++++++++++++++++++++ From: TBald53892 at aol.com Date: Tue, 28 May 2002 17:39:47 EDT To: elecraft at mailman.qth.net Subject: [Elecraft] FM Broadcast Station Interference Unfortunately I live about 6 miles line of sight from a FM station running 34kw of rock 'n roll on 99.9 MHz. I receive crud from this station without any antenna connected to the K2. Now thats Free Music! Using either a dc supply or external battery makes no difference. Interestingly enough, when I connect an antenna the interference does not change all that much. I could live with the crud but it seems to generally appear in the qrp cw segments (of course), especially on 20m as well as 40 and 80m. I have built two K2s and both exhibited this problem. Just wondering if there was any additional filtering etc I could install to help with this issue? In ALL areas except this one I much prefer the K2 to my 756 PRO: the PRO shows no evidence of this interference. Any suggestions (besides moving!) would be most welcome. 73 Tom KI5FM K2/2638 +++++++++++++++++++++ Reply-To: giantbug at earthlink.net From: "Mychael Morohovich / AA3WF" To: elecraft at mailman.qth.net Date: Wed, 29 May 2002 15:15:13 -0400 Subject: [Elecraft] Re: FM Broadcast Station Interference Hi- My mountaintop QTH has two FM / TV towers , one within a few tenths of one mile, the other 1.5 miles away, and one AM tower still within line of sight perhaps 4-5 miles away on another peak. With any receiver I have built of unshielded design, the QRM from these towers has been for the better part unbearable, though occasionally controllable with the use of a trap on the lead-in. Sometimes new neighbors even report picking up the signals on their telephones and answering machines. OTOH, my K2 has never experienced any QRM whatsoever from these stations. Given my history that was a concern I had while contemplating its purchase. I am curious to know the source of your problem, so as Vic has requested, Tom, please do keep us posted. Mychael AA3WF K2#1025 +++++++++++++++++++++ From: "Stuart Rohre" To: , Subject: Re: [Elecraft] FM Broadcast Station Interference Date: Tue, 28 May 2002 16:47:39 -0500 Tom, To have this RFI without an antenna, it must be getting into the rig from your shack having some resonant structure that tunes close enough to the FM station to act as a strong re-radiator, (gain antenna). Check your wiring lengths, phone wires, anything that might bring the signal into your operating position. Make a tuned wavemeter for this FM channel, and move it around the wiring, metal of desks, bench, etc. and see what is hot with RF at that frequency. You may find that you can "filter" the RFI by relocating the operating position of the K2, or take out some overly long wiring, or put ferrite beads on the phone line coming into the shack, if it is the source of high RF of the FM station. If it is reradiating off the AC wiring, in the room, you might get a brute force AC filter for the offending circuit. Sometimes even by pass ceramic caps of 0.005 mf across the outlet plug might derail the RFI. In the "old" days, hams often made up a standard AC plug with a 0.005 across line and neutral, (be sure it is 1000 volt rated disc ceramic,) and used that to bypass RF off the AC line. Make sure your DC supply leads even from a battery are not exactly resonant at the FM channel, and are twisted pair, or even better shielded twisted pair. Could be as simple as the length of that DC cord, or the mike cord, key cord, or headphones cord being resonant. RF ferrite beads might work on all. But, sniff out the RF carrying culprit first. A scope is nice for this, as well, as you can use a coax and a two turn or so sniffer loop to the scope and see where that FM signals is strongest. 