[ARDF] [Iaru_region_ii_rules_and_smartphones] GPS/Receiver

Sun May 13 13:31:41 GMT 2018

Regarding technical issues related to SDR, RTL, and ARDF:

The iPhone app "iSDR" was first released in The App Store in June 2010,
almost eight years ago. It was written to minimize the throughput delay, by
implementing its lower layers in assembly language. I haven't taken delay
measurements in years, but with iPhone 4S technology it measured at around
200 ms. I would guess that has improved somewhat with faster Apple devices.
Whether or not that is acceptable depends in part on your style of hunting:
it will not allow the signal you hear to keep pace with a quick rotation of
a beam antenna.

A direct-sampling detector, that samples the radio signal to directly
convert it to audio frequencies, requires very fast switching. That
translates to high power consumption. For a VHF direct-sampling detector
made with discrete components the current requirements might be in the
range of 100 mA. It would be more reasonable for an HF detector, but still
would be much higher than using more traditional radio technology. The high
power drain could be addressed using hardware designed for use in modern
cell phones, in which case one might also do well to eliminate the cell
phone/tablet from the receiver design. Although I don't think that it is
practical right now, I do think that eventually new hardware components
will allow SDR to be brought into homebrew designs more easily and with
better overall performance.

It has been some years since I experimented with RTL dongles such as Vadim
described. The devices I tested proved to be unsuitable for ARDF. Because
those devices were designed to serve as TV receivers, their sensitivity
suffered greatly at 145 MHz. Also, they sent an 8-bit audio stream, which
greatly limited their dynamic range. Their throughput delay, running on a
PC, seemed to be on par with iSDR running on an iPad: in the 200 ms range.
Also they seemed to be prone to various sorts of intermod. Perhaps RTL
dongle technology has advanced greatly since I experimented with it, if so
Vadim can probably shed light.

I don't think that SDR is likely to prove the answer unlocking broad
interest in ARDF. But I do think that ARDF has serious hardware issues that
must be addressed if ARDF is to become widely adopted.

73,
Charles
NZ0I

On Sun, May 13, 2018 at 2:22 AM, Bruce via
IARU_Region_II_Rules_and_Smartphones <
iaru_region_ii_rules_and_smartphones at openardf.org> wrote:

> Hi Gerald,
>
> I was thinking along similar lines to you.
>
> Charles released a iPhone based sniffer software,  but my understanding is
> he used external ADC as using the sound card proved problematic for  IQ
> sampling. I haven't tried it as I have Android phones.
>
> I was interested in this as a potential STEM (all the rage these days)
> student project, with both hardware and software components. Build the TX
> as well. If something like this could take off, it might be self
> sustaining. Even if only a few ever get interested enough to try ARDF, at
> least the exposure to many happens with minimal club effort.
>
> I measured the detection delay of an SDR play with typical free Linux
> software.  The audio delay was a total of 422ms. This is unusable for a
> hand held sniffer. Mind you, the Linux software would not be optimised for
> minimum delay as that wouldn't be a design criteria ; extra buffering to
> ensure gap free audio always would be more important for a normal receiver
> application. Therefore I'm not sure what delay you could get if you tried,
> but this is then moving away from standard software blocks. Guessing
> 200ms?  Still not good for a sniffer.
>
> A competitor noticed issues in bearings using Bluetooth headphones. I
> measured a couple of modules and that was around 50ms to 100ms end to end
> audio delay.
>
> I'd be interested to know the delay in Vadims Android TV tuner setup he
> mentions.
>
> Even if an SDR can't be made 'fast' enough with delay optimisation,  there
> is still lots of potential using the phone purely as the human interface,
> particularly for an entry level sniffer, and push detection back down into
> the hardware.
>
> Cheers,
> Bruce
>
>
> ---- Gerald Boyd via IARU_Region_II_Rules_and_Smartphones wrote ----
>
>
> Vadim
> I think you are missing the main point here. Every teenager in the US has
> a smartphone. That smartphone can be turned into an ARDF receiver with the
> correct helper hardware. It’s even possible to do software defined radio
> using a front end that provides an I/Q signal. I think I know someone who
> made some software that can do that.
>
> The purpose is not using the smartphone as some AI equipped automatic
> navigation device turns the user into a voice navigated zombie that just
> walks to the fox. After all in the real world that won’t help.
>
> However the smartphone is a platform that every young person in the US
> already has in their possession. Just think if there was a low cost mass
> produced circuit board that would turn that phone into an ARDF receiver
> development platform with a graphic display. Maybe that could attract the
> digital savvy youth into the sport.
>
> They are our future. Time Is marching on. Do we grow are just fade into
> the past?
>
> I have seen this first hand at the hamfest tech presentations.
> Traditional t-hunting  does not attract youth. I think part of the problem
> is the lack of access to low cost equipment problem. Just look at the cost
> of your receiver how many youth has a budget that can buy one?
>
> Another case in point. The software defined radio forums always have full
> packed rooms. Adriano talks have full packed rooms. Why? Because they have
> low cost hardware platforms.
>
> Botton line we need a very low cost easy to reproduce device ( for both
> receivers and transmitters) that enables youth to tray ARDF and radio
> direction finding in what ever format the hosted event may be. A cell phone
> or Pad is a wonderful platform to enable the realization of a low cost
> device that does not need an RF lab to align it. Just need some simple
> helper hardware to turn it into an experimental radio platform.
>
> Do we continue doing the same with no growth?  Or do we change our path
> and come up with a low cost platform and attract new folks (that allows
> experimenting) and maybe will start to see new host venues for national
> championships?
>
> For example I think CW on two meters is the way to go
> 1.it’s simple
> 2. Transmitters are easy to build and low cost. My practice transmitter
> uses a clock management chip and runs on a 9 volt battery for all day.
>
> Field testing this year showed that that mode works using the receiver
> development platform. We already use CW on 80. Let’s come up with something
> that can make  region 2 grow.
>
>
> Jerry
>
>
>
>
>
>
>
>
>
> Sent from my iPad
>
> > On May 11, 2018, at 11:39 AM, Vadim Afonkin via IARU_Region_II_Rules_and_Smartphones
> <iaru_region_ii_rules_and_smartphones at openardf.org> wrote:
> >
> > 1. Allowing smartphone/tablets directly violate ARDF rules as they are
> strictly prohibit "GPS with mapping capabilities"
> > 2. Having GPS and Compass inside receiver will help somewhat, but will
> not move you faster or make you think faster or make navigation decisions
> for you. Moving by straight line without looking at the map is not an
> option, if you have an obstacle on the way - for example lake - by
> following guided line you will hit lake shore and will not find TX. So
> orienteering skills are required anyway.
> >
> > Yes, again - it will hep you at some degree, but will not make you
> Champion if you cannot run ARDF without it. It also will not make you
> Champion if you are not well trained. Or dont have good orienteering skills.
> >
> > Solution would be to have separate categories for those who runs with
> tablets/smarphones, without suppressing engineering minds in what called
> ARDF.
> >
> > ARDF is Radio Sport afterall.
> >
> > 73!
> >
> > Vadim
> > _______________________________________________
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