Our next meeting

All,
Here is our meeting schedule.
The next meeting is on Wednesday the 9th december.

Tony has found the following useful link http://www.vintage-radio.info/docs/ The page contains a selection of scanned technical and historic documents that should be of interest to vintage radio collectors etc.

Here is our current schedule -


09/12/09 On the air/ RTTY
23/12/09 No meeting
13/01/10 AGM
27/01/10 VLF Demonstration and talk
10/02/10 On the air evening
24/02/10 DF Demonstration
10/03/10 Guest Speakers e.g. BDXC

MMANA - GAL Presentation 11/11/2009

Thanks to all who could make it to our meeting on the 11th. Here are the notes and a link to the software for any who would like to try modelling an antenna.

As we discussed, its best to use one of the existing models supplied in the library and modify it to look like the antenna you are testing.

73 Rex - G8UBJ

MMANA-GAL – Shares presentation 11/11/2009 - G8UBJ

MMANA-GAL is an antenna-analyzing tool based on the moment method, which was introduced in MININEC.

Once upon a time when you dreamed about an antenna you had to actually build it and hang it in the sky to find out anything about it.
With MMANA you can construct antennas on your home computer and see precisely how they perform. What can MMANA tell you about your antenna?

• Exact resonant frequency.

• Radiation resistance at the antenna feed point.

• SWR for a range of frequencies across the band.

• Precise length and thickness of wire or aluminium tubing required.

• What the radiation pattern looks like; the vertical take off angle.

• Effect of height above ground and the quality of ground.

• Gain and front to back ratio.

• The inductance or capacitance needed to match it.

• The diameter and number of turns of wire for a loading coil or trap.

• Optimise! Eg. Adjust Yagi element length and spacing automatically.

You can test many interesting things with MMANA, like bending your dipole to fit it into your yard, check the effect of height above ground of the ends of your inverted V, or calculate the gain and performance of your favourite Uda Yagi.

MMANA helps eliminate the uncertainties that plague antenna construction and lets you play antennas inside on a rainy day without upsetting the XYL.

ANTENNA ANALYSIS BY COMPUTER

With the proliferation of personal computers since the early 1980s, significant strides in computerized

antenna system analysis have been made. It is now possible for the amateur with a relatively inexpensive computer to evaluate even complicated antenna systems. Amateurs can obtain a greater grasp of the operation of antenna systems—a subject that has been a great mystery to many in the past.

The most commonly encountered programs for antenna analysis are those derived from a program developed at US government laboratories called NEC, short for “Numerical Electromagnetics Code.” NEC uses a “Method of Moments” algorithm. The mathematics behind this algorithm are pretty formidable to most hams, but the basic principle is simple. In essence, an antenna is broken down into a number of straight-line wire “segments,” and the field resulting from the RF current in each segment is evaluated by itself and also with respect to other mutually coupled segments. Finally, the field from each contributing segment is vector-summed together to yield the total field, which can be computed for any elevation or azimuth angle desired.

The effects of flat-earth

ground reflections, including the effect of ground conductivity and dielectric constant, may be evaluated as well. In the early 1980s, MININEC was written in BASIC for use on personal computers. Because of limitations in memory and speed typical of personal computers of the time, several simplifying assumptions were necessary in MININEC, which limited potential accuracy. Perhaps the most significant limitation was that “perfect ground” was assumed to be directly under the antenna, even though the radiation pattern in the far field did take into account real ground parameters. This

meant that antennas modelled closer than approximately 0.2 l over ground sometimes gave erroneous impedances and inflated gains, especially for horizontal polarization.

Despite some limitations, MININEC represented a remarkable leap forward in analytical capability. See Roy Lewallen’s “MININEC— the Other Edge of the Sword” in Feb 1991 QST for an excellent treatment on pitfalls when using MININEC.

Because source code was made available when MININEC was released to the public, a number of programmers have produced some very capable versions for the amateur market, many incorporating exciting graphics showing antenna patterns in 2D or 3D. These programs also simplify the creation of models for popular antenna types, and several come with libraries of sample antennas.

By the end of the 1980s, the speed and capabilities of personal computers had advanced to the point where PC versions of NEC became practical, and several versions are now available to amateurs. Like MININEC, NEC is a general-purpose modelling package, and it can be difficult to use and relatively slow in operation for certain specialized antenna forms. Thus, custom software has been created for quick and accurate analysis of specific antenna varieties, mainly Yagi arrays.

The most difficult part of using a NEC-type of modelling program is setting up the antenna’s geometry—you

must condition yourself to think in three-dimensional coordinates. Each end point of a wire is represented by three numbers: an x, y and z coordinate.

Websites -

Hamsoft Website - http://mmhamsoft.amateur-radio.ca/

Here is the antenna we modelled - G5RV JR

Here is the input to MMANA-GAL and some of the resulting infomation -

3d plot

Geometry

View

2D Plot

Next meeting & Pics

All,
Thanks to Phil for his talk on the One Valve receiver.


