Re: Topband: To clamp or NOT...that IS the question
When I build a preamp I install the cupped machine pins from an IC socket in the protection device mounting holes so that I can experiment with different protective devices and easily replace devices which have been damaged. If you have IMD from back to back diodes try two or three diodes in series. Mike N2MS Jim, Getting directly back to your original question, I built a KD9SV preamp, and it has clamp diodes included in the design (I did not add them, they were part of the original design by KD9SV). Does you KD9SV preamp already have clamp diodes protecting its input, and if so you have already answered your own question about adding clamp diodes to protect it (no reason to add them if you already have them). _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Oooops - sorta!! Checked the schematic for the KD9SV pre-amp I have and find it does have clamping diodes at the input...DUH.so, question/problem/concern resolved, in spite of myself!! Hi Hi Tnx to Don, WD8DSB, for querying me and suggesting I check my particular KD9V model!! 72/73, Jim Rpdenkirch K9JWV P.S. WOW! HL5ILV was rockin' in to s/w UT this morning around 1250Z at 569 to 579, at times...I did work him but needed 50 watts to do it..NO QRP QSO with HL land today! Also heard some STRONG JAs on 80 CW as well Hope condx continue for the CQ 160 next weekend and hope to hear and work y'all with my QRP peanut whistle! Date: Sat, 18 Jan 2014 13:53:01 -0500 Subject: Re: Topband: To clamp or NOT...that IS the question From: wd8...@gmail.com To: rodenkirch_...@msn.com Hi Jim, You might post that info to the topband reflector (about your preamp having clamp diodes already included as part of the original KD9SV preamp design), as some guys were questioning what I was saying. Even Gary KD9SV e-mailed me about my comment that the KD9SV preamp that you had might already have clamp diodes as part of the design and I reminded him that some of his preamp designs did indeed have diode clamps (1N914 diodes or equivalent) across the input to the electronics, and then he went and looked at some of his schematics and confirmed that I was indeed correct. There are several different vintages/designs of the KD9SV preamp which causes some confusion to even the designer (Gary, KD9SV). While I agree totally with what others have said about intermod as it relates to clamp diodes, I also believe in keeping systems as simple as possible. The folks having the most negative feelings about clamp diodes also are the ones using RX antennas that have gains many magnitudes greater than what your RX antenna provides. Just listen to what folks are saying and make the best decisions you can based on your own particular situation. 73, Don (wd8dsb) On Sat, Jan 18, 2014 at 12:53 PM, James Rodenkirch wrote: Yup - Don../good observation and I checked thw schematic for the preamp and it has clamp diodes at the front end.. > Date: Sat, 18 Jan 2014 12:02:03 -0500 > From: wd8...@gmail.com > To: w...@w8ji.com > CC: topband@contesting.com > Subject: Re: Topband: To clamp or NOT...that IS the question > > Jim, > > Getting directly back to your original question, I built a KD9SV preamp, > and it has clamp diodes included in the design (I did not add them, they > were part of the original design by KD9SV). Does you KD9SV preamp already > have clamp diodes protecting its input, and if so you have already answered > your own question about adding clamp diodes to protect it (no reason to add > them if you already have them). > > If you go one step more and follow the advice that others have provided > here, you might consider removing the clamp diodes (if you have them) based > on their comments, but please understand that the gain of you RX antenna is > approximately -36.3 dbi (based on the dimensions you told me), and it's > very possible that you will not encounter the same kind of problems (using > clamp diodes) as those using beverage RX antennas on 160 meters just due to > the greatly reduced signal strength that your RX antenna provides compared > with a full size beverage. > > That's all I'm saying on this topic, over and out. > > Don (wd8dsb) > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Jim, Getting directly back to your original question, I built a KD9SV preamp, and it has clamp diodes included in the design (I did not add them, they were part of the original design by KD9SV). Does you KD9SV preamp already have clamp diodes protecting its input, and if so you have already answered your own question about adding clamp diodes to protect it (no reason to add them if you already have them). If you go one step more and follow the advice that others have provided here, you might consider removing the clamp diodes (if you have them) based on their comments, but please understand that the gain of you RX antenna is approximately -36.3 dbi (based on the dimensions you told me), and it's very possible that you will not encounter the same kind of problems (using clamp diodes) as those using beverage RX antennas on 160 meters just due to the greatly reduced signal strength that your RX antenna provides compared with a full size beverage. That's all I'm saying on this topic, over and out. Don (wd8dsb) _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Indeed. I've had problems with ICE 196 receiver protectors for several years. I assume the intermod is generated by the diodes in those devices, though I do not know that for a fact. The problem occurs on nights when propagation is very good both in the AM BC band and shortwave in the 5-7 MHz range. I get some extremely strong SW BC stations on good nights. All are well below the threshold but the combined affect of many signals is too much. Removing the ICE 196 clears up the intermod, so I am reasonably