CARC MEETING March 2011

An Introduction to Microwaves Part 1 by Derek Atter G3GRO

For various reasons, it was necessary to have a change of programme for the March meeting. Without a speaker we had to find a replacement at relatively short notice. As valiant as ever, Derek G3GRO stepped up to the plate. His presentation, originally scheduled for the May meeting was titled “An Introduction to Microwaves - Part 1.”

Now as many of us know, in addition to his amateur radio activities, Derek in his working life was a professional microwave engineer and he has a wealth of knowledge and experience at his fingertips built up over many years to pass on in this specialised area of communications.

The microwave spectrum is usually defined as the frequency range from 1.0 to 300 GHz, with most common applications being within the 1 to 30GHz range. The microwave spectrum is divided up into a series of sub-bands as shown in Table 1. below.

L band 1 to 2 GHz
S band 2 to 4 GHz
C band 4 to 8 GHz
X band 8 to 12 GHz
Ku band 12 to 18 GHz
K band 18 to 26.5 GHz
Ka band 26.5 to 40 GHz
Q band 30 to 50 GHz
U band 40 to 60 GHz
V band 50 to 75 GHz
E band 60 to 90 GHz
W band 75 to 110 GHz
F band 90 to 140 GHz
D band 110 to 170 GHz

Table 1. Microwave Spectrum sub-bands

As a conversion guide, a 30-centimetre wavelength is equivalent to 1 GHz (to convert from frequency to wavelength, divide the speed of light 300,000,000 meters per second by the frequency in cycles per second to get metres of wavelength).

Starting with the basic means of getting a microwave signal from A to B Derek introduced us to coaxial lines in various forms, suspended strip line (or tri-plate line), printed circuit micro-strip, waveguide and the Goubau Line. Waveguides included rectangular and circular, size adapters and coax to waveguide transitions.

Derek suggested three typical routes for the newcomer to start on microwaves -
• Wideband Gunn Oscillator/DRO
• G4WDG Modules
• Mix and Match surplus units

Klystrons are used as amplifiers at microwave frequencies to produce both low-power reference signals for superhet radar receivers and to generate high-power carrier waves for communications. The klystron is capable of amplifying or generating microwaves with greater control and precision than is available from the magnetron.

Reflex Klystron Oscillator

Early amateur 10GHz Microwave Power source. Used as Local Osc.and FM TX - approximately 10mW RF output. Originally developed in WW2 as Radar LO.


Magnetron
The “secret weapon” of WW2 this high powered vacuum tube enabled the Allies to develop high power microwave Radar and can produce up to 5 MegaWatts of Pulsed RF. In addition to radar and communications use the magnetron is used in domestic microwave ovens.

Travelling Wave Tube (TWT)
The TWT is employed to amplify radio
frequency signals to high power, usually in an electronic assembly known as a travelling-wave tube amplifier (TWTA). A common use of TWTAs is as an amplifier in satellite transponders where the input signal is very weak and the output needs to be high power.

Travelling Wave Tube (TWT)

Input RF at (2) continuously interacts with, and velocity modulates travelling electron beam, to produce much-increased RF at output (6). - Capable of very high gain up to 50dB +. (4) is attenuator to suppress backward wave. Basis of BWO oscillator

The TWT was a very popular device on Amateur microwave bands before availability of transistor PA’s. G3GRO used TWT at Masthead on 10Ghz fed with 2.4kV helix voltage.


Gunn Oscillators 

 The “Solfan” Gunn diode oscillator & Mixer assembly ex- Doppler intruder alarm is readily convertible to 10Ghz ham band and popular for wideband FM or ATV use. Around 10milliwats RF output

Transmission Lines are the coupling devices used for transferring a microwave signal from one part of the transmitter, amplifier or other equipment to another part of the circuit. Transmission lines come in number of forms from coaxial cable through to waveguide, depending on the application.
This was an extremely interesting presentation, and an invaluable introduction to this highly specialised area of communications. We look forward with anticipation to Part 2 of Derek’s talk later in the year.

John Longhurst G3VLH

Another 2m Contest from CARC Hut 18

Following the recent success of Brain and Howard taking part in a 2m QRP contest from the CARC clubhouse, I was inspired to try my hand.

I had intended to spend the majority of the evening of Tuesday 5 July sorting out the equipment returned from Kent after the RSGB VHF NFD contest of the previous weekend. However it occurred to me that I had everything to hand to make a good stab at that evening's RSGB 2m UKAC contest. These run every Tuesday evening of the year with the first Tuesday of the month being 2m, the second 70cm, the third 23 and 13cms, the fourth Tuesday for 6m and when there is a fifth Tuesday in the month this is used for 4m.

You can find the calender here http://www.rsgbcc.org/vhf/

The rules are fairly simple with the normal 1pt per kilometer worked multiplied by the number of unique locator squares of UK contacts i.e. IO91, IO92, JO03 etc. You can of course work European stations and these do count for points (the number of km) but their locator squares are not counted towards the multiplier. This is deliberately designed to encourage UK stations to work each other and increase activity, at the same time giving stations all over the UK a fair chance at doing well.

