A New (Old) Direct Conversion Receiver

For a while now I've been participating in the "QRSS" aspect of the hobby, mainly by streaming my "grabber" or sometimes "grabbers" (I can run two simultaneously if I am feeling keen!).

Each of these grabbers ties up a radio and a PC.   As you may have realised I have quite a number of each of these commodities, a ridiculous number, if you were to ask my wife, but being brought up in post-rationing Yorkshire (though not of such Noble birth), I always felt that tying up a sophisticated multi-band multi-mode transceiver just to stream a Spectrum Laboratory grab onto the Internet was "overkill".

I've been pondering for some time knocking up a direct conversion receiver for, say, 10MHz which happens to be the most popular band with QRSS enthusiast.  I've built a few of DC receivers over the years.  They tend to be fairly "minimalist" devices, and yesterday it struck me in a flash that I have already got, gathering dust on a shelf, a 14MHz single-band receiver built back in the 1980s which would potentially fit the bill.

The receiver in question was dubbed the "RC-14", and was a project featured in Rad Com back in 1987, described as a "beginners receiver".   When built at the time it worked reasonably well, and I reworked it slightly to fit it into on of those ubiquitous die cast boxes as the one which came with the Cirkit (remember them?) kit was rather flimsy to say the least.  In my opinion, the nicest feature of that particular design by Steve Price GW4BWE was the AF stage which featured a nice two stage active low pass filter'  The performance of this filter meant that the radio sounded like a "proper" SSB receiver, when the received signal was strong and in the clear.

It hasn't had a great deal of use since then and it occurred to me yesterday that it would be relatively straightforward to "wavechange" it to the 30m band.

QRSS stations tend to operate around a single 200Hz channel either side of 10.140MHz, and just below the WSPR segment.   In  view of this, simply moving the built-in 14MHz VFO to 10.1MHz would probably not be the best thing to do.  Instead a fixed oscillator on the right frequency would fit the bill, or maybe a "VXO" to give a little more operational flexibility.

Now I haven't got a suitable 10.14MHz - ish crystal to hand at the moment, but as proof of concept I have temporarily modified the radio to accept an external oscillator, and used a synthesised signal generator as that external oscillator tuned to 10.1387MHz instead.   This puts the wanted frequency of 10.14 plus or minus right in the middle of the receiver pass band.  A slight tweak to the receiver's input tuned circuit was all that was needed to get the receiver up and running, and in this way I've been streaming this new (old) grabber receiver onto the Internet all afternoon with satisfactory results.

I am now wondering at the practicability of using this principle as the basis for a two or possibly three band dedicated QRSS receiver.  And so another project is born!

QRSS - And More on the Fascination with Propagation

I would be the first to admit that I'm a bit of an "odd fish".   Regarding my radio on-air activities I am most content just lurking in the background, listening and watching and taking note of what goes on whilst my transmitting activities are very sporadic.

I accept that in a way this is quite a selfish attitude - if all the other enthusiasts in the world did what I did, there would be very little for those like me to listen to!

Thankfully, we are all just that bit different, and the mathematics of probability dictate that the mainstream provides the required fodder for practically all of us.

However what I have learned to do over recent years is to make a contribution to the world of Amateur Radio in another way, by uploading information to the Internet in such a way that fellow enthusiasts can make use of it.

There are many ways of making this kind of contribution, all you need is a computer or computers, an Internet connection, and software which allows the uploading of information automatically.  There are a number of ways of doing this, each serving its own particular niche interest.

One I have been doing for quite a long time now is participating in the WSPR (Weak Signal Propagation Reporting) network.   This is actually one activity in which I make a regular transmitting contribution though that isn't essential.

One I have started to make a contribution to more recently is the self-administered network of QRSS enthusiasts.

For those not in the know, QRSS, which has been around for a number of years is a very slow signalling system, usually our old friend Morse Code but sent VERY slowly, used to modulate very low power (usually less than one watt) transmitters, and the reception of these transmitters is recorded using a suitable piece of DSP-based software, and the screen displays of these programs are uploaded to the Internet where they can be seen by interested parties.   The web pages displaying these are known as "grabbers"  Claudio, I2NDT maintains a web page of links to many of these "grabbers" - he calls it his "Compendium" and I would encourage you to click on the link to have a look.  In QRSS terminology, these low power transmitters are often referred to as "MEPTs" (Manned Experimental Propagation Transmitters) to distinguish them from "Beacon" transmitters, as there are licensing issues with the use of the latter terminology in some parts of the world.

I have built a little web page showing my own contribution to this system which can be found HERE. This will only be active for some of the time, as it does tie up equipment, but when it is active I make an announcement on the "KnightsQRSS" EMailing list, likewise when it is shut down.

