Homebrew GMRS 3 Element Yagi

Since I’ve built a ton of J-Poles and wire Antennas, I’ve wanted to build something different. I decided on a 3 element YAGI built for GMRS that is directly fed with 50ohm coax. After a couple of failed yagis and the help of another ham on QRZ.com forums, I finally built a Yagi that works! The reason I’ve chosen a Yagi built for GMRS is due to the ultra high frequency, which ends up being a small antenna. If I were to mess up (Which I did), the material cost would be low. I also wanted to use it on a GMRS repeater in the area.

The first Design I used is with a Web Site that has a Java base applet to design the Yagi, After getting all the Dimensions from the website, I went to work building the antenna. After everything was done, I learned two things. One is that my drill press does not drill straight (90 Degrees) through the tubing. The other thing is that when I hooked up the antenna to a simple SWR Meter, That didn’t work either (Pegged the Meter). At this point I got frustrated  and posted my issue on QRZ.com. A Ham by the call of WB3BEL (Harry) took my dimensions (That I got from the applet) and plotted my antenna into 4NEC2 software (Like EZNEC but freeware) and it would not work for the center frequency of the GMRS Band (or any part of the GMRS band).
WB3BEL actually re-designed the antenna to where it would work so I give him credit and major thanks for help. I took his Dimensions, Modeled the antenna for fabrication and built the antenna. I Hooked up the antenna to a transceiver and SWR meter and got a 1.2:1 SWR and a 1.5:1 SWR on the outsides of the GMRS band. The Design is calculated to yield 7.5Dbi of Gain. Considering connector and cable loss (Lets say 4Dbi using 50ft RG-213 W/ 3 SO-259 Ends and a Barrel Connector) still yields gain of around 3.5Dbi which is not too bad.

Here is rendered Image of the Antenna. The elements are Insulated from the boom using plastic shoulder washers for the Reflector and director. The Driven Element is insulated using a 0.750(OD)X.375(ID)X1.5″(L) Plastic spacer. Since the elements are going THROUGH the boom, It will make the elements electrically shorter so you have to compensate for the loss by adding 0.279528″ (7.1mm) to the element to correct the effect (Boom correction). The elements are secured using #8-32 Screws screwed to the boom. The screws are also insulated from touching the boom. The screws do not make any significant changes to radiation pattern of the antenna as long as it’s insulated from (not touching) the boom. I did notice that the screws actually lowered the SWR a tad which is great.

I didn’t add a matching network to the antenna because I wanted an easy to build and assemble antenna which is the entire point of this article. The antenna is fed using RG-213 Coax with terminals soldered to the core and shield. I tried to keep everything as short as possible because this and the ring terminals effect the performance and SWR of the antenna.

Here are a couple of screen shots from the antenna software that show the Radiation Pattern and gain. Nothing special here.


Here is the calculated results for the SWR of this Yagi. Please note that it’s in the ball park. By adding screws, coax leads and the ring terminals, it could or will effect the final pattern and/or performance of the antenna.


Here is a SWR Shot. As you can see, I don’t have a very good meter. I would like to buy a HF/VHF/UHF Antenna analyzer for my Antenna builds but I don’t think that will happen in the near future.


Here is the complete Antenna.
Overall it was a fun little project. It took a short time to build and it’s a great directional antenna with some gain to help your signal on GMRS reach its destination.

Continue reading if you want to build this antenna.

Continue reading “Homebrew GMRS 3 Element Yagi”

Ham Radio… IN 3-D!

Well, Not really.

When it comes to building things for Ham Radio, I shoot for perfection. Down to the point where I will reverse engineer every part in CAD and assemble my project in CAD before I even start building. It has saved my butt many times over and if there are people actually following this blog, you’ll see evidence of my pre-planning. Here are some examples of what I am talking about.

 

3D Code Key
3D Code Key

 

This is my dual touch pad code keyer. This took about a couple of hours to make because I was not sure what type of  touch pad I wanted. I wasn’t sure if I were going to user a horizontal or vertical setup. So I ended up going with both. The horizontal brass keys are inlayed into a piece of plexi glass. the vertical keys are insulated from each other using plastic grommets.

 

3D Code Key - Built
3D Code Key - Built

 

Here is the actual touch keyer. This project was considered a failure. Everything worked great until you placed the cover over battery/board, which caused some kind of interference and would not allow the “Dah” key to perform well.  I ended up mostly using the horizontal key pads. If I decided to attack this again, the Vertical keys will be omitted.

 

3D PL-259
3D PL-259
3D SO-239
3D SO-239

Here is something that most, if not, ALL hams have seen. It’s a PL-259 and SO-239 Connector that I reversed for an amplifier project. Once I have enough small parts designed, I will release just the models (Not editable) for others to use in their designs

Butternut HF9V Mount

Here is a Model of a Mount for the ButterNut HF9V.  It’s a 5gal bucket that will be buried then filled with cement and a pipe to sleeve the Antenna. On top of the Bucket will be my Radial plate I designed to attach the ButterNut to.

HF9V Plate
HF9V Plate

Here is the plate ready for Action. I will go into more detail about this setup when I install the ButterNut.

 

3D Vibroplex Bug
3D Vibroplex Bug

 

Here is a incomplete Vibroplex Bug. I wanted to see if it was possible to reverse the bug and it was almost successful. Things like my family and obtaining my extra class license push this to the back burner.  I am saving this to learn how to animate using the software. I still think it looks neat.

 

You might be wondering how I did this (really?). All of these parts were designed using  software called “Autodesk Inventor 2011”. This software is made by the same people who made AutoCAD. AutoCAD is one of the, if not, the most popular software for Computer Aided Drafting (CAD). There is another piece software called “SolidWorks” that I use as well. I find that Inventor separates the Sheet metal modeling from the 3D modeling which is perfect in my trade. These Two pieces of software are the most used software for design and fabrication for a lot of the items that you use today. Most CNC cutting, milling and forming machines uses the files that are generated by this software.  After designing the part in CAD,  it can printed on a blueprint to be giving to the fabricator, and/or the part can be imported into the software that will convert the information into G-Code for the CNC machine. Once the information is loaded and all the settings are correct, the CNC machine can now do it’s job cutting/milling/forming the part. All of the parts are modeled to 1:1 scale. Meaning if the part is a 12X12″ square piece of metal, I modeled it to 12 inches by 12 inches. That way you can see how it looks compared to other stuff.

If your a ham radio operator, 3D modeling software can be beneficial, even if you don’t have access to CNC a machine. From this software you can generate the blueprints and/or files needed (See my OSJ-Pole prints for example) by fabricators to produce your part. Since you already designed it and gave them the information that they need, it could save money in design/programming. I also think it’s more understanding reading a blue print with proper dimensions than someones chicken scratch or MS paint drawing.  My OSJ-Pole print is the most searched and downloaded file on this site because I think how it was presented to the reader.

Referances:
Autodesk Inventor – Software for 3D modeling parts (They have a free trial!)
Solidworks – Software for 3D modeling parts

MasterCAM – Software  used to generate G-Code for different type of CNC machines. (I would not suggest using this software Unless you own and/or know how use the CNC machine your trying to design for)

 

 

 

 

APCO 25 (P25) and DSD

Since I have a radio capable of transmitting Digitally using the Project 25 protocol. I wanted to test it out. The only issue is that there are no P25 ham radio repeaters in receiving distance from my house and I do not have another P25 radio to communicate with. After searching around Google, I found some websites discussing software that will decode the digital signal and convert it to analog over your computer’s sound card.

Hardware Needed:
Scanner – I guess it can be any kind as long as you can get at the discriminator output. I used a Radio Shack PRO-97.
Audio Patch cable – From the discriminator output to the computer
Computer – Not sure what the minimum requirements are. I used a 1.5Ghz single core AMD (Circa 2003) and a motherboard with a built-in sound card.
Sound Card (If you computer doesn’t have Sound Card) – I don’t think there is a need to go out and spend hundreds on a card that your going to use for this purpose. The money spent on a expensive card could have been spent on a scanner that can decode APCO25. I’ve found that a sound card using the AC97 Codec works the best.

Software Needed:
Linux OS Or Windows – That’s right L-I-N-U-X!! DSD Will NOT run on ANY KIND OF WINDOWS OS. Let me type that again. DSD DOES NOT RUN ON WINDOWS!!!  Sorry but I had to do that.  I’ve used UBUNTU Ver 10.04 . At the time of writing this, the current version of Ubuntu is 11.04 . For some reason DSD DOES NOT WORK WITH UBUNTU VERSION 11.04 . The reason I choose Ubuntu is that it’s downloadable,  free and has a Graphic user Interface. Since I never Ran Linux before, I felt a little more at home with Ubuntu. You can run a Dual Boot system so that when you start the computer, you can have a choice of which Operating system to boot into. With Ubuntu you can also run Ubuntu off the CD instead of installing the OS on the computer.  Please note that there is a lot of reading in installing Ubuntu which I will not cover on this website. Google questions you have and I’m sure there is an answer out there

 

DSD (Digital Signal Decoder) – This is the software that actually takes the digital signal and decodes it.
Mbelib
– This software actually takes the decoded information and synthesizes it so you can hear the decoded audio.

