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ten tec argonaut 5




 
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N2DTS
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« on: January 28, 2014, 11:57:41 AM »

I picked up an Argonaaut 5 because it looks good.
Neat little radio, and it sounds very good (to me) on RX on AM and ssb, even with the built in speaker, the line out sounds very good, as does an external speaker on the radio.
RX audio goes down quite low, at least 50 Hz.

It does not go real wide, 6KHz but the filters (dsp) are not sharp, so it sounds better then it should on AM.
160 to 10 meters, frequency is spot on, its got a variable bandwidth knob, as well as passband tuning.

20 watts pep out, that means 5 watts carrier, and I was surprised to work a bunch of people on 40 AM with good signal reports.

The TX has isssues that I am looking into.
Microphone gain is not excessive (there is a little pot inside you can turn up), mic levels are kind of critical, and something is up with the ALC I do not understand.
Looking at AM modulation on the scope, when I make a tone into the mic, I get a nice 100% in both directions, or very close to 100% positive.
With speech, I only get about 50% positive.
I get a solid 5 watts carrier, and no ALC light, but peak power is down.
Average power is also down on ssb, it seems to run about 10 watts out on the pep meter.
Turn it up and you get into the alc and it starts distorting on peaks.

The radio works by digitizing the audio and processing it in the dsp chip, then does a d/a conversion.
The mic and line inputs seem clean and unrestricted, as does the audio outputs, but as far as the TX goes, jaming more audio in the a/d converter does not equal more output past some point.

The alc works by reducing the output of the 3rd IF before it goes to the power amp, I can not find where it comes from, U7 but I can not find U7 on the diagram.

There are a number of adjustments, one for voltage reference of the output, one for final current limiting, one for final temp feedback (rolls back power if it gets hot).
I marked those controls and tweaked them, I can get more power out, but not more modulation on AM, and the radio distorts at the same point, so I put them back to where they were.

There is an ALC buss, and I was thinking of adding a small cap to smooth it out as a test.
Sine wave looks fine, speech looks bad from a 100% mod standpoint, so I will try smoothing out the ALC and see what it does.

TX audio bandwidth seems quite good for a modern radio, it goes out past 4000 cycles.

Fun little radio to play with, I just wish it worked better on TX.

 
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W1AEX
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« Reply #1 on: February 02, 2014, 12:03:26 PM »

It was working into Connecticut quite nicely this morning on 40 meters Brett. Very easy copy and the audio certainly did not seem low. The mp3 file was recorded with a 9kc receive filter and the screenshot shows how it was looking on the panadapter. Should be a fun AM rig to mess around with!

73,

Rob W1AEX


* n2dts.jpg (137.08 KB, 1137x752 - viewed 543 times.)
* N2DTS 7.285000MHz 2-2-2014.mp3 (2091.02 KB - downloaded 276 times.)
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N2DTS
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« Reply #2 on: February 02, 2014, 03:33:50 PM »

Thanks Rob!

Looks ok and sounds ok.
The signal did not seem real strong, but not bad copy.
It was a fun QSO.

Brett
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N2DTS
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« Reply #3 on: February 02, 2014, 05:15:23 PM »

The micro setup:
http://n2dts.smugmug.com/Ham-radio/i-fQfZ2Gc
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N2DTS
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« Reply #4 on: February 03, 2014, 08:26:29 AM »

Phasing the microphone got me much more positive modulation.
The dsp chip seems to have some sort of built in ALC, when the modulation gets close to 100% negative, it turns down the power, but on AM, that does not seem to distort, or turn the carrier power down, so it sounds good on AM.

On the sdr display localy, the radio puts out quite a bit of garbage around the carrier (no modulation), phase noise, mixing noise, or A/D hash, so it might not be the best rig to feed into an amplifier.
At least the hash would be in the passband though, and not all over the band.
The hash sounds like a hiss, and its not in the audio stages....

 
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N2DTS
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« Reply #5 on: February 05, 2015, 07:39:04 PM »

Been using the Argonaut 5 to listen to AM while I work on projects in the shack, and I think the receive is very nice, very nice audio with an outboard speaker. The built in speaker is not bad, but the radio sounds very good with a good speaker.
It also has a line out, but the built in audio sounds so good I do not use it.
I remember when Ten Tec did not have AM on their radios, and now they seem to have some of the best.
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