RE: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C?
[EMAIL PROTECTED] (Robert Schenck) made an utterance to the drakelist gang -- I guess we have ll seen most of the various mods over the years. Personally, I tested the radio out extensicvely and came up with the following mods: Replaced power supply board with a new board with largest filter caps for B+ and negative bias for minimum ripple. also has +/- 12 volt regulators for solid state circuitry. Replaced audio amp board with new one with a pair f LM 380 in a bridge output driving the original output transformer to still have anti vox work correctly. ANy bridge amp would do. LM 380 chaep and stable. Replaced If amp/ detector board with new board with 1496 product detector and precision AM detector I designed and on AM Fone website. Added a second first IF four pole filter in cascade with original. easily mounts on bottom oout of sight. First IF now 7.5 KHz BW and 85 dB stop band. Discoverd that sensitivity with 2509 Hz 2nd IF CW filter was not 10 dB better than with 2.4 KHz SSB filter as would be expected. was only 4 dB better. Problem was reltively low gain from ant to third mixer (6EJ7). Added a Mini-circuits MAR 3 at output of second switch that selects 2nd IF filter. made up for half increased gain by ading second cap to voltage divied signal to 50 KHz IF amp. The much lower noise figure of the MAR 3 reduced ovrall noise to be that of front end and now I get the 10 dB better sensitvity with 250 Hz filter. If you don't get a big noise peak with preseltor tuning then later stage noise is dominating. Love the radio now. ras __ Switch to Netscape Internet Service. As low as $9.95 a month -- Sign up today at http://isp.netscape.com/register Netscape. Just the Net You Need. New! Netscape Toolbar for Internet Explorer Search from anywhere on the Web and block those annoying pop-ups. Download now at http://channels.netscape.com/ns/search/install.jsp -- Submissions:drakelist@www.zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
RE: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C?
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Tue, 24 Jan 2006 22:07:16 -0500, Robert Schenck wrote: Added a second first IF four pole filter in cascade with original. easily mounts on bottom oout of sight. First IF now 7.5 KHz BW and 85 dB stop band. Hey, I asked about doing this a couple of years ago and no one had anything to say! I've got a second filter, it's just waiting for the same round tuit as the Velleman amp module. How did you go about doing it. Details, man! Details! 73 Jim -- Jim Shorney --.--Put complaints in this box jshorney (at) inebraska.com Ham Radio NU0C Lincoln, NE, USA EN10ps http://incolor.inetnebr.com/jshorney/ -- Submissions:drakelist@www.zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
RE: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C?
Gerry [EMAIL PROTECTED] made an utterance to the drakelist gang -- I haven't tried the R-4C mods in the Jan/Feb QEX for two main reasons. One is that the authors don't show any data to back up their claims for improved performance. Maybe they expect the reader to be impressed by their academic credentials listed at the end in order to quash criticism. After all, who would question the judgment of a BSc (Hons1), whatever that is? The other is that some of their assertions and interpretations of devices used are either incomplete or inaccurate. For example, their assumptions regarding the power supply are inaccurate and incomplete. They don't go into much detail and forge ahead with their own ideas. But who am I to question? The audio stage they used is indeed rated for 20 watts but that's in a 22 volt bipolar supply, plus AND minus 22 volts. In the 12V single supply they used it looks more like 2.5 watts, looking at the data sheet. And since the distortion and noise specifications apply only to bipolar supply and the data sheet doesn't show what happens in a single supply, noise and distortion can only be speculated. My experience has been that these two performance aspects increase, sometimes unpredictably when you deviate from the specified application data. I get questions from customers all the time regarding analog reference circuits published on the web with complete parts lists and data. They have a problem and swear up and down they followed directions only to find out they didn't use the