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.
Continue reading if you want to build this antenna.
In the past couple of weeks I picked up a couple commercial two-way radios. I’ve purchased a Motorola Maxtrac 300 (Mobile) and a XTS 3000 (Handheld).
I’ve been a fan of commercial radios since I got my hands on a HT1000 and beat it up pretty good. I’ve dropped it, thrown it, threw it into a puddle and who knows what else and they always worked out.
There are PROs and CONs about owning a commercial radio for Amateur use. One of the CONs is programing. Unlike amateur radios, the majority of commercial radios have to be programmed. With Motorola, depending on the situation, the software that is used to program these radios will end up costing as much as half (or more) of what you purchased the radio for. You could also have a local dealer program the radio. Another one of the CONs is the ability to change the frequency “On The Fly”. You can only change to a frequency (Channel) that is programmed into the radio.
One of the PROs are that you will get a radio that is built to public safety and/or military specifications. These radios can take a lot more abuse then it’s amateur counterpart. Another PRO is that these radios are built as “Part 90″ (Public safety, Private business, municipal, etc) radios. That means you can use these radios in both the LMRS and Amateur frequency blocks. Your not allow to take a amateur radio and modify it to transmit in the LMRS. So if you have a job that uses radios in the LMRS blocks or you want a radio that can do both GMRS/UHF (Or MURS/VHF) then you will have a radio that will possibly cover all 3 possibilities.
This is the Maxtrac 300 I got on e-bay for around $100. It was being advertised as a 430-470mhz split which is rare but when I hooked it up to the computer, it was the 450-470mhz split.
Just a note for anyone that is looking to buy this or it’s GM300 brother on eBay. Make sure the auction has the Model number in it. For example, the model number D34MJA7JA5AK means that’s it’s a 10-25w (2nd Number), UHF (3rd # ) Conventional (Numbers 4,5,6 and 7[MJA7]) 32 Channel (8th # [J]) A5 HEAD (9,10th #) Revision K (Last Digit).
So now you know your getting 10-25 watt 32 Channel UHF radio. However these types of radios have 2 splits per band. On Uhf you could get getting a 403-430 or 449-470 split. I’ve read that there is a 430-470 Split RF but I have yet to see it. The only ways to tell what split the radio is, by looking at the radio in the RSS (programing) software or actually opening up the radio to see what the part number is on the RF Board. So be careful if your looking for a Ham band Maxtrac.
This is my Motorola XTS 3000 UHF Handheld radio. I purchased this item because the “But It Now” price was just where I wanted it. Another reason is that it can decode/encode P25 Digital. Always wanted to mess around with it and now I have the chance. Only issue is that there is only two P25 systems for ham radio in the state of Massachusetts and they are both located out of range. If there is enough interest in the area, I would like to setup a repeater capable of P25. We’ll see…
Thanks for reading!