Homebrew multiband.

[brentoli]

Ok. In my area I need preformance on VHF, UHF, and 800 all three. What options do I have, I want to home brew it, but theres not alot of plans on homebrew scanner antennas I can find. Is there an acceptable multiband, or should I be looking at monobanders in to a diplexer?

 

[iMONITOR]

Is this for mobile, or base? If it's base I think the only antenna design that will perform well across a wide spectrum like that would be a log-periodic.

 

[brentoli]

Base.
I've been a ham for 12 years now, but inactive for about 6 of those, so I really have forgotten alot of theory. Looking for something on the cheap. I want to get into the fun of building antennas again. I just wana start of with something simple (recieve only) so I don't get too frustrated, because everything I do fails!

 

[brentoli]

Also. I live in one general direction of the systems I would monitor. However one is Southeast of me, and the other is Northeast of me. Just a top of my head guess is about a 45* to 60* diffrence.

 

[ka3jjz]

You have got to be kidding! For base antennas, look at the homebrew section of the following (anything in blue or underlined is a link)...

http://wiki.radioreference.com/index.php/Scanner_Antennas

Check out the AC6V supersite. There are lots of ideas there; likely a log-periodic or Yagi (although a Yagi generally isn't that wide banded) might be up your alley.

73 Mike

[edit] Well what do you know. At the bottom of the AC6V site, in the 'Y' listing, there are a few links for wideband Yagis. Learn something new every day...the links don't work, but I did find a good description, but these are for HF not VHF. Still, worth checking the AC6V site anyway.

 

[brentoli]

Ok.... lots of articles. But. I haven't seen one on a 150/450/850.

 

[kb2vxa]

You can easily build a "sputnik" ground plane from a flange mount SO-239 connector and 14ga solid copper wire. For VHF Hi Band, UHF and 800MHz the radial wires are 19" with the vertical wires being 19", 6" and 3" respectively. Mechanical construction as shown except for 4 radials, don't forget to solder for good electrical connections.

 

[davidmc36]

I have built three multibands very similar to the sputnik. The dimensions sound very familiar. Two I did with 14ga copper for indoor use and the latest I made from 5/32 piano wire for rigidity and is on top of my 40ft tower. I have been almost nothing but happy with the performance of this type of antenna. There seems to be a little dead spot right around 411 with the one on top of the tower and that was right where I want to llisten to the buses in town. I solved that by making a sweet little 5/8 wave for just that band and put it up about 25ft on the side of the tower facing town. It pulls comms in perfect. I used the SO-239 for the 14ga ones and salvaged on old base from an aircraft VHF antenna to make a more rugged base for the outdoor one. That sputnik looks like a good bet. I will try and remember to hunt down one of the indoor ones and pass along the details. This picture is not that great but maybe it will get you started. I will put a reminder in my outlook to post more details

 

[zz0468]

Broadband? Base? Easy to make? Maybe directional? Log-periodic, as was suggested. You could start with a smallish TV antenna turned vertical. They're not so directional that they won't get two systems 40-60 degrees apart.

 

[brentoli]

Interesting.
Reference the sputnik homebrewed, two questions:
1) How do you attach multiple vertical elements to the PL-259?
2) What/How do you find the length and spacing for the j pole looking element?

Reference a log periodic:
I like the idea of building one, but what research do I need to figure out lengths and spacing?

 

[blueangel-eric]

I wish someone will make a simplified homebrew version of a scantenna.

 

[ka3jjz]

He's asking about directional type antennas folks <sigh> Read message 4 in this thread 73 Mike

 

[davidmc36]

Interesting.
Reference the sputnik homebrewed, two questions:
1) How do you attach multiple vertical elements to the PL-259?
2) What/How do you find the length and spacing for the j pole looking element?

Reference a log periodic:
I like the idea of building one, but what research do I need to figure out lengths and spacing?

I have not built a sputnik but I would guess that you put one element into the connector and attach the other elements to it.

Give me a few mins and I think I can dig up the dimensions for the one in my pic from another group where I posted it.

 

[davidmc36]

The center radial is 20 inches. The upper "J" is six inches long and attached ten inches from the bottom. It is spaced one inch away from the center. The small "J" is three inches long and spaced 1/2 inch from the center. The ground radials are 19 inches long. Since this is "multi-band" the dimensions are probably not too critical and you could probably experiment with them and do some tuning for the bands that you are looking for.

 

[davidmc36]

I copied that ten inch dimension from another post that I made but after looking at the picture it appears to be quite a bit lower. I am not sure if that is just because it was sitting on an angle when I took the pic or what. I will dig it out when I get back to town and update. I am sure experimenting with lengths and positions could be fun anyway and when you are happy with the dims. then make a more rugged one.

 

[Wirelesstek]

The easiest and most effective design would be a 3 band 1/4 wave groundplane.

With 155 mhz radials and 155, 460, and 850 radiators.

Or just buy the Radio Shack 20-176 ground plane for $25.99

 

[brentoli]

Or just buy the Radio Shack 20-176 ground plane for $25.99

Quick lesson in reading comprehension.

I want to get into the fun of building antennas again. I just wana start of with something simple (recieve only) so I don't get too frustrated, because everything I do fails!

 

[davidmc36]

Is the antenna I described here pretty much what Wirelesstek was reffering to, 3 band ground plane? Adjust the dimensions as needed to get the 155 mhz 460mhz and 850mhz or whatever is good for common things in your area? I bet sticking with these dimensions will be the best though because sombody figured out what works good together. I did not come up with this, I got it out of a scanner book years ago when I bought my first scanner that had "800mhz". I got it measured since I am home now. The center radial is 19in, the grounds are 20in, the little "J" is 3.5in, the medium "J" is 6in and is attached 7in up from the connnector. The half in spacing for the little one is accurate and the one inch for the 6in one is good. I have to attest that this works VERY well in all bands in either 14ga copper variety or the 5/32 piano wire type that I made. The only thing that I am worried about is the piano wire rusting up on the tower. I should have held out and sourced some stainless wire.

 

[smason]

You can easily build a "sputnik" ground plane from a flange mount SO-239 connector and 14ga solid copper wire. For VHF Hi Band, UHF and 800MHz the radial wires are 19" with the vertical wires being 19", 6" and 3" respectively. Mechanical construction as shown except for 4 radials, don't forget to solder for good electrical connections.

Why do all the photos of the "sputnik" look like the 2 shorter vertical elements are the same size?

Also, while the SO-239 really fits the bill mechanically, isn't it a bad choice above 300MHZ due to impedance issues?

I'm planning to build one soon, trying to decide on the best mechanical configuration, will likely use an F connector as I have tons of 'em and they're dead simple to install on RG6, but a chassis mount F isn't conducive to 4 radial and 3 vertical elements.

 

[davidmc36]

Why do all the photos of the "sputnik" look like the 2 shorter vertical elements are the same size?

Also, while the SO-239 really fits the bill mechanically, isn't it a bad choice above 300MHZ due to impedance issues?

I'm planning to build one soon, trying to decide on the best mechanical configuration, will likely use an F connector as I have tons of 'em and they're dead simple to install on RG6, but a chassis mount F isn't conducive to 4 radial and 3 vertical elements.

I guess technically the SO-239 is made for lower frequencies but I do know that this antenna works well on all of the bands that the radials are cut for. ( I mean the one that I showed you, I don't have any experience with the sputnik but it looks like a good bet too)