++++++++++++++++++++++ From: "Don Brown" To: "Bob Lewis (AA4PB)" , Subject: Re: [Elecraft] 1N4007 diode question? Date: Sun, 6 Apr 2003 17:54:36 -0500 Hi Do not sub the 1n4007 with a lower voltage diode. These diodes are used as pin diodes to switch RF. The 1n4007 is the only one in the series that have the pin characteristics. Don +++++++++++++++++ From: "Don Brown" To: "Bob Lewis (AA4PB)" , Subject: Re: [Elecraft] 1N4007 diode question? Date: Mon, 7 Apr 2003 09:10:38 -0500 Hi The 1n4000 series of diodes are general purpose rectifier diodes designed for low frequency use primarily 60 Hz power supplies. The construction is the same for the series except the 1n4007. The lower voltage diodes are basic PN junctions and would not work as a RF switch. The 1n4007 however has an extra intrinsic (undoped) layer forming the P-I-N junction. This is, I would guess, is to get the 1Kv PIV rating but it also allows the 1n4007 to work as a RF switch like a true PIN diode The RF characteristics are not specified on this diode because it is not designed to do this type of work it just happened to work out that way and they are very cheap. True PIN diodes work better than the 1n4007 but are more expensive and not as readily available. Elecraft has designed the RF switching to work with the 1n4007 and making substations of different diodes may not work. Other 1n4000 series defiantly do not have the PIN structure so they will not work. Don Brown KD5NDB ++++++++++++++++++ From: "Don Brown" To: Subject: Re: [Elecraft] 1N4007 diode question? Date: Mon, 7 Apr 2003 17:11:04 -0500 Hi Pin diodes act more like variable resistors than diodes at RF frequencies. So think of D2, D3 and D4 in series when turned on and open circuits when turned off. If you replaced one of the diodes with a non PIN type (1n4005) then the other diodes may still provide enough isolation when in receive but I would still replace the diode with the correct type (1n4007) that has the PIN internal construction. Wayne may want to explain this more fully as I am not an expert on this and I am getting my information from several internet sites and the ARRL Handbook. Don Brown KD5NDB ----- Original Message ----- From: To: Sent: Monday, April 07, 2003 4:01 PM Subject: Re: [Elecraft] 1N4007 diode question? > I've been reading with interest the comments about substituting a 1N4007 > with a 1N4005. When I built my K2 I quickly needed a 1N4007 (I now > forget the reason) and got a 1N4005 from the local RS store. I installed > it and it's still there. > > As I recall, the location was on the rear of the RF board (in D2, D3, or > D4). After many hours of operation, I haven't noticed any problems in > T-R switching that might be due to this substitution. > > 73, de Earl, K6SE +++++++++++++++ From: "Don Brown" To: Subject: Re: [Elecraft] 1N4007 diode question? Date: Mon, 7 Apr 2003 19:32:21 -0500 Hi All Ok I must amend my statement on the 1n4007. My curiosity got me to thinking so an experiment was in order. I went out and bread boarded a circuit. It looks like the entire family of 1n4000 exhibit the PIN characteristics. I tried the 1n4001, 1n4002 and 1n4007 at different frequencies from 3 to 40 mHz at 5 volts Pk to Pk and they all work the same with a switching current of about 8 ma. Just for grins I tried a 1n4148 and it does not work at all. It rectifies the RF as you would expect. The 1n4007 passes the RF without distorting it at all. There are several articles on the web that mention that the 1n4007 is the only one in the series that will work as a PIN diode but my tests seem to discount that. So will a 1n4005 diode work in place of the 1n4007 in the K2 possibly, but I would still go back and use the proper part if possible. Don Brown KD5NDB ----- Original Message ----- From: "Don Brown" To: Sent: Monday, April 07, 2003 5:11 PM Subject: Re: [Elecraft] 1N4007 diode question? > Hi > > Pin diodes act more like variable resistors than diodes at RF frequencies. > So think of D2, D3 and D4 in series when turned on and open circuits when > turned off. If you replaced one of the diodes with a non PIN type (1n4005) > then the other diodes may still provide enough isolation when in receive but > I would still replace the diode with the correct type (1n4007) that has the > PIN internal construction. Wayne may want to explain this more fully as I am > not an expert on this and I am getting my information from several internet > sites and the ARRL Handbook. > > Don Brown > KD5NDB ++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'Don Brown'" , Subject: RE: [Elecraft] 1N4007 diode question? Date: Mon, 7 Apr 2003 20:26:03 -0700 I've used a great many silicon diodes as RF switches. That use goes way = back before PIN diodes. All one needs is sufficient bias to keep the diode = either conducting or not conducting, as you desire.=20 Isn't the unique feature of a PIN diode its ability to act as a variable resistor to RF as the bias is varied, rather than rectifying he RF? That capability isn't used in a simple T/R switch like, say, in the KPA100.=20 I just did a quick check and came up with the "CQ Antenna Roundup" book published in 1963 (FORTY years ago!) in which Don Stoner, W6TNS and L.A. Earnshaw, ZL1AAX describe the use of silicon diodes as RF switches with examples in a variety of applications. They were using early silicon = power rectifiers in this application. Ron AC7AC K2 # 1289 ++++++++++++++++++ From: "John, KI6WX" To: Subject: Re: [Elecraft] 1N4007 diode question? Date: Mon, 7 Apr 2003 20:46:00 -0700 A pin diode can actually block RF voltages that are higher than the reverse bias. This is quite true of the 1N4007's used in the KPA100 T-R switch. They would probably work fine with only 20-30 volts of reverse bias. With the 100 volt bias used on them, you have even more margin, especially when driving non 50 ohm loads. -John KI6WX ----- Original Message ----- From: "Ron D'Eau Claire" I've used a great many silicon diodes as RF switches. That use goes way back before PIN diodes. All one needs is sufficient bias to keep the diode either conducting or not conducting, as you desire. Isn't the unique feature of a PIN diode its ability to act as a variable resistor to RF as the bias is varied, rather than rectifying he RF? That capability isn't used in a simple T/R switch like, say, in the KPA100. ++++++++++++++++ To: elecraft at mailman.qth.net Date: Mon, 7 Apr 2003 20:58:52 -0700 Subject: Re: [Elecraft] 1N4007 diode question? From: k6se at juno.com Ron, AC7AC wrote: "Isn't the unique feature of a PIN diode its ability to act as a variable resistor to RF as the bias is varied, rather than rectifying he RF?" ========== I don't know how "rectifying the RF" got into this subject, because it doesn't appear to me to have anything to do with the question. D2, D3 and D4 are all forward biased by a solid (not varying) +8 VDC in the receive mode, while D1 and D5 are forward biased in the transmit mode. An RF signal has nothing to do with this. The low-level RF signal present in this circuit (in either xmt or rcv) certainly will not overcome the 8 volts of bias on the diodes and will not even come close to exceeding the 600-volt peak reverse rating of a 1N4005. 73, de Earl, K6SE +++++++++++++++++++