Very nice website & some cool software.
I also fully agree with your religious & political statements!


Thanks!


73,


Doug

 

----- Original Message -----
Subject: RE: Question on the DB420 antenna - From KG8ID


>
> Does your antenna look like it's been tampered with?
> 1. Has the phasing harness where the elements are different lengths apart
> been untaped & stretched out or kinked up to accomplish the different
> distances the elements are apart?
>
> 2. Are there marks on the mast where the hose clamps used to hold the
> elements & where the element mount used to contact the mast?
>
>
> If yes, most likely someone has messed with the antenna & I would return
> all
> elements to spec.
>
> If no, this antenna was probably a special order so it would have
> electrical
> downtilt.
> These types of antennas can be special ordered with electrical downtilt &
> changing the spacing between elements and varying the length of pieces of
> the harness is how that is accomplished.
>
>
> 73,
>
>
> Doug
>
>
> -----Original Message-----
> Subject: RE: Question on the DB420 antenna - From KG8ID
>
> I found this at repeater builders -
> http://www.repeater-builder.com/antenna/440fdipl.pdf
>
> it says 23 inches between each element, mine are from top to bottom - 22
> 13/16, 25 1/2, 22 5/16 then the next set are 22 7/8, 25 5/16, 23 1/16.
>
>
>
>> Howdy Perry,
>>
>>
>>
>> Open dipole array antennas like the DB420 are fairly broad band, that's
>> one
>> of the reasons I prefer them for most applications.
>>
>>
>>
>> There are 4 different models of the DB420. One model covers the "G"
>> (Government) band 406-420, another model covers the 450-460 band and the
>> third & fourth models covers the "T" (Television) band 470-488 &
>> 488-512MHz.
>>
>>
>>
>> Each model will have a SWR of 1.5:1 or better across the band it's
>> designed
>> to cover.
>>
>> And they'll go better than 7MHz outside of this band before the SWR gets
>> to
>> 2:1.
>>
>>
>>
>> Thus, the model made to cover the 450-470 band easily goes down to 443MHz
>> before the SWR gets to 2:1.
>>
>> Some will do better than that.
>>
>> Thus, if your repeater is Txing high & Rxing low in the 440 band, this
>> makes
>> an ideal antenna.
>>
>>
>>
>> The DB420 has a gain to the horizon of about 10Db and a vertical aperture
>> of
>> 7 degrees, thus making it an ideal antenna for a ground mounted tower.
>>
>> They don't make good antennas for high mountains where coverage is needed
>> close to the bottom of these mountains.
>>
>>
>>
>> Looking at your SWR of a little better than 2:1, it's obvious that you
>> have
>> the 450-470MHz model, which is the most common model for obvious reasons.
>>
>>
>>
>>
>>
>> I attached a spec sheet for you to review.
>>
>>
>>
>>
>>
>> From 30+ years of experience with this antenna in both professional and
>> amateur service, I've found that the aperture does not appear to change
>> as
>> you move lower in frequency as the SWR begins to climb above 2:1. Thus
>> they're ideal for repeaters in the 440 band. If you install an isolator
>> between the output of your Tx & your dux, that'll take care of any
>> reflected
>> power towards your PA & your antenna will perform as good as if you were
>> operating it in the 460 band.
>>
>>
>>
>> Hope I've helped you.
>>
>>
>>
>> Feel free to contact me anytime if you have more questions.
>>
>>
>>
>>
>>
>> 73,
>>
>>
>>
>>
>>
>> Doug
>>
>>
>>   _____
>>
>> Subject: Question on the DB420 antenna - From KG8ID
>>
>>
>>
>> I have a DB420 and am planning to put it on the tower for a repeater
>> antenna, is there a way to tell what the bandwidth of the antenna is as
>> far
>> and the model I have?, the information tag is missing, the SWR seems
>> acceptable, 57.5 out and 4.5 back.
>>
>>
>>
>> Perry/KG8ID
>>
>>
>
>
>
>
>
>
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> 1:40 PM
>