DSD and mbelib can be downloaded from here (See note at the end of this writeup)

After modifying your scanner and getting Linux to run, download Mbelib and DSD in Linux and remember where they are located. In terminal CD (Navigate) to the directory where both Mbelib and DSD are located, Unpack both Mbelib and DSD and then install Mbelib first then DSD. If your very new to Linux and have some computer skills, this thread helped me out.

After installing everything, in Terminal type “dsd” (without quotes) and If all goes well. The last line should be “Audio In/Out Device:  dev/audio”
Errors that I got at this point mostly have to do with sound.  Either your sound card is being used by another application (even the sound control panel) or DSD is not calling up the correct sound card. DSD is defaulted to use sound card device 0 (zero). So if your sound card device is in a different spot then you need to tell DSD the location for the sound card. You can check where your soundcard is (if it’s installed) by typing “aplay -l ” into terminal. If it’s device 2 for example then you type in terminal “dsd -i /dev/audio2 -0 /dev/audio2”

I’ve uploaded a video showing up how DSD works with APCO 25 (P25, Project 25). It also works on other digital modes but I have not yet tried.

I am loving this software. It’s not the easiest software to install or use but if your into scanning and just even wondered about Linux. This is the perfect project to get your feet wet in Linux.

Please note that I am not an expert on the DSD software or Linux. Most likely I will NOT be able to help you if you’re experiencing problems. The install went so great for me and worked so well that I wanted to install it on another computer. After installing it on another computer, I had nothing but trouble. The good that came out of having a hard installation is that I learned a bit about DSD and Linux.

Thanks for reading

UPDATES 10/24/2011
I haven’t been using DSD much as I’ve been out of touch with APCO but I was informed by a user on Youtube that There is a verison that runs in windows.

Here is the link to the RadioReference Thread

Basically what the Author did was compile all the stuff from the linux version of DSD into a windows .exe file.  If you just want to listen to P25, Download the version in the 3rd post of the thread. All you have to do is un-zip everything into a folder and run dsd.exe

I’ve tested it against my XTS3000 (P25) and everything looks and ran great. I think the Audio was a little better sounding on my Linux box but the audio is still legible and I’m glad to now have it on a windows box. Maybe I’ll listen to it more often.

Make sure to plug into the discriminator tap and put the other side into the LINE-IN (Blue). Before loading DSD make sure that the LINE-IN is your DEFAULT recording device and you should be all set. If you try to do this while the DSD is running you can run into issues just like when it was in Linux.

Thanks to the RR crew because it makes scanning more fun and less expensive.

OSJ-Pole – Adjustable

The thing that amazes me about the Open Stub J-Pole is it’s simple design that performs well. I am not saying it will out-perform commercially built high-gain antennas but that it performs well using a few parts. I think it’s even easier than building a copper J-pole and even ground plane antennas (maybe just a step up).

One of the big complaints that I’ve been reading about the Open Stub J-Pole is that it’s difficult to tune. The only way to tune the antenna is to actually cut the stubs a little bit at a time. If you cut too much the stub is now worth it’s weight in scrap.

Now that I am the owner of a GMRS radio, I wanted to build a OSJ-Pole that you can adjust with ease. I found plans on the internet for a  Copper Cactus J-Pole that used a brass screw threaded into the “Tuning element”, or the Short stub (By Glynn Rogers, K4ABT).   I am using that idea on the OSJ-Pole. What I ended up doing is cutting about 3/8″ off the top of the short stub, drilling a hole down the center of the rod, tapped it with a 10-32 thread and inserting a screw with a jam nut. Now I can move the screw in and out to obtain the best SWR and then tightening the jam nut to secure the screw.

Here is a picture of what I am talking about

Adjustable Open Stub J-Pole

I tried to make a custom angle bracket with what I thought was the correct spacing  but the SWR was horrible So I used a extra bracket from one of the many Dual Band OSJ-Poles I’ve built. It worked out pretty well.

Close up of "AOSJ-Pole"

Here is a close up of the tuning screw.  I ended up using a lathe and a drill bit (.159) to put a 2″ hole at the end of the 3/8″ round short element. I then used a bottoming tap to make the 10-32 threads as far as I can go. I then used a 1-1/2″ Screw and a 10-32 Jam nut to lock the screw in place. I am sure this can be applied to any of the Open Stub J-poles that are out there. Just make sure to cut some material off the elements so you have room to adjust above and below the calculated line. For the dual band you’ll have two adjusters. Since most people don’t have lathe access to make the hole in the center of the 3/8″ rod. A vice, center punch (automatic or not) and a steady hand with a drill will do. I would make a pilot hole with the smallest drill bit in your stock (under #21 or .159″).

I was able to tune the AOSJ-Pole from a 1.5 to a 1.0.  Since I am building more and more antennas, I saving my pennies to buy a antenna analyzer so I can give better reports with more information than what I am getting on my SWR meter.

Next project will be a GMRS 4 Element Yagi.

 

Homebrew Rigblaster Nomic Data Cable

Since I got the SignaLink I figured I can mess around with the Rigblaster.  I wanted to adapt it to the FT-100 so If I ever go out with it and a laptop, I can do some digital work using the rigblaster as a interface.

On their website they posted a article “Connecting your FT-897 to The Rigblaster NOMIC for digital operation” (Written By Jeff, K8YSV).

I Followed the directions to the T and here it is!

Just some things I would like to point out. The FT-817, FT-857D, FT-897, FT-100D, FT-950,  FT-2000 and I am sure many other makes and models use the MINI 6 PIN DIN connector which is the same as a PS2 cable that you find on a semi older keyboards and mouses (mice). I thought it would be easy and just find a old mouse or keyboard, clip the wire and use the connector. Well guess what? The PS2 Mouse and keyboard use 4 out of the 6 pins and the two that have nothing connected to them are need to wire up for the Yaesu rigs. You just might be lucky and come across a cable that works. I went through about a dozen keyboards and mouses until I gave up. Getting frustrated I went on Ebay and picked up a 6 pack of connectors for $10 w/ shipping.

If you follow the entire article on the above link you can make a cable with just basic soldering skills.  I added a ferrite choke to the data and audio cables to help cut down on the noise generated from nearby objects.

After constructing the cable and testing it out, I wasn’t too impressed on it’s performance compared to hooking the NOMIC up using the Microphone jack and audio patch cables.

I notice it didn’t sound right. I don’t have the proper analyzing equipment to give a detailed reason why but if you look at the band edges on the above picture, you will notice a drop off which I never seen with the unit normally hooked up. I also notice that the audio is not as strong either. I had to max out all the settings on my soundcard and radio. Even with the levels maxed and removing the resistor on the NOMIC board,  the audio still seemed low.

Overall I am not too thrilled about the outcome of the cable but it works. It makes it possible to use the microphone again and It’s going to help on a future project I have in the works.

Up, Up and Away! (Diamond X510 Installed)

This weekend I worked up the courage and installed my Diamond X510 on my roof. It wasn’t easy due to the pitch of my roof and lack of any safety gear and also making sure the ladder was secured to the house. I don’t picture myself climbing up onto that roof again.

In the above picture I designed and fabricated my own mounting straps to mount the antenna to the cast iron vent pipe.

The support pipe is  galvanized dipped and  then powder coated white to survive the elements

Here are roof brackets just after being cut with the 4kw laser. Brackets are made of 14ga (0.074) Staintless
All the hardware used in the installation was made out of stainless. I didn’t want a nice trail of rust running down my roof.

Other than the anxiety of climbing onto my roof , It was fun.  I couldn’t wait to get back into the house, run the RG213 through the wall and start transmitting.

Using Diamonds radiation pattern on the antenna I calculated the coverage of my antenna.

I think it calculated a little too much but it’s pretty close. From moving my antenna from 5ft off the ground to the top of my house using low loss cable and Type-N connectors, I see a major difference and wondered why I never bought a commercially built antenna. I notice that I can now hit stations further north from my QTH. before I couldn’t get past 10mi north. Now I can hit the W1UWS repeater on top of  Mt. Ascutney in Ascutney VT (100mi north of my QTH) and I could now hit Mt. Graylock in N. Adams MA  (60mi Northwest of my QTH) and many repeaters in the Berkshires. In the south direction I can now get repeaters in Litchfield and Hartford Counties in CT.  Compared to the J-Poles I can now contact 40 additional 2m repeaters. So overall I am extremely pleased of the results.

Now to get the Butternut Installed.

 

My Diamond X510NA 2M/70CM Antenna

Last week I managed to get a Diamond X510NA antenna for free! The only issue was that I had to go and retrieve the antenna off the roof and also remove another antenna which I also got to keep. Not sure what the other antenna is but my focus is on the Diamond X510NA. This is my first “Commercial” VHF/UHF antenna. All my previous antennas were home brews which performed just great.

When I got the antenna down, nature has taken it’s course and there was corrosion of the visible metal parts and the white lacquer coating is gone exposing the fiberglass tube. However the tubes were still intact and the copper inside looked great for the most part

In this closeup you can see the minor issues that nature caused.

 

I was determined to get this antenna looking and performing like it was new.  So I went to the hardware store to look for plastic spray paint  and rubber foam strips for sealing  joints around doors to keep drafts at bay.

Here is a photo with the Rubber foam stripping rolled around where the old foam was. I am doing this to prevent the actual antenna from rattling around inside the tubing.

I designed a bracket to use for the roof  installation. The straps will be made out of 14ga (.074″) stainless and I already acquired a 1.25″ I.D. galvanized pipe and had it powder coated white to match the rest of the antenna. I don’t want any rust up there.

Here is the finished antenna. I mounted it to the deck with zip-ties to make sure the antenna works before going onto the roof.

Here is another angle of the antenna. The joints and feedline were taped with “X-Treme Tape” which is a silicone based
tape that will make a watertight seal. I also used “Undercoat” rubberized spray where the radials are mounted to prevent any more corrosion to the base.

There is a night and day difference compared to my home made antennas. Even though it’s 5ft off the ground and the huge aluminum siding wall right next to it, I am hitting repeaters that I never could hit before. Can’t wait to get this up on the roof.

 

Open Stub J-Pole Project – Completed (Many times)

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

Assembled Open Stub J-Pole

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.

Plans for Dual Band J-Pole 1
Plans for Dual Band J-Pole 2

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.

(Update 12/2018) Radio-Shack has since closed and the SO-239 adapter I listed on my blueprints are no longer in stock. You can find equivalents on ebay, amazon and other amateur radio or CB supply shops. It’s known as a “SO-239 to 3/8″-24 Adapter”. There are some variants so please make sure it appears the same as the one in my blueprint. You will need to check the diameter of shoulder on the insulation washer and adjust the size of the large to to make sure it fits.

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

Aluminum J-Pole Base 2nd View

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.COM for 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 her website 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.

OSJNECplot1

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

OSJ-NEC3
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

OSJ-NEC4

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.

OSJ-NEC5

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.

NT1K-Jpole

NT1K-Jpole-page-001

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

JPOL144

VHF Side

JPOL440

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 QRZ.com 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.

CW Keyer In Fabrication

I had a chance to get started on fabrication of my code keyer.

Code Key Project / Metal
Fabrication on my Code Key Project

It’s nothing much but it’s a start. The vertical keys are spaced 0.75″ apart. I do not have easy access to 3/4″ Material so I’ve made the spacer out of 3 1/4″ Plates of steel. If I waited I could have used two pcs of 3/8″ But I designed it using 1/4″ blocks and the
opportunity was there.

I am not going to post for every part that gets made but when it’s assembled and painted I will talk more about it.

CW Project Underway

I purchased a CW Touch Key Kit which came in on Friday. It was easy to assemble and I have it taped to my desk using drywall ceiling buttons as code keys. My plan is to design and fabricate a Code key.

So far I’ve manage to design the key around the Touch kit.  Here are some of the drawings

The plan is to have two sets of keys. I am not sure what style I wanted so I figured I’ll do both. The base and vertical stand will be laser cut using 3/8″ Steel plate for weight. The enclosure will be 16ga (.062″) Steel with welded corners and the keys will be punched out of 16ga brass.  The vertical keys will be secured using extruded plastic washers to prevent any contact with the other keys and it’s metal base. The Horizontal keys will appear to be floating. However they will be inlayed into 1/4″ Plexiglas. I plan on using a DPDT Switch to activate one set of keys while disabling the other set. The only issue I see that the wires are sensitive to the touch and the switch might cause an issue.