| Author |
Message |
    
Snapperhead
| | Posted on Monday, June 03, 2002 - 4:48 pm: | 
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YUP, it's me again.......Hey 307, Taz, anybody.....I'm performing a clarifier mod on my TRC-457. I need a 8 volt power source. I checked IC mounted on right side. but all I found was 7.5 volts on my VOM. Will this do for unlocking clarifier mod????? Or do you know a different location.....Thanks guys.... |
Jyd
| | Posted on Tuesday, June 04, 2002 - 11:39 am: |
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should work |
Taz
| | Posted on Tuesday, June 04, 2002 - 11:39 pm: |
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yes, it should work. the center leg on the final would give you 13 volts. |
Taz
| | Posted on Thursday, June 06, 2002 - 12:51 am: |
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I know motarola engineers who have done that. I never said it would work or he should do it, i just said thats what you can get from it. |
Snapperhead
| | Posted on Thursday, June 06, 2002 - 11:21 am: |
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Hey Guys, Thanks for info, especially Ss8541. Talk about some in depth stuff. I went ahead and did mod on that 7.5v supply. It is off frequency from 12 oclock. And it only has about a 3kc slide down and about a 1kc, not able to slid 5kcs... I'm going to try that part from Retard Shack..7808 8v Reg. Where is the switched 13v source? And where do the .1uf caps go again... Thanks again guys. That's what I like about this forum, Ya just don't get a simple yes or no question answered. But a indepth answer from someone who knows...............73's |
307
| | Posted on Thursday, June 06, 2002 - 4:12 pm: |
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The Source for the 13.8 is the Off/On switch. (First Leg on the 7808) , The center leg is Circuit Board Ground NOT Chassis Ground) and the third leg is an 8 volt regulated output to 1 amp. Use about 100uF EL capacitor to ground on the input side (Leg 1) and use about .1uF Ceramic on the 8 volt side to keep oscillations to a minimum (Leg 3). This will do the trick.
The main reason you can not use the so called Final for power is because there are high voltages there when in the TX mode (RF). Adding a componant will alter the tank circuit tuning and may become unstable plus you will sink the RF to board ground via the echo return.
307
C.E.O Technical Operations
Copper Electronics
tech 307@iglou.com |
Taz
| | Posted on Thursday, June 06, 2002 - 7:08 pm: |
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thanks for clearing that up 307. |
Ss8541
| | Posted on Thursday, June 06, 2002 - 10:51 pm: |
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yes, i put the legs of the 7808 in -any- order, not the correct order. i didn't go indepth with that for the fact that it is on the back of the package. i hope i didn't mislead anyone with that.
as for the high rf voltages at what 307 labeled as the 'so called final'(called f.p.a. -final power amplifier- in all other forms of radio except cb and ham - we have enough sense to just use 'final' for short), it is low impedance, so the voltages are not high. after the 'matching' circuit the impedance is much higher, so the voltage is also much higher. a quick check on an oscope will confirm this. so adding the extra wire will drop the impedance even lower(usually), in return dropping the voltage even lower....but i think you all see what we both are saying, although in different terms.
and taz for your statement about batwing engineers, we all know that there are priest taking advantage of children. and we also know that even though they are doing it, it still isn't right. |
307
| | Posted on Friday, June 07, 2002 - 8:54 am: |
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Yes , we can't go into depth here because this is what happens...I don't mean to burst any bubbles here but 60 to 80 Volts P-P on the direct output lead of a Final/P.A. (Superstar 3900 for example)is Very High. At the Antenna Jack AFTER the tuning is completed you will have about the same IF it is a true matched system. This when driven anywhere near (coupled)into a "toy" with a High Impedance Input can do destruction to a TTL device (Echo Board). I think you may be thinking High is KV or something SS8541.
307 |
Ss8541
| | Posted on Friday, June 07, 2002 - 8:09 pm: |
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307, let me 1st say that i am not here to compete with you. so if you took it that way, i am sorry. i gave plenty of time b4 i replied so you and the other moderators could add your comment/s. when you didn't, i added mine. if you guys do not want me here any longer because i told mr massie i would rather not be a moderator, then let me know through my email that you do not want me here. i answered the email you sent me, but you never replied to my questions, so i had no idea of where we stood. that is the main reason why i declined. i came here because you guys have the largest amount of 'active' forum members. i am just here to give the knowledge and experience that i have. if i was here for anything else, i would have definitely jumped onto the copper moderator deal with or without my questions being answered.
as for your last post no bubble busted here. i'll explain why. the voltages at the finals collector and the antenna port -ARE NOT- the same. the impedance is transformed. along with that comes a voltage and current transformation. if that -was not- the case, a matching circuit would not be needed.
we will use your connex 3900 for the example, in this example it has 4w carrier. the 1969's collector has an rf impedance of about 5ohms(check the manufactures data).
here are some formulas, and 'plug in constants'.
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voltage(rms) squared = resistance x wattage
2.828 is a 'constant' to multiply an rms voltage by to get the peak-to-peak(p-p)voltage.
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so for the finals collector when you plug in the info we know into the formula.....
5ohms x 4watts = 20; the square root of 20 is 4.47(our rms rf voltage) 4.47 x 2.828 = 12.65vp-p. this 12.65v is not a very high voltage, even after full mod it doesn't reach 60-80vp-p. buy it is high enough to do damage as stated earlier.
now at the antenna end we still have 4w but at a 50ohm load.
so when we plug this info into the formula....
50ohms x 4w = 200; the square root of 200 is 14.14(our rms votage at the antenna socket). 14.14 x 2.828 = 40vp-p.
so we now see that there -is- a difference in voltages from the finals collector to the antenna port. over a 3:1 difference(one again, and oscope will confirm this). -anytime- impedance is changed, voltage and current ratios are also changed, while the wattage stays the same. its just like antenna and coax principles. and adding the extra wire here would most likely drop the rf impedance even more, causing your p-p rf voltages to drop just like i stated above. |
307
| | Posted on Saturday, June 08, 2002 - 8:58 am: |
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SS8541..Compete? You can compete with me ANYTIME , I am here to learn as well. Anyways , It does not really matter. I just looked with a scope at the PA Output. I see 40 to 80 V P-P Modulated. IT IS TO HIGH TO ADD A "TOY" to this area. That is the point!
Your Formulas are great and wonderful but most people on here do not understand them. You may want to do what I do on the side for a lot of manufactures. You will get free stuff. Its fun.
As for a Moderator , I would love to have you , but I am not going to dig into my long life history of working small jobs for many CB manufactures and give you a resume. Most if not all the people I have done things for years ago have long left the field except Workman , who is still around. . You obviously know a lot more than me...I am inviting you.
The reason I love this Forum and do many things for free is because I have been with Lockheed Martin for 20 years (Oct 4th) as an RF Engineer and that job supports me very well. I do not make a living off repairing some 60 radios plus a month. The real reason is give and you shall receive.
Case closed. Lets move on...
307 |
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