Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Makes sense, Lee Charlie -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Lee K7TJR Sent: Monday, August 31, 2015 12:44 AM To: topband@contesting.com Subject: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector) I believe the point of having the transformers in their circuit is to limit the maximum output. A transformer (ferrite in this case) can only output whatever maximum current determined by the core saturation level. They are relying on this property of the transformers to limit the current into the clipping diodes. I believe it was ICE that came up with this technique sometime way back. The diodes set the voltage level of clipping and the transformers limit the maximum current or power into the diodes. The combination realizes a somewhat soft clipping level with a fixed maximum output. Common mode isolation comes for free along with the design. Lee K7TJR _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
FYI - The S-QSK boards are now spoken for. Thanks for the replies. Paul, W9AC _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Another option for "front end" sequencing control involves the use of a microcontroller to time R=>T and the the reverse switching events. For the past two years, I've been using an Arduino Nano-based controller to manage amplifier switching as well as a PIN diode T/R switch to silently control RF switching of a Drake C line. To date, RF ingress has not been an issue. The Nano's I/O is completely optically isolated with the use of external photo transistors and photo-relays. The photo-relays are used to drive heftier devices like vacuum relays, PIN diodes, and Zener bias switching. The board has an integrated RF sample port such that switching events cannot occur in the presence of RF. Where RF needs to be sampled away from board, an external RF sampling board is used. In both sampling versions, RF is sensed down to less than 50 mW of power. The board samples up to 4 inputs (including RF presence) and switches a maximum of 8 output channels. To the point of this message topic, the same board also emulates the KD9SV "Front End Saver." On my QRZ.com page, I have written the C++ code to start basic control of the FES. Need more devices switched or need to conveniently change delay times? Just activate another port by modifying the software. Or, change switch times in 1 ms increments with a simple software edit. The board includes two optional relay coil accelerator circuits, and includes W8ZR's idea of using a small muRata DC-DC converter, bootstrapped to the +12V supply to generate +24V to power common vacuum relays. More board info is available in the 2014 ARRL Handbook or on my QRZ.com page. One only populates the parts on the board of interest. For example, if relay coil acceleration is not of interest, the parts are omitted and does not affect the rest of the board's operation. I still have a few bare boards remaining. PM if there's an interest. Paul, W9AC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
The Array Solutions device also uses the transformers to increase the voltage at the diodes then steps it back down which means that the diodes are not doing their limiting at 50 ohms. Therefore, your set of 2 series diodes or even one diode each direction is limiting at a higher power level than the Array Solutions device. From the QST article. "The transformer increases the voltage level to allow limiting by a pair of back-to-back diodes and then another transformer matches the output to a 50 ohm receiver input." Here are the problems: 1.) The peak voltage at 75 ohms and 100 mW (20 dBm) is almost 4 volts. 2.) Receiver impedances are all over the place. I've seen them as low as 20 ohms, and as high as 150 ohms. Most of those I measured are closer to 40-80 ohms. 3.) The voltage at the diodes is the vector sum of all signal voltages. If you have a wide band antenna, there can be considerable net voltage from many hundreds of small signals summing. I can light a 12V filament lamp dull red off my Beverages at night, and I am 30-40 miles from the closest active AM BCB station. It is the sum of hundreds of signal from hundreds of miles that is the problem. 4.) Receivers limit the signal range to something centered around the selected band, so they don't see that wide swath of summed voltages. The diodes in a limiter do. 5.) The miniciruits transformer mix and create IMD, and are very sensitive to dc current, even at pretty low levels. The point where they add IMD is so unpredictable compared to limiting, they are not a good choice in receive systems. This is especially true when you have no idea how many hundreds of signals that transformer has to process at the randowm receive systems in the field. (I tried them for antenna and amplifiers and abandoned them back in the 70's. My eight element look antenna array initially used them, but the LORAN signals and AM BCB signals killed them). The last thing in the world useful for RX protection is a soft limiter. It has to be a hard clamp, set just safely below whatever RX port voltage might threaten equipment. No clamping or distortion until that point. Premature limiting does absolutely no good, and potentially many bad things. If you pay thousands of dollars for a receiver that has a wide spaced dynamic range of over 100 dB, why would want to make it into 1970's Yaesu FT101 performance with a limiter? Remember, this is not a few signals in the passband. The diodes are pre-filter, and they clip at the sum of all the hundreds of small signals across them. If you use diodes, they become more acceptable is a modest amount of pre-filtering is used to keep needless signals (especially the AM BCB) out. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Array Solutions offers a 'RX Front End Protector' based on back-to-back 1N4148 diodes. Schematic: http://www.ok1rr.com/public/rxfep.png more details: http://www.arraysolutions.com/Products/as_rxfep.htm manual (also pictures of clipping etc.) http://www.arraysolutions.com/images/AS-RXFEPdatasheet.pdf It works as described, no problems although it can cause spurious radiations on densely equipped multi-multi contest sites using very high power amps. For single TX DXer it can be possibly preferred over relay devices we talked about. Anyway, you test! BTW if the AS-RXFEP will be housed in a plastic box it will provide a lot of additional CM suppression. 73, Martin, OK1RR Dne 30.8.2015 v 21:52 Mike Waters napsal(a): How about back-to-back 1N4148 diodes (2 in series) across the RX path, and a #47 incandescent lamp between those and the Beverage? That's what I do here, among other things. Those are in series with my preamp, which is almost always on. There's also some variable resistance in series with the lamp and the Beverage switching relays. I do that so that the signal from the Beverage is equal with the RX signal from the inverted-L. 73, Mike www.w0btu.com On Sat, Aug 29, 2015 at 8:06 PM, Charles Cu nningham charlie-cunning...@nc.rr.com wrote: It seems to me that a very fast operating preamp protection circuit could be constructed employing a good fast saturating NPN switching transistor across the antenna path. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
