Von: "John Douyere" <vk2eta@xxxxxxxxx>
Gesendet: Jul 21, 2011 3:18:25 AM
An: pskmail@xxxxxxxxxxxxx
Betreff: [pskmail] Lightweight, backpack "Pskmailing" - part 2
Hello,
Here is an update regarding backpack portable operations with Pskmail.
I was away last weekend for three days and out of mobile phone range. As usual, obtaining weather forecasts and reporting position and status was of real value to me. Access to email was nice for coordinating skeds too.
And although this time it was not a true portable situation, I needed to get the backpack system tested and ready for a late-October / early-November week-long kayaking trip in gorges and out of phone range.
So what worked and didn't this time?
Distance from the servers (VK2FWW-1 and VK2ETA-1) were a mere 110KM so NVIS again on 80M and 40M. Since it is winter here these bands were quite static crashes free and the links very good.
The efficiency seems very good since the servers moved up to PSK500R on reception with my FT-817 at 5 watts peak. And I have a noise floor of S6-S8 at home with preamplifier ON on 80M.
So the results were much better than in the tests I did with the portable G5RV (300ohms TV twinlead and MFJ portable tuner) in the past.
I suspect that two elements are at play to explain the difference: the efficiency of a tuned circuit versus a balun followed by a T tuner, and the length of the antenna (41M versus 31M).
Being and end-fed antenna the Fuchs is easier to setup too with a simple half filled water bottle allowing easy launches over 5 metres in the air.
So from now on that will be my portable antenna as the weight and volume is much lower than my G5RV setup and it performs better.
Energy wise I have had excellent results with a 3S Lipo battery pack carried in a metal box inside a fireproof charging bag. Usual precautions are required regarding the charging and discharging of these batteries and I use a small RC alarm circuit connected to the equalizing connector to alert me of a low battery condition. This provided hours of "Pskmailing" before recharging with 5AH capacity for a mere 500g of battery weight.
From a Pskmail linkup perspective, I tried two methods of transmitting position reports and status: one the traditional way with a netbook and signalink interface and then with pre-recorded PSK500R, THOR22 and THOR8 messages played from a smartphone into the microphone of the FT-817.
The first method of course worked quite well with PSK500 (down) / PSk500R (up) links happening several times.
The second method with the smartphone playing into the microphone was disappointing in it's results.
I expected at least the fsk modes (THOR in that case) to be quite resilient to distortion and surrounding noise issues but that was not the case.
The sound files were wave files recorded directly from Fldigi and therefore did not have any reduction in quality like mp3 files for example.
So this leads me to my next set of projects as it is not practical for me to carry a netbook at nearly 1KG when I have enough power in my android running HTC desire to do all what is needed.
also, the smartphone is essential as I use it with topographic maps with it's built-in GPS (I use OruxMaps for that purpose) and the weight factor is perfect with these kind of devices. Recharging is done via a hand-wind charger (essential for sun-less days) or a small portable solar pack.
So my objective now is to get a minimum set of Pskmail capabilities in the Android phone to at least report positions and send short messages (in unproto mode at the very least), and to build a low weight audio interface between the FT-817 and the smartphone.
The entire setup should end-up around 2Kg (1.2KG for the ft-817 without battery but with microphone, 0.5Kg battery pack, 300g antenna tuner,0.4Kg antenna wire and audio interface) - smartphone excluded, which is acceptable.
Software wise there seem two options: try go get an inter process communication capability and new modes developed in an existing Android digital mode application. I know of only one at present (Droidpsk) which seems to be working well but is not open source.
Or adapt/develop a combined digital modem similar to what Per mentioned a while back with the work of Franz-Josef Maas (DB3CF). Refer to the email trail below.
I would prefer this last solution as it would remain open source all the way.
Once we have a base with say PSKR modes and maybe some fsk mode (MFSK or THOR) running and the basic Pskmail client functions then we can build more capabilities quite easily.
My first step will be at least: Psk modes and unproto position and message transmission.
For RSID we can initially "cheat" by using pre-recorded RSIDs in wav files to be played (either automatically of manually) before the transmission. For unproto messages this is all what is needed as the presence of a reply from the server means that the message has gone through.
Your ideas and comments are appreciated.
73's, John (VK2ETA)
On Sat, Feb 12, 2011 at 12:31 AM, Per Crusefalk
<per@xxxxxxxxxxxx> wrote:
fre 2011-02-11 klockan 05:20 -0500 skrev Larry Levesque:
> On Fri, Feb 11, 2011 at 06:18:17AM +0100, Per Crusefalk wrote:
> > Hi John,
> >
> > Sounds like a nice setup. I am not very fond of the g5rv but thats just
> > me. I guess if its properly fed then it should be fine.
> >
> > > Maybe you guys can see better solutions. It would have been a great to
> > > have a full Pskmail in my Android phone for that. Java is part of
> > > Android so that should be workable but Fldigi is not available on that
> > > platform.
> >
> > Well, actually fldigi has been ported to java by Franz-Josef Maas
> > (DB3CF). It has a simple UI for testing but runs fine. I have been
> > meaning to get an android phone and make it run under dalvik (the
> > android java runtime) but I still lack a phone to test on.
> >
> > It will require some effort to get it to look nice but it does run in
> > java so the worst should be done already...
> >
> > 73 de Per
> > SM0RWO
> >
> >
> >
> >
>
> And where would we find such a gem??
>
It all started when we figured it would be nice to have the modem part
included in the pskmail client. Franz-Josef did a very nice job of
porting the necessary classes to java, he also built a simple user
interface for testing. I have attached an image of that, nothing much to
see there but it just shows that it does run on java and it works.
At a later stage we decided not to include it anyway as we would then
not benefit from all the hard work done by the fldigi group. But, it
would make a very nice addition to an android phone. With this mornings
announcement from Nokia I will immediately ditch my phone and get an
android device so I would like to see this there as well.
73 de Per
SM0RWO
