More hidden treasures

Still searching for lost magazines and some old projects and this weekend I came up with the magazine that had two of my very first projects:

A power supply

Incidentally the schematic had the wrong value on the zener resistor but I managed to figure that one out. I still have the original box were I placed this assembly.

...And the super transmiter....

The schematic:
Luckily for me I never finished this project, I didn't had the transformer and if I remember I connected, just for a quick test, directly to the mains power supply with an half bridge rectifier, of course it didn't worked, there were no return power line but if I had continued I was going for sure to put my finger there.... that would no be very nice to see.
I still have to find the board and components.

The magazine doesn't have a date stamped but some comercials refer that the prices are valid before 15 Feb 1986 so it's before that....

Well it was another weekend and another beach... here's my attempt to make a panoramic image holding the camera by hand and using the panorama script on "gimp" for the first time... sorry for the quality but at least I had a nice beach day.

VHF transceiver box....

Decided that the aluminium box I "found" is going to be used for an VHF FM transceiver, in fact there is going to be an transmitter and a receiver independently, that's due to design. Transmitter is a FM modulated VCO, PLL controlled at the tx frequency and receiver is a 10.7Mhz IF conversion with an Si570 kit VFO.

Its always a problem to make big holes in an aluminium front panel, for pot's and switches a simple drill is enough but for larger holes unless you have a punching machine available there's not many ways of doing this.
Here's the method I use:


First mark the boundaries and start your driller...for cuting the aluminium bettwen holes I used the drill bit edges. Use a lime to round the remaining aluminium....and, voilá, gives a lot of work but it works...sort off..will improve this for final assembly.



Now I am just waiting for the lcd to make the final assembly, probably I will use two different antenas, one for RX the other for TX and I am still developing the 1W VHF output amp for this transmitter.

stay tuned...

Some hidden treasures

For some time I was searching for this box (the one below), I knew I had it somewhere, last weekend I found it. The box was originally intended to make a bench power supply with multiple outputs (I bough at that time all the 78/79XX series of regulators values including for instance the 8V version.) and was built to my specs in a metal craft shop (at that time the closest electronics components shop was 30Km away, now the closest is 88Km..., I am not living in the same place, here is just 5km away). As a bonus I found an aluminum box I had forgot about and probably was to be used also in a multiple output bench power supply. If I recall the cassette player was used for music transmitting on my first ever transmitter...an FM 88-108Mhz one.... not everybody is perfect! Also found a board with some L200 regulators most probably for the power supply.

On the photo bellow you can see part of a schematic (also found) I think was for a school project of an digital thermometer using an temperature sensor, analog to digital converter and 7 segment displays...looking back, I must admire my past work...today I would probably search google... not avaiable in those times, only the local library and some brain power!

The board was an CB amplifier (if I recall), I guess I never finished it due the price of the output transistor, the only component not fitted. I marked the board with 94...so it's 1994... long time before my ham license :)
....I still have to find the board and the valve I had to make an AM (MF) transmiter, I know I have that somewere...that would make my day!

Now, the nice part is I got one "free" box, so why not using it to place another homebrew radio.
Some holes later and some grinding... here's the outcome. If you see the original aspect it was of no good as it was... you can say now it's even worse!
Removed the front panel of the airband receiver (it's only the Si570, the butons and the meter, fited the speaker and "voilá".


Now what shall I do with this...
My idea is to fit my new VHF receiver (the one using an SBL-1) but there's space on the left that can be used for this options, but, I am open to sujestions:

1 - An hf receiver comonly using the Si570 vfo.
2 - The companion VHF transmiter (still waiting for the pll board).
3 - A speaker grill, thus, removing the top speaker.
4 - Some input's and outputs plugs to be used as a test box
5 - A blank plate with a nice logo...

1W VHF Amplifier

..Still hot around here, so no soldering but here are some photos of the 1 W amplifier experiments. The amplifier is the part on the low side of the picture, the spare part is reserved for the PLL, the righ side of the board is the FM oscillator and Tone generator already done.
I have one amperimeter in each transistor to check for transistor drive since I already broke one with excess current.

As soon as I finish the amplifier, will post here the schematic, for now the number of variable cap's is to much but it's the best way to make experiments.

And for those experiencing winter here's another beach photo from last weekend!

Summer and 1W at VHF

Summer is here....so until at least end of August there will be few chances to spend some quality time in the shack (eg: doing soldering). Today at 22H00 there were still 36ºC inside the shack and it's isolated, I wonder if it wasn't.
Anyhow managed to make some more tests on the amplifier for the VHF FM transmitter I am building from my own schematic, since the ones I found were using un-existing components locally or were using dubious components for the function...namely frequency limit. For now I am getting already an impressive 100mW (more or less the test probe accuracy) from a 1.6mW input .... funny is that in the first tests I made (sightly different design) I managed at least 1W output first time (didn't measured exactly but the 1W dummy load was getting pretty warm), unfortunately it was not stable. The 100mW I am getting are "made" at the expense of 2.4W DC power so there's a long way to improve.
I Started from a design including 2n2219A, 2n3866 and a 2n3553 transistors but since the 2n3553 is 3 Eur cheaper than the 3866 (go and figure this one out...) I am now in the second stage of the 3 stage 2n3553 amplifier. Hope to get 1W when the third stage is complete. As always the schematic will be placed here when is fully tested and stable enough... not like many designs found in the internet.
One thing is for sure, you can easily get 1W at HF but to get 1W at VHF is a different story. After the 1W is accomplished the final 5W I want will be using an amplifier module, cheaper than the transistors needed for getting the 5W power mark.
Will continue this story, hopefully in short time...

Meanwhile have a nice summer.. or winter if your live in the southern hemisfere...

This time a photo from last weekend, and hopefully the next one, beach:


p.s. not mine the photo but will take and post some in the future.

Front panel labeling method

Due to time constraints and the hot weather I haven't much possibility to make some soldering's so decided to make some labels since that doesn't involve soldering.
This is my first try on one possible method for labeling, basicaly it's a normal paper (on inkjet printer) print of the labels and then placed on the front panel with transparent paper over them (with glue on one side).

Here's the outcome:




Care must be taken to place the label in the transparent paper so it doesn't fit in an angle as you can probably can spot on some of them.

The print was made with "Openoffice calc" software (a spreadsheet). I learn't only after printing that it's better to fit the cell size to the text size avoiding cutting later the paper so the labels can fit.


Latter will try also with some transparent glue and then some varnish over, that could end on a somewhat more professional look. Anyhow this is a cheap and fast way of giving some more good looks on your assenblies.

VHF Preamplifier with BFR91

Decided to place a frontend preamplifier for my last VHF FM receiver (will post the receiver schematic in the future).

This time instead of using the commun BF981/961 typical amplifier I went to the BFR91 transistor. The BFR91 should be a little more noisier but hell, this is not for tropo or moon bounce, it's just for the local repeater... I didn't checked values but I am sure that for this components values it should be working in class A or near it....

The idea and main schematic is from "PA0NHC" (site is down at the moment so will not place here link), with the usual changes/"extra" component removal (some filtering on the power line):

The 1N4001 if from the main receiver power supply...see the post bellow on the 78XX regulator for a clear understanding on why it's placed there...

The finished product (the preamp is on the top left side).



Well it did improve the reception but will have to make some more tests to see how well it goes. At this time I placed no input filter, just using the output filter before the SBL-1.