referenced components and board layout. Of course, 2.5 watts is still pretty good, so maybe the LM1875 is worth trying, never mind the data sheet. The point is the LM383 (obsolete) aka TDA2002 and TDA2003 (updated TDA2002) should still be the preferred choice. My main point of contention about the authors in the article is they don't show anything to back up their claims. Some of them might be OK, like the SN602 product detector. Others like the so-called power supply and the AGC system: proceed at your own risk. My impression is the article shows a SYSTEM, not a series of improvements that can be incrementally applied. Frankly, I wonder how this article made its way into a respected technical publication like QEX. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jim Shorney Sent: Sunday, January 22, 2006 7:48 PM To: DrakeList; Jim Pruitt Subject: Re: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C? Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Sun, 22 Jan 2006 15:58:17 -0800, Jim Pruitt wrote: According to the article itself (mods done on a late R4C with 6EJ7 first and third mixer). Thanks, Jim. Sounds like mostly old stuff, re-done a little. I'm always wary of AGC mods, sice the AGC is so good to begin with and is what makes the R4C so listenable. I did do the third mixer mod as descibed in Drakemods to my late R4C, and it seems to work as advertised. Otherwise, no other mods as of yet. I did wonder about the LM1875 audio amp (20 watt). My R4C needs work (motorboats) and I wanted to do the Sherwood PS4 mod and the audio amp. I have a Velleman audio amp kit that I was going to use but in reading Bob Sherwood (NC0B) mods a few decades ago in Ham Radio Magazine made me wonder how my Velleman audio amp would work since Bob said to be careful about lead lengths (had to be exact lengths or would oscillate). So the LM1875 audio amp was the one mod I was considering but did not want to butcher my R4C. 20 watts sounds like massive overkill. I would worry about power supply loading with that monster, unless the gain is limited somehow. I've got one of the Velleman amps. It looks good and works as advertised on the test bench. I think the warnings are scare tactics to make sure that people follow the manufacturer's recommendations as far as component dress and circuit layout - the devices are not tolerant of sloppy construction, but they are stable and robust with a little care. The one change I did make was the capacitance in the feedback circuit to roll off the high end around 3 KHz; this is a hi-fi amp module, and response to 20 KHz in a communications receiver is NOT a good thing. I wouldn't be afraid of trying the Velleman amp, as long as you follow Bob's hookup recommendations. I just haven't gotten the round tuit that I need to put mine in my R4C yet. Thanks again for the info, Jim. I may have to look at the article and see what it says in more detail. 73 Jim -- Jim Shorney --.--Put complaints in this box jshorney (at) inebraska.com Ham Radio NU0C Lincoln, NE, USA EN10ps http://incolor.inetnebr.com/jshorney/ -- Submissions:drakelist@www.zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe
Re: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C?
Jim Pruitt [EMAIL PROTECTED] made an utterance to the drakelist gang -- Hello Jim. According to the article itself (mods done on a late R4C with 6EJ7 first and third mixer). Major Features: High performance LM1875 audio amplifier (THD at 20 W/1 khz of 0.15% typically 12v regulated supply (+12v and -12v) for solid state circuitry. SN602 product detector SN602 as R4C third mixer. MiniCircuits SBL-3 double balanced mixer (+7dbm LO) as R4C second mixer. MAV-11 MMIC to increase IF gain after the R4C second mixer. Sherwood 600 Hz first IF CW filter, with realay switching so the stock 8khz wide first IF filter is retained for SSB/AM operation. Completely new three speed hang AGC system after the second IF crystal filters and allows the gain of all the stages before the R4C's third mixer to run at maximum. The AGC has one speed for very fast CW (35wpm-plus), plus one for slower cw and one for SSB. One thing that did not set well with me was that the author drilled a hole and installed a small toggle switch on the front panel. The artilce was written because the author had a basket case R4C and wanted to do the mods that W8JI had done but W8JI did not document his mods