37 pm

Re: SATELLITE MODE

Post by OK3SN » Fri Dec 17, 2021 9:19 pm

I tried with AO-91 and could hear it fine with narrow fm on my tyt-uv88 but just barely on the gd77. Squelch was open on both.
arrow antenna.

VK3KYY
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Re: SATELLITE MODE

Post by VK3KYY » Fri Dec 17, 2021 9:32 pm

camelopardalis wrote:
Fri Dec 17, 2021 9:19 pm
I tried with AO-91 and could hear it fine with narrow fm on my tyt-uv88 but just barely on the gd77. Squelch was open on both.
arrow antenna.
So what you are saying is that some other radio has better RX.

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