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Topic Created Posts Views Last Activity
Correct way of tuning an SB-200 Linear Feb 5th 2012, 17:38 7 17,172 on 10/2/12
What is RFI versus QRM? Feb 2nd 2012, 20:06 7 11,535 on 3/2/22

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Correct way of tuning an SB-200 Linear KD4SBY on 10/2/12
WA0CBW - Thanks Bill for your comments. I was asking about the RF output calculation because I always assumed that I would have a 50% efficiency. Turns out I may be a little bit too conservative there. Good! Then my amplifier is working OK.
Yes, I do everything in the CW mode. I prefer to use the Tuner, for I can get an excellent match that way. I adjusted my antenna with a MFJ Antenna Analyser to get less than 1:3 on all bands I use (measured at the antenna site), and the tuner brings it down to less than 1.5 as read with the meter of the Linear at full power. I never tried to hook the linear directly to the antenna, I have to try that sometime. I do not now what the impedance of the antenna is, the Analyser I used did not have the capability of measuring that.
I am on the lookout for a high power SWR bridge, so that I can keep an eye on the Plate current, the RF output and SWR at the same time as I tune up. (Looking at the finals to see if they start to run cherry red is definitely not the way to do it!)
Bernie - KD4SBY
Correct way of tuning an SB-200 Linear KD4SBY on 6/2/12
Thanks fellows.

Quote by KB0HAE
"You should alwayso tune the amp into an appropriate dummy load, never directly into an antenna.

This true in general, but at a certain point you have to connect to an antenna, which unlike the dummy load, might not be 50 ohms.
My question was directed in general. In my case, it is assumed that I have used the dummy load to approximate the settings of the Tuner and Linear for the frequency used.
From what I read from WA0CBW there is no set way to finalize the tuning procedure after you have made sure that there is a good match to the antenna with lower power. Just keep an eye on the input power
What would be a good estimate of the outpout power using the SB meter? If I read a plate current of approx 470-480mA and a HV of 2200V, what is my RF output?
Anyone using microcontrollers ? WB9IXS on 6/2/12
I am in the same boat as you are, I like to be able to use PICs after using the STAMP. The STAMP does not have the amount of ports I like to have and is relatively expensive. I have been on the Microchip's website and got completely overwelmed by the amount of information available. I have not been able to make any sense out of it, and therefore like to get in your circle of "hackers" to see if I can learn that way.
I bought the PICstart3 with the 44pin Demo Board Kit and found out too late that the Demo Board is not what I wanted. Also the CD that came with it, would not load. I have not been able to get the PICkit3 to work at all, I can not find the info how to use it. I had hoped that it would be on the CD, but no such luck.
I have not seen any BASIC for PICs in my searches, just assembly and C. But like I said, there is so much information that I could easily have overlooked it. I prefer Assembly, for I do not know C.
Correct way of tuning an SB-200 Linear KD4SBY on 5/2/12
I recently gotten a SB-200 Linear, and never have owned a linear, am wondering, what is the best way to tune it? In my case I have a IC-718, driving through a SWR bridge the SB-200 , which in turn is connected through a Heathkit SA-2040 Antenna Tuner to the antenna.
I have been told that the best way to tune the linear is to first use the IC-718 at lower power levels and use the antenna tuner to obtain the lowest SWR with the Linear not operating. Then the next step is to switch in the Linear and provide just enough power to it to get the Linear to work so that its meter can be read for plate current and SWR.
Here is where I get vague. Do I go back to the tuner and try to get a better match, or do I first try to do it at the linear, and then tweek up the Tuner for the best SWR on the linear's meter?
Then, when whatever the correct way is done, can I confidently apply full power to the Linear without fear of burning anything up and be assured that the originally determined SWR is constant?
Or do I have to readjust anything?
It is assumed that I keep the plate current within its limits while doing all this.
Any comments?
What is RFI versus QRM? KD4SBY on 2/2/12
I am using the terms "RFI" and "QRM" in trying to distinguish between local generated interference (RFI) and other noise received in a receiver (QRM). The latter can be man made too, offcourse, but is more distant.
The question is, if I have a lot of noise on the band, how can I find out what it is? The assumption here is that with RFI I might be able to do something about it, with QRM it is out of my hands and I have to live with it.
Any comments?

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