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Author Topic: Confused by Sangean 909x Archecture!!?, clarification before a hack.  (Read 495 times)

DIALAMONKEY

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I'm confused by Sangean 909x Archecture, and wondered if anyone could provide any info or avenues to google/investigate?

I like my Sangean 909x despite it's poor performance on SSb, while on FM it is superb.

I wondered if one of the possible contributing reasons might be how the Sangean deals differently with FM and AM signals:

With FM the signal is directly down converted and then A-to-D sampled INTERNALLY in the  SI4735 chip.. the core of the radio

While for AM and SSB the signal goes many several discrete stages (including two IF stages) BEFORE being applied at an IF of 455Khz to the Si4735 chip for further down-converting and A-to-D.

As far as I can understand the SI4735 can easily do ALL the AM/SSB/CW down-conversion and sampling internally without any real need for premixing of an IF.

Does anyone have any ideas why Sangean might employ this strategy for AM/SSB but not FM?

I guess from looking at the architecture it's possible this is done to employ some analogue filtering rather than digital, might there be other reasons?

Any ideas suggestions for this type of archecture?

Architecture pic attached

« Last Edit: August 16, 2021, 06:06:03 AM by DIALAMONKEY »
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HA3FLT

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #1 on: August 16, 2021, 06:23:26 AM »

The answer is in the question: presumably the parameters of the Si4735(-D60) were even worse to use it alone for a AM/SSB receiver. Still, it is seamingly worth to be used as an intelligent, programmable and cheap stereo FM/RDS receiver with some extras, plus an AM IF receiver/demodulator.

Originally, Si4735 is an AM/FM receiver, it is only hacked by writing a third-party firmware to work on SSB as well lately, analog filtering and perhaps a better than 1 kHz tuning resolution might be the reason to the 909 has got a superheterodyne unit before the Si circuit.

AFAIK, even the pin number 1 is wrong on the drawing, it should be the pin 2. :-)

Several years before I have built a nice receiver using this IC, I still have the video of it, but I cannot tell you how good it can be on AM, it was only tried on my bench in the middle of a city, surrounded by thick, RF blocking walls and steel and glass buildings... Anyway, it has dealt with the usual enormous domestic RF noises well, and it was sensitive at least on FM.
« Last Edit: August 16, 2021, 06:26:51 AM by HA3FLT »
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DIALAMONKEY

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #2 on: August 16, 2021, 06:45:34 AM »

Hmm OK that's good info, thanks for the input HA3FLT, I'll look into your suggestions a bit more.

And...yes of course the SSB code must have not been used by Sangean which would require the extra stages.!!

- I had read some where that the SI473XX preforms really well on AM, and I just shelved that info in the back of my mind, unquestioned
 
Yes ha-ha, I did see that it should be pin 2 ;) just updated..
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N6YWU

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #3 on: August 16, 2021, 07:10:15 AM »

My guess is that image rejection was poor for SSB in the HF bands using direct conversion, so they are trying to use an IF filter to improve that one characteristic.
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K7LZR

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #4 on: August 16, 2021, 01:04:30 PM »

I don't own a 909x but I do own an older 909 no suffix and I find SSB performance on that one to be great. But of course it is older and so no DSP anything, all analog.....

Regarding the 909x, I'm not sure why they even bothered with the way it is. In my mind it would have been better to simply employ audio DSP filtering in the low-level audio stages and stick with analog for everything else :).
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N2DTS

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #5 on: August 16, 2021, 05:46:13 PM »

When I see 455 KHz I think IF filtering, ssb is narrow, 3 KHz or less...
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VR2AX

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #6 on: August 22, 2021, 01:03:27 PM »

What exactly is the poor performance on SSB? My 909x works ok on SSB, the resolution is a bit wide compare to ham radio transceivers, but it works.

BTW the current version is 909X2 although the mods seem optical.
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KK4GMU

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #7 on: November 28, 2021, 10:08:39 AM »

Has anyone here who has had earlier 909s tried out the new 909X2 yet?  I read that it is much improved in several regards...

https://www.qsl.net/n9ewo/ats909x2.html
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IC-7100, RSPdx, AT-D878UVII-Plus HT, TGIF Spot

N4SZO

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Re: Confused by Sangean 909x Archecture!!?, clarification before a hack.
« Reply #8 on: February 13, 2022, 09:26:09 PM »

Has anyone here who has had earlier 909s tried out the new 909X2 yet?  I read that it is much improved in several regards...

https://www.qsl.net/n9ewo/ats909x2.html

Yes I own both and I would say the X2 is a noticeable improvement over the original (which is a great radio too) . My seat of the pants thinks that SSB audio is better on the X2 because it picks up less noise and is more enjoyable to listen to without getting "tired" if you know what I mean.
 "
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