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Hilltopper mod performance

Charles W. Powell
 

I replaced the audio chip in one of my Hilltoppers last night and hooked it to the signal generator.  -73 dBm - great! -107 dBm, still great.  Then for the more difficult tests.  -33 dBm used to send the radio into its howling squeal.  I turned down the gain at -33 dBm and slowly turned up the RF gain.  So far, so good; no squeal.  So rinse and repeat at 0 dBm.  With the gain at full I couldn't leave the ear buds in place, but no squeal.  Next test: full RF gain with a sudden signal at 0 dBm.  NO SQUEAL.  Now I have to admit that I need to change out the RC combination, but I still don't expect any significant changes in performance.

Just for reference, I don't think input to any of my radios approaches 0 dBm even when my neighbor, 1 mile away, is transmitting at 1.5 kW into his phased arrays pointed right at me.  It's not an RF level you are likely to encounter in the real world.

Dave has come through for us again, making a great little radio even better.

72,

Chas - NK8O

Dave Benson
 



Thanks, Chas!

If you've already got enough audio, you're done- the replacement IC is the 'biggie'

73- Dave


On Fri, Apr 12, 2019 at 7:49 AM Charles W. Powell via Groups.Io <doctorcwp=yahoo.com@groups.io> wrote:
I replaced the audio chip in one of my Hilltoppers last night and hooked it to the signal generator.  -73 dBm - great! -107 dBm, still great.  Then for the more difficult tests.  -33 dBm used to send the radio into its howling squeal.  I turned down the gain at -33 dBm and slowly turned up the RF gain.  So far, so good; no squeal.  So rinse and repeat at 0 dBm.  With the gain at full I couldn't leave the ear buds in place, but no squeal.  Next test: full RF gain with a sudden signal at 0 dBm.  NO SQUEAL.  Now I have to admit that I need to change out the RC combination, but I still don't expect any significant changes in performance.

Just for reference, I don't think input to any of my radios approaches 0 dBm even when my neighbor, 1 mile away, is transmitting at 1.5 kW into his phased arrays pointed right at me.  It's not an RF level you are likely to encounter in the real world.

Dave has come through for us again, making a great little radio even better.

72,

Chas - NK8O

Charles W. Powell
 

I had time this afternoon to complete the audio mod to my Hilltopper 30, by replacing R5 and C22.  It makes an audible difference, putting a signal at -107 dBm from faint to fair.  If i turned the RF gain down to where it is roughly minimum, I could still hear the -107 dBm signal input.  At full gain, it was noticeably louder, meaning there is at an absolute minimum 3 dB of audio gain, and probably more like 6 dB. I didn't measure it but you can hear a difference with a controlled input.  I tried again at 0 dBm to overload the audio.  It was L-O-U-D with the earbuds on the table, but no howl, no squeal, and no feedback.

Tip:  Solder R5 into place from the bottom of the board.  It's easier to get to it and it won't slide down through because its already secured by gravity.  If you are building for the first time it really keeps R5 out of the way of the pushbutton switch standoffs.

72,

Chas - NK8O