SDRplay RF gain and transmitting problem

[Sergei Konev]

I have SDRplay RSPdx and 2xFT818ND for satellites QSO.

RF=0, AGC=False - my only way to see moving watefall..
If AGC=True so waterfall stopped.
It seems my TX signal is too strong for my SDRplay RSPdx, hitting the receiver's gain, preventing the program from decoding and correcting it. There are so many interference signals on the screen, it's unclear what my primary transmitter signal is.

I have a 144 MHz filter on the transmitter (FT-818ND), but it doesn't help... the 435 MHz band is clogged with interference during transmission.

Second problem with my TX signal. It seems 
Anyway, I can nor recognize my TX signal , too many interference signals on the screen...and very strong and loude audio.
And no way fix it using manual correction. As the result, my TX signal not managing by Doppler at all, no Sat QSO available...
Who can advice anything?

Thanks,
Sergey Konev, ER1KW

[Jack Blake]

What software are you using for Doppler? Since you’re using Yaseu radio the CSN box will not work for you. What antenna are you using? I would suggest skip using the SDRplay for a downlink radio and use one the Yaesu radio. Also try using SatPC32 or HRD for Doppler control. Keep your uplink power down it will cut down on your desense. I would use SkyRoof for sat QSO. It’s great for decoding telemetry or just capturing the downlink. If you’re using two antenna one up one down there is a trick using a duplexer and leaving the 2 meter side not connected. Check Amsat website for more information 

Jack L. Blake

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[Sergei Konev]

Hello Jack,

Yes, 5 years long I'm  using two FT-818ND's as RX+TX (fell duplex) for SAT QSO (with SatPC32,  see  www.qrz.com/db/er1kw ), and I can still use them, but I want waterfall to have, you see....

And  SkyRoof with SDRplay RSPdx doing nice receiving and waterfall, indeed, untill I am starting to transmitt...After I start TX  - everything is over, I'getting a lot of splatters on the screen and Doppler control in SkyRoof doesn't work.
I am using two separate Yagi'es , one for 144MHZ and second for 435MHz.

I have two FT-818ND and I have a lot QSO's on satellites with such set, but I would like to have waterfall and Doppler control in one software... And I believed SkyRoof is right choice, but no way yet...
What about  a  a trick using a duplexer? I just (half hour ago)  tried  same idea to use duplexer MX72 - ANT 432 IN, TX 145 IN , ANT 145 OUT, but no signal to RX . WHich way to use duplexer did you meant?

Sergey Konev, ER1KW

пятница, 24 апреля 2026 г. в 17:48:53 UTC+3, Jack Blake:

[Jack Blake]

Good Morning Sergei, 

You leave the 2 meter side of duplexier open and only run the uhf side through the duplexer. On mode U/v when the two meter side is the uplink and the 70 cm side is the downlink when you get the desense. Probably your best solution is get a 9700 and a CSN Satbox which does everything you want and 9700 has a waterfall. I haven’t had much luck with SkyRoof on live satellite QSO. I do find it useful for downloading telemetry from different birds. I don’t think you can do what you want with SkyRoof using your current setup. From my understanding of the software for SkyRoof to control Doppler on both uplink and downlink requires a full duplex radio like the 9700. Contact Alex on SkyRoof he wrote the program. Only other way would be running two instances of SkyRoof at the same time. One for uplink using radio one for downlink using SDRPlay. I would suggest you experiment with a RTLSDR dongle first if you damage it cost is pretty low and they do receive the Leo Birds pretty good. Good Luck and 73. I have the old FT817 I used to use not full duplex but I make contacts

Jack L. Blake

To view this discussion visit https://groups.google.com/d/msgid/skyroof/59c3be2c-0849-4fd9-a306-6d3021915837n%40googlegroups.com.

[Thomas Schuessler]

Interesting comments now related to my original post about SDR playRF gains. I’m having the same problem that SENGI is having with the SDR play RSP1a. It receives fairly well on its own, but when I transmit even on relatively low power, I get a screen full of images and only if the satellite is very strong, can I be for certain that I hear myself. I am running a pair of M2 Leo pack antennas  down separate coax. I will admit that I have not tried this configuration with the UHF up and VHF down for a satellite like JO – 97.  Maybe I’ll have at that one this weekend and I will see if the same problem exists. Both antennas are connected to SSB electronics preamps mounted 10 feet away from the antenna feed points with the antenna’s mounted on the M2 provided cross boom.. I do not see this level of contamination with my Yasu FT 847 doing both transmit and receive.   I even tried encasing the SDR play box in aluminum foil with contact to the ground on connector on the side heading to the antenna, but that did not help. I have tried running. The SDR play box off of battery instead of DC supply that drives everything else with no improvement either.   I have put cores on every known non-RF wire in the shack and still get the problem.