72, and Good Luck, Stuart K5KVH +++++++++++++++++++ Date: Tue, 28 May 2002 15:11:23 -0700 From: Vic Rosenthal Organization: Transparent Software To: TBald53892 at aol.com, Elecraft Subject: Re: [Elecraft] FM Broadcast Station Interference TBald53892 at aol.com wrote: > > Unfortunately I live about 6 miles line of sight from a FM station running > 34kw of rock 'n roll on 99.9 MHz. I receive crud from this station without > any antenna connected to the K2. Now thats Free Music! Using either a dc > supply or external battery makes no difference. Interestingly enough, when I > connect an antenna the interference does not change all that much. Does it change when you unplug headphones and use the speaker? Headphone cords are a good length for an FM antenna. If this turns out to be the case, try a ferrite device of some kind on the 'phones. Also check the leads to the key. Tell us what happens! 73, Vic, K2VCO Fresno CA +++++++++++++++++++ Reply-To: "Ron D'Eau Claire" From: "Ron D'Eau Claire" To: Subject: Re: [Elecraft] FM Broadcast Station Interference Date: Tue, 28 May 2002 16:28:22 -0700 Tom - This is a follow-up to Stuart's excellent recommendations. A quite useable and cheap "sniffer" for whatever may be carrying/re-radiating the FM around your shack is a portable radio that will tune a frequency were you can hear the "crud". If it uses a whip, collapse it down to minimum size and then move it around looking around for any place where the signal gets stronger -- near house wiring, phone lines, etc. A not-so-cheap "sniffer" is your K2 itself! It only needs to supply a couple of hundred mA if you don't have the built-in battery option. Some dry cells can run it quite a while. . If switching to a battery supply cures the "crud", you know it's coming the power supply leads. If it doesn't, try disconnecting your key, mic, headphones, etc. If it's not clean with all the accessories disconnected, start moving it around looking for wiring or a piece of equipment where the "crud" gets stronger. Ron AC7AC K2 # 1289 ++++++++++++++++ To: elecraft at mailman.qth.net Date: Tue, 28 May 2002 18:26:45 -0500 From: n4so at juno.com Subject: [Elecraft] FM Broadcast Station RFI Check to see if you can use an individual Bandpass Filter-- these are used in Multi-operator stations. Rejection to out of band RF is about 60 dB. $35 from I.C.E. Industrial Communication Engineers, Ltd., Indianapolis, IN 46218 1 800 423-2666 Tech advice and orders. ...and stop out-of-band energy from nearby transmitters with I.C.E's full line of single band filters".... Ken Brown-N4SO Mobile, AL EM50tk Elecraft K-1 4 ele. monoband yagi N4SO at juno.com +++++++++++++++++ Date: Tue, 28 May 2002 19:45:13 -0700 From: Vic Rosenthal Organization: Transparent Software To: elecraft at mailman.qth.net Subject: Re: [Elecraft] FM Broadcast Station RFI n4so at juno.com wrote: > > Check to see if you can use an individual Bandpass > Filter-- these are used in Multi-operator stations. Rejection > to out of band RF is about 60 dB. But he says the interference is there with the antenna disconnected. My theory is that when he tries unplugging the key, the headphones, and/or the microphone it will go away. 73, Vic, K2VCO Fresno CA ++++++++++++++++++ From: "Robert Fanfant" To: , Subject: Re: [Elecraft] FM Broadcast Station RFI Date: Tue, 28 May 2002 20:00:46 -0700 I second this companies product as I also had RF getting into both my IC-765 and K2 WITH the antenna connected. It was coming from an AM station located nearby. Picked up the low pass filter from I.C.E. and it worked its magic. -rob N7QT K2#1406 ++++++++++++++++++++ From: Tim ORourke To: "'elecraft at mailman.qth.net'" Date: Wed, 29 May 2002 08:54:20 -0400 Subject: [Elecraft] FM Broadcast Station RFI I also live in middle of a triangle of FM and TV BC stations. I do not have a problem on as many bands only 20 meters near 14.060. Battery or Power supply, inside or outside house. Phones or speaker no differance. Only cure is operate portable on 20 away from house. I will try the band pass filters and see, but todate only changing operating location to several miles away has helped. Luckily I only use 40 and 30 most of the time. 72 Tim KG4CXH +++++++++++++++++++ To: elecraft at mailman.qth.net Date: Wed, 29 May 2002 08:08:27 -0500 From: n4so at juno.com Subject: [Elecraft] RFI suggestions cc: Carbon copy to Ed Hare, W1RFI, ARRL Laboratory Supervisor, your RFI questions and solutions to RFI problems. W1RFI at arrl.org Ken Brown-N4SO Mobile, AL EM50tk Elecraft K-1 4 ele. monoband yagi N4SO at juno.com ++++++++++++++++++++ From: TBald53892 at aol.com Date: Wed, 29 May 2002 12:18:55 EDT To: elecraft at mailman.qth.net Subject: [Elecraft] Re: FM Broadcast Station Interference Many thanks to all of you who have responded to my post about FM broadcast crud. I've also noted that others have the same problem. Just to further clarify the issues here at my QTH: 1. I am receiving the crud with NOTHING attached to the K2 but the power cord. Right now its coming in especially well on 14.068 MHz. 2. I've tried different power cord lengths, line operated dc power supplies, and external battery supplies (both gel cells and NIMH) and still experience the same level of interference. I am planning to fabricate a shielded, twisted pair power cable as was suggested. 3. I went portable with the K2 and NIMH battery pack inside my house and around the lot. Again with NOTHING connected to the K2 except the battery pack on an 8 inch cable. There were slight variations in the strength of the interference as I walked around the house and lot but no major differences. 4. I will soon be installing the KBT2 perhaps that will help. Just as an aside I installed the KAF2 last night. What a super option...that thing works great! 5. Perhaps this problem has something to do with my call. Oh well. I have easy 5-min access to the backcountry from my QTH but the FM transmitting tower is visible from just about every trail on this side of the mountain. I'm going to take the K2 about 20 miles away and see if that makes a difference! Stay tuned. Tom KI5FM +++++++++++++++++ Date: Wed, 29 May 2002 09:38:58 -0700 From: Vic Rosenthal Organization: Transparent Software To: elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: FM Broadcast Station Interference TBald53892 at aol.com wrote: > > 1. I am receiving the crud with NOTHING attached to the K2 but the power > cord. Right now its coming in especially well on 14.068 MHz. OK, so it looks like the signal is being picked up by the K2 itself. One possibility is a parasitic resonance in one of the inductors. That is, the inductance plus the capacitance between turns resonates someplace near the frequency of the FM station. This is more likely to happen with a solenoid-type coil than a toroid. One thing you might try is to make an fm-band dipole hooked to a little coil. Then open the K2 (top cover and bottom plate) and move the little coil around. See if there's a place that causes the interference to increase. PLEASE, when you finally figure this out, post the results! Vic K2VCO ++++++++++++++++++ Reply-To: "Ron D'Eau Claire" From: "Ron D'Eau Claire" To: "Elecraft List" Subject: Re: [Elecraft] Re: FM Broadcast Station Interference Date: Wed, 29 May 2002 09:36:18 -0700 > I have easy 5-min access to the backcountry from my QTH but the FM > transmitting tower is visible from just about every trail on this side of the > mountain. I'm going to take the K2 about 20 miles away and see if that makes > a difference! Stay tuned. > > Tom KI5FM Your symptoms sound like Stuart was on the right track when he suggested that the interference is being re-radiated from something. It sounds as if it is not inside your shack though. Exploring the outdoors is a good idea to see if you can identify any place where the interference gets stronger as well as weaker. Of course you call has a lot to do with it. I'm still getting AC hum reports on my sig from time to time. Ron AC7AC K2 #1289 ++++++++++++++++++ Date: Wed, 29 May 2002 12:07:20 -0500 To: TBald53892 at aol.com, elecraft at mailman.qth.net From: "Timothy A. Raymer" Subject: Re: [Elecraft] Re: FM Broadcast Station Interference At 12:18 05/29/2002 -0400, TBald53892 at aol.com wrote: >Many thanks to all of you who have responded to my