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Author Topic: Proper use of an RF Signal Generator  (Read 346 times)

WA4ZYN

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Proper use of an RF Signal Generator
« on: October 27, 2022, 04:57:02 PM »

I hope I don't end up feeling stupid for asking this question, but I'm going ahead anyway just "to make sure."  I have a Kenwood TS-440S that has differences in RF output, varying from band to band.  I have measured the DRIVE level output from the RF unit and found it to vary from very small to "almost normal," depending on the band.  I want to verify that the PA unit is indeed working appropriately.  Can I connect my RF signal generator output to the RF input of my PA unit and test it for appropriate output on each of the bands?  I am assuming I would need to measure the output of the signal generator to make sure that it is the normal drive level the PA would normally "see." Is this a do-able test? Are there any other considerations?

Thank you for your time, and in advance for any and all comments/suggestions.  I just want to do this right and cause no damage.

73,
Francis WA4ZYN
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W1VT

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Re: Proper use of an RF Signal Generator
« Reply #1 on: October 27, 2022, 05:43:44 PM »

Resistive pads are useful for terminating the input and output of the amplifier with well defined 50 ohm loads.
Careful measurements are a good idea unless you are using a quality generator like the HP8640.

Typically the greatest variation in signal levels are from the bandpass filters.  Some filters are lossier than others.  Often more loss is tolerated for better filtering.
« Last Edit: October 27, 2022, 05:46:00 PM by W1VT »
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N7EKU

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Re: Proper use of an RF Signal Generator
« Reply #2 on: October 27, 2022, 07:17:58 PM »

Hi,

Before I did that, I would first comfirm that the bandpass filter switching diodes are operating properly.  Often varying output is caused by burnt out switching diodes...

73,  N7EKU
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Mark -- N7EKU/VE3

KD6VXI

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Re: Proper use of an RF Signal Generator
« Reply #3 on: October 28, 2022, 05:02:50 AM »

Had the exact same problem with my TS440.  Output varied from 100 watts on 160-40 to around 20 on 10.  It was somewhat intermittent.

Took a insulated screwdriver (IF can style) and was moving wires around between the faceplate and the sandwiched boards in the radio.

Voila!  Instantly jumped to 100 watts on 10 meters!!!!  One of the coaxial cables going from board to board was making intermittent contact.  The silver plated connector was tarnished.  Little Tarn-X on a q-tip and my beloved radio was back in operation.  Until the dots, but fixed that too.

Maybe this will help?

--Shane
WP2ASS / ex KD6VXI
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WA4ZYN

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Re: Proper use of an RF Signal Generator
« Reply #4 on: October 28, 2022, 07:30:15 AM »

Thank you for all the suggestions, cautions, and good ideas.  I will carefully go through the suggestions.  I had shelved the 440 for a while out of “overload” from trying to deal with it.  I’m ready to tackle it again, so I thank everyone for the ideas for my next steps.  I really appreciate fellow hams helping me figure these things out as I learn to bring old radios back to life.

73, es tnx agn,
francis WA4ZYN

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KC3TEC

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Re: Proper use of an RF Signal Generator
« Reply #5 on: November 04, 2022, 06:18:15 PM »

The only stupid question out there is the one not asked.
You ask a question in search of an answer and that is the mark of the wise.

The first step in trouble shooting equipment is always check the simplest first.
Nothing can be more frustrating than wasting a lot of time looking for a fault only to find it was something simple you overlooked ( and i'll admit, been there, done that more times than than i want to say ;D)
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