That's similar to mine, but mine has two 1N4148 diodes in series, back-to-back, total of four diodes. However, after I did that, I got to thinking that it would be better with only two. Or that there was no need for four. (Don't ask me to explain, it's been a long time since I've thought about that.) 73, Mike www.w0btu.com On Sun, Aug 30, 2015 at 5:00 PM, Martin Kratoska mar...@centrum.cz wrote: Array Solutions offers a 'RX Front End Protector' based on back-to-back 1N4148 diodes. Schematic: http://www.ok1rr.com/public/rxfep.png _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
That's similar to mine, but mine has two 1N4148 diodes in series, back-to-back, total of four diodes. However, after I did that, I got to thinking that it would be better with only two. Or that there was no need for four. (Don't ask me to explain, it's been a long time since I've thought about that.) You probably used four diodes for a good reason. 20 dB is 2.73 volts RMS across 75 ohms. That is 3.86 volts peak. If you use back-to-back diodes, the system clamps at .7 volts peak and mixes at lower levels. That's like 5-10 dBm or less for the sum of all signal power. Remember that clamp is seeing the vector sum of voltages from ALL the signals on the RX antenna, not just signals on the band you are using or the signal you are listening to. I can't use diodes here because of IMD, so I use a hard limiting clamp that is preset by a Zener diode. Why would anyone want a clamp system that reduces the IM DR of a modern receiver? If you pay all that money for an RX, why not use it? I would think your 4 diodes are the absolute minimum to use almost any receiver's full dynamic range. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Mike, The Array Solutions device also uses the transformers to increase the voltage at the diodes then steps it back down which means that the diodes are not doing their limiting at 50 ohms. Therefore, your set of 2 series diodes or even one diode each direction is limiting at a higher power level than the Array Solutions device. From the QST article. The transformer increases the voltage level to allow limiting by a pair of back-to-back diodes and then another transformer matches the output to a 50 ohm receiver input. Jim - KR9U -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Mike Waters Sent: Sunday, August 30, 2015 6:23 PM To: mar...@centrum.cz Cc: topband Subject: Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector) That's similar to mine, but mine has two 1N4148 diodes in series, back-to-back, total of four diodes. However, after I did that, I got to thinking that it would be better with only two. Or that there was no need for four. (Don't ask me to explain, it's been a long time since I've thought about that.) 73, Mike www.w0btu.com On Sun, Aug 30, 2015 at 5:00 PM, Martin Kratoska mar...@centrum.cz wrote: Array Solutions offers a 'RX Front End Protector' based on back-to-back 1N4148 diodes. Schematic: http://www.ok1rr.com/public/rxfep.png _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Perhaps common-mode isolation of currents induced in the antenna coax shield?? Charlie, K4OTV Lee K7TJR k7...@msn.com wrote: Hmmm, I wonder why the Array Solutions circuit board picture shows MCL 1:1 transformers. Sounds fishy to me. Even the waveform pictures show clipping at a 1:1 with one diode voltage. Hmmm? Lee K7TJR _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Well, that's certainly true, Lee. I was just wondering aloud, if the transformers were indeed 1:1, if the point might be common-mode isolation like we work to achieve in the transformers of our flag, pennant and KAZ antennas - although in those cases the matching transformer also matches the 50/75 ohm feedline to a higher impedance of 800-1000 ohms. 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Lee K7TJR Sent: Monday, August 31, 2015 12:17 AM To: topband@contesting.com Subject: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector) Sorry Charlie, I don't think I made my thoughts very clear. James was quoting from a QST article that there was an impedance transformation because of the transformers. This was to make a higher voltage at the diodes. My point was that if the transformers being used on their circuit board are 1:1 then there is no impedance transformation and the diodes are fed with the straight RF from the RX antenna at the 50 ohm level. The design must have changed after the QST article or something. The QST description is incorrect if they are using 1:1 transformers as shown in their circuit board pictures. Lee K7TJR _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
Sorry Charlie, I don't think I made my thoughts very clear. James was quoting from a QST article that there was an impedance transformation because of the transformers. This was to make a higher voltage at the diodes. My point was that if the transformers being used on their circuit board are 1:1 then there is no impedance transformation and the diodes are fed with the straight RF from the RX antenna at the 50 ohm level. The design must have changed after the QST article or something. The QST description is incorrect if they are using 1:1 transformers as shown in their circuit board pictures. Lee K7TJR _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)
I believe the point of having the transformers in their circuit is to limit the maximum output. A transformer (ferrite in this case) can only output whatever maximum current determined by the core saturation level. They are relying on this property of the transformers to limit the current into the clipping diodes. I believe it was ICE that came up with this technique sometime way back. The diodes set the voltage level of clipping and the transformers limit the maximum current or power into the diodes. The combination realizes a somewhat soft clipping level with a fixed maximum output. Common mode isolation comes for free along with the design. Lee K7TJR _ Topband Reflector Archives - http://www.contesting.com/_topband
