| Author |
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Bigbob
| | Posted on Tuesday, August 05, 2003 - 8:30 pm: | 
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Considering the prices of 10 meter(or export)radios base and mobile ARE there any really improved ssb rigs that are triple conversion without having to go to kenwood,yaesu,icom,and the like? |
Alsworld
| | Posted on Wednesday, August 06, 2003 - 1:23 pm: |
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Call me dumb Bigbob but I'm not sure what you mean by "triple conversion".
Not that I can answer your question, but figured I'd step up and say "uhhh.....I'm clueless". I have ideas but I don't want to look any more confused than I already am  .
Alsworld |
Kirk
| | Posted on Wednesday, August 06, 2003 - 3:54 pm: |
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I don't everything that's out there BigBob, but I don't think you'll find any that go beyond double super-het in CB or 10 meter export, etc. Possibly because of the cost and Engineering that is involved would maybe end up to pricey? Just a guess....but I think you'll have to look into Ham Land for that kind of rig. I've got a TS-940 and it's a quadruple super-het. Very nice rx! Of course, it all depends on where the 1st/2nd/3rd stage of IF is....more •••• to think about. But it's fun!! Big HELLO to Alsworld! |
bruce
| | Posted on Wednesday, August 06, 2003 - 10:07 pm: |
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Interesting question ?
ALL "triple conversion" recivers use 3 IF frequencys Ok WHY? well the first is very high some at 70 mhz .... now WHY would you go from 27 up to 70 mhz? IMAGES and birdies is the reason the image of a 70 mhz if is 140 mhz too far to cause a problem ..REMEMBER RADIOS TODAY GO DC TO DAYLIGHT after this VHF IF most convert down to about 9 mhz and some 455 khz for narrow band fm. To avoid images all over this wide band spread you can see the VHF IF with a image 140 mhz away your frount end dosnt have to work very hard. Nothing wrong with a single conversion radio the problem is a single conversion radio with a 455khz if would if tuned to 27.455 could hear either 27.000 or 27.910 a real problem .... by dual converting and using 9 mhz as a first if the same image would be either 18 or 36 mhz probley outside of the bandwith of the rf stage so you would not hear it. The old Currer 1M boasted about triple conversion it used 9mhz 4.5 mhz and 262 khz as if's in some models VERY good design and a top proformer for its ( 1962) day.
A day before crystal filters were cheep enough to put in a cb set all you had was tuned coils inside IF cans and the Q of thoes coils is 1/100 that of a good filter....... so they are VERY wide by todays standards. |
Alsworld
| | Posted on Wednesday, August 06, 2003 - 10:46 pm: |
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Hello Kirk, nice to see you posting here. A big HELLO right back to you! I think you answered my question as well. Thank You. Although I cannot explain it, it at least follows my suspicions relating to high dollar equipment. I should do more homework on the subject, but so busy with other stuff, I figured I'd go the easy way and just ask the basic question. I think I've got the picture.
Good to hear from you again.
Alsworld |
Alsworld
| | Posted on Thursday, August 07, 2003 - 1:13 am: |
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Wow Bruce that was an awesome answer! THANKS!!! Very informative. It's amazing how RF systems work.
Alsworld |
Bruce
| | Posted on Thursday, August 07, 2003 - 10:19 am: |
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DRAWBACK everytime you convert a signal you add a fair amount of noise so except as a sales gimic it would not make much sence on a narrow coverage radio to use more than double conversion. single conversion using a high IF like 9 mhz would work fine except most use one filter at the output of the mixer so now you have a high gain 9 mhz IF amp .... most of the total receiver gain and lots of wideband noise at the detector. Idealy you should filter the bandpass just before you get to the detector but filters cost money.
Now if I was going to build a cb set that would be how i would do it ..... channel guards can be used this way and remember if you feed wide band noise into the detector you will hear it on the audio output if you filter out everything other that the frequency you want weak signals are much more readable......
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