++++++++++++++++++++ From: "Jason Hissong" To: Date: Sat, 2 Mar 2002 19:57:41 -0500 Subject: [Elecraft] BFO Dumb Question I have a silly question... I notice that tuning up and down the CW subbands, I here the CW signal on both sides of the BFO frequency. For example, tuning up the band, say I start on 7022.0. I start to hear a CW signal at 7022.44. I keep tuning up and I can zero beat him at 7022.71. Tuning up, the CW signal disappears at 7023.4. I zero beat him again on 7023.93. Then disappears again at 7024.5. Which side is he on? (i.e., which frequency is he transmitting on). I think 7023.4. If that is the case, which side of the BFO should I zero beat on him? I understand what the BFO does and what I hear in the speaker is the difference BFO frequency. I do not know why I have never thought of this before. I think in the past, I zero beat on the higher frequency (in my example, it would be the 7023.92) without giving it much thought. Sorry for the completely silly question... you can reply direct to me... (including flames :) Thanks Jason N8XE K2 #1270 ++++++++++++++++++ Reply-To: "John J. McDonough" From: "John J. McDonough" To: Cc: "Jason Hissong" Subject: Re: [Elecraft] BFO Dumb Question Date: Sat, 2 Mar 2002 20:25:39 -0500 Jason Technically, there really isn't a BFO. The BFO was something you used back in the days where we always did AM detection. Suppose you have a signal at 7040. Let's also suppose that your VFO will operate at 7040-4915=2125 KHz. Now the VFO and incoming signal are injected into the double balanced mixer resulting in the signal being centered in the 4.915 MHz IF passband. So far, so good, the crystal filters whack out any nearby signals and the only thing making it to the product detector is the original signal, now translated to the IF frequency. Here's where it gets weird. The product detector needs a local oscillator, close to the 4915 IF frequency. However, it shouldn't be EXACTLY 4915 (as it sounds yours might be). If it were, then when you were tuned exactly to the signal so that it is at maximum strength through the IF, you would be exactly zero beat in the audio amp, zero beat here meaning zero beat, zero frequency, below what you can hear. However, if the local oscillator were, say, 700 Hz above 4915, at 4915.7, or below, at 4914.3, you would hear a 700 Hz tone. Let's suppose your LO was working at 4915.7. As you tune down, 2 things are happening. First, the signal in the IF is moving up. Say you move the VFO down 200 Hz, to 2124.8. Now the signal is at 7040-2124.8=4915.2 in the IF. The tone you hear is now lower, only 500 Hz. But there is something else going on. The signal in the IF is starting to move away from the center of the IF passband, so it's getting weaker, too, as it runs into the sides of the filter. Depending on your filter settings, by the time you get to, say, 2124.3, not only is the tone so low you can't hear it, but it has gotten very weak, hopefully inaudible. As you tune farther, the tone will start to increase again, as the signal in the passband crosses 4915.7, but if the radio is aligned properly, the signal is so weak you can no longer hear it. The exact same thing happens if the LO were at 4914.3, except it would be backward. You may hear a very strong signal on the other side of the "null", but unless the signal is extremely strong, you shouldn't hear it at all on a properly aligned receiver. Hope this helps 72/73 de WB8RCR http://www.qsl.net/wb8rcr didileydadidah QRP-L #1446 Code Warriors #35 ++++++++++++++++ Date: Sat, 02 Mar 2002 20:29:00 -0500 From: "David A. Belsley" To: Jason Hissong , elecraft at mailman.qth.net Subject: Re: [Elecraft] BFO Dumb Question Jason: Which filter are you hearing this on? Is this true only of your broadest filter? And is this the OP1 filter from the ssb board? In any event, it sounds like you simply haven't adjusted your BFO properly. I will assume it is only the broadest filter causing problems. If you have spectrogram, adjust this filter so that your sidetone is down in the lower part of the passband, maybe the lower third. With spectrogram, you will be able to see the lower skirt of the passband. This should be above zero Hz so you won't hear much below zero. If this is the OP1 ssb filter, you might start using the bfo setting given in the ssb manual. This is really pretty good, and should avoid the problem you are getting. For further suggestions, one would need to know what filter is causing the problem. best wishes, dave belsley, w1euy +++++++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: "Jason Hissong" , Subject: RE: [Elecraft] BFO Dumb Question Date: Sat, 2 Mar 2002 17:41:22 -0800 start to hear a CW signal at 7022.44. I keep > tuning up > and I can zero beat him at 7022.71. Tuning up, the CW signal disappears at > 7023.4. I zero beat him again on 7023.93. Then disappears again > at 7024.5. > Which side is he on? (i.e., which frequency is he transmitting on). I > think 7023.4. If that is the case, which side of the BFO should > I zero beat > on him? I understand what the BFO does and what I hear in the speaker is > the difference BFO frequency. > Thanks > Jason N8XE > K2 #1270 Jason, You need to do the BFO/Filter adjustment in your K2 again. It sounds like you have the BFO frequencies set to the filter bandpasses are 'straddling' the zero beat