Ο λόγος στασίμων 1:1 ενός κεραιοσυστήματος, δεν συνεπάγεται τον 1:1 λόγο μεταφοράς ισχύος, προς την κεραία!

Wednesday, 21 September 2016

Oscilloscope 10:1 probe!

More than 10 years ago I bought a Heathkit oscilloscope Mod. IO-102 and other than the first switch ON, I haven't use it since.
It was a chance to use my electronic variac to give it a slow start and reform its capacitors in situ.
Everything went well and now I have a fine sample of a legendary brand in electronics working next to me!
Thing is, that I never had any probe for this oscilloscope so I had to make one.
Couldn't be easier! A pen empty plastic body, 2 resistors one 5M1 and the other 1M29, a couple of meters RG 174 and an appropriate BNC connector.
See for yourselves at the photo the schematic and the connections.
The ratio is 10:1, and it is calculated using the formula
1/(1/1.29 + 1/1) =0.5633...
(5.1 + 0.5633...) / 0.5633... = 10.05379 ratio
(there is a mistake reading the schematic. Shunt resistor is 1.29Mohm not 1.25Mohm.
You can buy a generic probe up to 100MHz from China for less than a fiver, but you don't have the pleasure to have a homebrew oscilloscope probe and the pleasant pass of time!
cheers all!
source of the idea

Πριν πολλά-πολλά χρόνια αγόρασα στην Αγγλία έναν Heathkit IO-102 παλμογράφο. Χωρίς διάθεση να τον πουλήσω, του άλλαξα τον αέρα του σε μερικά πανηγύρια και στο τέλος βρήκε τον χώρο του στην αποθήκη μου. Ποτέ δεν είχα ένα πρόμπ γι αυτόν κι έτσι χωρίς κανένα ιδιαίτερο λόγο βρήκα ένα σχέδιο στο διαδίκτυο σήμερα το απόγευμα και καταπιάστηκα να το φτιάξω! Ψάχνοντας κι ανακατεύοντας βρήκα το RG 174 και τον ειδικό BNC κοννέκτορα που χρειαζόμουν και σε πολύ λίγο χρόνο κι ακόμα λιγότερες κολλήσεις ήταν έτοιμο!
Δείτε στις φωτογραφίες το διάγραμμα και το γενικό τρόπο τοποθέτησης των υλικών.
Δείτε από πάνω τον τύπο υπολογισμού της σχέσης του προμπ. Εδώ στο συγκεκριμένο είναι 10:1.
Καλή επιτυχία αν ασχοληθείτε να το φτιάξετε!
(κι αν δεν σας κάνει κόπο στείλτε μια φωτό της κατασκευής!)
πηγή της ιδέας

Thursday, 15 September 2016

ur R is cracked!

Repairing an old friend!
Out of 4 grid resistors, 47R each, one is cracked and the other three shows a resistance of 35R each. Hard driving the amplifier, pays it toll eventually. Sadly enough and it wasn't me the one who did it.

Η υπεροδήγηση έχει συνέπειες. Ίσως όχι στο ακουστικό κομμάτι αφού ο ενισχυτής είναι φανταστικός αλλά, στο οικονομικό. 3€ θα κοστίσουν οι αντιστάσεις ν' αλλαχτούν. Λίγο είναι?!

Sunday, 11 September 2016

Sunday, 4 September 2016

99db bin gain!

I was listening to a QSO on 40m the other day and it was one ham telling to the other that the ground under his antenna adds 7db to his wire antenna gain! Don't bother mate. Here is a super-duper booster for you. A 99db bin!

Άκουγα ένα QSO στα 40m τις προάλλες και ήταν ένας συνάδελφος να λέει στον συνομιλητή του, ότι το έδαφος κάτω από την κεραία, του προσθέτει 7dB στην συρμάτινη κεραία του! Μην ενοχλείσαι συνάδελφε . Να σε δώσω εγώ κάτι να βρεις την υγειά σου. Έναν κάδο 99db !

Tuesday, 30 August 2016


That is a QRP transmitter having an interesting and uncommon output circuit. I will built it using a different approach on construction than the usual ugly or Manhattan. It is designed by Keith Ranger G0KJK and published in SPRAT Autumn 2015. More photos to come.

All I had to do was to design the transmitter on a piece of graph paper taking in consideration the dimension of the discrete components. After I mark the holes with a scriber, I drill them using a 0.8mm drill bit somewhere near! hi! hi!
This method of homebrewing calls the use of solder-able magnet wire to make the interconnections. I use the components leads instead!

During the build I found out that I don't have any 14.060MHz xtals left in my drawers so the 2N3953 transistor. It is easy to order an xtal, or many, from the club sales which I did promptly but the transistor seems to rare as hens teeth! As I comment to a Greek colleague I will use what I have in my stock and that is a PT4579.

Hard boiled and annealed inductors!

Wednesday, 17 August 2016

RCA 813 QRP transmitter!

The well-known radioamateur motto dictates to Listen, Listen and Listen again.
Since the presentation of the GU-81 regeneration receiver you had your chances to listen enough.

Now its time for you to transmit!
I'll give you the initial kick along with photos and the schematic for a QRP Tx based on the 813 tetrode tube!
Gentlemen, (and Ladies of course), warm your irons!

Μετά τον δέκτη ανάδρασης με την GU-81, τώρα κι ο ανάλογος πομπός.
Αυτοταλάντωτη 813 με κρύσταλο και QRP ισχύ εξόδου! (λέμε τώρα!)

Friday, 12 August 2016

5KW Electronic Variac.

What you see at the picture is a commercial AC 220V 5000W SCR Voltage Regulator Speed Controller Dimmer, ebay item number 171786606530. That with an AC 0-300V Round Analogue Dial Panel Meter ebay item number 231936883787 and a PC p/s box Tolis sv1edy gift, makes an excellent electronic variac!

I removed the power supply board from the box and opened the necessary holes using my laser guided hand file. The result is what I call the best possible given the circumstances!

Now I can start old radios with no fear of possible damage due to inrush current!
Or reform electrolytic capacitors.
Or vary the speed of power drills and motors.
Or wherever...

Another one bites the dust!

Another one balun bites the RF!

Wednesday, 27 July 2016

Tx Factor - Episode 12

Not one, but two rig reviews: the Sun Expert Electronics Transceiver MB1 and the elusive Icom IC-7300 are comprehensively analysed.

Bob teaches Mike a thing or two about amateur satellite operating, and our free-to-enter-draw is back with a chance to win a copy of the Getting Started with Amateur Satellites book featured in the item.

Και μία ακόμα περιληπτική παρουσίαση του IC-7300!

Thursday, 21 July 2016

Visit kalamata... visit beautiful Greece (4K UHD cinematography promo)

Summer indolence has cast a heavy veil over me. Happy holidays everybody and in a few weeks I'll be back here!

Η θερινή ραστώνη έχει ρίξει ένα βαρύ πέπλο πάνω μου. Καλές διακοπές και σε λίγες εβδομάδες, θα είμαι πάλι εδώ!