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Paul Burridge wrote:
Can someone kindly confirm what the hell "IP3" is?? I can only think of "3rd order intermodulation products" which might easily be completely wrong. It would be helpful if whoever first uses an uncommon abbreviation would have the courtesy to state what it meant! (as is customary first time around) snarl, hiss, etc I agree it's discourteous to use an uncommon abbreviation without explanation. But IP3 is a very common abbreviation when discussing mixer or receiver performance, and it's reasonable to assume that anyone more than superficially involved in receiver or mixer design or application has at least heard the term. Or that they can at least do a simple google search. (It really doesn't take any more time than making an angry newgroup posting!) A google search of "IP3 mixers" brought about 2500 hits. I'm sure that if you read one or two of them, you'll get the idea. Roy Lewallen, W7EL |
On Mon, 23 Feb 2004 21:12:44 +0200, Paul Keinanen
wrote: If you have a very high-Q tunable front end filter, you usually get away with a mediocre IP3. However, if wide open (1 octave) front end filters are used, you would benefit from a high IP3 if you are using a decent antenna. If you try to receive the 7000 .. 7100 kHz amateur band in Europe, with 100-500 kW broadcast transmitters every 5 kHz starting at 7105 kHz, the input IP3 number would have to be at least 20 dB higher than the strongest broadcast signals or even 30 dB higher if you try to receive QRP stations. Attenuating the whole antenna signal with a passive attenuator will also rapidly drop the IP3 products, but sooner or later the weak desired signal will be lost in attenuator thermal noise. Paul OH3LWR for 40m band even an SBL1 may be found inadequate and the solution is - as you say - a high-Q input selectivity using a 7040kHz ceramic filter which passes 7,0-7.1MHz within -6dB bandwidth. I've been told that my FT-902 with schottky ring mixer is worse than FT-901 with DG-mosfet 1st mixer, but I have no idea what is the main problem. I tested a mosfet mixer on 136kHz and found it adequate in most respects apart from IF leakage, and ended up with 74HC4066 mixer - used more for reason of being curious about it than that it was really needed, see http://home.online.no/~la8ak/L1.htm , but it couldn't be used on 60MHz as the orignal request was for, it might work on 40M with HEF4013 LO divider on +10VDC. Again you are fed with lot of crop from persons who don't understand the difference between what is optimum and what it the most expensive, so I expect somebody to telll me the nonsense of using FST3125 instead of 74HC4066 without understanding that the latter has almost 6dB higher IP3, and it is more fun to use an inexpensive device in spite of having the house filled up with lot of other better and expensive devices you won't have time to use in a lifetime. 73 JM ---- Jan-Martin, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/ |
On Mon, 23 Feb 2004 21:12:44 +0200, Paul Keinanen
wrote: If you have a very high-Q tunable front end filter, you usually get away with a mediocre IP3. However, if wide open (1 octave) front end filters are used, you would benefit from a high IP3 if you are using a decent antenna. If you try to receive the 7000 .. 7100 kHz amateur band in Europe, with 100-500 kW broadcast transmitters every 5 kHz starting at 7105 kHz, the input IP3 number would have to be at least 20 dB higher than the strongest broadcast signals or even 30 dB higher if you try to receive QRP stations. Attenuating the whole antenna signal with a passive attenuator will also rapidly drop the IP3 products, but sooner or later the weak desired signal will be lost in attenuator thermal noise. Paul OH3LWR for 40m band even an SBL1 may be found inadequate and the solution is - as you say - a high-Q input selectivity using a 7040kHz ceramic filter which passes 7,0-7.1MHz within -6dB bandwidth. I've been told that my FT-902 with schottky ring mixer is worse than FT-901 with DG-mosfet 1st mixer, but I have no idea what is the main problem. I tested a mosfet mixer on 136kHz and found it adequate in most respects apart from IF leakage, and ended up with 74HC4066 mixer - used more for reason of being curious about it than that it was really needed, see http://home.online.no/~la8ak/L1.htm , but it couldn't be used on 60MHz as the orignal request was for, it might work on 40M with HEF4013 LO divider on +10VDC. Again you are fed with lot of crop from persons who don't understand the difference between what is optimum and what it the most expensive, so I expect somebody to telll me the nonsense of using FST3125 instead of 74HC4066 without understanding that the latter has almost 6dB higher IP3, and it is more fun to use an inexpensive device in spite of having the house filled up with lot of other better and expensive devices you won't have time to use in a lifetime. 73 JM ---- Jan-Martin, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/ |
On Mon, 23 Feb 2004 16:12:55 -0700, Jim Thompson
wrote: It's only an "uncommon abbreviation" to certain Brits who think they can learn by insulting the masters ;-) Look up 3rd order intercept point. ...Jim Thompson thought everybody had studied Ham Radio December 77 throughly - even in UK..... 73 ex-G5BFV (at BPO radio station Bearley/SOA) ---- Jan-Martin, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/ |
On Mon, 23 Feb 2004 16:12:55 -0700, Jim Thompson
