RTL SDR desense with arrow antenna, BPF?

[glassn3rd]

i'm attempting to use an IC-706 for uplink and FT-857 for downlink for linear contacts with this incredible Skyroof software! i have cat control working both via skycat and rigctrld. i'm using an arrow II antenna and RTL SDR v3, no filters or duplexer.

i'm able to to align my downlink with manual correction for RS-44 and FO-29, with surprisingly large offsets even after calibrating my SDR ppm several times. it works, the next time i try the CW beacon both are picked up right away and track via doppler, really impressive! based on the user guide i believe my next step is to align my uplink and then move the downlink from my SDR to my receive radio, and i should be aligned.

however i'm experiencing what i think is desense, the RTL SDR appears overhwelmed and completely deaf everytime i transmit at lowest power, whether CW or SSB. i also tried reversing the radios and transmitting with the FT-857, identical desense problem.

is there a band pass filter solution that is recommended for my scenario?

[Alex VE3NEA]

You are moving in the right direction and making good progress! Re. SDR de-sensing, you are not alone. I have the same problem with my TS-9700 and Airspy Mini, the SDR is deaf when I  transmit. This is not surprising since I have two omnidirectional antennas close to each other. I tried different filters, but with my setup nothing worked, so I use SDR only during reception. When I operate FT4 and need to receive while transmitting, I use the transceiver audio output for decoding. If your interference is not as strong as mine, you can try a coax stub filter to suppress 3-rd harmonic of your 144 MHz transmitter. One user posted a schematic in this group about a year ago, you can try and find it.

[Jack Blake]

Alex what is a TS-9700? I have a Icom IC-9700 and a Kenwood TS-2000. Is there a newer version of the 9700 out there? And I also get desense when trying to use phone on RS44. 

Jack L. Blake

--
You received this message because you are subscribed to the Google Groups "SkyRoof" group.
To unsubscribe from this group and stop receiving emails from it, send an email to skyroof+u...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/skyroof/11c925e5-0741-4b09-8bfa-3c8bb005ed66n%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Alex VE3NEA]

Oops. My radio is IC-9700. I do not use phone, in the CW mode I have some desensing but still can use SDR for uplink adjustment, but in the FT4 mode SDR reception is totally destroyed during transmission. 

The link to the notch filter that suppresses 3-rd harmonic, http://dl2kg.de/ , no longer works, but a similar filter is presented in this video: https://www.youtube.com/watch?v=Fd7d6oKHr_A . The only difference is that DL2KG uses a 75-Ohm coax between the two stubs to bring the input impedance to 50 Ohms.

[glassn3rd]

are there any commercial filter options available that would be sufficient? maybe this https://www.nooelec.com/store/ham-filter-bank.html 

i'm afraid my interference is very strong, i'm hearing nothing at all during transmit, but i would like to try a filter. 

[Alex VE3NEA]

This is a good filter, 2m/70cm suppression is on the order of 50/70 dB. Whether it will help or not depends on the nature of the interference that you have. If the fundamental 145 MHz frequency signal kills your SDR, it might help, but if desensing is caused by the 3-rd harmonic, 145x3=435 MHz, that is in the passband of that filter, then there will be no effect.

Try to determine which of the two scenarios you have. One possible approach is to use some software that scans the whole frequency range 100-500 MHz, with SDR gain sent all the way down until there is no overload anymore, and see where the peaks are and what their magnitude is.

[John Kludt]

Jack and Alex,

Following the KISS principle I am curious why we complicate the system with an SDR.  I work satellites all the time using just the capabilities of the IC-9700.  I do use a mast mounted preamp on  70cm,  something I have done for years.  I use SDR's for other applications so it's not that I don't understand or use them.  In this application with the IC-9700 for satellite work, it just seems like an extra complication.  Maybe I am missing something.

John

To view this discussion visit https://groups.google.com/d/msgid/skyroof/62b5a45e-1c8e-41d3-9162-edeb1498fe9dn%40googlegroups.com.

[glassn3rd]

John,

i need SDR to help me find where i'm transmitting to align my uplink in the Skyroof software, i'm trying to use Skyroof to achieve doppler control between my IC 706 and FT 857 for portable linear satellite contacts. 

Alex i really appreciate your help, i'll try to find SDR software that can scan 400mhz at once and try to learn more about interference.

incredible software, thank you again!
-Ross

[Thomas Schuessler]

So he is trying to use an SDR with one of those two radios, either the Icon or the Yaesu,  by the Email it sounds like he’s trying to use both of those radios along with the SDR, but that would not make sense.

I will tell you the only SDR I have that works fairly well without desence is my FUNCUBE dongle pro plus which is not supported by sky roof/Soapy SDR. The guy that designed the modifications to the DVB stick that ultimately became the FUNCUBE dongle, built very good front end filtering into the device so it handles the 2 m to 70 cm interaction very well.  

You might try taking a diplexer in front of the SDR feeding your 70 cm antenna into that input and the output going to the SDR. That’ll help with filtering third order stuff.  

Sent from my iPhone

On Jul 11, 2026, at 23:52, glassn3rd <n3rd...@gmail.com> wrote:

John,

To view this discussion visit https://groups.google.com/d/msgid/skyroof/3a73255a-d44f-4b3d-bfb2-b0e743bd86a5n%40googlegroups.com.

[Marcus PY2PLL]

I use V/UHF transverters driven by an HF rig for TX and the RTL SDR for RX, to take advantage of SkyRoof features (doppler tracking, easy click and tune and etc). I'm thinking to buy an AirSpy Mini to replace the RTL V4. Occasionally I use the HF rig for RX.

My antennas are ~5m apart: a general RX only 137MHz Eggbeater with a built in generic unfiltered SPF5189Z pre amp. 146MHz TX still a simple J-Pole only because I did not build a QFH yet. On 432-435 a QFH. VHF 12W, UHF 20W.

I built a couple of traps that are replaced at the RTL input: when I TX in UHF, a 435MHz one is inline. When TX = VHF, the 146MHz one. Not ideal yet but at least this allowed me to operate full duplex. But I need to turn RTL agc off and decrease the gain slider a bit.

Recently arrived a ceramic capacitor kit, I'll assemble not bandpass filters but a couple of elliptical low/high pass ones, with at least one pole notching the fundamental TX frequency: the VHF low pass version with a null at 435 and the UHF high pass with a trap at 146. May be another elliptical low pass at the TX output to get rid of any 3rd harmonic that exists there.

This Arrow antenna seems to have a diplexer? Or does it has 2 cables, one for V another for U?

73 Marcus PY2PLL