Sunday, 9 February 2020

Ham Radio-Receivers

Ham Radio Receivers

Ham Radio Receivers

My ICOM IC-7100 general coverage receiver-repaired a few years ago.

Ham Radio Receivers, are designed and manufactured in handheld and desktop versions, they differ in many ways offering features and benefits to suit individual needs. A separate receiver covering the Ham Bands you use on a regular basis is a useful addition to any shack because it allows you to monitor your own transmissions.

The AOR DV-1 capable of demodulating digital transmissions.

I would suggest that you look for a receiver that covers all of the Short Wave bands and many give you coverage of the radio spectrum from the longwave, and through the medium wave band, coverage starts from around 150 Kilohertz through to 30 Megahertz.

New receivers offer the benefit of wide coverage, they incorporate the Very High-Frequency spectrum allocation and some continue coverage through the Ultra High-Frequency band. V.H.F. and U.H.F. contain special allocations for Radio Hams to use and you will have the advantage of being able to listen to local repeater stations which are designed to extend the range of handheld transceivers.

All mode Ham Radio Receivers are in my opinion an essential requirement, there is nothing more frustrating than finding a transmission that you cannot resolve. Look for a receiver capable of resolving Morse code, and single sideband transmissions. Receivers are now capable of demodulation digital transmissions, for example, the AOR DV-1 receiver.

These modes of operation are usually described as C.W. and S.S.B., you need L.S.B. and U.S.B., lower sideband is used below 7 megahertz and Upper sideband above 7 megahertz. An anomaly in this rule is the 5 megahertz band where Upper sideband is used by radio Hams for their transmissions.

Other modes to consider are N.B.F.M, Narrow Band Frequency Modulation is used on ten meters, the upper part of this band especially around 29 decimal six megahertz is used by repeaters. When conditions are good on this the band it is possible to listen to radio Hams communicating with fellow enthusiasts between different continents.

Short wave receivers capable of resolving all of the modes of transmission mentioned above can be extended to cover other parts of the radio spectrum, by the use of frequency converters, used in conjunction with the ten-meter allocation at 28 Megahertz, frequency converters are available to extend your listening entertainment, many covers the Ham Radio two-meter band, located at 144 Megahertz.

Building a frequency converter has additional benefits for the radio enthusiast.

Education is one of them, great satisfaction and a sense of achievement is gained when you build an additional piece of apparatus to extend your hobby. Buying second-hand converters and modifying them to cover other allocations within the radio spectrum, for example, the Marine V.H.F. band, it is not only interesting it also adds to your growing knowledge of how radio receivers work.

Ham Radio-Receivers

Ham Radio-propagation

Ham Radio-Propagation 

Ham Radio-John G4YDM

Ham Radio-John G4YDM

Ham Radio-propagation, I often hear new radio hams that have not spent time as listeners complaining about the noise on their receivers or transceivers after they have spent thousands of pounds on their transceiver equipment. Please do not despair; it can be cured with a little patience and some education.

If we live in tightly packed housing estates where space is at a premium, we often forget the general rules of thumb when it comes to aerials. 

Ham Radio and the Natural Propagation of Radio Waves

The transceiver on the bottom is a PYE WESTMINSTER converted to two meters 144 MHZ Amateur band

Always try to get your aerial as high and as clear from objects as you possibly can. This is a fundamental rule, for all Short wave radio listeners and Radio Ham operators, however, we sometimes forget this golden rule. 

If your dipole feed point is close to your house it may be right next to a high voltage cable it may be the one that feeds your shower, this will be capable of supplying thirty amps, a radio wave is a source of electromagnetic radiation produced by an alternating voltage, remember how a transformer works by inducing a voltage in the secondary winding, the same effect happens with your aerial and your 30 amp shower supply. 

Remember where your aerial feed point  is located, attempt to get it away from your property because of that high current and voltage source that feeds your shower,  this voltage may be inducing noise into your aerial, it works the other way too where your aerial couple to mains wiring.

Long wires are fine but they are high impedance aerials fed at the end of their length, this makes them voltage fed aerials once again these are inherently noisy aerials, they will impede those weak signals trying to get into the front end of your receiver, end fed work well when you are working portable in the hills away from man-made noise. 