I also have on the bench as a construction project a little QRSS transmitter from a QRP Labs (brainchild of Hans Summers, G0UPL) which will hopefully take to the airwaves on 30m very soon.  This will use my alternate callsign of G8LBT which, in Morse Code terms has a more even distribution of dots and dashes, and should, I think be slightly more useful as a QRSS source.

Expect more Blog contributions relating to this fascinating arm of the hobby, and in the meantime if you want to have a look for yourself at "live" QRSS transmissions, I would suggest you dial in either 7.000MHz USB or 10.139MHz USB into your HF receiver, and feed the output into a PC soundcard, and run appropriate FREE software such as ARGO or Spectran (my personal favourite is Spectrum Laboratory by DL4YHF), and see what crawls across your PC screen. www.weaksignals.com/ is one good source, as is DL4YHF's page if you want to download Spectrum Laboratory.

Huff and Puff Stabilisers - they really DO work!

In an earlier post I alluded to the fact that I was building an X-lock by Cumbria Designs with a view to incorporating it into my 30-year-old Yaesu FT-107M as that particular radio has (or had) a bad case of "driftitis".

X-Lock is a software based derivation of the "Huff and Puff" oscillator stabilisation technique whereby the frequency of an oscillator is sampled, compared with a crystal or other high stability reference, sampled again and frequency nudged in the opposite direction to any detected drift.

A couple of sessions with the soldering iron saw the kit completed without any issues, and then followed quite a bit of "circuit-bashing" (study of schematics!) plus reading up of other implementations of X-lock into old equipment.   After all this I had on the back of an envelope a plan for interfacing the two pieces of equipment.

Last weekend I lashed up a test which looked promising, and finally, this weekend the project was completed and I now have an "X-locked FT-107M".

The X-lock fits very snugly into the radio, and all of my interconnections are such that no mechanical or electrical changes have been made, and it could all be removed without a trace, if required.

This will all be written up properly in due course and posted on my web site - here and now isn't the place for detailed explanations, but the following two "Argo" screen grabs illustrate just how effective the unit is on received signals.

They both show reception of the 14MHz beacon IW3ICH and were grabbed withing minutes of each other, one with X-lock controlling the frequency, and the other with just the bog-standard built-in circuitry in control.

The above trace is with X-lock disconnected, in other words how the "vanilla" FT-107M performs even after the radio has been powered for some considerable time.

Now look at the same signal with X-lock in charge :-

I would say that's quite an astonishing result and the screen grabs speak for themselves!

One of my long-term objectives has been to improve the frequency stabilityh performance, if possible of my old radio gear to the point where they could be used without any embarrassment on modern modes such as WSPR, and I would say that the X-locked FT-107M is now "good to go" on WSPR.  I just might try it today ...

JT65-HF - remarkable!

I've been using Joe Taylor's weak signal modes for a while now, mostly WSPR, but recently my attention has been drawn to an interesting spin-off which calls itslelf "JT65-HF".

Clearly many people have been there before me, as there is quite a bit of activity in this mode, which seems to be able to produce quite remarkable and astonishing results.

Having downloaded the software, set it up (easy peasy) and left it running for some hours, the resulting decodes have never ceased to amaze me, given the modest aerial setup I have here.

I presume that much of this is due to the "FEC" (Forward Error Correction) associated with this mode of transmission. Stations such as mine with modest capability therefore stand a good chance of getting their messages through, or conversely can successfully receive weak transsmissions from elsewhere to a remarkably high degree.

I would recommend anyone at least to have a look at this mode, and at what it can do.

WSPR - Low Power Beacons and Beaconing (and snow...)

I'm not sure if the word "Beaconing" actually exists or if I've just made it up. WSPR has been around for a while and as I am enjoying a break from work, and am "excused" household DiY duties on the basis that (a) it's Christmas and (b) it's freezing cold, I have been up to some serious dabbling with my Amateur Radio hobby. My objective this holiday was to get stuck into Eden Valley Radio Society's "Eden 9 Project" - a 70MHz SSB QRP transceiver, and at the moment I haven't made much forward progress, but I still intend to do so. However, WSPR crept into my consciousness again and I indulged myself, and as often happens with these kind of specialist interests, things spiralled off in a slightly different direction to that which I intended. To cut a long story short the unusually cold weather has deposited quite a significant amount of snow on the roof of my house, and the roof of my house is where some of my Amateur Radio antennae are. It is trying to analyse (albeit in a casual, qualitative way) the effect of that snow on the performance of my WSPR set-up which has taken me off in flights of fantasy and let me to the conclusion that the "double helping" of snow has reduced the potency of my WSPR transmissions by around 13 dB, or to one twentieth of what it was before, in layman's terms. Well that is something I didn't know a couple of days ago! In case you don't know what either snow looks like, or indeed a roof, then may I refer you to Snow