| Home |
| Search |
| Today's Posts |
|
|
|
#1
February 25th 07, 12:01 AM
posted to rec.radio.cb
|
|||
|
|||
Cobra 2010 loses Tx audio
Resistors can have complex impedances, especially film resistors. Carbon
film resistors can get by up to 30MHz or so, and metal film resistors shouln't be used above 10MHz. The problem with these devices is that they consist of a sprial etched resistance material that has a fair amount of reactance as you go up in frequency. Carbon composition resistors are preferable in RF applications, but even their lead length becomes too reactive at higher frequencies. Nowadays, we use 0603 or smaller size components at higher frequencies. 0402 geometry is presently being used at higher frequencies, with 0201 size soon to become the norm. This is what I have been working with for the last couple of years. Pete "Frank Gilliland" wrote in message ... On Mon, 19 Feb 2007 19:12:33 GMT, james wrote in : On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland wrote: +++Conjugate match is needed for maximum power transfer. +++ +++ +++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is +++when the impedances are complex, which isn't always the case. *********** I have found that it is rare in the real world that impeadances are not complex. Outside transimission lines, there is little that is not complex. You just said that resistors have complex impedance and transmission lines are flat. Then again when you conjugate match, the imaginary part of the complex impedances is nulified and you are then left with the real part. Reactances don't just disappear. They create a current between the source and load that must be assessed to see if it is going to cause any problems. Sometimes it doesn't and sometimes it does. |
|
#2
February 26th 07, 01:56 AM
posted to rec.radio.cb
|
|||
|
|||
|
Cobra 2010 loses Tx audio
On Sat, 24 Feb 2007 18:01:09 -0600, "Pete KE9OA"
wrote: +++Resistors can have complex impedances, especially film resistors. Carbon +++film resistors can get by up to 30MHz or so, and metal film resistors +++shouln't be used above 10MHz. The problem with these devices is that they +++consist of a sprial etched resistance material that has a fair amount of +++reactance as you go up in frequency. +++Carbon composition resistors are preferable in RF applications, but even +++their lead length becomes too reactive at higher frequencies. +++Nowadays, we use 0603 or smaller size components at higher frequencies. 0402 +++geometry is presently being used at higher frequencies, with 0201 size soon +++to become the norm. This is what I have been working with for the last +++couple of years. +++ +++Pete +++ ************* And carbon composition should be avoided. They absorb moisture and change resistance with time. I have seen to many 100K carbon comps measue around 60K with time. I would aviod them like the plague. I have worked with chip components for over 20yrs. I stay away from the samllest one unless the board density constraints or the design dictates it. james james +++"Frank Gilliland" wrote in message m... +++ On Mon, 19 Feb 2007 19:12:33 GMT, james wrote +++ in : +++ +++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland wrote: +++ ++++++Conjugate match is needed for maximum power transfer. ++++++ ++++++ ++++++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is ++++++when the impedances are complex, which isn't always the case. +++*********** +++ +++I have found that it is rare in the real world that impeadances are +++not complex. Outside transimission lines, there is little that is not +++complex. +++ +++ +++ You just said that resistors have complex impedance and transmission +++ lines are flat. +++ +++ +++ Then again when you conjugate match, the imaginary part of +++the complex impedances is nulified and you are then left with the real +++part. +++ +++ +++ Reactances don't just disappear. They create a current between the +++ source and load that must be assessed to see if it is going to cause +++ any problems. Sometimes it doesn't and sometimes it does. +++ +++ +++ +++ |
|
#3
March 4th 07, 05:11 PM
posted to rec.radio.cb
|
|||
|
|||
|
Cobra 2010 loses Tx audio
I like to use 0805 series, at higher frequencies, I see 0603 and smaller
sizes being used. As far as carbon comp resistors, they are the best through-hole components for RF, at least up to a certain point. True, they can and do change value over the years, and they can absorb moisture. Pete "james" wrote in message ... On Sat, 24 Feb 2007 18:01:09 -0600, "Pete KE9OA" wrote: +++Resistors can have complex impedances, especially film resistors. Carbon +++film resistors can get by up to 30MHz or so, and metal film resistors +++shouln't be used above 10MHz. The problem with these devices is that they +++consist of a sprial etched resistance material that has a fair amount of +++reactance as you go up in frequency. +++Carbon composition resistors are preferable in RF applications, but even +++their lead length becomes too reactive at higher frequencies. +++Nowadays, we use 0603 or smaller size components at higher frequencies. 0402 +++geometry is presently being used at higher frequencies, with 0201 size soon +++to become the norm. This is what I have been working with for the last +++couple of years. +++ +++Pete +++ ************* And carbon composition should be avoided. They absorb moisture and change resistance with time. I have seen to many 100K carbon comps measue around 60K with time. I would aviod them like the plague. I have worked with chip components for over 20yrs. I stay away from the samllest one unless the board density constraints or the design dictates it. james james +++"Frank Gilliland" wrote in message om... +++ On Mon, 19 Feb 2007 19:12:33 GMT, james wrote +++ in : +++ +++On Sun, 18 Feb 2007 18:24:33 -0800, Frank Gilliland wrote: +++ ++++++Conjugate match is needed for maximum power transfer. ++++++ ++++++ ++++++IMPEDANCE match... for maximum power transfer. A 'conjugate' match is ++++++when the impedances are complex, which isn't always the case. +++*********** +++ +++I have found that it is rare in the real world that impeadances are +++not complex. Outside transimission lines, there is little that is not +++complex. +++ +++ +++ You just said that resistors have complex impedance and transmission +++ lines are flat. +++ +++ +++ Then again when you conjugate match, the imaginary part of +++the complex impedances is nulified and you are then left with the real +++part. +++ +++ +++ Reactances don't just disappear. They create a current between the +++ source and load that must be assessed to see if it is going to cause +++ any problems. Sometimes it doesn't and sometimes it does. +++ +++ +++ +++ |
| Reply |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| A long post on audio for SWL. | Shortwave | |||
| Sony 2010 loses memory, resets itself | Shortwave | |||
| Amateur Radio Newslin(tm) Report 1385 – February 27, 2004 | Dx | |||
| stuff for all hams | General | |||
| FS: Cobra 2010 Base CB | CB | |||
Hybrid Mode