The answer is simple,  make a balanced aerial with its feed point away from your bricks and mortar. My suggestions will not solve all of your noise problems but they will help.

I use 75-ohm twin feed for feeding aerials, the twin is less noisy, placing a 1:1 choke at the transceiver end to connect your receiver or transceiver to the so-239 socket via a short length of coax.

I hope that helps you when you get disappointed because you cannot hear signals due to noise on your receiver. Propagation changes all the time, you will find days when the noise goes down and the signals rise above the noise. 

Radio propagation is after all parts of the Worlds natural science, the weather changes constantly and so does propagation. Siting your aerial away from a building will help your station receive weak signals when conditions within the ionosphere are poor.

Ham Radio-John G4YDM. Aerials are balance entities, meaning that the current in each leg of your dipole is carrying the same current as the cycle changes, consider using the balanced line as opposed to coax. 

Think about those weak signals again, braid on coax acts as a radiator and as an absorption device just like a dipole, keep it balanced by using twin line, you can build a simple balanced to unbalanced transformer to connect the aerial to your transceiver, using a short piece of coax on the opposite end of the transformer.

The formulae for a half-wave dipole is 468 feet divided by the frequency or band you intend to use.

Loops are good aerials too and I have found they are quieter when it comes to noise, they are constructed by dividing your intended frequency into 1005 feet, 14 MHZ, is around 72 feet, build it into a triangle shape called a delta loop, feed it from a quarter of a wavelength from the apex, in our case around 16 and half feet, using a 4:1 balun at this point the aerial will work well on 28 MHZ too.

I hope this helps you, please drop me a line if there is something I can help you with.

Ham Radio-John G4YDM

Ham Radio Digital Modes

Ham Radio Digital Modes 

How does it work?

Ham Radio Digital Modes.  P-25 is a communication system essentially created and utilized by public service agencies in North America, the system allows communication between several agencies such as Fire Fighters and Paramedics and Police Officers. 

P-25 used by emergency services

This is the Washington County Durham appliance, Callsign Foxtrot 181

Digital communication systems are available to Ham radio Operators, D-star and Fusion to name but two. Like all other digital modes, the normal analog signal which we produce when we speak is sampled, in the case of G.S.M. mobile phone technology 8000 times per second each sample produces an eight-bit word totaling 64 kilobits.

We have a similar digital system used here in the United Kingdom for our Public Service personnel; it's called TETRA, or Terrestrial Trunk Radio. 

Many of us started out in Ham radio by listening to the Emergency services although in those days the Emergency services used Amplitude Modulation and Frequency Modulation to communicate between mobile and base stations and there was no encryption in those days. I learned a lot about radio by converting receivers to the Emergency service frequency allocations, being a member of the fire service helped too.

Short wave listening or utility monitoring gave you a great sense and awareness where other services transmitted, utility listening added to this awareness and soon you became knowledgeable about out-of-band transmissions and how to keep harmonics from your transmitters to a minimum. The requirement by law for the active Ham Radio Operator.

Digital communication has the advantage over analog technology because it allows many operators to use the same channel by splitting up time into bite-size portions; these bite-size chunks of data are converted into digital streaming packets of data and can be sent around the World via the Internet. By using this method of superimposing speech on a radio signal, radio bandwidth is used more efficiently.

 Digital systems have the advantage over analog in many other ways, once the speech is converted into digital signals, they can be mixed up in a particular way that's how encryption is produced, making the transmission secure. Frequency hopping is also employed to make the process of recovering the digital signal more difficult to intercept.

Ham Radio Operators can now send and receive these digital signals from all over the World because devices are placed before and after transmissions to allow these digital streams to be sent over the World-Wide Web.

My Ham Radio days started with building a simple crystal set receivers and tuned radio frequency, T.R.F. equipment to listen to Hams on top band, 160 meters or 1.800 MHZ I soon developed an interest in the V.H.F. and U.H.F. spectrum two meters, 144 MHZ, and seventy-centimeter, 433 MHZ bands where I soon discovered transmissions from Aircraft and Ships.

Ham radio is a rich and varied subject and many find themselves experimenting with all of the modes and bands. I have no doubt that P-25 will be on the experimental radio hams experimental agenda.

Ham Radio-John G4YDM