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Wednesday, February 27, 2008

New harmonic for 9W2ALX

Today morning 27 Feb 08 at 9:03am a fellow ham members' XYL safely delivered their second harmonic. A YL they named Seri Nur Farisya binti Muhammad Firdaus. I would like to personally congratulate 9W2ALX (Alex) and his XYL for their new bundle of joy. You were targeting 29 Feb but i guess it didn't happen. :)

From
9W2GU

Sunday, February 24, 2008

SWR

What is VSWR or SWR?
VSWR is Voltage Standing Wave Ratio.
SWR is Standing Wave Ratio.

Fine! But you still don't understand what it is and does.
SWR meter checks how much power is transmitted by the antenna as compared to how much is transmitted by rig/radio, and how much is reflected back. This reverse/reflection of power can damage you rig if the loss is too great.This is known high SWR.

To put is simply, SWR is a way to check for loss of power. The best SWR is said to be 1.1:1 and anything from 3.0 and above (is the RED zone on the SWR meter) is potentially damaging. There are many factors contributing to high SWR. An untuned antenna, bad grounding, cables with high loss, wrong length cables...and many more.

How to get the best SWR?
  1. You need to ensure your antenna mounting is not shorting, and placed in a appropriate location. The antenna itself must not make contact with any conductive materials.
  2. Use a good quality cable and connectors. If you cannot solder the connectors on, get help from someone who knows how to do it.
  3. Mount the antenna in the place you intend to use. Antenna at different location will give different reading.
  4. DO NOT coil extra remaining cable.
Tune the SWR to the center frequency. Example, for 2 Meter, use 146MHz as center frequency. Before you start tuning your SWR, Check you cable for electrical shorts and broken connections. Though broken connection are rare in a cable, but bad soldering could result improper contact.

Cable Length

From my experience, it is best to use the coax in multiples of ¼, ½ or 1 wave length of the center frequency. For VHF 2M, the center frequency is 146MHz. This is derived for the 2M VHF of amateur allocation, 144 MHz – 148 MHz. 144, 145, 146, 147, 148. Now you can clearly see that 146 MHz is the center frequency.


So, coax of 1 wavelength = 300/146 which equals about 2.05 Meters. To get the optimum performance this value has to be multiplied with the coax velocity factor. If your coax has a velocity factor of 0.92, then coax of 1 wavelength = 2.05 * 0.92, which equals to 1.886 Meters. Now you know how long one wavelength of your coax is, you should cut it in multiples of 1.88 Meters or ¼ or ½ of that value.

Example, you need to use approximately 26 Meters of cable.

First, find out how many wavelengths that is.

26 Meters/1.88 = 13.82 wavelengths

13.82 wavelengths is not multiples of 1.88.

So you could use 14 wavelengths. This works out to be 26.23 Meters.


NOTE: The velocity factor used as example one. Below is a table of commonly used coax and velocity factor. For detail info please download the data sheet from you coax manufacture.


VF = Velocity Factor
CF = Center Frequency

CF = 146 MHz
Wavelength at CF = 2.05Meters


COAX
VF
VF x CF
RG-8
0.66 1.35
LMR-400
0.85
1.74
RG-11
0.75
1.54
RG-58
0.661.35
RG-213
0.661.35
RG-400
0.6951.42



Testing Coax

Now that you have your coax ready with connectors soldered on both ends, it is time to test if there is an electrical short or open circuit. For this task you will need a multi-tester.

The outer braiding in the coax is called the ground (GND) and the inner core is the positive (+). The same is true for the connector, the outer part of the connector is the GND and the inner part is the positive (+).





Set the tester to Ωx1 or to the buzzer position.
Touch each end of the coax GND to the testers’ tip. Either the buzzer will sound or the indicator on the tester will move. This indicates that the coax GND is has connectivity.










Do the same for the positive part of the connector, the result should be same.













Finally test the GND and (+) for electrical short. This time, there should be no sound or activity from the tester. If there is, you need to rectify the problem before testing SWR. Most likely the soldering is bad.










Tuning SWR

There is a misconception that tuning SWR is tuning your antenna. The cable, mounting and other factors also play a role in tuning the SWR. SWR is affected by many factors and not just the antenna.

Mount the antenna at the place you intend to use it.

Connect the coax from the antenna port marked ANT on the SWR meter.

Connect the rig/radio to XMIT/Transmit port of the SWR meter. I suggest that this coax be at least ½ wavelength. Most people use ¼ wavelength and it tends to be too short, especially when testing in cars.

Turn on rig and in VFO mode set to 144MHz.

Set the meter to CAL (calibrate)

Press PTT and calibrate the meter.

