[Elecraft] Receiving AM on the K3 - Odd behavior

[GRANT YOUNGMAN]

If you use Sync AM mode, the K3 is single (selectable) sideband on AM.  The bandwidth you see displayed is NOT the DSB bandwidth, it is the bandwidth of the ONE sideband that is being received.  So if you open the bandwidth display to say 4 kHz, in sync mode, you are receiving one sideband, with an IF bandwidth of 4 Khz and and effective DSB bandwidth of 8 KHz.

IMO, the sync AM mode in the K3 is one of the best sync detectors I’ve used (pick one, I’ve probably used it).

Grant NQ5T


> On Jan 27, 2015, at 11:20 AM, Edward R Cole <kl7uw at acsalaska.net> wrote:
> 
> Harry,
> 
> Others may have replied off the list, so what I say my be redundant:
> 
> You are confusing RF bandwidth with audio bandwidth.
> 
> For AM 6-KHz RF bandwidth is proper for best quality demodulation and either AM or FM filters work as bandwidth is controlled by DSP ckts and not by the roofing filters.  Audio output of the K3 is limited to 4-KHz so you will note that you cannot open the bandwidth higher than 4-KHz in SSB (FM is fixed and you will see "N/A" if you try to adjust the "width" knob).  BTW I see 5-KHz displayed at max width in AM on my K3 (still, I believe audio is limited to 4-KHz)(I am using the 13-KHz roofing filter for AM).
> 
> Note: I do not have the P3 so what it displays may be counter to what I have said (my comments are for the K3).
> 
> 73, Ed - KL7UW
> 
> From: Harry Yingst via Elecraft <elecraft at mailman.qth.net>
> To: Elecraft Reflector <elecraft at mailman.qth.net>
> Subject: [Elecraft] Receiving AM on the K3 - Odd behavior
> Message-ID:
>        <631043647.573239.1422324055017.JavaMail.yahoo at mail.yahoo.com>
> Content-Type: text/plain; charset=UTF-8
> 
> I noticed something odd when receiving AM.
> I have the AM and the FM filter installed and both enabled for AM Receiving.
> The manual states:In AM mode, the I.F. bandwidth required for good fidelity is about twice the AF bandwidth.?This is why a 6 kHz or wider crystal filter is needed to effectively use the 3 kHz NORM?setting. If a 15 kHz FM filter is installed, it can be used in AM mode to provide good?fidelity at even higher AF bandwidth settings.?
> 
> Watching on The P3 as I adjust the Filter width between 1.3 kHz and 3 kHz it tracks properly but?between 3 kHz and 5 kHz it's really only varying between 3 kHz and 4 kHz (with 4 being the max)?3 = 3 , 3.5 = 3.25, 3.5 = 4, 4.5 = 3.75, 5 = 4
> I confirmed this by loading up Spectrogram and looking at the audio output and it tracks the same way.
> To further test I went in to SSB mode set FC to 2 kHz and BW to 4 kHz then moved the shift ?to 2.2 kHz and the output moved to 4.2 kHz and the P3 tracked it as well as Spectracom.
> I also looked at the Spectracom display in FM Mode with the squelch open ?and it appears that the audio?stages could easily reproduce out to 6 kHz with little roll off and ?even displayed out to a bit over 18 kHz.
> 
> Have others noticed this?
> 
>