[Elecraft] PX3 Problem?

[Dave Sublette]

Good morning all,

I read all of the latest suggestions, and they were good ones.  I got into the menu and determined that the noise blanker was off, as it should have been.  The PX3 seems to be working properly now and the main thing that helped was turning on the preamp in the KX3.  I use the KX3 on 28 MHz as an IF for several VHF transverters.  Since I have mast mounted preamps for each band, I thought it would be better to turn off the internal preamp in the KX3.  BUT — I also work HF with the KX3 and that is where I was having the “spur problem”. So, when I turned the preamp back on in the KX3 it all went away.  

I thank you all for your patient and kind help.  I learn a little every time I go through one of these exercises.  It’s good for me to keep up.  60 years ago, when I got my first ticket, the equipment to do what the KX3 does today would have filled a wall in my shack. In fact, there wasn’t any equipment available to do what the KX3 does in some ways.  It’s a great thing, this radio stuff.  But I think the best thing about it is the people we interact with.

73 all,

Dave, K4TO

> On Jul 17, 2017, at 4:42 AM, David Anderson <gm4jjj at yahoo.co.uk> wrote:
> 
> This comes up quite often, and here is a reply from Wayne about it. You can check your PX3 as follows.
> 
>> Are you using a PX3 or P3? Assuming it's a PX3, try this:
>> 
>> - make sure RX I/Q is set to ON (KX3 menu)
>> - make sure the PX3->KX3 cables are fully seated
>> - connect an antenna to the KX3
>> - switch to 20 meters
>> - turn the preamp ON and set the PREAMP menu entry on the KX3 to 20 dB
>> - set the PX3's SPAN to 50 kHz or lower
>> - adjust the REF level so the "grass" (noise floor) is close to the bottom of the spectral <x-apple-data-detectors://7>plot
>> 
>> With the above setup, there will typically be no visible fixed spectral lines on the PX3.
>> 
>> As described in the PX3 FAQ on our web site, very wide SPAN settings and low front-end gain (e.g., turning off the preamp) will reduce the signal-to-noise ratio of an RX I/Q-based pandapter, including making wideband spurs more apparent. The same limitations apply when using the KX3 (or other quadrature downconversion radio) with a PC sound card. Typically this doesn't impact usability, e.g. locating signals of interest. In fact most sound cards are limited to displaying about 48 kHz of spectrum, while the PX3 can go wider thanks to its high-performance/high-speed A-to-D converter.
> 
> 73 from David GM4JJJ
> 
> On 16 Jul 2017, at 23:47, Dave Sublette <k4to at arrl.net <mailto:k4to at arrl.net>> wrote:
> 
>> Tnx Roger and Matt.  Roger — I don’t have the KX3/PX3 interfaced with the audio on the computer.  I do have the usb port connected.
>> 
>> Matt — I believe it is the 2.5 mm jacks that carry the Rx I/Q between the KX3 and PX3.  I unplugged the antenna and the spikes are still there.  I unplugged the Rx I/Q plug from the PX3 and the irregularly space spikes went away and the regularly spaced spikes were still there at the same levels as when the cable was plugged in.
>> 
>> I’m still thinking there is a failure in the PX3.
>> 
>> Dave
>>> On Jul 16, 2017, at 6:06 PM, Dave Sublette <k4to at arrl.net <mailto:k4to at arrl.net>> wrote:
>>> 
>>> I have had my PX3 for a little over a year (I think).  It has been used sparingly.  Until this afternoon, it has worked perfectly.  Now I see a spike in the center of the display and periodic spikes across the entire screen. Almost all are symmetrical in frequency and amplitude about the center line. There are some that are not symmetrical.  I have plugged and unplugged all the cables, taking care to see that each is fully into the socket.
>>> 
>>> So, perhaps I have a failure that requires returning to Elecraft?  Have any of you had the same experience?
>>> 
>>> 73,
>>> 
>>> Dave, K4TO
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