[hpsdr] Mercury and 28Mhz receive

[Graham / KE9H]

Mike:

As far as any Mercury alias, the equation will be Alias = ABS(122.88 MHz 
- Fc)

So, could be FM two-way radio at 122.88 + 28.xxx MHz, or FM broadcast at 
122.88 - 28.xxx MHz.
But if not near-by and you have ALEX in line, then that is an unlikely 
source.

As far as the cross modulation, it sounds like you have one or both 
Noise Blankers (NB or NB2)
turned on.  Turn off both noise blankers and try again.
The current noise blankers in PowerSDR have a known behavior that they 
produce
cross modulation in the presence of a strong signal.  Most noise 
blankers will do this, because
the noise blanker signal gate is behaving like a mixer.

--- Graham / KE9H

==

On 9/26/2011 9:05 AM, Mike Stevenson wrote:
> Hi Graham
> FM broadcasts are in the 80 to 100 MHz band but not too strong here.
> My first reaction was a local FM transmission from a taxis or other 
> VHF user.
> Alex in or out makes little difference and I have ferrites on coax cables.
> The modulation that I can hear is coming from stations in the 28.5 MHz 
> band.
> I had the case of just two S7 to S9 signals on the spectrum display, 
> tune one in and could detect the audio of the other. Also the audio 
> (low level ) from the second station stopped when the second station 
> stopped transmitting. I could also see the DC spur being modulated by 
> the second station.
> As I said I cannot hear any of these effects with Bill's software but 
> they may exist on the DC spur 9khz away.
> Having said all of this I am having a great time on 10m using 
> Pennywhistle driving a Expert 1K linear with 400watts output. My K3 
> gets little use.
> This was for information and HPsdr is still a great product and fun.
> Thanks again to all who have made this possible.
> Mike G8ALS.
>
>     ----- Original Message -----
>     *From:* Graham / KE9H <mailto:KE9H at austin.rr.com>
>     *To:* Mike Stevenson <mailto:mike.g8als at ntlworld.com>
>     *Sent:* Monday, September 26, 2011 2:21 PM
>     *Subject:* Re: [hpsdr] Mercury and 28Mhz receive
>
>     What is the frequency of the FM broadcast station closest to your QTH?
>     --- Graham / KE9H
>
>     ==
>
>     On 9/26/2011 4:25 AM, Mike Stevenson wrote:
>>     ***** High Performance Software Defined Radio Discussion List *****
>>
>>
>>
>>     I have been spending quite a lot of time operating on
>>     10m now is open again.
>>     There has always been a higher level of spurious signals on this
>>     band than any other even with Mercury input terminated directly
>>     in 50 ohms.
>>     What I am now seeing  using Doug's, W5WC software with zero
>>     frequency IF is between about 28.300 and 28.650 a spurious signal
>>     at 0Hz in the receive pass band.
>>     Also I am hearing what sounds like intermod produced by other
>>     signals in the display pass band producing an audible output. I
>>     have see the effect produce by signal of only S7. Also at the
>>     same time I see the 0Hz spurious being modulated by the off
>>     frequency S7 signal.
>>     The above applies to Doug's software 1.19.3.4, 1.19.3.5 and 2.2.3.
>>     Using Bill's KD5TFD software with 9Khz IF I see much the same
>>     spurious on the spectrum display but 0Hz spurious is offset by
>>     9Khz and so far have not detected any unwanted products in the
>>     audio output.
>>     Current cards
>>     Mercury  V2.9
>>     Pennylane  V1.4
>>     Metis   V1.4
>>     Excalibur
>>     Alex
>>     Has anyone else seen this or do I have a one off problem.
>>     Mike G8ALS
>>
>>
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