wrote: It's only an "uncommon abbreviation" to certain Brits who think they can learn by insulting the masters ;-) Look up 3rd order intercept point. ...Jim Thompson thought everybody had studied Ham Radio December 77 throughly - even in UK..... 73 ex-G5BFV (at BPO radio station Bearley/SOA) ---- Jan-Martin, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/ |
In article , Paul Burridge
writes: Since you don't specify anything important like IP3, Can someone kindly confirm what the hell "IP3" is?? I can only think of "3rd order intermodulation products" which might easily be completely wrong. It would be helpful if whoever first uses an uncommon abbreviation would have the courtesy to state what it meant! (as is customary first time around) snarl, hiss, etc Heh heh heh, can't say I blame you for being a bit confused. The "3rd Order" label is due to the mix products of F_a +/- 2F_b with F_b being twice its original frequency. "Order" comes from the constant multipliers, 1 for F_a and 2 for F_b so "1" + "2" equals 3 or the 3rd Order. What happens is that the slope of the "3rd Order" mix product is steeper than the normal F_a +/- F_b (order of 2) equation's power slope. The "3rd Order Intercept Point" is where the two slopes intersect. It is much much easier to show this graphically than in words. The reason for defining intermodulation distortion that way is in that it is simpler and more accurate to test on both the production line and in any test lab of a finished product. The old way had been to just increase the input level and VERY carefully note the output level, especially when the output level slope departed from a straight line (indicating some compression, the start of intermodulation distortion). That old system being very prone to instrument calibration errors led to some arguments between makers and buyers, not to mention non-standard notations of "1 db points" and "3 db points" of distortion relative to input levels. The Mini-Circuits website used to have some mention of the above plus the Avantek website and, of course, Agilent when the T&M division was the original Hewlett-Packard. You might find something on a search for "3rd Order IP" on the 'net that will also have graphs. Len Anderson retired (from regular hours) electronic engineering person |
In article , Paul Burridge
writes: Since you don't specify anything important like IP3, Can someone kindly confirm what the hell "IP3" is?? I can only think of "3rd order intermodulation products" which might easily be completely wrong. It would be helpful if whoever first uses an uncommon abbreviation would have the courtesy to state what it meant! (as is customary first time around) snarl, hiss, etc Heh heh heh, can't say I blame you for being a bit confused. The "3rd Order" label is due to the mix products of F_a +/- 2F_b with F_b being twice its original frequency. "Order" comes from the constant multipliers, 1 for F_a and 2 for F_b so "1" + "2" equals 3 or the 3rd Order. What happens is that the slope of the "3rd Order" mix product is steeper than the normal F_a +/- F_b (order of 2) equation's power slope. The "3rd Order Intercept Point" is where the two slopes intersect. It is much much easier to show this graphically than in words. The reason for defining intermodulation distortion that way is in that it is simpler and more accurate to test on both the production line and in any test lab of a finished product. The old way had been to just increase the input level and VERY carefully note the output level, especially when the output level slope departed from a straight line (indicating some compression, the start of intermodulation distortion). That old system being very prone to instrument calibration errors led to some arguments between makers and buyers, not to mention non-standard notations of "1 db points" and "3 db points" of distortion relative to input levels. The Mini-Circuits website used to have some mention of the above plus the Avantek website and, of course, Agilent when the T&M division was the original Hewlett-Packard. You might find something on a search for "3rd Order IP" on the 'net that will also have graphs. Len Anderson retired (from regular hours) electronic engineering person |
By the way, the topic of third order intercept point is covered very
nicely in _Experimental Methods in RF Design_. As in its predecessor _Solid State Design for the Radio Amateur_ (Hayward and DeMaw), the authors point out that it's not always obvious whether the intercept is at a circuit's input or output, and consequently the importance of specifying which is meant. So in that book, you'll also find the more obscure but unambiguous abbreviations IIP3 and OIP3. Roy Lewallen, W7EL |
By the way, the topic of third order intercept point is covered very
nicely in _Experimental Methods in RF Design_. As in its predecessor _Solid State Design for the Radio Amateur_ (Hayward and DeMaw), the authors point out that it's not always obvious whether the intercept is at a circuit's input or output, and consequently the importance of specifying which is meant. So in that book, you'll also find the more obscure but unambiguous abbreviations IIP3 and OIP3. Roy Lewallen, W7EL |
On Mon, 23 Feb 2004 16:12:55 -0700, Jim Thompson
wrote: Look up 3rd order intercept point. And pay special attention if this is input IP3 (the power of the test tones are measured at the input of the device) or output IP3 (power levels measured at device output). This is especially important, since a typical active Gilbert cell mixer (1496, NE602) have some gain, while a typical diode ring mixer (SBL-1) have a 6-7 dB loss. Paul OH3LWR |
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