Airband rf preamplifier

Done!

No big deal here, the preamplifier is working... sort of... with the antenna connected to my Kenwood TM-D700 I have S4, with the preamp on in circuit and same antena I have S5, funny is with the preamp in line and no power I have S2, so the last coil in the circuit is a very good antenna!
This results are really subjective...since I have no means to test deeper I have to trust the S-meter...

Bellow the antenna, the circuit in test (with the magic cable adapter) and the schematic.
I changed some components from the original drawing... when I have all boards connected will try to improve the design.

Seting some standards

After some making circuits with different type's of support (including no support) I decided to set myself an standard on PCB experimental board's so everything looks the same.
I buy PCB on 20*30 (cm) chunks so after some complex math....(rest should give 0) I set on 10*6 (cm) which give's me 10 smaller PCB's, enough for a 5 conversion super duper heterodyne transceiver :)







From left to right some of the boards in fabrication process: RF pre-amp (to be brewed), First mixer, attenuator, audio amp.

I placed in each board 2 holes for fixing inside their box.

The cable adapter

...It's monday... not a very good day :) But I had a nice Sunday with lot of brew, so now a little thing for those who are still trying to wake up!
If you're like me, when you need to test something (connect diferent meters) you have millions of adapters and cables for different connectors like bnc to rca to pl to uhf to sma...you name it I/you have :)



Most testing's I do are with BNC and PL plugs so I brew this adapter to use with PL and will brew another to use with BNC (my frequency counter uses BNC)
To do this I used a piece of PCB and with an hacksaw make sone cuts so I can connect the input and output cables and bettwen something I am going to test, this avoids soldering directly on the tester cable.


Above: Ready for testing the attenuator

I think the photos are self explanatory, if you have questions... don't send any email :)

Attenuator, RF probe and some matematics

Made an rf attenuator for an radio front end. I decided on copying values from one of the radios that I like, the FT-1000 (no I don't own part of Vertex :P) so I decided on 6, 12 and 18db attenuation because if it's good to Yaesu it should be good to me :)

Went to an online calculator for attenuators at: http://www.microwaves101.com/encyclopedia/calcattenuator.cfm
and got myself some resistors values... I chose the "Pi" attenuator because.. I like the "Pi" shape...

The values for the resistors are:
Att ----- R1---------R2---------R3
6 - 150.47 ---- 37.35 --- 150.47
12 - 83.54 ---- 93.24 ---- 83.54
18 - 64.40 ---- 195.43 --- 64.40

Schematic is on the pictures or in ascii art:

IN------+-----R2-----+---Out
| |
R1 R3
| |
GND GND



Then was time to test.... how do they do that ?....

Having brewed an rf probe I though... power on a 50 Ohm load gets smaller if we increase attenuation before gets there.... so applied power to an dummy load and measure the voltage across it in the different levels of attenuation...

In the paper schematic is missing the dummy load that is connected to the output of the attenuator pad's; rf probe measures voltage across the dummy load.

Labels in the various parts of the testing...

If my calculation is right, values are this ones:

For 6 Db I got 6.7, for 12 I got 14.17 and for 18 db I measured 22.29.... honestly for something measured with a frequency generator, and all the rest homebrewed, I am quiet happy with the results....I think the values are correct, anyhow I am open to sugestions.



Formula for relation in dB is => "20 * Log (V/V0)"
My V0 is my value without attenuation to the load.

p.s. There are lot's of online calculators here: http://www.educypedia.be/electronics/electroniccalculatorscircuit.htm
case you need further info.

Sound test of the airband receiver

Just a small video (for those who don't believe my word...) It's not airband (which in fact also receives) but packet on 144,800Mhz




I now must add squelch, signal meter, rebuild the pre-amplifier (not working good) and make a beter bandpass filter....and a box :)
IF of 10.7 whas allready set on the Si570 kit.

From DC to Daylight....

I was looking for past circuits built and found my first buildup and secound and third... it was an power supply (on the left image) an batery tester and an FM transmiter (bellow).

The power supply only worked after I correct the initial circuit that came in a magazine, it was something to do with dropdown voltage for an zener that had the series resistor too low, not giving the output voltage wanted.... these were simple circuits but giving lot of fun and a sense of acoumplisment, they were done by the age of 14/15. The power supply box was also made and was part of a school project for one of the electricity lectures.

The batery tester, red for low, yellow for medium and gren for 13.8v











The FM transmiter bellow, range was around 100m from inside the house and with an small wire as antenna.











Probably will rebuild the power supply, after all it's allready a classic... and the 2N3055 used is more tham 20 years of age!

Tuna Fish ( Atum )

Tuna Fish or in Portuguese "Atum" it's one of my favorite fish's ! See the pictures for better understanding....

Some years ago I found the "pixie" an simple transceiver with an simple performance but giving a lot of fun to build....

Some had put the litle transceiver in tobaco boxes or "altoides" boxes... I went a litle further and built the whole station...in tuna can's; the "pixie" (in the center) the tuna power supply (near the cat), the tuna speaker (on the right of the image) and the tuna frequency counter...bellow













The counter is from kd1jv and the pixie design came from the net... similar at: http://www.qsl.net/we6w/projects/pixie2.gif

Never quite make an qso with the litle think but sure was lot of fun....to eat the tuna fish.

Circuit was built, I think, in 2002.

Cat name is "Pipas", is not mine, and lives now in the north part of Portugal hunting birds and sleeping.