Antenna Builders.

[KC8JPZ]

I am just curious to see if there is anyone else into building antennas? I think I have built a dozen antennas here the past few months. I've got a bigger bad pile than a good pile. I'm fortunate enough to have become good friends with another ham who is a retired antenna engineer who worked on some really neat projects for aircraft throughout his career .He has been a great help in my projects. I usually build mostly directional antennas for UHF. They are usually allot smaller than the lower band antennas and easier to build. So far the best antenna I have built has been a double diamond style antenna with a reflector. I work a UHF repeater 18 miles away on about 3 watts from the ground floor window of my apartment. I used solid 8th inch brass rods for the element and a PVC frame for the reflector which is rapped with aluminum window screen. I am pretty happy with the performance of the antenna so I think I may buy some aluminum and tig weld a reflector and make a much sturdier antenna.

Anyhow, I'd like to see if anyone has built an antenna they are proud of and, tell us about it.

 

[Bill2k]

I've built a simple quarter wave ground plane antenna for VHF (155MHz). I use it as my primary antenna at home. It was the best 5 bucks I spent! I've designed a couple of other antennas to build but the wife always has other plans for me when the tools come out.

 

[Andruw]

That sounds like a good anteanna, I would try to build some, but I don't have enough time and money.

 

[TooLate]

Antenna Builds

Are these antennas always base antennas or are any of them for use on mobiles? My interest for both discretional and security issues is in the possibilities of constructing various antennas in various frequency spectrums (10-11 m to 155 MHz) that utilize the smaller low profile GPS type pods. Does anyone have an exploded view of one of the commercial units so I could see what components are necessary? Then, I could determine if various fractional wavelengths would be possible. I've seen elsewhere on RR the formulas used to calculate antenna lengths etc for certain frequencies and could go from there.

That said, and assuming that a 1/4 to 1/8 wavelength would be workable (i.e. wire helix or other patterns would be doable and still keep it to pod size), what issues (physics) will need to be considered? (If a helix, do the coils touch each other, what diameter of helix, what diameter of copper wire (or other element used), what other possibilities for the windings are there (concentric, stacked concentrics, insulators needed etc)?

Granted, this list of questions would be more specific if the fabricated antenna were to be used for both tx and rx. However, my main interest is for monitoring purposes.

I've spent a rainy extended weekend off perusing RR and associated links and found good information w/respect to some antenna calculations as well as some vendors that have some pod type antennas for various paired sets of frequencies (155 and 450, 155 and 800, 450 and 800 etc) but my interest is in the low bands (10-11 meter). As I mentioned, monitor only...no transmit.

Any suggestions or reference sites would be appreciated.

73
tl

 

[ReceiverBeaver]

Some say that half the fun of playing with radios is the experimenting involved. Ah the smell of solder resin....really gets ya going in the mornings! Many hams traditionally build their own antennas especially ones made of wire for the HF bands.

As mentioned above, the 1/4 wave verticle ground plane is a popular design and easy to make. Good construction materials are commonly available. This one design below will create a 1/4~ gp that will TX/RX anywhere from CB at 27mhz up to 800mhz. Just cut the elements down to your desired tuned frequency. Best to have a radio that transmits on your desired band + an associated SWR meter, or an antenna analyzer device, or lacking that and for receive only, just cut elements by the mathmatical formula. Will be close enough for monitoring.

1) 102" stainless steel CB whip
2) Trucker Heavy Duty Mirror Mount
3) 4 pieces of 1/8" or similar aluminum rod stock, 10 foot lengths

The mount comes with 4 bolts for tightening the mount down to the mounted surface (in this case your mast). Place one of the 4 rod stocks under each bolt and tighten down. Arrange them so they end up evenly spaced at 90 degree angles.

Screw the whip into the supplied 3/8 x 24 threaded mounted, connect the coax into the SO239.....instant 1/4~gp for CB. To convert it up to 6 meters at 50 mhz or VHF or UHF, just use the formula of [ 234 divided by freq. ] and cut the whip and ground radials to this length. For transmitting, I'd cut the elements LONG and use the radio & swr meter or antenna analyzer and then further trim the elements down 1/8" at a time until the desired center freq. resonance is obtained. For listening only, this is not critical. The formula length will be close enough.

