Ham Radio - AGC, Filters, and digital modes reception.

[@bhead56]

Thanks Kevin, as a new General, this helps me to understand the various controls on my radios.

[@DonDegidio]

Hi Kevin, Those visuals were perfect to show how a narrow filter narrows the passband and how the IF shift will shift that passband. 73 WB3BJU

[@magnehaneberg8605]

I've been using the IF Shift on SSB to avoid nearby stations, but it never occurred to me to use it with digimodes. Thanks a lot for saving me from a great deal of fiddling with the VFO, Kevin! 73 de Magne LA1WUA

[@RoyGNH]

That was a great explanation and helped me better understand AGC and what IF shift actually does! Thank you.

[@prestonshute7243]

Excellent video! Great explanation on IF shift, that's something a lot of new and old timers don't realize how it works to help you receive station when the band is crowded. Thanks & 73 wd4dda

[@jfrede1976]

Hello Kevin, Nice Video! Next time you could explain what to set the PreAmp/IPO to. Also note that you sometime have to reduce the RF-Gain manually so that you don't get to much noise from the input amplifiers when not using the AGC. Most of the time less gain means a better signal to noise ratio which is always what we want in digi modes.

[@BubbaWarbucks]

Cool halo buddy! Narrowing the filter width works for single signal digital modes like PSK, THOR, Olivia, and RTTY, but for the JT and FT-8 modes you need to keep your receive bandwidth all the way out to the end of the audio range, rather than narrowing it down for one specific frequency because the software is looking at the entire audio spectrum at the same time to decode all the stations it can within the audio passband.

[@MichaelLloyd]

I hadn't thought of using the IF shift and filter width in digital modes. Great tip. 73 NE5U

[@gilbreathca]

Excellent explanation of the IF Shift Kevin! Thanks! Very cool to see the filter "shifting" up and down the band.

[@loughkb]

It's also handy when you're in QSO on SSB and there's another QSO nearby. If you're hearing that high pitched crackle, or that low pitch warble from the nearby conversation you can shift the IF a bit and reduce the interference dramatically.

[@samglaim4274]

Great info. First thing I normally do when switching to CW mode is set the AGC to fast. Just an observation of the video.... The 'hula-hoop' loop was right in the centre, behind you, and I couldn't help thinking you had a 'halo' ..... once I'd seen it, I couldn't help looking (I must have had too much coffee! ;-) ). Cheers, 73

[@eduardopower5254]

Hey "Saint" with a sparkling 😇 behind. This is one of the most useful and informative videos from your channel Kevin. I really like the way you explain it and make it easy to chew. I'm gonna share it! 👏

[@alzeNL]

nice, i 'play' with the filters, without really understanding what they do, your diagram and explanation really helped me. thanks !

[@W4CJB]

Thanks for the video. I had been chasing signals with the vfo. I never even thought about the if shift. Duh... I also use the venerable TS-440S. Mine has the AT. Great video

[@loughkb]

Mine is also the 440Sat version. I only wish the tuners range allowed it to manage 160 as well. Thanks.

[@W7LDT]

Thanks, Kevin. The best explanation I’ve heard. Now it makes sense. I hope Carl meant “Holy” rather than “Holey.” hi hi.

[@zsradioham]

Hi Kevin, Nice tutorial to understand the AGC & Filters. Used to have an old TS-830S but these days utilize a Icom-7300. I would like to get rid of the garbage on the spectrum scope by narrowing down my filter on a spec signal. Will experiment more to understand the radio and FT8 mode. Thnks for the info and discussion. Emil

[@DAVIDGREGORYKERR]

OR a dual channel ADC for the I/Q input from the Tayloe Mixer feeding something like a Texas Instruments Blackfin DSP processor with a single channel DAC for outputting audio to the speaker. AGC Feedback=(1/SQRT(I*I)+(Q*Q))) feeds a DAC that controls the RF preamp gain.

[@ralphwilmot6351]

FB Kevin I found that very useful gen, especially as lately some stations overdrive or have the AGC set too high, and will help using RIT. 73

[@timb4655]

Really helpful Kevin. Not sure how i missed this when it was released but I'm now getting interested in digital modes (starting with JS8Call actually) and need to get to understand how to optimise my FT857d. This will be a big help. 73 de 2E0IEH 👍

[@gerryorlandostagehand3705]

Thank you Kevin, enjoyed your video.