certain that is where it is generated. I need to either find another way to protect my front end or use band pass filters. Sometimes people do not recognize IMD, even when they have it. IMD is also not the only issue. There are multiple problems besides IMD, some are not even noticeable to the station owner. For example, in almost all transceivers the receiving antenna port is common to filters and stages used in the transmitter function as a predriver. Most transceivers do not have disconnect relays for the receiving antenna port, they depend on diodes to switch the antenna port off. When levels get too high, the RX port isolation diodes allow TX RF back into the transceiver predriver stage. This creates all types of wideband spurious signals up and down the band. That is not a rare problem, and some external clamps still allow the RX port feedback to affect the transmitter signal quality. Giving general advice, or selling a universal product, I focus on something that should generally work for everyone and not cause problems for anyone, especially if it can pollute the band for others. While sometimes excused or dismissed as "bad radios" or setup anomalies, if we all do not plan properly and understand the limits, the accumulation of "unimportant" planning errors damages the spectrum for everyone. This is why, in any quiet location, a large percentage of signals that could be copied on nights of low activity cannot be copied with high activity. The band fills with spurious stuff unrelated to receiver defects. The last thing we want is to not make things as good as we reasonably can. Poor planning, marginal systems or methods, and bad advice eventually catches up with all of us in one way or another. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Thanks to all for the insightful replies/advice. It would appear the use of clamping FETs is worth a try... 72, Jim R. K9JWV _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
On 01/18/2014 06:20 AM, N1BUG wrote: Indeed. I've had problems with ICE 196 receiver protectors for several years. I assume the intermod is generated by the diodes in those devices, though I do not know that for a fact. The problem occurs on nights when propagation is very good both in the AM BC band and shortwave in the 5-7 MHz range. I get some extremely strong SW BC stations on good nights. All are well below the threshold but the combined affect of many signals is too much. Removing the ICE 196 clears up the intermod, so I am reasonably certain that is where it is generated. I need to either find another way to protect my front end or use band pass filters. Sorry... I should have noted this is using Beverages +/- 600 feet long. 73, Paul N1BUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
On 01/17/2014 09:51 PM, Tom W8JI wrote: Intermod is a function of the TOTAL voltage of all the signal sources at the point where the diodes are. This is why some systems work with diodes, and some systems completely fall apart. The problem can come from a hundred small signals, each signal far below threshold, or just one large signal near threshold. Impedance also matters, both in band and out-of-band. Indeed. I've had problems with ICE 196 receiver protectors for several years. I assume the intermod is generated by the diodes in those devices, though I do not know that for a fact. The problem occurs on nights when propagation is very good both in the AM BC band and shortwave in the 5-7 MHz range. I get some extremely strong SW BC stations on good nights. All are well below the threshold but the combined affect of many signals is too much. Removing the ICE 196 clears up the intermod, so I am reasonably certain that is where it is generated. I need to either find another way to protect my front end or use band pass filters. 73, Paul N1BUG _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: To clamp or NOT...that IS the question
Hi Tom, You said : "What works OK in one place will almost always not work the same in another" You just confirmed what I was trying to say, and that is in some applications it just might work. If I had not tried simple clamp diodes in my application I would have made my system complicated via relays and control signals when they really were not needed. Same thing goes for the W7IUV preamp, if I had not tried using it without a front end saver I would have gone and spent money and complicated my system when it was not really needed. But after reading that W7IUV did not use a front end saver with his preamp I tried the same and could not be happier with the results. I'm suggesting that Jim try clamp diodes if he so desires and if he notices intermod then he should remove them and try a more complicated/elegant solution. Don (wd8dsb) _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
I use protection diodes on the front end of my W1FB preamps (as well as before an IC amp in the preamp, and on the output of the preamp) and have never been able to detect receiver performance degradation on 160 meters due to the clamping diodes (had to include the diode clamps before the IC amp in the W1FB preamp to prevent continuous failures of this IC when transmitting). What works OK in one place will almost always not work the same in another. Intermod is a function of the TOTAL voltage of all the signal sources at the point where the diodes are. This is why some systems work with diodes, and some systems completely fall apart. The problem can come from a hundred small signals, each signal far below threshold, or just one large signal near threshold. Impedance also matters, both in band and out-of-band. A regular diode is about .5 volts or before peak it starts to generate junk, some are less and some slightly more. Assuming .5 volts peak, that would be .35 volts RMS. .35V RMS is only 