| Author |
Message |
    
Silvereagle
Junior Member
Username: Silvereagle
Post Number: 29
Registered: 4-2003
| | Posted on Thursday, July 10, 2014 - 7:23 am: | 
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Having a problem,swr ok and power out ok.My receive drops way down when tied to my ranger 2950dx.What is causing this.I checked the 2 transistors that I saw ,they are ok.Stumped. |
Dale
Senior Member
Username: Dale
Post Number: 2099
Registered: 12-2002
| | Posted on Saturday, July 12, 2014 - 10:46 am: |
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sounds like a bad jumper to amp . take out
the amp and jumper see if recieve goes back
to normal.
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
|
Possum_lodge
Member
Username: Possum_lodge
Post Number: 55
Registered: 5-2014
| | Posted on Wednesday, July 16, 2014 - 9:46 pm: |
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I'm confused, what make and model amplifier are you talking about? What antenna do you have it connected to? The only thing I got out of that was that you have a Ranger 2950DX.
How are you keying the amplifier?
Is there an adjustment for the AGC?
What are you using for a tuner?
What is the ALC set at? |
Possum_lodge
Member
Username: Possum_lodge
Post Number: 56
Registered: 5-2014
| | Posted on Thursday, July 17, 2014 - 7:51 am: |
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My bad, it is a Texas Star 250...
I'm not familiar with Class C Amplifiers.
Technically, they should only be used for CW, not for phone operations..
I would compare them to Doc Brown on Back To The Future, when Doc put a bunch of useless clock parts into a bomb case and told the Libyans that it was a working bomb.,
You would probably be better off putting up a nice beam antenna and forgetting about the amplifier. |
Tech237
Moderator
Username: Tech237
Post Number: 1802
Registered: 4-2004
| | Posted on Thursday, July 17, 2014 - 3:13 pm: |
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Dale - a bad jumper would affect transmit power and SWR too.
Possum-Lodge, unless my memory is getting bad Class C is also good for FM.
Not knowing the amp, I cannot say if it has relay or transistor switching, but if relay you may have dirty contacts on the RX side. Also possible an internal jumper may need to be changed.
Tech237
N7AUS
God made me an athiest, who are you to question his wisdom?
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Dale
Senior Member
Username: Dale
Post Number: 2103
Registered: 12-2002
| | Posted on Thursday, July 17, 2014 - 10:38 pm: |
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hmm good point tech 237.my bad
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
|
Possum_lodge
Member
Username: Possum_lodge
Post Number: 57
Registered: 5-2014
| | Posted on Friday, July 18, 2014 - 5:22 pm: |
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Class C Amplifiers are not DC forward biased. Collector current, IC, flows over significantly less than 50% of the RF input cycle.
Class C amplifiers have a very limited dynamic range (0 to 6 dB) and have a tendency to snap off if the RF input signal is reduced below the rated level.
Pro's
Excellent Efficiency
Compact Size
Multikilowatt Pulse Output Power
Cool Operation
CW, FM, Phase and Pulse Amplification
Con's
Poor Dynamic Range
Cannot Support AM Signals
As my Elmer Marty would say, Amplitude Modulation, when you increase modulation you increase the amplitude of the signal waveform.
When the waveform no longer fits the bandwidth, the remainder of the waveform just spills over into the adjacent band and does no actual work, and he wiggles his finger up and down..
Frequency Modulation - when you increase deviation, the waveform can only get so big and then it clips off the top and the bottom of the waveform. The waveform moves back and forth between frequencies and he wiggles his finger left and right.
Had no one gotten the bright idea that they could get cheap power from using a Class C amplifier on AM, we never would have had all the problems we have had over the last 40 years on CB radio..
Everyone wanting to be the King of the CB radio with cheap power.. |
Dale
Senior Member
Username: Dale
Post Number: 2104
Registered: 12-2002
| | Posted on Monday, July 21, 2014 - 11:31 am: |
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possum i agree with ya on class c amps. imho
i think think only class b or ab should bemade
and im not really sure about class b even
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
|
Moonraker
Intermediate Member
Username: Moonraker
Post Number: 315
Registered: 3-2005
| | Posted on Saturday, July 26, 2014 - 8:27 pm: |
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Possum Lodge, do you realize a Texas Star is not a class C amplifier? The bias circuit is nothing to brag about but it still has one. How are you not familiar with class C amplifiers? Take something that is ab biased, ground the bases of the transistors and you have class C, you should know this. I like how you justify not understanding something because it's below your standards. The rci 2950 you have in your profile causes far more problems throwing spurs on the 10 meter band than the average Joe with a cobra 25 and Texas Star ever will. |