Release the PTT and set the mode to REF (Reference/Reflected).

Press the PTT and make note of the reading.

Repeat this again wit 146 MHz and 148 MHz.

144 MHz is the lowest end if 2M band.

146 MHz is the center of 2M band.

148 MHz is the highest of 2M band.

If all goes well, there should be little or no movement on 146 MHz. SWR on 144 MHz and 148 MHz should be 2.0 or less. If above 2.0 then you need to check the antenna mounting, check the grounding of the mounting or maybe place the antenna in different location etc.

Some SWR meters have no switches and buttons, for more information on how to use and read the meters, please refer to your SWR meter manual or ask a fellow HAM for help. I use the Diamond SX-400 in my example.



Tuning Antenna

If SWR on 144 MHz is more than 148 MHz, you will need to lengthen your antenna. Especially for jalopies, this can be done by adding additional spring mounting. For base antennas refer to the length chart that comes with the antenna.

If SWR on 148 MHz is more than 144 MHz, your will need to trim your antenna. Refer to the cutting chart/length adjustment chart that comes with the antenna. Some antennas have a small Allen screw to adjust the length.

If SWR is above 3.0, check for electrical shorts, improper grounding, etc.




Factor that contribute to high SWR

Low quality coax has high loss.

Coax is too long.

Bad soldering.

Excess coax is coiled.

Antenna length not tuned according to length chart..

Little or no ground plane.

Location of antenna is not the best.

When testing SWR on jalopies, do in open area with doors shut.

Antenna mounting not grounded or shorting.


There are other factors too, but these are the most common ones.



I hope I have not made things too complicated for the newcomer. I could get more technical but I don’t want to. Best of luck tuning your SWR. If you need help, you could leave me a comment.

73s to you and all monitoring stations.

9W2GU.


If you have an questions, please leave your comments.

Thursday, February 21, 2008

Cheras Eyeball

TO : Friends of RKK / RKL / RUK and all HAM /SWL members.
The time has come for our next central region "HAM CENTRAL ROTATION EYEBALL". The cheras group lead by 9w2KNS , 9w2 EET, 9w2BGL and.9w2SEE cordially invites all HAM members and SWLs to CHERAS on 22 Feb at 9.30 PM RESTORAN AMEER EHSAN FOR Cheras eyeball. At last, there will be a GOGOPAL road show at the eyeball. They will be giving a talk on their GPS system and a demo of their product . Food will be served to members with special offers from the suppliers for their GPS products. Two location maps are attached above close up (micro) and overall view (Macro) for you to find the restaurant. Many Cheras members will be there so come and join us.
GPS Coordinated to Restoran Ameer Ehsan Cheras
LAT=3.129932 & LON=101.731912
Address :-
Restoran Ameer Ehsan Cheras
no 186, Jalan Mahkota, Cheras
Next to Maybank Taman Maluri
We hope to bring together all Amateur radio members.
I would like to thank the Cheras group for organising this eyeball and gogopal road show.
73 TO ALL
9W2AXE

Please forward this email to other HAMs who might be interested.
(Kindly email to 9w2axe@gmail.com if you want to add your friends to my mailing list.)




QSP 9W2AXE

Saturday, February 16, 2008

PIC Burners

Of course, before you start building a program, you'll need to store it into a PIC chip. To do that you will need a PIC programmer. You can buy commercial ones, or build your own. I personally get the satisfaction build my own and even more so when it works. :) I have a :-
All the above mentioned except the PICKit2 use the PC's serial port to program the chip. The PICKit2 uses the USB port.

The PICKit2 I purchased came with a ICSP/ICD port only and not a ZIF socket or any socket to program the chip. So based on the Feng3 design I made a ZIF socket to program the chip and also included an ICSP port.

The schematics for my version of Feng3 and the PICKit2 ZIF available from download section.

Available from the sidebar under the heading :

Downloadz--PIC programmers


Which takes me to development of the PCB. The fun stuff. But that for another day.

Thursday, February 14, 2008

PIC

For those interested in PIC programming i recommend MikroE's C or Basic. Whichever programming language you comfortable with. If you have not program before, i suggest you try out both C and Basic. MikroE compilers are free, for code up 2K of hex code.

For even lower level, then download Microchip's MPLAB IDE. It free and assembly compiler.

Learning to program is beyond the scope of this blog. There is lots of site out there that can inform you on how to get started. I suggest that you download the help files and go thru the the examples given with these compilers. But I will from time to time post some programming tips.

Sunday, February 10, 2008

RAE 2007-2

MCMC announced the RAE 2007-2 results on late Jan.
Download and view the PDF file to check and see if you got thru.

Best of luck..
73's.