frequency, and that's why you are hearing a response on both sides. A properly aligned K2 will exhibit a 'single signal' response, meaning that you can hear the station on only one side of Zero Beat (that's where the signal disappears, NOT where you can "zero beat" it with the sidetone). That's a function of the bandpass of the K2's i-f filters and the setting of the BFO. If you use a very low beat frequency and tune in a very strong signal, you may hear a little response down near zero beat on the "wrong" side, but normally you should hear nothing on the "other side". Ron AC7AC K2 # 1289 ++++++++++++++++++ Date: Sat, 02 Mar 2002 19:13:21 -0800 From: Vic Rosenthal Organization: Transparent Software To: Jason Hissong Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] BFO Dumb Question Jason Hissong wrote: > > Looks like I will need to do some readjusting. This was happening on the > widest CW filter. I will go through the alignment process again. One suggestion: get the Spectrogram program that others have mentioned. Not only does it make it easy to adjust the radio precisely, it helps you to understand exactly what's going on. 73, Vic, K2VCO Fresno CA ++++++++++++++++++ From: "Jason Hissong" To: Subject: Re: [Elecraft] BFO Dumb Question Date: Sat, 2 Mar 2002 22:48:58 -0500 I just got done using Spectrogram and aligned the filters to 600 Hz as suggested in the filter adjustment information on the elecraft site (I also like 600 hz as well). I do not get the tone on both sides now, only on the high side. It is acting like I am used to with other radios. Thanks guys for the information!! When I did the adjustments, I did it on 30 meters using the background noise. I noticed that the DAC value must be below the value where the pitch is the lowest on bands lower than 18Mhz and above on bands above 18Mhz (per the doco). Do I have to go back and adjust the filters for the upper bands so that the values are above the DAC? My values are as follows (Not CW Rev): Filter - Lowest Pitch DAC Value - Bandwidth - DAC value bF1 - 154 - 1.50 - 132 bF2 - 143 - 0.70 - 125 bF3 - 140 - 0.40 - 123 bF4 - 138 - 0.10 - 121 Are these values supposed to change on the upper bands (DAC value above the Lowest Pitch DAC value)? Please excuse my ignorance. Thanks again! Jason N8XE K2 #1270 getting better and better ++++++++++++++++++ Reply-To: From: "Ron D' Eau Claire" To: Subject: RE: [Elecraft] BFO Dumb Question Date: Sat, 2 Mar 2002 23:16:08 -0800 > When I did the adjustments, I did it on > 30 meters using the background noise. I noticed that the DAC > value must be > below the value where the pitch is the lowest on bands lower than > 18Mhz and > above on bands above 18Mhz (per the doco). Do I have to go back > and adjust > the filters for the upper bands so that the values are above the DAC?... > Are these values supposed to change on the upper bands (DAC value > above the > Lowest Pitch DAC value)? No, you do NOT have to adjust the filter for the various bands. Do it on ONE band only per the adjustment procedure and it will be right for ALL bands. That's the big advantage of a Superhetrodyne receiver: whatever frequency you are tuned to is converted to the intermediate frequency where the filters are. They are tuned exactly the same for every band. I don't know what you mean by "lowest pitch value". In following the spectrogram procedure, you will not care at all what the value of the BFO frequencies are(represented by the numbers you have above). This is not the time to get inventive. Get it working per the procedure, then you can play around all you want, knowing that you can always "put it back" if you get "lost". If you are like a lot of us (me included) the first couple of weeks you have the K2 running you will probably tinker with the filter setup using Spectrogram as much as you operate on the air Ron AC7AC K2 # 1289 ++++++++++++++++++ From: "Don Brown" To: "Gregg R. Lengling" , Subject: Re: [Elecraft] Query on BFO alignment Date: Fri, 27 Dec 2002 11:42:46 -0600 Hi I would go forward with the building. You are close enough to the bottom end. If there is a problem it will show up when you try to align the filters with spectrogram. If you need more range you can add a 47pf cap in parallel C174 and a 120pf cap in parallel with C173 to increase the range. Add the caps to the bottom of the board Don Brown KD5NDB ----- Original Message ----- From: "Gregg R. Lengling" To: Sent: Friday, December 27, 2002 11:19 AM Subject: [Elecraft] Query on BFO alignment I'm in the process of building my Christmas present from my wife....K2 S# 3075 (with all the options...she's a big spender), and I'm doing just fine. I was just doing the BFO Test and I've got a range of 3.77kHz which according to the book is good (must be equal to or greater than 3.6kHz). However the BFO high freq is >=4916.3 (actual reading 4916.86) but the BFO Low Freq. is supposed to be <= 4912.7kHz (actual reading is 4913.09)....now that means my low reading is meeting spec....is this a problem. The 4MHz oscillator calibration is done properly (Used an IFR1200S to smell the oscillator and the IFR is in calibration). So is any of this minor descrepancy a problem...or should I just continue onward???? Thanks in advance .... Gregg R. Lengling, W9DHI PSYCHOLOGY: The science of inventing words for things that do not exist. +++++++++++++++