locked Spur 4.8kHz upper from Centre Freq with recent Firmware Releases of HF+ 1.6.7 & 1.7.0

Ian DXer
 

Hi Youssef & all,

A couple of weeks ago I updated firmware from 1.6.3 to 1.6.7 with the HF+ ...and all seamed well...but..

However today whilst tuning around parts of the FM BCB I'd noted a spur that consistently sticks to 4.8kHz above the 'centre tuning' freq
on many frequencies & varies in intensity from anywhere from approx 5-7db to 25dB (and sometimes briefly disappears) above the noise floor depending on freq.
Spur presence is enough to disrupt dxing when signal stuck in centre of spectrum display.
I had not noted this until today for some reason (though haven't spent a lot of time tuning past two weeks).

After many hours investigating today I've made these edited observations on the FM BCB (at this stage.)

1. Spur only noted with BW's 192 to 768kHz (not noted with BWs 96kHz & below)
2. Can avoid the problematic spur with sticky tuning & free tuning modes as opposed to the centre tuning option where part of the problem resides.

The spur is still there at reduced level even with 50ohm dummy loads on both VHF & HF antenna inputs & noted on both HF & VHF freqs with firmware 1.6.7

Noted the problem disappeared when going back to firmware 1.6.3. But returned when re-flashing with firmware 1.6.7 & 1.7.0
Given Youssef's extensive AGC work  with Firmware 1.6.7  & given my present HF+ spur symptoms I wanted to introduce some loss into the antenna feedline to see if it would help the situation.
No attentuators available so tried my homebrew 2 stage variable FM BCB preselector which I could use to also introduce attenuation.
This enabled me to attenuate the desired BCB signal a little, but was enough to cause the spur to disappear below the noise floor.

So some questions, comments & decisions now arise.

1. Youssef are you aware of this problem?
2. Can I be presumptive and guess that your future development work with addon preselector for HF+ (and maybe software) might assist with removal of the spur (hopefully not just HF, but also VHF?)
3. Whilst the new AGC, gain & attention controls with recent SDR# releases assist with reception on HF & MW etc, they do nothing for FM BCB reception, or to rephrase; there are no
software gain, attenuation controls for FM BCB or VHF with the HF+ on SDR#. So can VHF (FM BCB) gain/attenuation controls be considered for future with SDR# (if not already on your planning development list)
if it fixes the problem without need for external hardware?

Hope the above is of interest.
Would welcome any advice as I decide whether or not to go back to firmware 1.6.3 - there's pros & cons with that choice re performance.
Advice & plans by yourself Youssef at this stage would be most helpful.

(Tried to keep message short, but wanted it to be helpful to others.)

Cheers

Ian

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