post about FM broadcast >crud. I've also noted that others have the same problem. Just to further >clarify the issues here at my QTH: > >1. I am receiving the crud with NOTHING attached to the K2 but the power >cord. Right now its coming in especially well on 14.068 MHz. > >2. I've tried different power cord lengths, line operated dc power supplies, >and external battery supplies (both gel cells and NIMH) and still experience >the same level of interference. I am planning to fabricate a shielded, >twisted pair power cable as was suggested. I don't remember from your earlier postings, but do you have the problem with headphones, internal speaker, external speaker, or all three? You might want to consider a couple of additional things. Fabricate a cord that runs both leads through a ferrite core, (common mode) a choke or core on the hot lead, and tinkering with the grounding. We have some real pros on here that can recommend the best core type and number of turns to suppress 88-108 Mhz. Try putting a capacitor across the power input of the K2 to ground. The rev C manual shows C196 as a .047. Try a .47 and a 47 across the power input as well. If that is where it is getting in, some more suppression won't hurt. Find the ground for your house, and set the K2 up there. Hook PS negative lead and K2 ground to house ground with as short and stout of a lead as possible. There were some words of advice on here recently about keeping HF RF out of the K2, and that may be sage advice for this as well. It is possible that the same thing in the K2 that is suceptable to AC fields is suceptable to very high RF fields at FM frequencies. You are probably in what used to be referred to as the "blanket coverage" area of the FM station. This is an area that has rf fields that exceed the normal limits imposed on devices that are approved under Part 15 and other FCC regulations. There may be some help from the FM station. Drop a dime to them, ask for the Chief engineer, explain your situation, and ask him if he has any suggestions. Don't expect miracles, but he might have something up his sleeve from working with others that will help you as well. >3. I went portable with the K2 and NIMH battery pack inside my house and >around the lot. Again with NOTHING connected to the K2 except the battery >pack on an 8 inch cable. There were slight variations in the strength of the >interference as I walked around the house and lot but no major differences. > >4. I will soon be installing the KBT2 perhaps that will help. Just as an >aside I installed the KAF2 last night. What a super option...that thing works >great! > >5. Perhaps this problem has something to do with my call. Oh well. Look on the bright side, somewhere there is a TV2RFI that probably does. >I have easy 5-min access to the backcountry from my QTH but the FM >transmitting tower is visible from just about every trail on this side of the >mountain. >I'm going to take the K2 about 20 miles away and see if that makes >a difference! Stay tuned. I suspect that you will be able to find sites within a couple of miles of your home that the problem goes away. You will hit nulls in the pattern of the FM station, and the problem will vanish. >Tom KI5FM Good luck Tom. Tim Raymer 73 de KA0OUV Timothy A. Raymer Missouri Department of Health and Senior Services +++++++++++++++++ From: "w8krr" To: Date: Wed, 29 May 2002 13:53:25 -0400 Subject: [Elecraft] FM Interference Back in the "old days", we did a synthesized rig at Heath called the HW-2026. All spurs were at least 40dB down. Guess what? That's not good enough, and we had to eat those things for our stupidity. Testing confirmed BC siugnals can be re-radiated from the darndst things - don't ignore anything! GL, Mike +++++++++++++++++ Date: Wed, 29 May 2002 14:16:57 -0400 (EDT) From: Brien Pepperdine To: elecraft at mailman.qth.net Subject: [Elecraft] FM broadcast interference When I got my (soon to leave) OMNI VI+ I was getting CBC radio (94.1) on 20 m cw portion for about 20 kc or