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Latest Topics

Topic Created Posts Views Last Activity
power loss in tuner ? Jul 17th, 00:37 3 178 on 18/7/16
questions about AM broadcast band images Aug 24th 2015, 13:20 2 427 on 24/8/15
Use of old laptop power packs ? Dec 28th 2014, 15:30 1 792 on 28/12/14
Strange RFI on 10 meters and 6 meters Jun 19th 2014, 17:12 2 1,001 on 19/6/14
Two important functions missing in new radios ? Feb 4th 2013, 15:16 5 1,667 on 28/2/13

Latest Posts

Topic Author Posted On
power loss in tuner ? AB3FN on 17/7/16
It seems obvious that some power loss will occur in an antenna tuner, and it also seems that many factors determine the loss, e.g. SWR, resistance in the inductor(s) and wiring, frequency, Q of components, etc. Although we could, hypothetically, use high quality instruments to measure the loss in any specific situation, how would the loss be calculated?

For example, assume that we know the frequency, component values, purely resistive losses of wiring, etc., how would we calculate the theoretical loss.

Given today's modern equipment, I doubt losses are high enough to worry about in most circumstances. But perhaps this matters more when running QRP, or when building miniature tuners or matching networks from scratch.

Thanks in advance for your comments, thoughts, guidance.
Lightweight, small HF rig - used Lfox368806 on 1/11/15
Suggest you look at the Yaesu FT-450. Its very compact and lightweight, but is a solid performer and has many features. Used ones are well under $600. The menu system is not too complex, although all radios have their idiosyncrasies.
questions about AM broadcast band images AB3FN on 24/8/15
I want to explore the spectrum below the AM broadcast band. The second IF in my late-model triple-conversion radio is 455 kHz, and I'm getting swamped with broadcast band images. E.g., an AM station broadcasting on x kHz has a powerful image at x-910 kHz. My radio is a modern one, but I live near a large metropolitan area with a lot of AM broadcasters.

Is this a common problem with modern radios? Any comments about specific brands / models? I've had marginal results with a home-brew filter - any suggestions about filters? Of course, I'm only interested in receiving, not transmitting.

Thanks in advance for your comments and suggestions.
Use of old laptop power packs ? AB3FN on 28/12/14
Laptop power packs typically put out 16-18 VDC at a few amps. Is there any obvious problem with using several and putting the outputs in series to get higher voltages ? Is there adequate isolation between the 110 VAC input and the output ? Problems with regulation ? Has anybody done this ? Of course, depending on the specific power packs and the desired output, there might be a need to insert a series resistor or something else to reduce the voltage. Thanks in advance for your reply, insight, and suggestions.
Multimeter Calibration in Atlanta KK4ZWM on 17/11/14
Note that the left-most digit in the display can only be "1". Referring to the operation manual, you will see that the maximum display for the 20 volt range is 19.99. The lab is probably referring to the 20 volt range. This approach was very common with older gear.

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