Greetings all,

I solved the issue of no/low audio levels in my QDX - one of the toroids didn't have a good solder joint and one of the switching diodes also needed the solder joints reflowed - but that fix did not solve an issue that had been present before. Referencing the picture below, you can see what looks to be a huge amount of signal on the left side of the waterfall, but as is illustrated for the time periods when I had the QDX set to the 15m band, it's not someone at 100-125Hz with a HUGE amplifier, located a few miles from my house.

The audio/RF/image sweeps are all good, though there is quite a bit of room for improvement for the 15m band (lots of signal loss). The LPFs for 40m and 20m are the standard QDX filters. The LPF for the 15m band is a custom filter that has been specified here in the forum.* As for my BPF, I have a tap at 16 turns for the 15m band (it goes over and utilizes the BPF pad that would normally be used for 80m), and then the rest of the BPF is as per the instruction guide, save for it stopping after 36 turns at the 40m pad.

What could be causing this problem? The 15m tap on the BPF comes to mind as a possible source, but the problem gets 'better' when you go to 20m, and then worse when you go to 40m - might it be a case of 'the perfect storm', filter components interacting Just Right so as to cause the observed changes in the different bands? FYI, the screenshot was taken with the QDX being fed by an EFHW antenna - a quick check of things with my Xiegu G1M showed that it wasn't the antenna system - though without IC5** and the BS-170s, I can't tell you what, if any, actual (transmission) performance impact there is due to this issue.

I appreciate the input and suggestions!

Charles Johnson
KF4AYT

* Once I get the parts in, I'm going to remove the existing 15m LPF components and replace them with the components/values that Hans is using for the 17/15m LPF in the 20m-10m QDX. The existing filter seems to work, but the RF Sweep has me wanting the sharper roll-off that Hans' filter has (as according to Elsie plots).

** Removing IC5 fixed my current draw problem. Without IC5 and the BS-170s, the QDX is drawing ~150 mA in idle/receive.

-------

Charles,

I am not sure I understand your question.  I do note that you have the "Flatten" box checked.  For the QDX, the flatten adjustment for SSB filter response is not needed.  Try it unchecked, and let us know if there is still an issue.  I also like to have a larger spacing on each time cycle.  You can change that with the N Avg setting.  I usually use 1.

The BPF does not have any impact on transmission, only receive.

73
Evan
AC9TU

Uncheck flatten and have the waterfall start at 200 Hz. Hans says any data less than 200 Hz is meaningless on the QDX.

Steve N9SZ

On 28 Nov 2022 at 17:43, Charles Johnson wrote:

Referencing the picture
below, you can see what looks to be a huge amount of signal on the
left side of the waterfall,

on 'regular' transceivers i have seen that sort of pattern at
left and sometimes right end of the waterfall -- caused by
too narrow an AUDIO filter ... liks an ssb filter at 2800Hz;
change to 3600Hz and the 'noise' goes away.

I haven't studied the ckts of the QDX yet, so cant offer
any specific ideas.

w2jc