[Lowfer] Question about SDR Dongle with Win-XP

Mon Oct 8 13:04:07 EDT 2018

Hi Andy,

There are several "moderately-priced" options:

While one of those $20 RTL-SDR dongles may look attractive - and will 
(more ore less) work for LF (if you get one that does "direct" input 
such as the "RTL-SDR.com" sells - AND if you remove the DC power 
insertion jumper as noted in their documentation) the "only 8 bits" of 
A/D conversion is a huge factor.

There are those (more expensive) with built-in "up-converters" (e.g. 
they take LF/HF signals and convert them up to >100MHz) rather than 
using the "direct" mode:  Even though they may have 1ppm TCXOs in them, 
you'll likely see a bit of drift on very narrow-band signals.  Whether 
or not this mixer is good down to LF/MF - or even capable of the dynamic 
range of the device itself depends largely on how well-engineered it 
was.  (I personally avoid the up-converter if it's reasonable to do so.)

While I am (sort of) able to get away with this sort of thing on the 
"AM-160-120M" receiver on the Northern Utah WebSDR, this is possible 
only with with (what is possibly over-the-top) levels of filtering 
coupled with judicious amounts of amplification (see: 
http://ka7oei.blogspot.com/2018/02/managing-hf-signal-dynamics-on-rtl-sdr.html 
)

The upshot is that these dongles are "marginally usable" for anything 
other than the VHF/UHF frequencies for which they were designed - but 
there are a few things that *may* make them usable - particularly in 
light of their very low cost:

- Use a band-pass filter only for the frequency of interest. (Usually a 
good practice no matter what).

- Carefully set the RF input level so that they will "clip" (maximum 
A/D) only occasionally under "strong signal conditions".

- Even more important is to set the level so that under "quiet" 
conditions that you are always "tickling" the bottom 2-3 bits: 
Under-driving (too-low signal) is arguably more deleterious than 
mild/moderate overdriving.

- To do the above, the software needs to have some way of monitoring the 
raw A/D levels as it may not be difficult to find the "sweet spot" - or 
even know if you are over/under driving without it.  I don't know if the 
available RTL-SDR dongle programs for Windows even have this capability.

As for which will work with XP:  You may need to dig around and find 
some old drivers as the current crop of drivers from "Zadig" do *NOT* 
support XP.

* * *

Another option that will probably yield */far superior/* results 
(because of much better RF circuitry and the use of an A/D converter - a 
sound card - with 16 bit depth) would be to use an "Softrock" type 
receiver.  Ones that I would recommend are those from "fivedash.com" and 
there are two to consider:

- The "LF/MF" version of the Softrock Ensemble II.  As a kit it's in the 
$70 range and a pre-built is already available This is a self-contained 
receiver with switchable band-pass filters that can cover from 
130kHz-3MHz - provided that you use a 192 kHz sound card (the local 
oscillator, as designed, doesn't really go much below 200 kHz unless one 
added another divide-by-two and reconfigured the USB interface chip to 
account for that - both of which are easily done, but not well 
documented.  I use this for monitoring the range for monitoring the 
range that includes the 2200 and 1750 meter bands and it works well.

- A modified "Softrock II Lite" receiver, available as a kit for around 
$20.  If your PC already has a half-decent sound card (which will 
probably be only 48 or 96 kHz sampling rate) this may be the most 
economical option. The Northern Utah WebSDR uses this for its 630 meter 
band receiver (a receiver for covering 2200-1750 is available, but 
pending some infrastructure work to allow the installation of an antenna 
that will work <250 kHz) and I have documented how this may be done, here:

http://websdr1.utahsdr.org/info/rx_equipment.html#lf_mf_receiver

This shows the revised input filtering and modifications for these 
receivers to work at 630 and also 2200-1750 meters, including revised 
band-pass filters that are specifically designed for 2200-1750 and also 
630 meter use, being optimized for use with a 96kHz sound card - needed 
if you plan to cover 2200+1750 meters.  (A lowly 48kHz sound card is 
find for 630 meters.)

Not shown in the diagram - but described elsewhere on the above page - 
is how these are interfaced with the $18 "SoftRock" kit (from QRP labs)  
as the local oscillators:  The QRP labs kit can produce up to 3 LO 
signals, so just one of these will produce the two LOs needed for 
2200-1750+630 meter coverage.

The /second/ option (the modified Softrock II Lite) is almost 
hardware-agnostic:  As long as you can find some sort of program that 
will run on your computer and do the audio processing, you will be 
fine:  Older version of programs like HDSDR, etc. work and I've used 
them in the past on XP machines.

* * *

If you have old hardware kicking around, one should not completely 
ignore the possibility of using them with a "ham radio" version of Linux 
(free!) that will do everything you need, and be more "lightweight" in 
its processor and memory requirements. There are some "live boot" (e.g. 
run from a DVD or thumb drive - no need to install to try them out, you 
can install later) "ham radio" distros out there with which one can 
test, but it would require a bit of a learning curve.  There are a 
number of programs in these Linux distros that will work with both 
dongle and sound-card based systems.

I hope that this helps.

73,

Clint

KA7OEI

On 10/7/2018 4:29 PM, Andy - KU4XR via Lowfer wrote:
> Greetings all:
>
> The quickest way to obtain information ... ask those who ARE ... I have a couple of windows XP machines that
> I would like to possibly put back into service as a " Remote Receiver " setup using a Dongle and software..
> As always, I am budget oriented, so, which Dongles, and which Software will work with Windows XP ??
>
> Thanks for information, and 73:
>
> Andy - KU4XR
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