Category: Gear

A Practical Interpretation of Antenna Gain, donuts included.

Antenna gain is not an easy notion for a new radio operator to pick up. Some even go as far as supposing that the antenna gain shows the increase in radio power.

But is not that the actual energy radiated is increased by the better antenna, this is not allowed by the law of the conservation of energy. It is because the radiated energy is handled, shaped-formed and directed better towards you.

A look at wikipedia tells us: ” In electromagnetics, an antenna’s power gain or simply gain is a key performance number which combines the antenna’s directivity and electrical efficiency. In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power.”

Now this explanation is correct but let’s make it simpler.

Continue reading “A Practical Interpretation of Antenna Gain, donuts included.”

HAMsmithing July 2017

This is a DIY USB charging cable for my Kenwood TH-F6A/F7E handheld radio.

web-IGP3869It is the same concept like the Baofeng USB to 10V charging cables that are found on eBay and amazon. But the virtue of the Kenwood HT is that it accepts a wide array of operating and charging voltage. Plugged to a 12V source it both charges and operates.

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Introduction to Surecom SR-112 Simplex Repeater Controller

The Simplex Repeater Controller Principle

The Surecom SR-112 Simplex Repeater Controller is a device that allows you to setup a “field” or “emergency” simplex repeater. In other words it is -and as we call it locally- a Parrot. It records and replays what it hears from the radio it is connected to.

So what the user has to do, is define the simplex repeater frequency, set it on the radio and connect the radio to a Simplex Repeater Controller by a purpose made/bought cable. The device will start repeating what the user will speak on the radio.

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It is a dead simple, easy and economical way to set up a repeater and cover dead ground, but it does have its shortcoming. While simple technically, it is a bit complicated operationally. It requires all involved parties to expect a repetition of what they are hearing.

Let’s assume that a Simplex repeater is placed on the top of a ridge to cover its two sides. The caller will input the message on the repeater and another user on the other side will hear the repetition. but what if there is a third user on this side of the ridge, within range of the caller? It will hear the message twice! And if not advised Not to, he will probably try to respond on the call, disturbing the repetition….

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Μια ματιά στις Απώλειες των Ομοαξονικών Καλωδίων των Κεραιών μας

Ο παρακάτω πίνακας συντάχθηκε κατά την προετοιμασία της παρουσίασης για το επόμενο Σεμινάριο Ραδιοεπικοινωνιών.

Δεν είναι λίγες οι φορές που ένας νέος ραδιοερασιτέχνης ή χειριστής επιλέγει ένα κοινό ομοαξονικών καλώδιο μεταφοράς για την κεραία του, το RG-58. Αυτό βρίσκεται εύκολα, είναι σχετικά οικονομικό, εύχρηστο αλλά παρουσιάζει μεγάλες απώλειες ισχύος, ειδικά στις μεγάλες συχνότητες.

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More Easy Antennas for the VHF/UHF

For the purposes of the next Radio Communications Seminar I constructed 2 antennas.

The first one is a ground plane field antenna using a folding handheld radio antenna.

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An SMA to chassis mount adapter is used and the radials are just solid core wire twisted through the adapter mount holes. The good thing about this method is that the antenna requires no tuning as the vertical element is already pretuned.

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The Ultrapack Battery Pack for QRP Low Power Radios

Survival Tech Nord has an open project running for making a small external battery bank for radios that operate at low output (5+ watt).

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The basic principle is using 18650 lithium-ion (Li-Co or Li-Mn) batteries that have big energy density and match their voltage to that of the radio.

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