Friday, August 9, 2013

ARRL Homebrew Challenge 3 radio update: re-use of an old radio chassis

I picked up this old Nemes Clarke receiver at a local hamfest. It is a VHF FM tube receiver.

I then salvaged the chassis of this receiver, removing all internal components and saving those for a later date for re-use in other projects.

Some of these salvaged components included a nice power supply transformer for tube gear, two chokes, and a pair of 10 uF oil capacitors. A number of tubes were pulled out including a few 12AU7's, a full-wave rectifier, and a voltage regulator. Sounds like the beginnings of another vacuum tube audio power amplifier to me....

I plan to use this rack-mount chassis for my homebrew challenge 3 radio. Chassis like these are readily available at local hamfests at very low cost, therefore i believe that it is a valid part to use. Furthermore i believe that we homebrew radio enthusiasts should recycle this legacy equipment instead of throwing it in the trash, sending it over seas to be recycled, or letting it sit on the shelf for decades without use.

read more "ARRL Homebrew Challenge 3 radio update: re-use of an old radio chassis"

Tuesday, August 6, 2013

update on the MIT Prof Ed 1-week radar course: SAR image of Kresge auditorium

Student results from the final day of the MIT Professional Education 1-week radar course, where everyone learns about radar, then makes one, then uses it in a series of field tests.

Shown here is a SAR image using the student-built radar kit of the outside of Kresge auditorium. The railing around the underground garage entrance shows up really well, as does the edge of Kresge itself.

An excellent image for a radar built out of coffee cans.
read more "update on the MIT Prof Ed 1-week radar course: SAR image of Kresge auditorium"

Monday, August 5, 2013

What are these lines I wonder.....?

10 metre WSPR 5th August 2011

I noticed the 10metre beacons were a bit active this morning, first I heard F5ZWE/B (10:13utc) RST 549 , followed by I0KNQ/B (10:18utc) RST 428.

Then I had to go QRT for a few hours

Later in the afternoon I set up WSPR on 10 metres to see if there was anybody about, given the beacon reception this morning.

As luck would have it, on what seemed a completely quiet band ...... the following were put in the log..

 2011-08-05 15:44  MW0MJB  28.126109  -22  1  IO71lu  1  CN8LI  IM63nx  1993  185 
 2011-08-05 17:32  MW0MJB  28.126131  -26  0  IO71lu  1  CT1JTQ  IM57ma  1678  192 
 2011-08-05 16:26  MW0MJB  28.126094  -24  0  IO71lu  1  OK/AD6XP  JN89ff  1541  92 
 2011-08-05 18:28  MW0MJB  28.126082  -27  0  IO71lu  1  DL2ZQ  JO42vj  1013  81 
 2011-08-05 18:16  MW0MJB  28.126103  -13  -1  IO71lu  1  DK6UG  JN49cm  967  100 
 2011-08-05 18:16  MW0MJB  28.126079  -26  0  IO71lu  1  DL8BBY  JO43jb  945  76 
 2011-08-05 20:28  MW0MJB  28.126090  -14  0  IO71lu  1  G3THQ  IO91un  329  94 

Beacon 28.242,7 MHz
Loc : JN02tw
FOIX alt 1205 m asl
What are these lines I wonder.....?
I noticed on the WSPR graph this curved this caused by aeroplane scatter?

I don't know enough about what the WSPR graph represents, perhaps someone can explain what these lines are exactly...

There is a transatlantic flight path just to the North of my QTH ...I wonder if that has something to do with the  unusual WSPR trace...

73 fer now 

Mark  MW0MJB
read more "What are these lines I wonder.....?"

Sunday, August 4, 2013

update on the MIT Prof Ed 1-week radar course: RTI plot of Longfellow Bridge

Student results from day 3/5 of the MIT Professional Ed. 1-week radar course.

Range time intensity plot of vehicles crossing the Longfellow bridge from Cambridge to Boston. This plot shows both the remarkable range of the coffee cantenna radar kit and this student's ability to make a small radar and use it to acquire real measurements.

read more "update on the MIT Prof Ed 1-week radar course: RTI plot of Longfellow Bridge"

20m WSPR report de MW0MJB.

