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Greetings,

I'm new to this SDR "thing" but would like to try it cheaply and safely. I have some general questions about the RXTX Ensemble:

1) I've seen it referred to as being 2 watts but the web site says 1 watt. Please clarify.

2) None of my computers have a stereo I/O. I guess I could purchase a card for my main computer but would really prefer to use one of my laptops. I'm told that there is a box that converts a USB port to stereo I/O. Does anyone have experience with this method?

3) Is the RXTX Ensemble capable of using the weak signal protocols such as from WSJT?

40 What band grouping do you recommend? I'm thinking 40-30-20 given the sunspot cycle and the size of my back yard - simple vertical with lots of radials.

Thanks for your help,

Dan K8XW

Dan,
It is capable of 2 watts but only 1 watt if you want linearity.
You need a usb sound card for your laptop.
You can use wsjtx but it is convoluted. You first need to use something like HDSDR or PowerSDR to demodulate to audio then use a virtual audio cable to connect the output of that program to wsjtx.
I have the 40-30-20 unit myself. Probably good for upcoming solar cycle.
Gary
W9TD

Gary,

Thanks for your reply.

1) OK, I understand. In the article in Feb CQ the operator was running just CW so 2 watts is OK. I would think that the digital modes don't require linearity too. Am I correct?

2) There's no way to put a sound card in my laptop. Are you saying that one of these external USD-to-stereo audio boxes won't work? Am confused, sorry.

3) OK on WSJT software being convoluted. Is there a simpler way to run FT8? Perhaps that question belongs on a different forum.

73,

Dan K8XW

________________________________
From: [email protected] <[email protected]> on behalf of Gary W9TD <w9td@...>
Sent: Friday, March 12, 2021 2:11 PM
To: [email protected] <[email protected]>
Subject: Re: [softrock40] SoftRock RXTX Ensemble XCVR general questions

Dan,
It is capable of 2 watts but only 1 watt if you want linearity.
You need a usb sound card for your laptop.
You can use wsjtx but it is convoluted. You first need to use something like HDSDR or PowerSDR to demodulate to audio then use a virtual audio cable to connect the output of that program to wsjtx.
I have the 40-30-20 unit myself. Probably good for upcoming solar cycle.
Gary
W9TD

Daniel

1) OK, I understand. In the article in Feb CQ the operator was running just CW so 2 watts is OK.

I've never got much more than 1 watt, do not expect more.

2) There's no way to put a sound card in my laptop. Are you saying that one of these external USD-to-stereo audio boxes won't work?

You are describing what is normally called a USB "Sound Card" or just USB audio, it must be stereo.

3) OK on WSJT software being convoluted. Is there a simpler way to run FT8?

No. You must use SDR software. It has to be connected to WSJT-X or whatever by a virtual audio cable.

Details

73 Alan G4ZFQ

Just to put my 2 cents in here. I would recommend starting with the 80 meter version. That version, with the correct filters will work on all bands. I bought the 40 meter one, and 80 meters has reduced output because the transformers are not designed to cover 80 meters. The filter designs are published, so you can easily build them for other bands.
As far as audio is concerned, I use the Startech USBAudio2D device. It has a stereo input, for the Xmit input audio and the IQ output. For the microphone in the speakers I use a Trechrise USB device. Beware however that many motherboards do not have the resources to support 4 usb audio devices. If you can use the audio on the motherboard, with the Startech it should be oK.

You should only use Softrocks on the bands that they were designed for and avoid using the 'stretch' bands. That's because the interstage transformers are tuned to specific bands and are essential for eliminating intermod products. Using a Softrock outside of it's designed frequency range, while it may function, it's likely not meeting the -43 dBc spurious emission spec which might be OK with a 1 watt transmitter but starts to become an issue if you amplify the signal.

The ASUS XONAR U5 us an excellent 192kSPS USB sound device if you can find one.

73,
Jim WA2EUJ

They are readily available, New or used.

--
Forsan et haec olim meminisse iuvabit

Regarding # 2, I would highly recommend the Creative Soundblaster X-Fi
SB1095 USB sound card. There are many places on internet selling it. Do a
Google search for Creative SB1095. Typical price is around $80. It will do
96 kHz bandwidth. I like the unit so much that I listen to music through
high-quality headphones with it all the time.

73, Zack W9SZ


On Fri, Mar 12, 2021 at 12:45 PM Daniel R <roedj@...> wrote:

Greetings,

I'm new to this SDR "thing" but would like to try it cheaply and safely. I
have some general questions about the RXTX Ensemble:

1) I've seen it referred to as being 2 watts but the web site says 1 watt.
Please clarify.

2) None of my computers have a stereo I/O. I guess I could purchase a card
for my main computer but would really prefer to use one of my laptops. I'm
told that there is a box that converts a USB port to stereo I/O. Does
anyone have experience with this method?

3) Is the RXTX Ensemble capable of using the weak signal protocols such as
from WSJT?

40 What band grouping do you recommend? I'm thinking 40-30-20 given the
sunspot cycle and the size of my back yard - simple vertical with lots of
radials.

Thanks for your help,

Dan K8XW

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<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

I have had excellent results with this USB soundcard, in the 96 kHz mode:

73 Alex VE3NEA

Jim:
In a direct conversion system, the only intermod products are between the modulating audio and the carrier. Interstage transformers cannot filter that out. For a push pull output stage, the strongest harmonic is the 3rd harmonic, which as a rule of thumb is -10dB or more from the carrier frequency. As long as the LPF is designed to suppress the 3rd harmonic by at least 33 dB the system is usually withing spec. A 5 pole Chebychev 1% ripple is more then adequate. Of course you need to validate the performance with a spectrum analyzer.

The ASUS is certainly a better USB adapter fir the application then the one I mentioned, but it costs 3x as much, more then the RXTX is you buy it new.

Howard

"In a direct conversion system, the only intermod products are between the modulating audio and the carrier"

This is only true if the system uses linear mixers and sine wave LO's. The massive harmonic content created by using square wave LO's and analog switched requires filtering before amplification. If the 3rd harmonic of the output of the mixer isn't at least 15-20dB down prior to amplification the intermodulation products will be significant. Even with proper filtering the LO feedthru and image products are smaller than the intermodulation products, as seen in these SA plot: