A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.



Block การใช้ USB Storage บน Windows 8

Windows 8 Group Policy Disable USB Read / Write

Setting group policies in either the Computer, or User Configuration can prevent people from reading (or writing) to a USB device, or copying files to the USB stick.  Using a policy in the Computer Configuration section is simple and absolute.  While configuring ‘Removable disks: Deny read access’ in the User Section is more flexible, it leaves you open to permissions problems, or to be realistic, opening the door for administrators to remove data from machines.
Windows 8 Group Policy Removable Disks Deny read access

Computer Configuration
. Administrative Templates
… System
….. Removable Storage Access
……. Removable disks: Deny read access

Normally you would also Enable the ‘Deny execute access’, and ‘Deny write access’ next-door group policies.  As I mentioned earlier, you could also set the same policies in the User Configuration.

Note 3: To reverse this group policy I set Removable disks: Deny read access, back to ‘Not configured’ rather than setting it to: ‘Disable’



Open Stub Dual Band J-Pole Antenna

Open Stub Dual Band J-Pole AntennaPre tuned, easy to assemble , very use full for emergency communication


Freq 144~146 MHz/ 430~440 MHz

Gain 3 dBi

SWR 1:1.5

Power 1kW max

Longest element: 58 Inch

Weight: 1.5 Kg

Available with camouflaged bag











อุปกรณ์น่าสนใจ Diplexers & Triplexers


Comet CFX-324B    $67.95

CFX-324B   Manufacturer NCG Comet Model # CFX-324B Product Description Triplexer Band Pass 1.3-150MHz 200-320MHz 390-500MHz Insertion Loss 0.2dB 0.25dB 0.3dB Maximum Power (Watts) 600w PEP 600w PEP 600w PEP Isolation 40dB Connectors Output: SO-239 Low…

วิทยุเครื่องเดียว ไปออก 3 สายอากาศ หรือกลับกัน



fullair_zps5a5f1fce fullground_zpsc00fd932 mid_zps23a90d25 midclose_zpsfaf23391 naked_zps8bd97eb8 naked2_zps7fda745f naked3_zpsf2b464d4 topclose_zpsd7bdeb95 topdetail_zpsb2f99e61

Feed Point
so239_zps4342535e so239coax_zps749d2176

Bandwidth กว้างมาก
144mhz_zps237f7068 146mhz_zps72dabf0c 148mhz_zps5203bd85


Homemade 2M/440 J-Pole for $35

2m/70cm Dual Band J-Pole by KK4ICE

If you have any questions about this project, contact KK4ICE@ARRL.NET.

(Step-by-step instructions with photos can be seen below, following the project description and safety disclaimer.)

DSC4508-300x220 DSC4509-300x208 DSC4511-300x199 DSC4513-300x199 DSC4514-300x220 DSC4518-300x199 DSC4522-300x199 DSC4524-300x199 DSC4526-300x199DSC4525-189x300  DSC4528-199x300 DSC4529-199x300


Open Stub J-Pole

I’ve constructed a 144/440 Dual band Open Stub J-Pole Antenna.

I saw the plans for this on the internet (link to plans) by Allen Lowe (N0IMW). Since I had a Metal Fabrication background, I thought this would be an easy build.

I understand that everyone else in the world uses Metric, You can convert these numbers to MM and use 10mm aluminum rod and thread for the elements.
However I am not sure about the SO-239 adapter. I’ve read that it can be difficult to obtain the adapter in Europe.  Any EU/Metric users, please help me out and give me details on what you did.

Here is a Step-By-Step video with me stammering on. Getting a little bit better every time I make a video.


I did some minor changes from the above. Instead of using nuts I used pressed “PEM” nut on the underside and used thread protecting vinyl caps on the tips

It was a really fun and quick build. Plus it works okay. It’s no Diamond X510. What else do you expect for around $20 in parts? I love it.

If for whatever reason you can not build this. It is manufactured by the designer of this antenna and has them for sale on his website for a reasonable price. So check out ARROWANTENNAS.COMfor the OSJ and other quality crafted antennas.

Due to many e-mails, I just want to state that I do not and will not manufacture these antennas for sale. I think those sold at Arrow Antennas are well worth price.

Antenna Gain, Pattern and NEC data

Some people were curious as to what the gain and pattern is of this antenna is.  Arrow Antenna basically said they weren’t posting figures as competitors use gain as a marketing ploy and inflate numbers. However they did publish the patterns. I’ve tried to model the antenna in 4NEC2 without much luck. What I was inputting into NEC was nothing near comparable to what I and some others have measured. Thankfully I wasn’t the only one who was having issues modeling a J-Pole. C Bronson Crothers (AA1ZB) has talked about modeling the J-Pole and wrote quite a bit about it. Carol Milazzo (KP4MD) took it a step further and modeled the Open stub J-pole.
She modeled the antenna in various situations (mounted to mast, free space, free space with ground) and even published the NEC files for all to see. I’d strongly suggest to check out herwebsite for the NEC files and other information that has helped me along in the hobby.

I took the files and messed around to see what happens.


Depending on the height about ground, your looking at anywhere between 3-7dBi (or .85dbd-4.85dBd) gain according to NEC Data. In the perfect world, if that antenna was fed with 50 watts, it would effectively radiate anywhere from 60 to 150watts. But that is in the perfect world which we are not in. Things like the type and length of coax used, connectors used, nearby structures, type of ground and a bunch of many other variables factor into how well an antenna performs.

In the antenna gain world you will see dBi and dBd depending on the manufacturer. You just don’t measure Decibels.  In this case it’s used as a reference against either an isotropic antenna (dBi) or against a dipole (dBd). So if you see antenna readings in dBi, it’s in reference to a theoretical perfect antenna that radiates evenly in every direction. If you see dBd, the antenna is being compared against a half-wave dipole antenna.  The difference between dBi and dBd is 2.15. dBd is comparison against an actual antenna. Some hams confuse dBi and dBd and some manufacturers confuse the buyer by not telling you the reference (It has 9dB of gain!!). Most manufacturers use dBi as it’s a bigger looking number. Just subtract 2.15 and you will know the gain compared to a half-wave dipole.

I bring up dBi vs. dBd gain for the reasons why Arrow Antenna doesn’t want to talk about it. An antenna shouldn’t be just about gain. It should factor in your shopping but you honestly won’t really know how an antenna will perform until you get it in the at. There are times I hear that the J-pole is no different than a dipole or even a ground plane which is not true. This particular antenna has some gain. It’s not as high when compared to the claims of large scale antenna manufacturers but considering the materials used, ease of assembly and use, I think this is a really good antenna. Okay, now that I am done ranting… let’s look at the pattern

This is a 3-d wireframe of the pattern (in gray) with an outline of the vertical polarization. The antenna is pretty much Omni-directional Horizontally. Vertically, the focus of energy is between 15 and 85 degrees.  It would be ideal to mount the antenna above the roof line or at least 10ft off the ground as the signal radiates more from the side. This antenna wouldn’t really be ideal for Sat use as there is a huge null and less gain when looking towards the sky.

SWR and analyzer results

SWR plays an important role as well. If the antenna is not correct, some of the power sent to the antenna will come back to the radio. Modern rigs can see this and if too much power is coming back, the rig will step down in power to prevent damage to the finals. This usually happens if the SWR is above 2:1 or 3:1 depending on the rig. We need to get the SWR of this antenna down to 1:0 as possible. If this antenna is fabricated and assembled correctly, there should be little concern about SWR but it’s safe to make sure and check before using or even installing it


Here is what 4NEC2 Predicted On the VHF Side. By looking at the blue line towards the top of the image, you will see that it has excellent SWR throughout the 2M band. Looking at the green line, you will see that the impedance is also decent.


The UHF Side of the antenna doesn’t look so great when compared to the VHF side of the antenna. But it’s still useable. Once again these are predictions from the software. It’s doesn’t mean that’s how the antenna is going to exactly perform. But it will give you an idea of what’s going to happen. Let’s do some real measurements.

Someone let me borrow their Antenna Analyzer a few years back. You will see at 145.98Mhz I got a reading of 1.0SWR with a 51ohm impedance. The antenna was resting on a wooden chair so I am not sure what the value would be when fully installed but I don’t think it would change that much since it doesn’t need grounding. But coupling to nearby fixtures

After making various antennas, I felt I needed some kind of analyzer of my own. I purchased a mRS MiniVNA PRO. It covers HF/VHF only but it give me a better idea of how the antenna is performing throughout the band.




Here is a plot of the antenna installed. You will see that the antenna is usable from 135MHz to around 155MHz. It’s a nice wide band antenna and you will see how it differs from what 4NEC2 Predicted. But it’s not far off

Thanks to Jon (KI6RT), he provided some SWR plots from the VNA. What’s great is that he measured the UHF side of the antenna which I’m un-able to measure with the equipment I have. According to Jon, this was measure with the antenna installed at height


VHF Side


UHF Side.

 Known Issues:

Even though I did not design this antenna, I often get e-mails from people who had trouble with this particular antenna. I helped troubleshoot a lot of the issues and found out that the majority of problems were in result of the person not following the instructions as listed on either my or Mr. Lowe’s prints. Most common mistakes were people cutting the lengths short or people substituting the  materials called with others. For those living in the rest of the world, I know you might have trouble trying to find SAE/Imperial material and will substitute 3/8″ with 10mm rod and hardware. I am not sure if they make a Metric SO-239 to 10MM adapter. But I’ve heard from multiple people that it work with 10mm.