I mentioned this to a guy in my local club who commented that SDR play devices notoriously are not shielded well and that’s probably the up shot of the problem that Sengi, and I are having. I know Alex originally wrote his software around an SDR play so his results obviously differ. He did say that he was using egg beater antennas At the beginning.

I’m not giving up yet and I am going to try to reinstall proper driver connections for RTL SDR because the latest versions have a metal encasement around the dongle, maybe that will help. Although I know they traditionally didn’t have the level of switchable filters.

Hope that helps clarify and add to the conversation

Tom, N5HYP

On Apr 25, 2026, at 09:41, Jack Blake <jblak...@gmail.com> wrote:



To view this discussion visit https://groups.google.com/d/msgid/skyroof/CAMMUZ_GxkSYxq4esqn6r4yFAdd_%3DJs_yr3KRzMfDFuGYpPQSRg%40mail.gmail.com.

[Sergei Konev]

Yes, Thomas, I did exactly the same steps you did with my SDRplay and its wires\box\etc - no way.  I have also Band Pass Filter on 144 MHZ on my FT818ND, but no helps...
And I almost ready to finish this experiments because it is clear that SDRplay+SkyRoof can not work VU with so big level of  interferences from any nearest TX.
I believe in UV-mode it will not the same terrible, but UV is not interested for me.

May be, Alex VE3NEA will advise something.

Thank you, I will continue test..but only a weekk long..no more. :-)  

Best regards,

Sergey ER1KW

суббота, 25 апреля 2026 г. в 18:12:45 UTC+3, Thomas Schuessler:

[Alex VE3NEA]

Just to clarify, SkyRoof controls both uplink and downlink frequencies for all supported radio types. With duplex radios both frequencies are tracked simultaneously, simplex radios track downlink frequency whern receiving and uplink frequency when transmitting.

I also have an unsolved problem with receive desensing during transmission, when transmitting on 2m. Both of my antennas are omnidirectional, so TX signal gets into the receiver easily. Looking for a solution to include a reject filter in the TX path tuned to the 3-rd harmonic, and a bandpass filter in ther RX path. The reject filter is easy, it is just a pair of coax stubs.

On 2m I used to have terrible interference from a comminications tower very close to my location that transmits in the 140-143 MHz range and overloads the SDR. IC-9700, which is also an SDR inside, did not have this problem. It looks like 16-bit ADC used in the Icom is what's required in my environment, 12-14 bits in the stand alone SDR's are not enough. Anyway, I solved this problem with a helical filter, now I can receive on 2m without problems.

[Sergei Konev]

Jack, thank you, I tried such method already. Becides, I have  separate Ban Pass Filter 144MHz on my TX...not helps.
So, i believe you are right about 9700 !  I like my two FT-818ND's  ( www.qrz.com/db/er1kw ) , but they are old a bit...  I will save\keep money for this nice new solution! :-)

Regards,

Sergey ER1KW

суббота, 25 апреля 2026 г. в 18:31:11 UTC+3, Sergei Konev:

[Sergei Konev]

I tried already few Band Pass Filters ( homemade DL2KG.DE , 144-160MHz from market e.t.c), but there was no noticeable improvement with any of the options. It seems there's no reliable solution. It's so pity,  because the reception and watefall is excellent...

суббота, 25 апреля 2026 г. в 18:36:26 UTC+3, Sergei Konev:

[Sergei Konev]

For better imagination:
1 stage (green arrow) - normal receiving, all OK yet.
2 stage (red arrow) - short TX CW of my first FT-818ND with BandPass Filter from Aliexpress. Sdr become desoriented.
3 stage (orange arrow) - short TX CW of my second FT-818ND with Band Pass Filter hommade DL2KG.DE .
4 stage (blaxk arrow) - SDR desoriented.
To return to normal "green" stage I need to switch "TRANSMITTER" to "Mode U Beacon" and back to "Mode U Transponder" once or twice...

