Re: Phase noise suggestions
Locked
 
|
>"...i am pretty sure that synth phase noise and the recent change in >topic regarding magnetic interferance are slightly different." >========== I'm sure this is true. I have been able to induce modulation of the carrier by a magnetic field, but I have also noted that the K2 carrier is wider than other rigs tested, regardless of whether an adjacent valve linear is connected or switched on. Unfortunately none of the recent posts have suggested a cure. Bob G3VVT did mention that some time back L30 was put forward as the weak point in terms of magnetic susceptability. Has anyone attempted to magneticallly screen it, and if so with what success please? I had a QSO with Colum EI5CP some weeks back. He suggested putting a low ESR capacitor across C67, which seemed a good idea. We both tried that but it had little noticeable effect, (in my case a 100uF 6V tant with measured low ESR). Another possibility discussed was reducing the tuning range of the VCO varacters so that just the ham bands are covered, without the largish overlap either end. I'm not sure if that would give enough improvement to warrant the hassle involved? Another thought; some of the newer LDO regulators have a much lower noise output than the 78L05, so it may be worth swapping one in for U8. Again I don't know if U8's noise contribution to the 5V rail (5B) is a significant factor, at least it's an easy thing to try. Less important, but is the 8V rail (8B) clean enough? Probably the main factor is screening of the VCO/PLL. I'm not sure how feasible that would be? Geoffrey GM4SID suspects the sidetone modulates the VCO, and if so what other internal signals can effect it? He also suggests D8 and D13 as possible noise sources - is there a feasible lower noise alternative? I welcome any comments and/or further ideas. I won't be able to do much on this myself for the next couple of weeks. 73 Fraser G4BJM _________________________________________________________________ It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
This topic runs and runs with no obvious solution. It should be possible to
bread board the affected area of the K2, make measurements, and work out corrective action. It may be easier to analyse the results of any mods by using a received signal than a transmitted one. Here is a post 'that I made earlier' 73 Stewart G3RXQ -------------------------------------------------------------------------------- The problem of a power transformer close to a K2 such as to cause problems on SSB has oft been reported. What I have not seen so far, is, that because it is the PLL that is affected the problem can also be observed on receive. Instead of transmitting a "gungy" signal, asking for reports, moving the PSU or K2 around and repeating the process, I used the following procedure on receive:- I ran SpectroGram with my soundcard connected to the K2 loudspeaker socket. A strong unmodulated carrier (XG1 set to 50uV) was applied to the ANT input. It is necessary to get the smallest frequency resolution (5.4Hz) on SpectroGram so set the Scan Input (F3) to these settings :- Sample Rate 11kHz Resolution 16bits Scale 60dB Freq Scale Linear FFT Size 2048 Average 70 Using either the SSB or CW filters tune in the signal until an audio signal of 800Hz to 1kHz is obtained, and adjust the displayed signal amplitude to around 0dB. The noise floor in the filter is approx -60dB. Any modulation of the K2 PLL will now appear as sidebands to the main signal. They will be spaced at either 50Hz (Europe) or 60Hz. If the problem is intense there may be harmonics. Switch PSU's On/Off to confirm (Not the K2 one !) A small homebrew PSU in a diecast box placed 12in away from my K2 gave sidebands of -40dB. I dread to think what the field from a high power linear amplifier could produce. -------------------------------------------------------------------------------- _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by Fraser Robertson
In a message dated 22/03/05 07:38:18 GMT Standard Time, [hidden email] writes: Any modulation of the K2 PLL will now appear as sidebands to the main signal. They will be spaced at either 50Hz (Europe) or 60Hz. If the problem is intense there may be harmonics. --------------------------------------------- Take care with this test as the PC itself also can produce these effect I presume due to the PC PSU. I ended up having to put in a 600 ohm 1:1 transformer to remove the effect here with harmonics going well up towards the top end of SSB bandwidth at 100Hz intervals from 150Hz after the initial 50Hz spike. Thought it was the inclusion of an LF/RF filter system in the 230AC power input to the PC, but find I get exactly the same effect with a recently acquired laptop on it's own 230VAC SM PSU. The bottom line is before condemning the K2 check that the effect does not occur on other radios first! Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by Fraser Robertson
G4BJM may have been talking to himself:
>Probably the main factor is screening of the VCO/PLL. I'm not sure how >feasible that would be? >Geoffrey GM4SID suspects the sidetone modulates the VCO, and if so what >other internal signals can effect it? He also suggests D8 and D13 as >possible noise sources - is there a feasible lower noise alternative? The numerous reports of what appears to be the MPU getting into the receive audio ("cricket" like sound [as in the insect] often heard in receive audio when K2 responds to frequency polling via KIO) may be worth considering, as I have found the same on transmit ["cricket" like sound is heard in transmitted audio]). I would think that this sort of thing needs to be sorted before it's possible to pursue other nastiness. Lack of power supply rail decoupling has been the source of countless problems in another life dealing with digital TV set-top boxes, but it used to be a fairly reasonable assumption that sh*te on the rail stayed there. Perhaps not so with the K2 - as it's the first rig I can hear responding to remote control commands by just listening to the receive audio... but perhaps my expectations are unreasonable & this has been the correct behavior all along. 73, VR2BrettGraham _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by Fraser Robertson
G3RXQ mentioned:
>The problem of a power transformer close to a K2 such as to cause problems on >SSB has oft been reported. What I have not seen so far, is, that because >it is >the PLL that is affected the problem can also be observed on receive. Receive only, KSB in path/not in path - no difference: same-same. 73, VR2BrettGraham _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by Stewart Baker
A simple brute force test would be to procure a simple mild steel box
sufficient to contain the K2 on all sides save the front panel. See if the K2 in the box is still sensitive to nearby power fields. If not then proceed to use less shielding in a series of tests: Experiment with sheets of steel to cover just the bottom of the radio, one or both sides, etc. to effect the simplest shield arrangement. Foil shielding tapes are available, and could be used to fashion smaller shields as needed. Perhaps only shielding the areas of circuit involved with frequency generation by under board added steel ground plane will be sufficient. _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |