Home built antenna help needed

[earl]

I am looking to build some antennas to use with some of my kenwood 805D radios. the first 2 of these will be installed on a base station

 

Antenna 1  Priorities are: low cost, ease of build, low swr.

 

Antenna 2  Priorities are low swr, durability, max range in one direction.

 

 

Antenna 3 This antenna will be a field deployed on a 20' mast at a camp site

                   Priorites are Maximum Durability, ease of erection, low swr

 

Antenna 4 This antenna will be used on an atv

                   Priorities are small size, safe for the atv rider nothing to poke in the eye or back, low swr

 

Antenna style recomended for each application and reason why, building tips, exact measurements

 

My skill set includes drilling soldering, welding, cutting glueing  My materals available include ridgid copper pipe, solder joints, plastic pipe glue joints for plastic pipe, coper wire of varied sizes. several car radio antennas. some old CB antennas including long steel whips. a large old fiberglass base station CB antenna (radials are gone) Several pieces of coax some with ends some without ends Several old parts radios with coax ends other parts misc.

 

I know I am asking for a lot of advise. Thank you for your help.

 

[Guest spd641]

Earl,

 

Since you have the copper give this  j-pole antenna a try. I am sending you the link to do the calculations for it.

 

http://www.aralb.org/Commitees/Technical/J-POLE/design_a_jpole_antenna.htm

 

Give it a try and have a good weekend...William

[PastorGary]

With many commercial and business operators going to 700 to 900 MHZ last year, there are many radio shops that have "trade in" antennas in warehouses just collecting dust.

 

An excellent way to fabricate a permanent or movable base station antenna is to buy a used NMO mount and attach that mount to the center of a piece of 20 or 22 gauge galvanized steel cut in a circle 12 inches in diameter as a ground plane plate.  Get a used gain type, center loaded mobile antenna and secure it to the NMO mount.  Use a couple 6 inch per side "L" brackets (for putting up shelves on a wall) attached to the underside of the ground plane plate so that the legs of the "L" brackets are as far apart as the diameter of a mast pipe. Secure the "L" brackets to the mast with two spiral radiator hose clamps and bingo - a base station antenna with around 3.7 to 5.4 db gain (depending upon your antenna element choice) that can be placed just about anywhere.

 

Varied NMO mounts:  http://www.theantennafarm.com/catalog/mobile-antenna-mounts-264/

 

The ATV situation may pose problems because most bodies are fiberglass or carbon fiber. But we can use the same type of NMO mount and steel and use a compact 6 inch 1/4 wave mobile antenna tucked out of the way wherever it would be convenient to mount. 

 

Whip imaging: http://www.theantennafarm.com/catalog/laird-tech-qwft120-763.html

 

I personally have no experience building directional, vertically polarized yagi's, so I'll defer to others for suggestions there. 

 

This is an example of one: http://www.theantennafarm.com/catalog/tram-browning-br-6355-3581.html

 

If you do contact a radio shop for used components, just check with them to see if they might have a trade in UHF base station antenna resonant to around 460 to 464 MHZ.  I recently picked up a used Tram antenna for $18.00 - it is like the one in this link:  http://www.theantennafarm.com/catalog/tram-1486-1575.html

 

 

Good luck with the projects.

[earl]

Thank you for your sugestions.   I also found this site http://www.packetradio.com/ant.htm

 

Would you recomend a ground plane for #1 and a J-pole for #3.

 

Would the 45 watt of the 805D blow out a antenna off of a hand held ?

[earl]

The #4 radio is being setup as a bag radio.  It will stay on the atv most of the time but can be used as a carry around.

[PastorGary]

It may not be advisable to place a 'rubber duckie' antenna directly on the connector on a mobile radio.  I have seen that done with a Motorola Radius and the high RF field coming off the antenna literally caused smoke to come out of the RF final, internal power regulator and receiver IF sections.  It was toast.   Get the antenna away from the radio by 3 to 4 feet if possible with coax and some type of mobile mount with metal ground plane plate of some type to manage the SWR. 

[Guest spd641]

I will stress one thing when working with any antennas DO NOT place them close to your body,the results could be be long term and a slow process,causing cataracts and RF burn could result in skin cancer.Be careful and use caution anytime you working in any RF environment.One example of why RF if dangerous,if you place a hotdog of a long wooden stick maybe 5 ft long and touch it to a antenna while transmitting (100 watts) and it will cook that hotdog.Imagine what it does to your body when in close proximity to that antenna.

 

The results may not immediate unless direct contact is made but the long term affects will affect you later in life so be safe when doing these projects,the eye sight you save may be your own have fun experimenting be watch out for yourself and others.On another note when working in high RF environments as in tower locations,make sure all power is cut off before you climb any tower or expose yourself to a area where transmitters are located...William

[Guest spd641]

Thank you for your sugestions.   I also found this site http://www.packetradio.com/ant.htm

 

Would you recomend a ground plane for #1 and a J-pole for #3.

 

Would the 45 watt of the 805D blow out a antenna off of a hand held ?

I have bought from Buxcomm in the past when I first got into GMRS.I do not remember the model of the antenna but it was a Opek UHF base antenna it cost $47.47 it was one of the best antennas I ever owned.I used it to get into north Georgia repeaters that were 130 miles away and the band spread was wonderful,it would accommodate both 70cm amateur and GMRS with a SWR of 1.5.1 or less all the way across the band.If I am able to locate the number again I will let you know...Have a Great Weekend...William

 

Here is the antenna from a different supplier but it has the same model number,if you want try and look it up on packetradio.

 

http://www.americanradiosupply.com/opek-uh-2401-200w-uhf-vertical-base-station-ground-plane-antenna/

[earl]

I thank you all for your suggestions and help.  The reason I ask about building in place of buying is two fold. First while I have access to a small salvage yard I do not have access to money. I live on around $1000. per month.  That being the case a $50.00 purchase will require saveing for several months. The second reason I want to build and not buy is that I want the knowlage and experience of building the antennas.  I guess I should have mentioned that. 

[Billy]

earl here is a list of build ideas.  For your budget, if you have the half inch copper a J-Pole should be a easy build.  Some gain is better but these antennas will work. 

 

http://www.dxzone.com/catalog/Antennas/J-Pole/

[Shriekmau]

When it comes to mobile units keep in mind that nearly all mobile units need a 50ohm feed line between the unit and the antenna. Connecting an antenna directly to the mobile unit is never advisable due to the power output. As spd mentioned earlier, you are dealing with RF and EMF. This is and produces radiation. There are RF exposure limits and it is very important to adhere to those limits. Not doing so can result in immediate damage such as an RF burn, or cell damage which is not noticeable immediate but turns into cancer later down the road.

 

Best to read up on those limits so you know what they are and can prevent future health issues. 

[PastorGary]

This link below gives BASIC info on RF fields as they apply to human exposure from cell equipment, etc.   At .01 to 10 nanometer wavelengths, human cell destruction is cumulative with time as ionizing radiation (XRay machines, etc.)   This may not fully apply to frequencies as low as GMRS, but this info should be considered for safety reasons -

 

CLICK >>> http://www.fcc.gov/guides/human-exposure-rf-fields-guidelines-cellular-and-pcs-sites

[Shriekmau]

Gary,

 

Keep in mind, the lower the frequency the more penetration it has. For instance, a 50MHz wavelength has a much shorter maximum exposure limit than a 460MHz wavelength. The way I read your post seems to indicate the shorter the wavelength the more dangerous it is.

 

 

Thanks,

Jeremy

[PastorGary]

I had some incorrect or arbitrary info from WIKI again... So, I changed the text a bit to be more accurate

[Shriekmau]

I found some information on the ARRL website. This is a ham site but it has a chart 2/3 of the way down which can help you determine the MPE or Maximum Permissible Exposure.

 

http://www.arrl.org/the-fcc-s-new-rf-exposure-regulations