Monday, January 31, 2011

ATV...a blast

Couldn't wait for making some ATV tests so with cables connected in the air and the transmitter still outside a proper box, here we go..... got some "interference" in the satellite receiver (the antenna was only the input cable end), but not a steady image. Fired up the TM-D700 and was receiving (I checked for audio) a little bit outside the supposed frequency so I have to check dip switches settings...

Some more tests and then one of the loudest bang's I ever heard... in the first microsecond I tough the television set had fall to the floor... a quick head turn an hell break loose, lot's of smoke coming from the back of the TV set, a quick response (I am used to it, almost a pro on this subject!) and I turned off the tv.... now it's just a matter of letting the window stay open for a while to remove the smoke.

here's the video on the smoke, unfortunately I wasn't recording the initial explosion but I am considering a closed circuit recorder just for this emotive moments...:


I love when things I just have to find another tv...and recover some components on this one, I am sure it was something in the HT part.

Getting ready for ATV

Not much spare time to be in the shack soldering so decided getting started on ATV, at least getting ready for ATV.
After, I think, 6 years in the same place without use I fired the satellite receiver that will allow me to monitor the transmitter signal. I works connected to an old 8 channel color TV with front panel tuner (do you remember those?).
Still have to connect the camera (an old video conference one) to the transmitter... and then test...

Here some photos on the setup:

The transmitter (freq. set by dip switch)

Receiver, camera, sat LNB and sat signal meter:

The LNB was just for testing, not needed on my setup since the transmitter is on the 1.2Ghz band.
The signal meter was of great help when I helped some friend's installing satellite dishes.

Configuration of the satellite receiver

Just have to connect some power cords and I will be on "candid camera"!

Saturday, January 29, 2011

Antenna experiments - coffee caps

First let me tell you I am not affiliated in any way with the coffee capsules brand reported here (Nespresso). Neither I like closed format or standards.... from what I can tell this experiment could had been realized with the use of any other brand of coffee (Nexpresso is a proprietary format....whatever!)!

Basically I wanted to see the influence of capacitive elements in antenna impedance values. The antenna is just a vertical element of around 50cm (1/4 wave on 144Mhz band) and no ground plane was made except that the meter body acts as such (more or less).
Here the 2 versions with and without the capsules:

Capsules were randomly distribute over the element and are made of aluminum (were empty since I drink the coffee)....

Now the obtained values with the MFJ analyzer: the "scientific" fact is that coffee capsules can lower your antenna SWR.

Have fun!

p.s. I promises one of this days I will make a more mathematical analysis on this subject but for now this is amateur radio...

Saturday, January 22, 2011

YALNBI (Yet Another LNB Internals!)

I have another LNB laying around and decided to find if I can find a MMIC MAR-6 or other similar device inside.

This LNB is for 10.7 to 10.86 Ghz and 11.8 to 12.75 Ghz reception. Output is 950 to 2050 and 1200 to 2150 Mhz.
No luck on the MAR-6 but I found some references worth future investigation.

References are:

EXI : function as amp or buffer...
C1H: probably is a mixer or buffer amp
D: Amp
K: Amp
..have to find an SMD cross reference list...

For now I am not going to experiment higher than 440Mhz...but I want to do an GPS external amplified antenna hence the need of a MAR-6 device, or something similar. I have an old GPS receiver that was powered on last time in 2005 and want to do some experiments with NMEA output. If it had "PPS" out I could use it to an reference oscillator, oh well, can't have it all

It took more than 15' to get an accurate position (on clear south faced sky), after that it lock's faster but it's not state of the art for 2011, it works.