so. A real drag! With antenna disconnected it was almost just as load.. just came pouring into the rig. I told this to my elec. engineer ham friend and he said 'do you have a low pass filter on the coax'. Well, no. I had one on for ages but had taken it off to do a test at one point on a rig with some trouble. Put the lo pass filter on and the BCI problem was gone. Vanished. Filters in the rig stock just did not block enough. A low pass filter was of course standard station gear before cable/satellite TV. I guess seen to be not necessary these days but in fact many people in my area still have TV antennas on the roof, as do I. So maybe borrow a low pass filter (Drake, Vectronics, MFJ) and put it in line and see if it blocks the BCI or not. Brien Pepperdine Amateur Radio Station VE3VAW Toronto, Ontario Canada ARCI QRP #8773 - NORCAL QRP "ZOMBIE" ++++++++++++++++++ Reply-To: From: "Sverre Holm - LA3ZA" To: , Subject: RE: [Elecraft] Re: FM Broadcast Station Interference Date: Wed, 29 May 2002 20:18:42 +0200 I cannot recall that you have reported the effects of the gain controls of the K2 on the broadcast interference, except that you say that it varies somewhat with the tuned frequency. - does it vary as you change the preamp/attenuator settings? - does it vary with the RF gain or with different XFIL's? - does it vary as you turn on/off the high current drain option of the post-mixer amplifier (optimized intercept point) - and last does it vary with the AF gain control? (I'm sure it does!) This will help isolate where the interference enters the K2. Apart from this one guess could be that RFC11 could pick up outside interference, see http://www.elecraft.com/Apps/17m_18m.htm point 1 for a change to a toroid. 73 Sverre Sverre Holm, LA3ZA Asker, Norway (59.8N, 10.4E) --------------------------------- www.qsl.net/la3za ++++++++++++++++++ Date: Wed, 29 May 2002 13:14:55 -0500 To: TBald53892 at aol.com, elecraft at mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] FM Broadcast Station Interference Tom: Just for grins, see if DISCONNECTING your KEY lead reduces or eliiminates the interference. I think I'm experiencing the same problem. 73, Tom Hammond N0SS +++++++++++++++++++ From: TBald53892 at aol.com Date: Wed, 29 May 2002 18:31:40 EDT To: elecraft at mailman.qth.net Subject: [Elecraft] Re: FM Broadcast Station Interference Again, thanks to everyone for all the postings and private communications re my RFI problem. Took the K2 about 20 miles up the coast to a more rural setting and tried the same test/conditions. With no connections to the K2 except the gel cell/power cord everything was as quiet as a mouse. No evidence of RFI on any frequency. Tom KI5FM +++++++++++++++++++++ Reply-To: "Ron D'Eau Claire" From: "Ron D'Eau Claire" To: Subject: Re: [Elecraft] Re: FM Broadcast Station Interference Date: Wed, 29 May 2002 22:23:14 -0700 > Again, thanks to everyone for all the postings and private communications re > my RFI problem. Took the K2 about 20 miles up the coast to a more rural > setting and tried the same test/conditions. With no connections to the K2 > except the gel cell/power cord everything was as quiet as a mouse. No > evidence of RFI on any frequency. > > Tom KI5FM Now you need to find out where it gets worse and whether it appears in other receivers (BC band?). I know an op who lives in the shadow of several high-powered broadcast stations including FM, and he doesn't have this problem - at least he's not mentioned it. I wouldn't write off the situation as "normal" by any means. Ron AC7AC K2 #1289 +++++++++++++++++++ Date: Thu, 30 May 2002 07:39:46 -0500 To: TBald53892 at aol.com From: Dave Gingrich K9DC Subject: Re: [Elecraft] Re: FM Broadcast Station Interference Cc: elecraft at mailman.qth.net At 18:31 5/29/2002 -0400, you wrote: >Again, thanks to everyone for all the postings and private communications re >my RFI problem. Took the K2 about 20 miles up the coast to a more rural >setting and tried the same test/conditions. With no connections