and the NC0B and K8RRH mods used parts no longer readily available. As one other Drakelister pointed out to me off list was that the author does not recommend the mods on a good and working R4C. I did not read that but did read that it was done on a basket case. In reading the article I did keep thinking that the guy was sure not improving resale value but as the author stated, he has no intention of ever selling his modified R4C so the estetic value was totally unimportant. I contacted Fred at FAR circuits and asked if he was going to make pc boards for this article (the article used only dead bug and breadboard). Fred said he had no plans to make any pc boards and I can understand that since it would not be a popular mod (for one thing, a lot of us do not have the late R4C). I did wonder about the LM1875 audio amp (20 watt). My R4C needs work (motorboats) and I wanted to do the Sherwood PS4 mod and the audio amp. I have a Velleman audio amp kit that I was going to use but in reading Bob Sherwood (NC0B) mods a few decades ago in Ham Radio Magazine made me wonder how my Velleman audio amp would work since Bob said to be careful about lead lengths (had to be exact lengths or would oscillate). So the LM1875 audio amp was the one mod I was considering but did not want to butcher my R4C. Hope that information was helpful. Thank you. Jim Pruitt - Original Message - From: Jim Shorney [EMAIL PROTECTED] To: DrakeList drakelist@www.zerobeat.net Sent: Sunday, January 22, 2006 8:02 AM Subject: Re: [drakelist] Has anyone done the mods from the Jan-Feb 06 QEX for the R4C? Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Sat, 21 Jan 2006 17:57:13 -0800, Jim Pruitt wrote: Has anyone on the list done any or all of the mods from the QEX Jan-Feb 06 article The Harmonized R4C-A High Performance Analog HF Receiver by VK6APH and VK6VZ? Can you briefly describe the mods? -- TR7/RV7, TR6/RV6, T4XC/R4C, L4B, NCL2000, SB104A, R390A, GT550A/RV550A - all vintage, all the time! -- Submissions:drakelist@www.zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
Re: [drakelist] Mods in the Jan-Feb 06 QEX for the Harmonized R4C?
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Sun, 22 Jan 2006 15:58:17 -0800, Jim Pruitt wrote: According to the article itself (mods done on a late R4C with 6EJ7 first and third mixer). Thanks, Jim. Sounds like mostly old stuff, re-done a little. I'm always wary of AGC mods, sice the AGC is so good to begin with and is what makes the R4C so listenable. I did do the third mixer mod as descibed in Drakemods to my late R4C, and it seems to work as advertised. Otherwise, no other mods as of yet. I did wonder about the LM1875 audio amp (20 watt). My R4C needs work (motorboats) and I wanted to do the Sherwood PS4 mod and the audio amp. I have a Velleman audio amp kit that I was going to use but in reading Bob Sherwood (NC0B) mods a few decades ago in Ham Radio Magazine made me wonder how my Velleman audio amp would work since Bob said to be careful about lead lengths (had to be exact lengths or would oscillate). So the LM1875 audio amp was the one mod I was considering but did not want to butcher my R4C. 20 watts sounds like massive overkill. I would worry about power supply loading with that monster, unless the gain is limited somehow. I've got one of the Velleman amps. It looks good and works as advertised on the test bench. I think the warnings are scare tactics to make sure that people follow the manufacturer's recommendations as far as component dress and circuit layout - the devices are not tolerant of sloppy construction, but they are stable and robust with a little care. The one change I did make was the capacitance in the feedback circuit to roll off the high end around 3 KHz; this is a hi-fi amp module, and response to 20 KHz in a communications receiver is NOT a good thing. I wouldn't be afraid of trying the Velleman amp, as long as you follow Bob's hookup recommendations. I just haven't gotten the round tuit that I need to put mine in my R4C yet. Thanks again for the info, Jim. I may have to look at the article and see what it says in more detail. 73 Jim -- Jim Shorney --.--Put complaints in this box jshorney (at) inebraska.com Ham Radio NU0C Lincoln, NE, USA EN10ps http://incolor.inetnebr.com/jshorney/ -- Submissions:drakelist@www.zerobeat.net Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net --