Saturday, January 15, 2011

LNB internals

In the shack, siting for more than 5 years lays an ATV transmitter. It's assembled in form of a pre-mounted kit and should work, but I never tested. It's companion is an old video camera and a satellite receiver for transmission test. Honestly I bought that just for having ATV capability but no real need. Now I decide to slowly getting ready for ATV. The analog satellite receiver for transmission monitoring comes with it's own LNB and I decided to have a look to try to learn a little more on this small length wavelengths.
On to the dis assembly:

A closer look:

The fist thing noted was the big screw on such a small package (low right side), before removing it I thought it sould be some mechanical protection for a dissipator or EMC protection but even so it was to big for the purpose...
let's open a little more:

WTF? A piece of ceramic, this is new for me...

Now after some searching on the internet and some obvious conclusions (the antenna is quit obvious) here's what I found about this circuit:

1 - Horizontal antenna
2 - Vertical antenna
3 - Fet amp (I was hopping for a MAR something...)
4 - Fet amp
5 - LM324 : Still didn't found yet the porpouse
6 - Filter
7 - Fet Amp
8 - LM555: Maybe for negative voltage to the Fet amps
9 - Filter, looks like a bandpass
10 - LM7806: Voltage regulator
11 - Mixer and amp togheter? it's a metalic case in the unserside.
12 - DRO (Dielectric Resonator Oscillator): It's the oscilator and the screw should be for fine tuning at the factory

There's a lot more on LNB uses and info you can read here: (especially the excellent first link pdf)

On other subjects:
Still didn't received any UHF signal om the UHF-VHF converter (a previous post)...well.. neither the TH-F7 used for monitoring the bands, looks like that UHF it's sparse around here. But I did received some WFM transmissions.... 40 + 88-108 = 128-148... bloody broadcasters...

Friday, January 14, 2011

Variable capacitor idea

I have seen some designs of homebrew variable capacitor, one of my favourites is the piston type using copper tubing and coaxial cable. Why? Well it looks from the mechanical point of view the simplest to make and the most forgiving to mechanical tolerances.
Said that, here's some tests I made thinking in building one of 300pf for a long waiting antenna tuner project.

Movable part will be the coaxial cable... well correctly speaking it depends on your reference point of view...

I only have to found a smaller diameter cooper tube since this one used for tests leaves a 1mm gap to the coaxial cable and I want a tighter tolerance.
Only have to and build 10 similar pieces to get the expected capacitance.

Wednesday, January 12, 2011

On an LC Bandpass Filter for receivers… in PHP

Yesterday I was reading "" blog and there was a nice piece of software code for an LC bandpass filter design, the code was in Python and although it can run on my computer decided to convert it to PHP as an relaxation exercise...

Here's the result of the quick hack on the original code, I named it lcbandpass.php.


#!/usr/bin/env python

# An simple program to compute the value of components needed for a
# Doubly Tuned Circuit LC filter that can serve as a bandpass filter
# for homebrew receivers. The equations come from the sidebar equations
# presented in EMRFD (I have the first edition, where it appears on page
# 3.14)
# Written by Mark VandeWettering
# changed (lousily) to php by Ricardo - CT2GQV

// from math import sqrt, pi

// edit bellow to suit your needs...
$F = 7050000; # frequency of operation in Hz
$B = 100000 ; # bandwidth
$R0 = 50; # load resistance
$L = 0.000001156; # inductance of the two coils
$Qu = 250; # "Q" of the coils, approximate
// end edit

$k = sqrt(2)/2; # I hardcoded the Butterworth filter equations
$q = sqrt(2);

$pi = 3.1415927; // I think...from memory

$omega = 2.0 * $pi * $F ;
$c0 = 1. / ($omega * $omega * $L) ;
$c12 = $c0 * $k * $B / $F ;
$qe = ($q * $F * $Qu) / ($B * $Qu - $q * $F) ;
$ce = 1.0 / ($omega * sqrt($R0 * $qe * $omega * $L - $R0 * $R0)) ;
$ct = $c0 - $ce - $c12 ;

$breakline = "\n";
// use br for the web...