So instead of tidying the clubhouse (don't worry I did that on Wednesday 6th), I dug out my old IC275H and the 400W 2m PA, hooked it all up to the club 17element beam and tested it out. All seemed to work OK despite not having the masthead preamp which has been repaired but is awaiting fitting to the tower. I didn't bother with a CQ caller as the contest is only 2.5 hours long, starting at 1900Z and finishing at 2130Z. This proved to be the right decision.

Unfortunately neither did I have my adapter lead with microphone preamp to allow the normal Heil HC4 headset to be used with the IC275. Most Icom radios supply 8V on the microphone pin which at a minimum need a capacitor in line to prevent damage to the Heil mic insert. This 8V is present to power a mic preamp built into Icom microphones. This means that the level of other non Icom microphones is too low and needs an additional microphone preamp.

I ended up just using the Icom fist mic that comes with the radio.

As I had little idea how well or badly the club site would work for a 2m contest I wasn't sure how many QSOs were likely. I opted to use the Minos logging software written specifically for RSGB VHF contests by Mike Goodey, G0GJV. This excellent piece of software has all the contests preloaded ensuring that they are scored correctly. Simply enter the station information such as your call, your locator etc and the software does the rest. A good tip is to ensure that your PC clock is correct. Minos uses this clock to log the QSOs.

You can find documentation and downloads here http://minos.berlios.de/

Operating as G6RC, the contest itself proved to be very enjoyable. At times it was more like HF than VHF with 3 or 4 stations replying to a QRZ call. In total I worked 131 QSOs in 2.5 hours with ODX being MM1DDD/P at 598km. Also worked were GI, EI, GW, F, DK ON and PA. I deliberately didn't spend much time with the antenna pointing at Europe but in hindsight it might have been worth a short period bagging the big stations at 700+km for extra points.

The claimed scores for the contest can be found here

http://www.rsgbcc.org/cgi-bin/claim.pl?Contest=144MHz%20UKAC&year=2011

At the time of writing, with the execpition of Bryn, G4DEZ and Dave GI4SNA both of whom have excellent VHF QTHs, equally good equipment and are seasoned operators, the other stations above G6RC are all portable, a huge advantage in a VHF contest.

So lessons learned.

The CARC clubhouse is a great site for UK VHF/UHF/SHF contests.

The IC275H is a great receiver. I barely suffered from QRM despite many other big stations on the band. It is certainly my radio of choice.

I need to be better at working pileups. Picking the full call, first time from the melee will certainly speed up the QSOs leaving time for even more.

Get the headset working properly. Bring the right lead.

Move the computer screen down making it easier to operate the logging. The radio doesn't need much tweaking and can easily sit off to the right of the computer screen.

So the next 2m UKAC contest is on Tuesday 2nd August. I hope to be at the club to give that a go. I will have had knee surgery the week before so it might not be possible. If anyone else is interested in this or other Tuesday evening events, let us know.

Alternatively if you fancy a portable entry that too can be great fun. Remember to claim the score both individually and for the Crawley ARC.

73
Mike
G0KAD

Summer Social Event Saturday-23rd July 2011

FOLLOWING recent the Successful Club Dinner Held in May,

The Hon. President and the CARC Committee Extend an

Invitation to Members, XYLs/Yls and Family Members

to join them in a new Venture :

“The President’s Lunchtime Garden Party”

To be Held at the QTH of the Hon. President, Derek Atter, G3GRO at No.1 Little Crabtree, West Green, (Off Ifield Avenue ) 12-00 for 12-30 until approx 4-00 pm

A Substantial, Mainly Cold Buffet Lunch will be served including
with it a Glass of Wine and Soft Drinks etc. plus afternoon tea later.

Proposed Menu :

Assorted Sandwiches :
Brown & White Bread With the following fillings :
Cheese & Home-made Chutney, Ham & Tomato,
Egg & Cress Mayonaise, Coronation Chicken.

Crudités :
Batons of Carrots, Cucumber, Celery, Peppers,Spring Onion,
Cherry Tomatoes, Tiny Pickled Onions.
Bread Sticks, Assorted Crispsands Savoury Biscuits

Dips :
1000 Island, Mild Curry chilli & Philadelphia Cheese
4-Cheese dip, Honey & Mustard

Hot Items :
Sausage Rolls, Barbecued Chicken Legs, Cocktail Sausages on Sticks
Mini Meatballs on sticks, Chicken, Bacon & Mushroom Vol-au-Vents

Deserts:
Old Fashioned Sherry Trifle; Chocolate, Strawberry & Cream Gateau

Cost per Head : £8-00
Bring a bottle if you fancy more than one glass of wine (If you are not driving !!)

It is planned that the event should take place in the garden but if we happen to
be unlucky with the weather, we plan to transfer inside to the conservatory and
sitting room etc. - even, God forbid, to the shack !!!
( Note, Parking on Little Crabtree is restricted until 5-00pm on Saturdays but some parking
spaces will be available. - Collect a resident parking permit immediately on arrival at
No.1Little Crabtree and place on the dashboard. Alternatively free parking is available
directly across on the opposite side of Ifield Aveue 100 yards away in the car park by the
Horticulture Club and Labour Party Club )

To reserve places for the lunch, please contact Richard, G4ANN, the Hon. Treasurer
ASAP at the Club or telephone on 01342 715333 or via e-mail : G4ANN,
g4ann@copthorne.org.uk so we can quickly establish numbers.