[@jimjeffries2735]

Excellent presentation, Kevin.

[@goneflin]

Good job Kevin. I needed to know that.

[@larrypicard5969]

Thanks Kevin. I am a big fan of the conversational digital modes. I have thought about these same issues. Everything that you state makes perfect sense. However, my real world experience with narrowing the passband and centering the signal within the narrower passband has been disappointing. In other words it does little to increase the intelligibility of weak signals. I am not sure what is under the hood of FLDIGI. My impression is that it may form a virtual filter in software around the relatively narrow signal. When set to PSK31 or Olivia 8/250, the software "knows" the bandwidth of the signal of interest. Newer rigs with DSP filtering allow you to choose the filter width and offer very narrow settings. At some point it may be that too narrow a setting obscures the difference between signal and noise. More specifically narrowing the filters does little to the signal to noise ratio that I see FLDIGI displaying. Ultimately, the problem with a low signal to noise ratio may not be fixable at the radio. Improvement in the antenna may be the way to go. You did not get around to the strategy of turning off AGC entirely and setting the RF gain manually. As you point out, AGC is meant to handle the situation where the signal of interest occupies most, if not all, of the passband. With digital modes multiple signals may appear simultaneously in the passband. However, even with multiple signals all of the RF energy only fills a fraction of the passband. This is different than AM or SSB reception.

[@loughkb]

The idea behind narrowing the filter is to prevent nearby strong stations from pumping the agc. It also makes things easier on the software that's processing the desired signal.

[@RonanCantwell]

St. Kevin. Love the Halo. Excellent video as always.

[@normk7nwf323]

Another great video Kevin, always learn from your videos. Keep up the good work and GL 73 Norm

[@cuban9splat]

Excellent presentation of a difficult subject. Well done and thank you. We always see good helpful information put out on your channel. 73 de K7RMJ Frank

[@vronp]

This is a tremendous video. I learned a lot. Thank you!

[@Mach7RadioIntercepts]

Good presentation indeed. Seeing the waterfall certainly shows the effect of using a wide passband and how strong signals can affect weak signal reception. I'm a strong proponent of reducing the RF gain until the external background noise is low but audible, then hunting about with a 1 kHz bandwidth. Not good for using a skimmer to watch the whole psk band, but less havoc when strong signals are abundant. Any issues with ringing when using really narrow CW filters? I haven't tried that, being more into wide analog / narrow DSP filtering.

[@loughkb]

No ringing. But then again, it's a really good filter that Kenwood made. My FT-817 also has a clean 300hz filter that doesn't ring.

[@richharover495]

Very clear and helpful. Thanks!

[@johnfindley8793]

Thanks Kevin. Excelant vid!

[@ShortwaveBavaria]

great video. Greetings from Germany

[@glenngoodale1709]

Thank you.....Appreciate your work KM4BAP

[@willgilliam9053]

Kevin: Well I hope you found that useful... Me: ... I hope to be a digital op mostly my first Field Day. There is a good chance I'll be close to some other high power from a 2nd club here in town. Is IF Shift and RIT, same or are they different.

[@loughkb]

Different. RIT shifts the VFO, like turning the tuning knob for the receive side only.

[@loganv0410]

Fantastic - Thanks!

[@glenngoodale1709]

Can You do a Review of SDRplay SDRduo Two-Tuner SDR Radio ??

[@loughkb]

I already have a video on the SDRPlay RSP2, along with build scripts to automate setting it up under Linux. Scroll back through my vids, or just search YT for SDRPlay and my call sign.

[@glenngoodale1709]

The Two Tuner SDR radio ?? thanks

[@loughkb]

If they send me one. But I suppose it would be about the same as the existing one. Just add the ability to monitor two frequencies at once. I believe that's the only difference.

[@JimN5QL]

Saint Kevin

[@MoTown44240]

There actually was a Saint Kevin.

[@JimN5QL]

There is a saint for every name! But there's not a Saint Kevin, patron saint of magnetic loops!

[@colincolin30]

Thank you, I learnt something.73 colin vk2jcc

[@cwebs1000]

Nice HALO Keven but I don't think your that holey. lol

[@loughkb]

Yeah, I didn't think about the background. Noticed it while editing, but decided against filming the whole 16 minute clip again.

[@nr3rful]

Carl Webster yea, was gonna say the same thing. Thought it was planned that way....hi hi