Aircraft reception issue

[NK7B]

I'm a long-time scanner user and also very familiar in a basic way (I think) with use of radio gear (Extra Class Amateur NK7B, licensed and on the air since 1957). I am frankly mystified by a new issue that has popped up in my otherwise flawless SDS 200. I continuously monitor several aircraft traffic control frequencies here in the Mpls-St Paul area (e.g. MSP tower freqs 126.7 and 123.95; Minneapolis Approach on 126.35, etc.). For the past six weeks or so -- and this has never been the case before -- some, but not all, signals have a severe voice distortion that sounds very much like "front end overload" or like the weird abnormality you hear when a ham on SSB is "eating the mike" and overdriving her/his transmitter. These new observations concern always strong signals from aircraft that are very close to or on the final approach courses at MSP International Airport. In addition to the distortion in such generally strong AM signals there is a very loud, audible "scratch" at the termination of their every transmission. I was just now driving home from an errand and listening to KLM 655, a heavy jet arriving from Amsterdam and this phenomenon was there in spades. This audio quality problem happens regardless of the antenna used (viz. broad-band 'scanner antennas', resonant quarter-wave whips, etc.). Does anybody have a remotely similar experience with the SDS200 gear? Thanks.

 

[dave3825]

Did you recently update the firmware or change any filter settings?

 

[NK7B]

Thanks for rapid response. Yes -- I updated the firmware very recently. I just refreshed my knowledge of the "filter setting" rigmarole, which turns out to be a Hornets' Nest not yet completely explained by product literature. I will go back into my SDS 200 and do some T&E (trial and error) checks to see what's up on Conventional Filter settings. It seems to me that I may have changed the setting here but cannot recall exactly. Thanks for putting me on what sounds like (no pun intended) the right path to a solution.

NK7B

 

[donc13]

I do not have that issue so can't give you any specific advise other than... What changed?

A problem like you are reporting where something was working and now isn't typically 'just cause.'

First thing I would do is try a different SD card. All kinds of strange things can happen when the SD card gets a quirk in it.

Something broke or changed. Presuming you did no change in settings, and knowing Minnesota weather in the summer, any possibility you had a nearby lightning strike that caused a power surge? I hope you would have some form of surge protector on the a/c line.

You mention this occurs in your vehicle also. Same radio?

And finally, there is new firmware for the SDS200 that was just made available. The update isn't supposed to have anything relative to audio based on the release notes, but some of us believe the audio sounds better after the update.

 

[NK7B]

Thanks ! No lightning issues here, the SDS200 is in my vehicle always in undergound garage. Your point about a new SD card is something that was on my "try it" list here already. I do have the latest firmware installed. I will report back here as to progress or lack of same. It is a GREAT radio and worth the uber expense in my view.

NK7B

 

[donc13]

Thanks ! No lightning issues here, the SDS200 is in my vehicle always in undergound garage. Your point about a new SD card is something that was on my "try it" list here already. I do have the latest firmware installed. I will report back here as to progress or lack of same. It is a GREAT radio and worth the uber expense in my view.

NK7B

Agree, I love my SDS200 also, very happy with it.

 

[Whiskey3JMC]

I can't speak specifically for the 200 but my 100 certainly is prone to overload on AM. My goto for aviation monitoring is my trusty Icom IC-R20. Crisp, clear, great sensitivity even with stock telescopic antenna

 

[racingfan360]

I've had this severe voice distortion with aircraft transmitting in close proximity problem for years, on Unidens (3600 and 3600) Yupis and Icoms.

 

[Ubbe]

There where no update to the DSP, that controls the decoding of signals, but still some people claim improved receive quality using the new firmware. One explanation could be that the gain have been increased in the receiver chip. The problem with that are that the dynamic range of the AGC are not enough to handle really strong signals and will result in distorted AM reception. But then more people living near airports or have low altitude aircrafts passing nearby would be reporting overload issues with AM modulation.

/Ubbe

 

[JoeBearcat]

I suspect (but do not know) that you changed the filter settings previously, updated the firmware, but never changed the filter settings back.

I believe several users have reported WIDE-NORMAL to work well for the Aircraft band.

 

[n1chu]

I’ve experienced weird reception on the AM. aircraft band with both the SDS100 & SDS200 before the update for the recent SDS200 FW update and chalked it up to Uniden’s first fully SDR radios going through growing pains. The volume started low and then increased when a transmission was heard on the AM Aircraft band. I haven’t experimented after the SDS20 FW update but if the filtering was dafaulted when it was installed, there may be the need to reset them. I laid back and waited for improvements to happen before the newest FW update. But the pandemic happened and things got slow. So I started researching dedicated aircraft receivers… good radios such as what Icom might offer. I haven’t purchased anything yet. But a good aircraft receiver, tuned to just one band should perform better than a multiband radio.