Steve, You can download free acoustic spectrogram software that will run on a PC; at least it is free for ten-day use. I run the KX1 audio out into my PC microphone input. There is a link to the spectrogram software on the Elecraft website. It is commonly used to peak a K2. It works great to peak the KX1 receiver trimmer capacitors also (so does an AC voltmeter).
My KX1 filter peaks are noticeable on narrow settings. I used the Visualization software and characterized my receiver response as follows (- 6 dB low frequency, peak frequency, - 6 dB high frequency): Filter setting -6dB Low F Peak Audio F -6dB High F Maximum 159 Hz 592 Hz 1214 Hz 1.0 259 Hz 500 Hz 697 Hz 0.5 321 Hz 442 Hz 554 Hz Min 337 Hz 444 Hz 516 Hz You can see in the data that the 6dB down points on the minimum bandwidth filter setting is less than 200 Hz wide and is more than 1 KHz wide at maximum setting, quite noticeable to the ear. I am not experienced with filter design but I notice that the filter uses varactor tuning of the second and third stages of the crystal filter. Varactor tuning looks like it should bend the resonance of the second two stages lower. So the end effect should lower the frequency of the central peak of the total response as the filter is narrowed. On mine the peak moves from approximately 600 Hz (filter design point) down to less than 450 Hz. I can lose a weak signal if I zero beat (600 Hz offset) and then narrow the filter. I have to use RIT to then peak it again at a lower offset. Because of the effect of needing to retune on narrower filter settings, I made a small modification to my BFO. I paralleled a 10pf capacitor across C13 to create a lower offset, around 500 Hz. I now zero beat at 500 Hz and have acceptable signal at all filter settings. I can hear very strong signals on the opposite side band; I have not measured the rejection on my unit but I find it acceptable. When I think back to my Novice days in 1969, this is a much better receiver than the Heathkit HR10 I had in those days. Elecraft did a nice job. Mike Scott Tarzana, CA Phone (818) 708-9722 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of n0tu/Steve Sent: Friday, March 24, 2006 5:23 AM To: elecraft@mailman.qth.net qrp-l Subject: [QRP-L] KX1 rx filter query I had a blast working the Foxes last nite on 40/80 with K1 and KX1 with 100MW to full throttle 5w depending on cndx. It's like fly-fishing with with the lightest weight gear you can find and if you land one you'd better be careful to give him all the line he needs but not to much or he'll snag ya and walk away. Ok, so much for the fishiin analogy. Back to QRP radio. I notice however my KX1's rx filer is nowhere as clean as as my K1's? It's been awhile since I built both rigs. I know they're different designs etc. But my KX1 I can often hear the opposite sideband note coming through when in 1KHz or even 500hz positions. K1 seems to have stronger rejection in this area? Also the K1's peak is very pronounced ...as I switch thru the filters the signal amost appers to increase in signal strength (assume this is just because the qrm in being reduced by the filter?) BUT on my KX1 when incresing filtration the desire signal stays the same or even gets slightly weaker? It almost sounds like there's no peak or if there is it's low and broad? Sorry I don't have any audio SW to analyze what I'm hearing. Can't load any on this business PC or the IT folks go nutz anyway. I'm just wondering if I have a fried xtal in my xtal filer in the KX1? I should try and find a local who has a KX1 and do a side by side comparison. That would tell the story. Sure love the radio inspite of the issue. Hasn't stopped me from many enjoyable QSOs from my tent in the woods. To summarize my question is: does your KX1's filter sound as good as the K1's or K2's in your opinion? Steve/n0tu and Rooster/Peanut my 2-pack goats ______________________________________________________________ QRP-L mailing list Home: http://mailman.qth.net/mailman/listinfo/qrp-l Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[EMAIL PROTECTED] ______________________________________________________________ QRP-L mailing list Home: http://mailman.qth.net/mailman/listinfo/qrp-l Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[EMAIL PROTECTED]
