Trimming Sputnik?

[W6KRU]

The sputnik has a 19" main element that would be 1/4 wave at ~146 MHz. The smaller elements are 4.5" which is a 1/4 wave at 624 MHz. I have been thinking about trimming a short element or both 1" to make them a 1/4 wave at 800 MHz. Which band will this hurt?

 

[mancow]

400 Mhz Uhf

 

[W6KRU]

400 Mhz Uhf

But the main element is about 3/4 wave at 450. Would that not work for 400ish type freqs. ???

 

[W6KRU]

No one else has an opinion on this?

 

[smason]

I'd agree with you, seems like the 3/4 wave of the main element is what works at 400 mhz UHF.
However I'm not sure why they'd do 4.5" on the shorter elements. But then I only really understand the basics.

Hopefully someone with more antenna knowledge, and perhaps modelling software could comment.

 

[kb2vxa]

NEVER CUT THE ELEMENTS trying to "improve" a proven design, you'll only louse it up!

For one thing 3" is 1/4 wave on 800MHz and 9" is 3/4 wave, I don't know what 1" is offhand but it's a good bet it's in one of the low microwave bands. A Sputnik is easy enough to build so using the above information have a go at one for 800MHz just for the heck of it.

 

[Mike_G_D]

DDan,

Theoretically, you are correct. It is interesting that the small elements are 4.5in long rather than about 3in. It is possible that they are longer than the theoretical length so as to better match the antenna when you take into consideration the entire antenna including the 19in element and the fact that you have two 4.5in elements. Only putting one of these on a network analyzer and mounting the antenna in an open space would prove or disprove that possibility.

If you do cut the elements I would be curious what your observations are as to the apparent resulting performance is!

-Mike

 

[PHOENIX_SCANNER]

Don't mess with it. It works fine as is and the engineers who designed it probably knew what they were doing. Whatever you do will not help 800mhz reception, and probably hurt overall performance. But, if you insist on burning up $30, feel free.