to the K2 >except the gel cell/power cord everything was as quiet as a mouse. No >evidence of RFI on any frequency. FM-DC-AC comments aside, I still find it unusual that your K2 is plagued with this problem at all, especially from an FM station 6 miles away. 34 kw is not really a big FM signal. I live on the edge of the tower forest here with six 1000 foot towers in the neighborhood, five of them less than a mile away. Eight of the ten TV stations serving us and a dozen FM stations are on these sticks. At least two of the FM are 500kw smokers. Never an extraneous peep out of the K2. [Now receiving anything on VHF is an entirely different situation, HI.] Would it be possible for you to get another K2 owner to bring his radio to your shack and see if another rig has the same problem? There are a lot of these rigs around, particularly in CA. This technique worked for me when I was troubleshooting an AM broadcast interference problem on my K1 from a 5kw station 2 miles away. It turned out the other K1 had the same problem at my station, so I turned to antenna mods, etc. (ended up elimiating it entirely by using an 80 meter horizontal loop, rather than an end fed wire). But perhaps your problem is inside your radio, i.e. bad solder joint etc. Bringing another rig over would certainly let you know whether the problem was inside or outside the box. I still puzzled how you could even tell. You identified the station, apparently heard rock music, but FM broadcast sigs modulation is +/- 75 KHz deviation. How could you even begin to detect that on anything inside a K2? -Dave ================================================ Dave Gingrich, K9DC - Indianapolis, Indiana USA K2 #2211, K1 #931, QRP-L #2376, ARS #1109, FPQRP #389, IRLP #473, k9dc.ampr.org, CCIE #6748 ++++++++++++++++++++ Subject: RE: [Elecraft] Re: FM Broadcast Station Interference Date: Thu, 30 May 2002 12:59:39 -0400 From: "Smith, Richard" To: I have experienced exactly the same problem with my K2 - interference on = the low end of 20 meters from a local FM station. The antenna was not a = factor. The modulation of the noise wasn't exactly FM quality, but it = had a certain, identifiable hiphop beat to it. Although not completely = cured, I was able to reduce the effect by winding the power cord a few = times through a ferrite core. Still looking for a better, internal = solution. Rich W1EZ w1ez at arrl.net ++++++++++++++++++++ To: elecraft at mailman.qth.net From: CHARLES K BROWN Date: Thu, 30 May 2002 17:02:05 EDT Subject: [Elecraft] FM Broadcast RFI If this is the power supply leads, try filtering the plus and minus leads with ferrite beads of the proper size, or similar ferrite cores for the power supply cable. Switching power supplies use ferrite beads because of objectionable amounts of RF noise. On one Switcher, six Amidon FB-73-2401 ferrite beads were used on each DC cable. Internally, Type 73 beads are used for more RFI filtering. FB-73-801 is one type for wires inside the case. Ferrite beads or ferrite cores would work on any of the other cables that could be acting as an antenna for FM broadcast harmonics. N4SO Ken Brown Mobile, AL/EM50tk NorCal-20/5 watts/4 ele. beam +++++++++++++++++++ Reply-To: From: "Sverre Holm - LA3ZA" To: "Elecraft at Mailman. Qth. Net" Date: Fri, 14 Jun 2002 18:58:02 +0200 Subject: [Elecraft] Update on BCI Here are replies to questions I have received on the cause of FM BCI pick-up in the K2: 1. Filtering on power supply leads. This has already been tried, and it is quite certain that the K2 picks up the BCI directly on the RF board, either on some or more components or the PCB-tracks itself. I suspect that maybe the relays (K16, K17) that switch the preamp/attenuator in/out could pick up something since they are possibly not shielded, but I am not certain, but moving a small transmitter probe around does not produce any single position on the PCB with maximum interference. I believe the problem can be identified and fixed and thus make the K2 an even better tranceiver! 