I've been rearranging the shack recently and tonight was the first night that all was back to normal.
I thought why not try out all the connections and cables with a bit of

These past few weeks I 've been thinking  of trying out a cb vertical on the 20m band 
By using a cb half wave antenna I could have a fair chance of WSPR on 20m,and hopefully a quite good antenna  to pick up the beacons on 10metres.......

Still haven't put it up though....
 No rush...  HI.....  :0)

Tonight's WSPR report from IO71LU:
 2011-08-04 21:28  MW0MJB  14.097006  -27  0  IO71lu  1  WB8HWF  EN80sc  5832  290 
 2011-08-04 20:52  W3GXT  14.097142  -24  0  FM19ol  5  MW0MJB  IO71lu  5505  50 
 2011-08-04 20:52  WA3DNM  14.097136  -21  1  FM29fw  5  MW0MJB  IO71lu  5390  51 
 2011-08-04 19:48  CN8LI  14.097030  +8  0  IM63nx  5  MW0MJB  IO71lu  1993  4 
 2011-08-04 19:56  MW0MJB  14.097003  +2  0  IO71lu  1  CN8LI  IM63nx  1993  185 
 2011-08-04 19:38  LA6TPA  14.097067  -31  0  JP54rl  0.02  MW0MJB  IO71lu  1694  222 
 2011-08-04 19:18  SM0IKR  14.097157  -2  -1  JO99cc  1  MW0MJB  IO71lu  1660  251 
 2011-08-04 19:38  OK2SAM  14.097158  -22  0  JN99du  0.5  MW0MJB  IO71lu  1646  287 
 2011-08-04 19:32  IV3DXW  14.097164  -4  0  JN65qq  5  MW0MJB  IO71lu  1508  304 
 2011-08-04 21:20  MW0MJB  14.097010  -30  0  IO71lu  1  IW4ENS  JN54kp  1420  118 
 2011-08-04 20:50  MW0MJB  14.097001  -23  1  IO71lu  1  LB1A  JP50mt  1398  38 
 2011-08-04 20:34  LB1A  14.097099  -19  0  JP50mt  5  MW0MJB  IO71lu  1398  232 
 2011-08-04 19:24  DH5RAE  14.097167  -3  0  JN68pv  5  MW0MJB  IO71lu  1337  291 
 2011-08-04 21:06  SA6BOK  14.097074  -26  -1  JO67pj  10  MW0MJB  IO71lu  1326  250 
 2011-08-04 20:04  MW0MJB  14.097001  -4  0  IO71lu  1  I1-12387  JN44ln  1313  123 
 2011-08-04 20:06  IW2OHP  14.097112  +1  0  JN45lq  1  MW0MJB  IO71lu  1231  309 
 2011-08-04 19:20  M6SSA  14.097033  -26  -1  IO93  5  MW0MJB  IO71lu  325  238

It's about time I tried some PSK31, it's been weeks since I had a look at the waterfall......

Something for the next report maybe.

Might catch you in my psk log...

73 fer now

Mark   MW0MJB.
read more "20m WSPR report de MW0MJB."

Saturday, August 3, 2013

More on The Spiral Challenge

A Homebrew_PCB Yahoo Group User; DJ, suggested that I try to fix my flawed 10 mil Spirals as reported on my previous post. With the aid of a 15 power Microscope I was able to fix each of the "opens". A few were hard to find, but tracing them around-and-around with an Ohm Meter under the Microscope did the trick.

Fixing the trace breaks was a job for very sharp soldering iron and a steady hand. Building a solder bridge at this scale is an interesting process.

The Flaw Fixed with a Solder Bridge
Click Image to Enlarge
The above photo show a typical solder bridge fix. The Tee Pin is included as a pointer and for scale.

Solder Bridge

When all flaws were fixed, each of the trace resistance was measured end-to-end and then between traces:

  • First Trace = 23.4 ohms
  • Second Trace = 23.3 ohms
  • Trace to Trace = multi-meg ohms

The Challenge suggests the resistance should be 18.0 ohms per trace.

