Homebrew multiband.

[prcguy]

A good quality SO-239 or PL-259 is good to at least 500MHz without anything to worry about. Even Motorola uses them on duplexers past 500MHz where the signal is passing through four sets of SO and PL connectors and there is no significant loss to speak of.
Using an SO-239 as an antenna junction at 800MHz should also not be a problem because you can tune the vertical element to resonance with the connector in place and it becomes part of the antenna.
prcguy

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.

 

[kb2vxa]

"...you can tune the vertical element to resonance with the connector in place and it becomes part of the antenna."

Consider this, when making a ground plane type the vertical wire fits all the way down inside the solder connection so if it's cut to proper length to begin with the overall length doesn't change. Strictly speaking, electrically it does not become part of the antenna but part of the transmission line as do all RF fittings and connectors. It's only purpose in this instance is a mounting hub for the elements.

You've got the right idea PRC but you're speaking physically, not electrically which could possibly confuse some less technically minded.

 

[iMONITOR]

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 found these:
http://images.google.com/imgres?img...flange+mount&start=36&ndsp=18&um=1&hl=en&sa=N

 

[smason]

A good quality SO-239 or PL-259 is good to at least 500MHz without anything to worry about. Even Motorola uses them on duplexers past 500MHz where the signal is passing through four sets of SO and PL connectors and there is no significant loss to speak of.

Interesting. I had read somewhere, guess I should Google it, that they really don't perform above 300, though my UHF transceivers all have SO_239s. Most duplexers I've seen (even VHF) used N connectors, though I don't doubt what you're saying about Motorola.

I'm surprised Warren didn't comment on the subject.

 

[prcguy]

Thank you for the comment but I was speaking both physically and electrically and here is an exercise that may better explain what I was trying to explain.
Make a ground plane with a high quality female N chassis connector as the element junction and an identical version using an SO-239 chassis connector, I'm speaking of the vertical element soldered to the center pin of the chassis connector and the coax connector side goes to your feedline.
Tune them both to 800MHz and you should find the element lengths are very slightly different because the SO-239/PL-259 junction is not a 50 ohm impedance at 800MHz like an N connector and the vertical element will end up longer or shorter to tune the antenna to resonance using the SO-239. The end result should be two antennas that perform nearly identical but one has a vertical element that has been tuned to offset a slight impedance mismatch. If the same SO-239/PL-259 connectors were simply in the feedline you would incur the full loss of the mismatch where it can be mostly tuned out when the junction is at the antenna feed point.
prcguy

"...you can tune the vertical element to resonance with the connector in place and it becomes part of the antenna."

Consider this, when making a ground plane type the vertical wire fits all the way down inside the solder connection so if it's cut to proper length to begin with the overall length doesn't change. Strictly speaking, electrically it does not become part of the antenna but part of the transmission line as do all RF fittings and connectors. It's only purpose in this instance is a mounting hub for the elements.

You've got the right idea PRC but you're speaking physically, not electrically which could possibly confuse some less technically minded.

 

[prcguy]

This thread got me thinking of the Sputnik I had many years ago with an approx 16" long VHF element, two approx 3" long identical elements that will resonate near 800MHz and the apparent lack of a UHF 460MHz element.
It turns out the 1/4 wave VHF element of approx 16" will also act as a 3/4 wave element on UHF and will match close to 50 ohms there. If you were to have a 6" element in the mix there would be two active elements at UHF and the impedance would about 25 ohms with similar current flowing in both elements.
I believe RS took the correct approach with the Sputnik by adding 800MHz elements to a VHF ground plane and let the VHF element work as the UHF element. On the home brew multiband groundplane in this thread, I would remove the 6" long J and just have the VHF element and the "little J".
prcguy

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]

On the home brew multiband groundplane in this thread, I would remove the 6" long J and just have the VHF element and the "little J".
prcguy

That's some interesting info. Although it seems to work well for me on all bands, the 411-416 range that the city buses here use comes in a bit weaker than most anything else. They are a little distant from me which may contribute but they boom in with the 5/8wave that I built strictly for that band and it is only 25ft vs 40ft that the multiband is at. I may be tempted to try taking off the 6in "J" next summer when I plan to take the RG6 down and replace it with some RG8 that I got this fall.