[CQ-Contest] Stubs

[Jeff Stai]

The right way to tune a stub is to tune for maximum attenuation (null) at
the center frequency you want to exclude, if the stub is meant to be
shorted or open, measure it that way. Don't measure an open stub and then
short it expecting it to end up in the right place.

I tune my stubs using an antenna analyzer connected to a TEE which is
connected to a dummy load. At the dummy load I measure the RF across the
load using an oscilloscope. The stub under test is connected to the "base"
of the TEE.

I like using a scope because it's easier to see the low voltages at the
null from an antenna analyzer, and you can sweep using the analyzer, but
any other arrangement of sweep-able RF source, and voltage or wattage
measurement is fine too.

Sweep the RF source around the desired null and trim until the null is in
the right spot. I use a small alligator clip for a temporary short if the
stub will be shorted in use.

If you want to know more (and you should) this is the best book on the
subject and dollars well spent:

http://www.arraysolutions.com/Products/Books/W2VJN_Interference.htm

73 jeff wk6i



On Tue, May 7, 2013 at 3:28 PM, Joe <nss at mwt.net> wrote:

> Anyone with the answer about the "TEE" connector?
>
> When making the stub because the "TEE" will introduce some added length,
> so to cut the cable right on. I'd have to have the "TEE when making the
> cable with the MFJ unit.
>
> but what should I do with the other end of the "TEE"  leave it open? put a
> 50 dummy across it?  etc?
>
> Joe WB9SBD
>
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
> On 5/6/2013 7:49 AM, Joe wrote:
>
>> Getting ready for Field Day here.
>>
>> The only bands we seem to have problem on are 40 & 20 with the two
>> stations hearing each other.
>>
>> So plan on making up a pair of stubs, for each station.
>>
>> Now from wat i have found seems pretty simple.  and will this actually be
>> correct?
>>
>> It looks like the 1/4 wave (electrical) on 40 un shorted will block 0 an
>> pass 20  yes?
>>
>> and the exact same stub shorted will pass 40 and block 20  yes?
>>
>> so adding at the far end a small SPST toggle switch should make a easy
>> switch 20 or 40 stub  yes?
>>
>> Now I plan on using them in the usual manner right at the rigs with a "T"
>> connector.
>>
>> To make them we plan on using a MFJ 259B
>>
>> The way they say to make a stub using it is pretty plain and straight
>> forward and easy, "BUT"........
>>
>> I'm assuming I should include the "T" when making the stub to have it
>> include the extra length it is making.
>>
>> Now what do I do with the open end of the "T"?
>>
>> does it need to me terminated? like with a 50 ohm dummy load? o9r left
>> open is ok, or what?
>>
>> Anyone?
>>
>> Joe WB9SBD
>>
>> For Field Day The Yellow Thunder Amateur Radio Club
>> WB9FDZ
>> The field Day Zombies
>>
>>
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-- 
Jeff Stai ~ wk6i.jeff at gmail.com
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