суббота, 25 апреля 2026 г. в 20:04:21 UTC+3, Sergei Konev:

[Thomas Schuessler]

You do not need a full duplex radio to benefit from skyroof. I have an FT 847, which is a full duplex radio but does not have a waterfall. I use skyroof to control only the TX from the 847. The receive antenna is plugged into the SDR play and skyroof natively handles the Doppler shift through the SDR Control. That’s what he wrote it for. The fact that it can control both sides of the 9700 is gravy but doing what Sengi want to do which is use a legitimate SDR receiver to allow view of the entire passband all three MHz of UHF Satellite segment, it can perfectly do. 

I am a fan. 

On Apr 25, 2026, at 10:36, Alex VE3NEA <ve3...@gmail.com> wrote:

Just to clarify, SkyRoof controls both uplink and downlink frequencies for all supported radio types. With duplex radios both frequencies are tracked simultaneously, simplex radios track downlink frequency whern receiving and uplink frequency when transmitting.

I also have an unsolved problem with receive desensing during transmission, when transmitting on 2m. Both of my antennas are omnidirectional, so TX signal gets into the receiver easily. Looking for a solution to include a reject filter in the TX path tuned to the 3-rd harmonic, and a bandpass filter in ther RX path. The reject filter is easy, it is just a pair of coax stubs.

On 2m I used to have terrible interference from a comminications tower very close to my location that transmits in the 140-143 MHz range and overloads the SDR. IC-9700, which is also an SDR inside, did not have this problem. It looks like 16-bit ADC used in the Icom is what's required in my environment, 12-14 bits in the stand alone SDR's are not enough. Anyway, I solved this problem with a helical filter, now I can receive on 2m without problems.

To view this discussion visit https://groups.google.com/d/msgid/skyroof/dd6c569a-3331-4770-a1f8-f1cea160dfe4n%40googlegroups.com.

[Sergei Konev]

You wrote you are  using Skyroof to control only the TX from the 847.  But that is the problem I am talking about - my TX FT-818ND on RS-44  just crushing down the SDRplay+SkyRoof by its transmittion (upload), then  SkyRoof become desorinted and has no chance to calculate Doppler and give me correct uplink frequency. Have you correct uplink frequency (after Doppler) on RS-44 and can you hear yourself during your transmittion (U=uplink) on RS-44 (VU) ?
 I don't.
 I see on waterfall just strong net of QRM from my VU upload transmitting (see screenshot attached in above post). So, waterfall (and SkyRoofwith no Doppler) is not usefull in that set as well.

воскресенье, 26 апреля 2026 г. в 19:19:17 UTC+3, Thomas Schuessler:

[Marcus Ramos]

Can be this RFI related? Had you tried to simulate using a dummy load or QRPp on TX?

73
Marcus PY2PLL

To view this discussion visit https://groups.google.com/d/msgid/skyroof/42d23eb0-2bd2-4042-8713-3de4b3570833n%40googlegroups.com.

[Sergei Konev]

Yes, I did. I,ve tested both FT818ND with dummy load, then with 1Watt, with stick rubber antenna, with Yagi e.t.c. But SkyRoof does not work with upload on RS44.

May be just FT818nd is old model with unacceptable level of RFI initially...

My two FT818nd are fresh and new, bought them only 3years ago  especially for sat rover activity as RX+TX (full duplex in the field).

пн, 27 апр. 2026 г., 01:15 Marcus Ramos <marcus...@gmail.com>:

To view this discussion visit https://groups.google.com/d/msgid/skyroof/484f8c8a-5958-41be-84bd-50551dda7629%40gmail.com.

[Marcus PY2PLL]

I see; well I use different rigs (AirSpy Discovery and a SDR RTL V4 on RX; the TX is an Elecraft K3S with a UR3LZR transverter on 144 and a DownEast on 435). The CAT still via RIGCTLD. I'm not able to create the JSON file for my rig to use SKYCAT.

So all this rigs share the same USB BUS. And I have no issues.

What a mystery ...

73 Marcus PY2PLL

[Alex VE3NEA]

Sergei please provide more information about the problem you have, " SkyRoof does not work" is not enough. Is SkyRoof configured to use separate radios for RX and TX? Are you running two instances of skycatd.exe program to control two radios? Are there any errors in the skycatd.exe log? Are there any red icons on the status bar in SkyRoof?