And you can experiment further. One of these with the verticle whip cut for VHF will also receive UHF fine also. Leave 2 of the ground radials at VHF length and cut the other 2 down to UHF lengths.

The mentioned Antenna Analyzers, like an MFJ 259B or 269 are really cool. Use them also to test your portable duckies to see where they are tuned at. Use adapters to go from the analyzer's SO239 input down to the BNC or SMA, Motorola ect... connectorthat is on your ducky. They are available at Ham radio supply shops. However, do not buy them directly from MFJ Enterprises, they will sell them but at inflated list prices so that they are not directly competing with their distributors....the ham stores.

The 269 covers from HF thru VHF, upto about 172 mhz. & from about 420-470mhz UHF.

good luck and have fun

 

[TeRayCodA]

My projects are at:

 

[Napalm]

My favourite antennas lately are slim-jim's made from 300 ohm line...

Really easy to make... If you need waterproofing just shove it inside a PVC pipe.

 

[Hoofy]

I enjoy experimenting with antennas. I have built quite a few mostly for the 2 meter band. I built a 5 element beam that I could take apart the elements and store them in the boom for remote hill topping and a 4 element quad that would fold down for transport. Lots of different sized j-poles made from aluminum, copper, 300ohm wire. Lately I have been building scanner antennas which are easier because they are just for receive.

You never know unless you try.

 

[KC8JPZ]

TeRayCodA:

Those are some fine examples of antennas. Truly impressive. I have also thought about a few folded dipole experiments. My main problem is matching them. My engineer friend has shown me how he made a few matching stubs or pieces of home made hard-line that have the desired impedance to match the driven element to coax. I'm just not that advanced or focused I guess at the moment. I would just like to complement you on your craftsmanship of the antennas on your site.

TooLate: There are a few sites on what might be helpful for you on the antennas you described. I do not have them handy at the moment but I will attempt to email you with the sites. They are about PCB board antennas. I’m not sure how effective they are on lower freqs. I imagine they do rather well up around 800mhz - 2.4 gig. I will also try to find the info I have on the Helix antennas. They are very tricky. I have tried a couple of experiments with not much success. I didn’t try all that hard though. All of the dimensions you mention go hand in hand with the design factor of a helix. The helix is nice because of its circular polarization. I am assuming that is why you are interested in that antenna. A good place for info on helix antennas is from the satellite guys. It seems to be more popular with them. That is another work in progress I have going on at the moment. basically what I am building for satellite is a much more affordable AZ+EL rotor that is very portable. I imagine that I will have around 300 in the project. That may be wishful thinking though. I would like to hear more about your ideas for your projects sometime if you feel appropriate.

 

[TeRayCodA]

Thanks.I have experimented with a gamma match for my folded dipole stack for MURS.The SWR is 1.2:1.

I guess,I would have not needed the folded elements,as,a straight 36"aluminum rod would work as well for each elements.

One of these days,if I can find a 20ft length of high tensile strength 1&1/2" aluminum pipe,I'm going to attempt to build a four element dipole array.

The wiring harness is the challenge.I try to make all the feedlines the same length,I start out building one dipole,tuning it to 151.820,getting the SWR down to the lowest,Then,I build the next dipole to the same EXACT specs as the one I tuned.
When working with that antenna,each dipole must be in tune,so,what you do to one,you must duplicate to the other.(like co-phase)

That thing has an awesome range for only a couple of watts on VHF!
I would still be hard pressed to buy a commercial antenna-it works.
I had a problem last summer when I changed the feedline to 1/2" heliax.The SWR went too high.(different velocity factor than the RG-8?)
I had to re-tune the gammas,but,with the heliax,it's now better than ever.We use our MURS system quite a bit.1 base,2 mobiles,three handhelds.