// Work nice only on fixed size font terminal.
echo" CE C12 CE";echo "$breakline";
echo" +---||---+---+---||---+----+---||---+";echo "$breakline";
echo" | | | | | |";echo "$breakline";
echo" < ( | ( | <";echo "$breakline"; echo" > R0 ) L - Ctune ) L - Ctune > R0";echo "$breakline";
echo" < ( - ( - <";echo "$breakline"; echo" > ) | ) | >";echo "$breakline";
echo" | | | | | |";echo "$breakline";
echo" V V V V V V";echo "$breakline";
echo "$breakline";

// no rounding was provided in the output...
$F = $F/1000000; echo "F = $F Mhz $breakline";
$B = $B/1000000; echo "B = $B Mhz $breakline";
echo "R0 = $R0 ohms $breakline";
$L = $L * 1000000; echo "L = $L microhenries $breakline";
$c12 = $c12*1000000000000; echo "C12 = $c12 pf $breakline";
$ce = $ce*1000000000000; echo "CE = $ce pf $breakline";
$ct = $ct*1000000000000; echo "Ctune = $ct pf $breakline";


Run it on a terminal with the command: php lcbandpass.php (or: php yourfilename.php) and this is the result:

The original post and software is at:

Sunday, January 09, 2011

Simple UHF converter

Found this schematic on the web and decided to print it for testing "one of these days"...well it was now.

It works when tested in the shack with the HT about 2m from the receiving antenna but I didn't tested in real life condition since there's not much UHF activity around. Anyhow, don't expect a super performance but an acceptable for the complexity it shows...

The coil was wound on a plastic wall plug about 6mm diameter with 22 turns (the wire ended before the 24 one on the shcematic) just because ceramic coil formers are rare in the shack... only have one from an old antenna tuner but diamenter is 10 times bigger than neded.
Had to put an 82p cap in the emitter because the oscillator was not starting.

I had no OA5 diode so I guess the OA90 used should be similar. Probably will work with others Ge of similar type.

The video:

It should be enough for local coms monitoring... with the advantage or disavantage that due to the mixer nature (and diode capacity) you can still receive in the "normal" frequency, eg: if the receiver is at 144Mhz, you receive that (let's call it "fundamental") and 144+300 and 144+20 and 144+80.... etc etc...that's good in one way and bad in the other... life is not perfect!

Can't see well in the video well but the handy TX frequency is 436.650, the "receiver" is at 136.600 Mhz, so the "oscillator" 15th harmonic is at: 300.050 Mhz. That, makes the fundamental at: 20.0033 Mhz.... I measured 20.0029 Mhz... removing the 3 errors (receiver, transmiter and frequency counter) and it's everything as expected...on frequency!

I am happy with this experiment! Will try to improve a litle bit on the schematic.

Can't remember exactly if this was the original article but the image is similar from here:

Wednesday, January 05, 2011

Happy New Year

A little delayed..I know! Anyhow: Happy New Year everybody with lot's of health and some money to spend on electronics :)

I decide to start the new year with a sparking new soldering iron tip... the old one just didn't "cut" enough and was completely worn out.

Here's the old and the new one:

That's an JBC R-05D 1mm diameter, nothing small exists for this soldering iron model ( JBC 30S)
Quoting the manufacturer:
"....The tips are made of copper protected by various layers: iron, nickel and chromium, respectively, and they are also pretinned and ready for use.

With this treatment, deformation and wear are thereby avoided. Its working life is equivalent to 20 copper tips......"

I can say it is true, none of my previous soldering tips (and irons) had last as this one.
Incidentally, in the local electronics shop I had the number one invoice of the year... pity I am not one of the shareholders :)

Also starting the year replacing batteries on the 2 UPS protecting the computers, they just don't last 1s... here's the reason for one of them:

Not easy to see but the battery is open in the bottom, probably overheat or some other violent cause since it's not easy to break this type of plastic case.

The circuitry inside the UPS:

Have a nice year!