Sunday, March 31, 2013


When you try to multitask on a single tread then for sure something gets behind...

Here some projects tested but lacking a proper finish touch:

Light TX and RX pair:

Work's but didn't tried yet with a magnifier glass to increase range.

A BITX 20:

Needs the front panel drilling and now the front end transistor that was needed for another project.

An 6m downconverter:

then used as a test board for VHF receiver using some BITX 20 modules.

An SWR meter board:

..and the "display":

...Still unboxed.

A full HF transceiver:

 Working but never QSO'd. Will change audio path and need to put the low pass filters.

..many other projects still waiting conclusion most of them just need a box...

Think I have "work" for the next decade!

Have a nice week!

Thursday, March 28, 2013

Got this... the mail yesterday:

...thanks to my PayPal account!

Those are 100 units of BB909B from DSI and about 50 (not exactly counted) BB909A from Philips.

The idea is to place them to work on the Speaky band modules replacing original BB409 varicaps that I can't find at reasonable prices.
I don't know if these "replacements" they will work but they were relatively cheap and can always be used for something else.

Here's capacitance versus reverse voltage on the "Speaky" BB409 units :

And here for the BB909 :

  They almost match...

I measure some units received (both BB909A and BB909B) and seem to match the datasheet values, the Philips ones have a little higher capacity than DSI make.

Still in need of the toroids...

Friday, March 22, 2013

Speaky band module expander - issues

....ah... the smell of success.... followed by disappointment... nothing beats the thrill of trying to find the problem without success guaranties!

I was building an expansion band module (for the band module expander...confusing hum?),

 basically a blank band module that will allow me access from outside the radio bandpass and VFO signals

Then I was injecting an external VFO signal and noticed some instability in frequency using the 40m band.
(On the left using the Si570 as external VFO)

After debugging a little bit I discovered the culprit...

 ..the cable linking the two boards, the VFO part, so, for now the solution is simple, if I remove the cable, loosing the extra 5 band expansion I have no problem but I want to know the cause. The next few days I will experiment with cable length and some blindage, strange is that on the 17m band the problem doesn't show, so, I guess is more a capacitive issue than an inductive one given the wavelength difference. Funny is I tried to make the distance between the 2 boards the smallest possible just to avoid this possible issues.... yeah this time I thought before soldering...useless!

Have a nice weekend!

Wednesday, March 20, 2013

Speaky band module expander - rebuilt

Just rebuilt the band module expander boards. Rebuilding allowed me to save some "veroboard" and correct inter-board wiring mistakes I made first time.

 Here's the support for the five extra modules, the first five stay in the radio main-board.

 For supporting to the chassis, used a 90º wood support transformed in double 90º with my special angle maker tool....the hammer! 

Some varicaps are on the way to the shack so I can start building the modules still missing:

I also included, inside, another board for a second audio amp, main amp will  be only for headphones and the computer audio interface:

..still unbuilt..

And here: 2 of my 3 transceivers....none is complete...
 ...but will be some day....

It's a long road...

Saturday, March 16, 2013

Standard diodes for RF switching

This idea of pressing ordinary diodes for RF work is not new, many LED's are working as varicap's, some diodes are protecting antenna front ends, other are working as zener's for transistor biasing and the list can go on...can you imagine that some diodes are even working as rectifiers?!!!...

 Now, this idea come because I have some (8) band modules to build for the Speaky and each module uses 4 PIN diodes, so, that's 32 diodes more than the ones I have... or for the mater, the local electronic shop.

(PIN diode is BA479 on the schematic)

Using ordinary diodes for RF switching is nothing new, many circuits use them.... but are they good? Or just reasonable? I had to test for myself!

Built a small circuit: the diode being tested in series with an 82pF capacitor and connected to an C meter. By placing in series I avoid any possible influence on the meter measuring method by DC blocking with the series cap, anyhow I think the measuring method of the multimeter is by impedance, injecting an alternate signal, and not by capacitor charge.

Here's the measured and computed results from the series association:

Light blue/grey is capacitor impedance above 500 Ohm, less than that and gets to close to the usual 50 Ohm influencing circuit performance. That's the importance of having a very low diode capacitance for RF switching. If signal is of high value it's also needed a diode with high forward current to keep things linear.

So, from this simple test results, and if you go bellow 28 Mhz, the 1n4148 is probably a safe alternative for RF switching. Interesting is also the yellow LED result by would not use it in circuit due to voltage drop.
I don't know what was the issue with the Germanium diodes, didn't investigated further since I was more interested in Si type.

 In the 14Mhz band module I built for the Speaky I used 1n4007 and 1n4148 without noticeable issues, let's see if it doesn't mess things with more modules in parallel.

 Just a side note:
BA479 diodes have an capacity of 0.5pF at 100Mhz (from datasheet), 1n4148 have 4pF at 1Mhz (also from datasheet), so, if you go the VHF side I think the only way is to use real PIN diodes for RF switching. I have to find alternative varicap's and ferrite cores...

Have a nice weekend!

Thursday, March 14, 2013

Reader alternatives

I use google reader service to keep up with blogs and sites I normally follow.
It suits the porpoise and it's easy to work with, plus it's web based so I can keep up with followed blogs/sites as long as I have network access and a browser.

Here's a screenshot when all the news for the day are read:

(no special order in the blogs list, except mine first :))

Now the problem is: Google will decommission this nice web app in July first.

I wonder what software fellow readers use to read blogs/feeds/site feeds.

Of course I could get an XML/RSS parser lib and make a small hosted app for the purpose but time is already short for soldering and I put soldering first in my free time...

I'm open to ideas, preferably web based, but I'm considering also Linux based ones also. So let me know your opinions!

Have a nice day!

Sunday, March 10, 2013

New antenna tuner

Ok, I have enough projects to finish, inclusive my "old" antenna tuner,...

...anyhow decided to rebuild it and re-use the nice box for other projects.
The "new" tuner will get a wooden box, it's cheaper and adds less inductance for the coil. So my only weekend project was to make new L shaped aluminum brackets to support the variable caps.

There's also a new coil made that I need to test.

Maybe during the week I can have more time for other projects in mind.

Have a nice week!

Saturday, March 02, 2013

Speaky band module expander

The "Speaky" comes standard with 5 band module slots, I wanted a little more.

Here's the idea, five original modules in the right and five more on the left.
At this point (on the next photo) I only had soldered the support for one additional module on the left (with my crude 20m module just for testing).

 First live tests when I realized I had incorrectly wired the jumper cables between the two boards:

Still have to rewire the expansion (for the bandpass filter) cable (lower left on the "veroboard").
Also realized I don't need to duplicate all five original support mounts, just need to parallel one of them to the expansion board, sparing some "veroboard" for other projects. Again I went to fast from idea to solder...

Have a nice weekend!