4 dBm at 50 ohms. This would be the peak composite voltage level, not the single tone or composite power calculated from the simple sum of powers. This paper would apply: www.minicircuits.com/app/AN60-037.pdf _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Hi Jim and gang, I use protection diodes on the front end of my W1FB preamps (as well as before an IC amp in the preamp, and on the output of the preamp) and have never been able to detect receiver performance degradation on 160 meters due to the clamping diodes (had to include the diode clamps before the IC amp in the W1FB preamp to prevent continuous failures of this IC when transmitting). On the rare occasion (only happens during a contest) when I've heard what sounds like ever so slight intermod I switch to my TX vertical for RX and the odd phenomena has always still been present so I've never been able to find fault with my added diode protection system. I have half size pennants feeding my preamp and they have an approximate gain of -46 dbi, and suspect this is the key to my success with diodes as clamps (very low input levels from my RX antennas). Therefore I certainly don't agree with avoiding diode clamps 100% of the time, as I believe they should be considered on a case by case basis depending on the gain of your RX antenna, etc. I also have W7IUV preamps and don't use diode clamps with them at all since their front ends appear bullet proof based on the transistor used. P.S. I only run 100 watts output, but my TX vertical is within 30 or 40 feet of my RX pennants. 73, Don (wd8dsb) _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Hello Jim, 3x fast relays, 2x switching transistors, 3x resistors and box with connectors... You have KD9SV front-end saver. No diodes, no RX performance degradation. I never had issue on my K3 with KD9SV saver in ext.RX front-end. Let me know I will send You the drawing. Hope it helps my friend, best regards, 73 - Petr, OK1RP http://160mband.blogspot.com On Fri, Jan 17, 2014, at 06:37 PM, James Rodenkirch wrote: > > > > A friend of mine is building me a switching arrangement with a reed relay > to switch between my transmit antenna and a receive delta loop to the one > antenna input for my Ten Tec Jupiter (I operate at QRP levels for > contests). > As an added measure of protection for the KD9SV low noise pre-amp I use > with my 160/80 delta loop antenna, he believes clamping the RX antenna > port or shunting to ground during TX sounds like a nice thing. But, he's > seen arguments that clamping receiver input with diodes degrades the > receiver performance. He find this believable, but I don't know how true > it is, e.g., he knows KD1JV claims his RX performance is achieved by > using 2N7000 FETs to do T/X switching. > He has a bunch of 2N7000 and will probably use one to turn on the relay. > He can turn on another one along with the relay driver that will shunt > the RX antenna port to ground but he wonders if that would degrade > receiver performance. > Thoughts? 72/72, Jim Rodenkirch K9JWV > > > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: To clamp or NOT...that IS the question
Not lkely, I think, Jim. I presume the FET would have some significant bias ( perhaps 5-12 V) on its drain when it is not conducting, so relatively large signals are not very likely to produce non-linearities and intermod or cross modulation as the diodes might. My TCW. Of course on could also add an additional relay (perhaps mercury wetted) right at the RX port to clamp it when thetX is enabled. 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of James Rodenkirch Sent: Friday, January 17, 2014 12:38 PM To: Top Band Contesting Subject: Topband: To clamp or NOT...that IS the question A friend of mine is building me a switching arrangement with a reed relay to switch between my transmit antenna and a receive delta loop to the one antenna input for my Ten Tec Jupiter (I operate at QRP levels for contests). As an added measure of protection for the KD9SV low noise pre-amp I use with my 160/80 delta loop antenna, he believes clamping the RX antenna port or shunting to ground during TX sounds like a nice thing. But, he's seen arguments that clamping receiver input with diodes degrades the receiver performance. He find this believable, but I don't know how true it is, e.g., he knows KD1JV claims his RX performance is achieved by using 2N7000 FETs to do T/X switching. He has a bunch of 2N7000 and will probably use one to turn on the relay. He can turn on another one along with the relay driver that will shunt the RX antenna port to ground but he wonders if that would degrade receiver performance. Thoughts? 72/72, Jim Rodenkirch K9JWV _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: To clamp or NOT...that IS the question
A friend of mine is building me a switching arrangement with a reed relay to switch between my transmit antenna and a receive delta loop to the one antenna input for my Ten Tec Jupiter (I operate at QRP levels for contests). As an added measure of protection for the KD9SV low noise pre-amp I use with my 160/80 delta loop antenna, he believes clamping the RX antenna port or shunting to ground during TX sounds like a nice thing. But, he's seen arguments that clamping receiver input with diodes degrades the receiver performance. He find this believable, but I don't know how true it is, e.g., he knows KD1JV claims his RX performance is achieved by using 2N7000 FETs to do T/X switching. He has a bunch of 2N7000 and will probably use one to turn on the relay. He can turn on another one along with the relay driver that will shunt the RX antenna port to ground but he wonders if that would degrade receiver performance. Thoughts? 72/72, Jim Rodenkirch K9JWV _ Topband Reflector Archives - http://www.contesting.com/_topband