While investigating the Double Spiral Challenge, it seemed like my traces were smaller than proposed by the Challenge. But, I did not have anything to verify my PCB Toner Transfer Method fabrication results.

Until, I thought of including a calibrated scale inside of the photos. But alas, I do not have a small calibrated scale, so I decided to use a coin, but it was far to big. Then I hit upon the idea of using an Standard SMD part. The following photo contains a Standard 0805 SMD Resistor, from it a scale can be calibrated and distance measured.

Looking at the circuit board at this Magnified scale you wonder how any electronic device could possible work, with all of its flaws.

I may need to think about this more (later, it is very late at night) and now my thinking is dull. An update will follow.

The Tee Pin, Solder Bridge and the 0805 SMD Resistor
A Side Note: While futzing with my Cell Phone Camera and the add-on Attachment Lens (which was used to take these photos), I inadvertently twisted the Lens into two parts. With only the Lens base part attached, the Lens becomes a much higher power Macro Lens.    Hum, . . I wonder why I did not know that before.


I received the following email from DJ, the owner/keeper of the Challenge, via the Homebrew_PCB Yahoo Group, it is included here for completeness.


Here's a tip: you know the track-to-track spacing is 20 mil (you did say 10/10 pattern, yes?). Given that, you can calculate the actual DPI of the photo (about 4300 dpi for the spot I was measuring). Also measure a track, and you can compute the actual track width (about 9.2 mil in some spots, 7.1 in others).

But simply measuring pixels-of-copper vs pixels-of-space should tell you how close to "perfect" you are.

Your ohms are a little high, some things that might cause that:

* pinholes cause "necks" in the copper which add resistance
* cleaning/scraping/sanding the copper might thin it somewhat
* thinner traces on average would increase it

If you just go by the ohms ratio, it says your average trace width is 18/23 * 10 = 7.8 mil, which sounds close enough.

Did you measure the high ohms between the two tracks?

Also, if you have a flatbed scanner, they're often useful for high-accuracy PCB scans.

read more "More on The Spiral Challenge"

Tuesday evening RSGB 144MHz Activity Contest de GW0LVH

I make it well known that I’m not a contester or for that matter have any interest in that part of the hobby. 
For me a 59 and serial number is not what amateur radio is about.

Anyway I’d been contacted by a couple of friends from my old club, Macclesfield & District ARS, to try and hook up in the RSGB 144MHz Activity Contest that’s held on the first Tuesday evening of the month. 

I was intending to operate in the low power section running 5 watts from my FT-817ND.

Greg, 2WØRXX was on holiday in Anglesey, almost a totally sea path from my location at Dale Airfield and we’d arranged to have a QSO prior to the start of the contest.

    The Cloud SOTA Summit G/SP-015 Xmas 2009.

My 5 element yagi had been packed away since a rather cold & windy outing to activate The Cloud SOTA Summit G/SP-015 Xmas 2009.

The antenna had been subjected to a garden test over the weekend and all appeared fine. 

Of course all was not to be fine once it was up in good time for a QSO with Greg. 

A high SWR was a problem I was unable to fully resolve. I think it may have had something to do with coupling to the wire sheep fence directly below, because the only way I could get an acceptable SWR to transmit was to hand hold the antenna well away from it. 

Saying that the SWR wasn’t that high to compromise its ability to receive and I only heard two stations, both of which were way too weak to even resolve their call signs.

                                             144MHz AC attempt 2 August 2011:

I never heard my other colleague either, Roger  M0GMG, who was operating from the Macclesfield Forest. 
I gave up and went onto 20 metres CW, far more fun.

Initial conclusions, IO71jr is probably not a good location for VHF around the UK, although from my cliff top looking over the sea to the west I had expected to have worked several EI stations.

Perhaps it’s worth another go when I’ve fully resolved the SWR problem.

Charles GW0LVH

read more "Tuesday evening RSGB 144MHz Activity Contest de GW0LVH"