Another common mistake is when it comes to testing. Testing should be done with the antenna installed or at least mounted to a pole to simulate an installation. Some people were laying the antenna on the ground, holding it with their hand or placing it against large metallic items  (like a car) which will produce different readings. You won’t know how it performs SWR wise until you have it installed. Even though it’s rare, be prepared to install and remove the antenna multiple times while taking readings.

There is an issue which I haven’t touched on. Much care should be taken to prevent water from getting into the threads of the SO-239 adapter or in the adapter itself. Even more so if you live in colder climates where water can freeze and expand.

If you are unsure about cutting the elements to the proper length, it’s best to cut it a little longer and grind or re-cut the elements. It’s better to have elements that are too long instead of being too short. If you happened to cut it too short, it’s possible to use a coupler to adjust the length of the antenna but I would suggest re-making the element in question.

Others who built the OSJ-Pole

I like when people send me their creations. Some follow instructions exactly while others are creative and use what they have to make a working antenna. Here are some links to those who also made the antenna. Maybe they can provide some insight into things I forgot.

F6FZU’s OSJ-Pole – French reader who managed to make the antenna using metric tubing as well as different materials while getting decent results on the analyzer. The one thing that stands out is that the angle he using to mount the elements is made from Galvanized dipped steal. I would avoid using steel at all costs. It appears he is taking steps to weather proof the steel.

Michigan Amateur Radio Alliance (MARA) – Couple of their club members (KD8PVS &  KD8UCP) decided to build the OSJ-Pole using my prints. They did a very nice job and they also found another source for the vinyl caps and provided clamping and installation photos of their antenna. Nice job!

KI6RT’s Profile – In Jon’s profile, he built the OSJ-Pole. He manged to run the antenna through a high end analyzer showing SWR results of both the VHF and UHF portions of the antenna. It shows that at least the SWR is decent in both the bands.


สายอาการ Super J

The Super J-Pole antenna for 430 – 450MHz was constructed and used for FM simplex and repeater operation at my previous residence in Melbourne, Victoria from 2002 – 2007



The Super J Pole antenna is a co-linear vertical consisting of a number of half wave length vertical elements separated with half-wave length stubs (Tuning stub) feed with a folded matching stub. The sub doesn’t receive or radiate any energy; it is simply a way of picking off the desired feed impedance.

Additional half wave length section can be added with addition of a half wave length tuning section (Tuning stub). The addition of half vertical elements could be added indefinitely, subject to reality of diminishing returns. This arrangement can be applied practically and usefully on bands within the VHF and UHF spectrum. The use of the J pole feed arrangement creates an antenna that is relatively ground independent compared to many other designs.


Frequency:                       435Mhz

Polarisation:                    Vertical

(A) Main element:             502mm           (0.75 Wavelength x 300/f x k)

(B) Matching stub:            167mm           (0.25 Wavelength x 300/f x k)

(C) Additional section        344mm          (0.50 Wavelength x 300/f x k)

(D) Tuning stub:                344mm          (0.50 Wavelength x 300/f x k)

(E) Feed point:                  Approximately 10 – 30mm from the bottom.

Subject to adjustment for lowest VSWR


The dimensions of the Super J-Pole have been determined as follows:

Length (Mtr) = 300/f x k x el


f = Operating frequency e.g. 435.5MHz

k = The effect of the diameter of the material in relation to the wave length


el = Chosen element e.g.  Wavelength main element, wave tuning stubs

or wave matching

stubs,   0.75, 0.50 or 0.25 respectively.


The associated photos are of my successful in service (2001 – 2006) version that covers the entire 70cm (430 – 450 MHz) band.

Practical construction

Construction is very simple. After determining the various element lengths, mark them out accordingly on a continuous length of copper wire and bend to achieve the antenna shape. The tuning section that separating the additional half wave length elements can be bent around to form a semicircle (see photos). Tape the wire formed antenna to a suitable length of dowel or fibreglass rod for stability.

After successfully impedance matching the coax feed point with a VSWR meter the antenna can be mounted inside a suitable length of conduit to protect the antenna from the effects of weathering.

It is recommended that the coax be attached through some sort of feed line choke arrangement to mitigate possible common mode currents in the transmission line.

 superjpole_image01  superjpole_image03  superjpole_image04
Adjustable feed point. Tuning stub Complete assembly
Note: The above photo of the adjustable feed point shows the coax connection polarity per the original construction as the polarity was viewed then to be unimportant. I have been convinced since that it is crucially important that the  coax connection polarity be the reverse of that shown in the photo, that is the centre of the coax attached to the main element and the shield to the J pole stub.See: J-Pole Coax Polarity


The above 3D radiation plot of the Super J Pole was modeled using MMANA Antenna Analyser software by JE3HHT, Makoto (Mako) Mori.

For more information on the J-Pole see:



DIY เครื่องคัดแยกมูลไส้เดือน


Page 5 of 61« First...34567...102030...Last »