2. Switching the external RX antenna in/out. External RX antenna input (160 m option) does not go through LP filters, so there could be more sensitivity to BCI on that input. Switching the antenna has no effect. The only control with effect on the BCI is the Preamp/Atten control. 3. How can you receive an FM signal on a CW/SSB radio? Every FM receiver has a detector which in effect is a frequency to voltage converter. The slopes of the crystal filter give such an effect, but much more narrowband than required for broadcast FM. Therefore one will not get Hi-Fi sound, but will be able to hear rhytm etc from music and be able to identify the station by comparing with an FM radio BTW, if you want to hear this effect but don't have a nearby FM transmitter, a 6 meter transmitter will do the job: 51.9 MHz will be picked up at 14023 kHz, since the 3. harmonic of the oscillator is (14023.33 + 4915)*3 which is 51900 + 4915 73, Sverre Sverre Holm, LA3ZA Asker, Norway (59.8N, 10.4E) --------------------------------- www.qsl.net/la3za +++++++++++++++++ Date: Mon, 19 Aug 2002 22:00:11 +0200 From: Heyder.Family at t-online.de (Norbert Heyder) To: elecraft at mailman.qth.net Subject: [Elecraft] K2 receiver trouble with local FM Broadcast Stations If you will ever have trouble with the the K2 concerning local Broadcast FM Stations making receiver noise on 14.060Mc or somewhere else, you should check the nut securing the key input jack on the rear. I had such problems as soon as the paddle was connected to the K2. The reason: The nut of the jack made no contact with the rear panel although the grey paint was removed there! I just tightend the nut a bit more until it made a "solid" contact with the rear panel. That completely removed the noise. gl es 72 de Bert DL8BDF K2 #433 ++++++++++++++++++++ From: Marteinn Sverrisson Date: Thu, 26 Sep 2002 09:09:13 +0000 To: elecraft at mailman.qth.net Subject: [Elecraft] Resolving AGC activation from Broadcast Stations Resolving K2 S-Meter activation from broadcast stations I have had trouble with S-meter/AGC activation from short-wave broadcast stations on 40, 20 and 17 meter bands on my K2. The largest S-meter indication S9 (SSB mode), being on 17m. I traced this to leakage to the SSB module, as the activation was much stronger on SSB (S9) than on CW (S5). Moving I.F. Out to output of 2nd Xfilter I then looked at the K2 schematic and observed that the I.F. OUT signal to the AGC/S-meter circuit is picked up ahead of the 2nd Xtal filter instead of after it. So I removed the capacitor C181 and routed the IF signal from output of the 2nd Xtal filter, to the AGC circuit. Connected pin 1 of the product detector U11, via 1.5 kOhm + 0.01uf (C181) to I.F. OUT, removing the 5.6 kOhm resistor previously inserted by the 2nd Xfil mod. This did the trick, I now have no S-meter/AGC activation from broadcast stations even if their signal strength is S9+40dB on the 17m band. 73's de TF3MA http://www.raunvis.hi.is:~matti/TF3MA ++++++++++++++++++++++ From: Marteinn Sverrisson Date: Sat, 28 Sep 2002 10:27:02 +0000 To: elecraft at mailman.qth.net Subject: [Elecraft] Finally? resolving AGC activation from Broadcast stations Finally? resolving K2 S-Meter activation from broadcast stations Wayne Burdick, n6kr, pointed out to me that taking the I.F. Out from 2nd Xfilter would result in BFO leakage into the AGC mixer making the AGC action no better than audio derived AGC. I built a new 2nd Xfilter using two 4.9152 crystals and 12pf cap (this is just a copy of the 2nd Xfilter in K2, in SSB mode), and put it in place of C181. -----XTAL------XTAL---- | = 12pF | gnd The filter cleans up the IF signal and eliminates the AGC activation from the broadcast stations and does not sound bad, no "ploppy" sound on SSB or CW signals. I have observed strong, S9+40dB, broadcast stations below the 17m band and now there is no AGC activation from them now on the hamband, before I had the S-meter on S5 with no signal, SSB mode. 73's Matti, TF3MA ++++++++++++++++