Here is our meeting schedule. The next meeting is on Wednesday the 11th November where Rex will be giving a presentation on antenna modelling software.

Evan will be giving up a presentation on Operating Digital Modes on HF on the 25th

11/11/09 Antenna modelling with MMANA-GAL
25/11/09 Operating Digital Modes on HF
09/12/09 On the air/ RTTY
23/12/09 No meeting
13/01/10 AGM
27/01/10 VLF Demonstration and talk
10/02/10 On the air evening
24/02/10 DF Demonstration
10/03/10 Guest Speakers e.g. BDXC

SHARES radio club meet at the Coach House, Church Hill Road, Surbiton on the 2nd and 4th Wednesday of each month at 8:00pm - 9:30pm

We are a short walk from Surbiton mainline station.

Here is a map showing our loaction -

Next Shares meeting 28th October

All,
Here is our meeting schedule. We meet on the 2nd and 4th Wednesday of each month. The next meeting is on Wednesday the 28th October where Phil Moss will be giving a presentation on a single valve receiver.

28/10/09 A single valve receiver
11/11/09 Antenna modelling with MM-ANA
25/11/09 Operating Digital Modes on HF
09/12/09 On the air/ RTTY
23/12/09 No meeting
13/01/10 AGM
27/01/10 VLF Demonstration and talk
10/02/10 On the air evening
24/02/10 DF Demonstration
10/03/10 Guest Speakers e.g. BDXC

SHARES radio club meet at the Coach House, Church Hill Road, Surbiton on the 2nd and 4th Wednesday of each month at 8:00pm - 9:30pm

We are a short walk from Surbiton mainline station.

Here is a map showing our loaction -

A New Call!

Congratulations to James Sales who has passed both his foundation and intermediate exams to take the call - 2E0TTL

VY 73 and well done James, we look forward to working you in the near future.

Schedule

All,
Here is our meeting schedule. We meet on the 2nd and 4th Wednesday of each month. The next meeting is on Wednesday the 14th October.

23/09/09 Restoration of valve broadcast receivers
14/10/09
28/10/09 A single valve receiver - Phil Moss
11/11/09 Antenna modelling with MM-ANA - Rex Lester
25/11/09
09/12/09 On the air/ RTTY
23/12/09 No meeting
13/01/10 AGM
27/01/10 VLF Demonstration and talk
10/02/10 On the air evening
24/02/10 DF Demonstration
10/03/10 Guest Speakers e.g. BDXC

SHARES radio club meet at the Coach House, Church Hill Road, Surbiton on the 2nd and 4th Wednesday of each month at 8:00pm - 9:30pm

We are a short walk from Surbiton mainline station.

Here is a map showing our loaction -

Kempton Park & RTTY

All, I hope everyone enjoyed Tony's intersting talk last night on restoring broadcast recievers. I will be keeping an eye out for potential receivers.

This email is just to keep you up to date with our planned events and activites.

This Sunday (27th) the club will be running a stall at the Kempton Park Rally. http://www.g4cdy.co.uk/

This is indoors (So you won't get wet if it rains) and is our closest event.

If you plan to attend do pay us a visit, we will have lots of components and other intersting items for sale at competitive prices. Of course buying from SHARES you will be supporting the club.


We have decided to re-start a club net (Hurrah I hear you say). The net will be slightly different as we will be using RTTY (No bothersome speaking involved).

Details of the net are as follows -

Frequency - 144.500 Mhz

Time 17:30GMT (6:30pm) Sunday evenings.

Mode will be AFSK 45.45 baud – Mark tone = 2125 Hz Space tone 2295 Hz.

First date for the net will be Sunday the 27^th September. The net will run for an initial month to gauge interest. Content of the transmissions will include propagation forecasts and club events in addition to any other subjects club members wish to discuss.

Don't let the RTTY part put you off. Its very simple to install RTTY on your PC and get going on receive by connecting the audio output from your tranceiver to the soundcard of your PC. MMTTY which is a very easy to use RTTY program can be downloaded for free at - http://mmhamsoft.amateur-radio.ca/files/programs/MMTTY166G.exe

The MM website is at - http://mmhamsoft.amateur-radio.ca/mmtty/

Once you have recive working information for a very simple interface for TX can be found at - http://www.geocities.com/n2uhc/interface.html

Once you have this working you will find it can also be used to monitor or work DX on HF.. have a listen on 20M around 14.085 MHz 73 and hope to see you Sunday

Rex - G8UBJ & Tony - G7DGW

--------------------------oOo-------------------------------------------

SHARES radio club meet at the Coach House, Church Hill Road, Surbiton on the 2nd and 4th Wednesday of each month at 8:00pm - 9:30pm

We are a short walk from Surbiton mainline station.

Here is a map showing our loaction -