Success!! AO-51 Received!!

This afternoon I ducked up Red Hill on my way home from work to attempt my first reception of a satellite, and I'm happy to say I had success. VK2AY (I think) was heard co-ordinating traffic on AO-51 from all around VK land (I heard at least other VK2s and VK4s). This was done simply from my car with the FT-8900 and mobile whip. I manually adjusted the dial to accomodate doppler. All up I got about 3mins of good clear reception (probably limited more so by my doppler shifting skill) and the S meter even got up to S1 at one point.

I'm very happy with this my first attempt and look forward to trying more and eventually transmitting!!

Oh, I also used HAMSatHD on my iPad for tracking.

Amateur Radio and Satellites

There is a regular section in the Australian Amateur Radio magazine dedicated to AMSAT VK. I see it each month but have generally thought I probably don't have the required gear. However, this month I read a bit more of the detail and started to think, "hey, maybe this is possible!" The claim is that you should be able to make a contact with basic handhelds… So, I'm now reading up in earnest and have even started to monitor the downlink frequencies for AO-51 and ARISS. Further, there's even a cheap yagi design for amsat operation….

Anyway, as I get more happening on it maybe I'll post some more info. But for now, I've joined AMSAT VK in the hope of understanding more.

On a side note, my PA0RDT Mini-Whip is now complete and permanently installed. I hope to post up some photos and details tonight – fingers crossed. 😉 (Oh, and I've added another antenna project to my list, but more on that soon…..)

WSPR Demonstrating IPS Hourly HAP Charts

Well, what a good correlation of observed conditions against the IPS Hourly HAP Charts.

In these images first you can see the HAP chart for Canberra at 0300hrs UTC; the second image is a screen capture showing the signals I'm receiving in WSPR around 0300hrs UTC; and the final image is a map from WSPRnet showing the other stations on 10m.

Basically the HAP chart predicts there should be an opening on around ~10m from Canberra up into Darwin, then the second image shows that I am indeed for 0300hrs UTC receiving a signal out of Darwin; and then the final image shows there's a whole lot of other stations around but I'm not receiving them at all.


(Oh, and this is with my newly completed PA0RDT mini whip – more on that later.)


FSM Sensitivity Improvement Experiment 1

This week-end I finally attempted to increase the sensitivity of my Field Strength Meter (FSM). I originally built it with a 50uA analogue panel meter from Jaycar, but have reported previously that I found it rather insensitive.

I was thinking this was simply due to the 50uA meter having a high resistance of 3,000 ohm. So for an experiment I grabbed myself a 1mA meter from Jaycar which only has a resistance of 200 ohm.

Well, it appears that I forgot that ultimately they're calibrated dials and as a result I found that the change of dial made no different to the sensitivity at all. To try and understand this, I resorted to the maths and all became very clear.

50uA Analogue Panel Meter
Resistance: 3000 ohm
Minimum reading: 1uA

Thereby, the minimum signal strength that will be detected (in uV) can be calculated:
E = IR
= 1e-6 x 3000
= 1e-6 x 3e3
= 3e-3
= 3mV or 3000uV

1mA Analogue Panel Meter
Resistance: 200 ohm
Minimum reading: 0.02mA

Thereby again, we calculate the minim signal strength:
E = IR
= 20e-6 x 200
= 20e-6 x 2e2
= 40e-4
= 4e-3
= 4mV or 4000uV

For comparison, I hooked up the FSM to my digital multi-meter (DMM) instead (as suggested by the original article) for improved sensitivity. I placed the meter on the 200mV range and had a few tests.

And as suggested, there was a huge increase in sensitivity! With the analogue meters, once I was more than about 0.5m away from the unit nothing was detected. But with the DMM in use, I could stand at one end of the house and still make a reading when transmitting with only 1W.

As comparison, the minimum reading I can accomplish with the DMM in 200mV range (seeing it supports 1 decimal place) is 0.1mV or 100uV. This is a significant difference, so let's summarise.


The minimum signal strength that the following meters can display:
50uA Panel Meter: 3000uV
1mA Panel Meter: 4000uV
DMM: 100uV

Changing between the two panel meters almost had no effect – although the 1mA meter is slightly less sensitive than the 50uA meter (opposite to what was expected). On the other hand, the DMM in theory is around 30x more sensitive than the 50uA meter.

Going forward

I'm actually now tempted to find a uV Panel Meter and see how that goes. My understanding is that in commercial radio gear it is much more common for signal strength to be measured by a uV meter rather than an S meter, so this seems like a good idea. However, I know Jaycar does not sell them so I've no idea how hard they'll be to source.

After that, I'll again look at an RF amplifier.

Currently Reading: PICs and PICAXEs

Well, with all my study happening etc. I'm coming across more and more things I want to play with. In this case I've been looking at PICs and now PICAXEs.

But there's a couple of problems:
1) I'm starting to really build up a back log of radio projects now; and
2) I really should try and only focus on technical topics for my exams (which microcontrollers are not even slightly mentioned) as there's still a few items I need to re-visit to really embed.

Oh well, hopefully eventually I can play with these. Maybe once I start building some basic radios I can incorporate these. Maybe for a morse keyer, or a digital read out, or some kind of cool computer interface for either SDR or digital modes, we'll see.

All Ready for the Softrock

Alrighty, today I went back to Jaycar and they'd restocked their flux pens. As a result I now have the last item I need in order to commence work on my softrock. But as per my previous post I also now finally have the items I need to complete my PA0RDT Mini Whip. Seeing I did start the Mini Whip first, I will attempt to apply a bit of discipline and finish that first.

Also, while at Jaycar I grabbed a 1mA analogue panel meter. I plan to substitute this into my Field Strength Meter (FSM) to see what effect it has alone on the sensitivity. This is because I believe the rather low sensitivity is due to the high load of the 50uA meter (it's 3,000 ohm); but this 1mA meter is more than 10x less at only 200 ohm. Hopefully I can easily drop it in and compare – or maybe to start with just some jumper cables. Either way it's a nice easy experiment which will help me understand some theory – always good to solidify theory with practical application.

Depending on the results from that – or maybe regardless – I'll then look at adding a RF amplifier to the FSM. But perhaps I should leave that until I complete the Softrock (and maybe the CMoy that I have the parts for now).