Re: Low Audio, CP2 Proximity sensitivity
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Hi Norbert. Since I was using the RF Probe on my VTVM to get what I incorrectly thought was the peak-to-peak value, I simply used it again. However, this time, I used the formula to calculate RMS to peak-to-peak. As Dennis explained earlier when the matter of smoking the D882 came up, when I set the VTVM to what I thought was 4 volts, if you do the math... 4 x 1.414 = 5.656 then 5.656 x 2 = 11.3 volts peak to peak. Ouch! So I just calculated it out backwards and came up with following: 1.6 v RMS x 1.414 = 2.262 then 2.262 x ?2 = 4.52 volts peak-to peak. So with the RF probe hooked back up to J3 and ground, I backed R1 down until I got a reading on my VTVM around 1.5 to 1.6 volts. For the past two days, D882 has been happy. The heat sink helps tremendously as well.
I tried using my scope, but the trace is so blurry that I couldn't even guess as to where 4 volts would be. The trace was actually taking up the entire space between 0 and 4 volts on the division lines. It has to be rebuilt so it's horribly inaccurate.?
Aaron - N2HTL
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Hi!
Interesting information Aaron, I would not expect the d882 to be tied to the RX side of the circuit. Puzzling indeed, I'll take a closer look at mine tonight. ?
?How did you reset the peak to peak volt output of R1 ? I'm thinking ?more from a new build standpoint. Let's say somebody builds the kit and installs R1 for the first time, how do they make sure R1 is not "factory" set at a level that will let the smoke
out when they flip the switch.?
Keep up the good work
73s
Norbert
-------- Original message --------
From: "Aaron Heverin aaronhev@... [SoftwareControlledHamRadio]" <SoftwareControlledHamRadio@...>
Date: 4/28/2016 10:33 PM (GMT-05:00)
To: SoftwareControlledHamRadio@...
Subject: Re: [SoftwareControlledHamRadio] Re: Low Audio, CP2 Proximity sensitivity
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Gents,
This is indeed a puzzler.. and there's something else I want to bring up on the odd chance that somehow it's related. As you know, I blew out my original D882 output transistor. While I was waiting for the replacement, I reset the peak-to-peak voltage
output of R1 so that I wouldn't smoke the replacement transistor. I also did some testing on the LM386 chip to see if I could improve the quality of the audio as a whole, and if needed, build an outboard audio circuit independent of the 49-er. The results
of this testing aren't in yet... and of course, my 49-er was suffering from very low audio. Yesterday, the replacement D882s arrived from Tayda Electronics. I constructed a pretty nifty heatsink for it... making it large enough to dissipate heat, but not so
horribly ugly and out-of-place looking. With my mod in place, I fired up the radio.?
Now I think I'm a pretty level-headed guy even though I tend to get a little skittish about throwing that power switch for the first time because I don't like letting the smoke out. I also don't always completely understand how a circuit works without
dozens of hours of study and a little help from my very knowledgable friend when I get stuck. But darned if when the 49-er came up it sounded different! I mean, it was loud! Signals were all over the place and I could actually hear band noise for the first
time. I actually made a few contacts with it even though NOW I was only putting out 3 watts of power. Good thing. :-)
So my question is this... is there a logical explanation why the D882 would affect the audio output - or the signal output/input - of the 49-er? I see that the collector (pin 2) of the D882 is tied to C14, then L4 to pin 1 of the antenna connector - which
would be the center conductor of a piece of coax. The base (pin 3) of the D882 is getting fed from the preamp circuit through C-15 with D3 tied to ground. I'm just sitting here scratching my head because I'm stumped on trying to completely understand the preamp
and final part of the circuit and how it could possibly be tied to the RX RF section and the audio chain. But perhaps it's not the audio chain at all that's causing the "low audio" problems folks are having. If the D882 is in line with the antenna jack, and
it's got problems, it stands to reason that the incoming signals are weak and that's what is causing the "low audio."
My 49-er is an entirely new radio. It's darned loud now. I'm just trying to get my hand around a logical reason for it.?
Aaron - N2HTL
On Thu, Apr 28, 2016 at 9:14 PM, Jack Purdum
jjpurdum@... [SoftwareControlledHamRadio] <SoftwareControlledHamRadio@...> wrote:
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Keep us posted...this is a puzzle...
Jack, W8TEE
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In the interim, I've ordered another forty-9er kit from a different supplier. I'm going to check each component and compare the two boards. I'll build the new one and try and still figure out what's wrong with the other..
Steve NS3L
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Aaron
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