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Filter Cavity Question
开云体育
I have a filter cavity question for those who are experienced with the DB4001-series high band cavities. They're listed as adjustable from 148 to 174Mhz but do they actually tune lower into the 2m band? I'm not equipped to sweep this one at the moment and was
wondering if the answer could be found among this group's vast experience.
Thanks,
Gary
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I’m sure you can squeeze an extra couple MHz?
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One of the limiting factors is if the tuning rod has been cut and it isn't long enough. What frequency is it on now and how much tuning rod is sticking up?
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Jow On 9/21/2021 8:25 PM, n6lrv@... wrote:
I have a filter cavity question for those who are experienced with the DB4001-series high band cavities. They're listed as adjustable from 148 to 174Mhz but do they actually tune lower into the 2m band? I'm not equipped to sweep this one at the moment and was wondering if the answer could be found among this group's vast experience. |
开云体育
? ? Every one I've tuned went down into the ham band.? When stretching the tuning of cavities lower in frequency, aside from running out thread the concern is as the plunger gets closer and closer to the bottom end of the cavity, there is more capacitive coupling which begins to degrade the Q.? Whether or not the extra half inch (or whatever the difference is between resonance at 144 MHz vs 148 MHz) is going to make enough of a change in C to worry about I can't say, but would easy to determine via measurements. ? On the opposite end of the scale, I also ended up with a large quantity of aircraft-band (108-136 MHz) DB4001 cavities, and those went UP to the 2m ham band no problem as well. ? ??????????????????????????????????????????????????????????????????????????????? --- Jeff WN3A ? |
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From: [email protected] <[email protected]> on behalf of Jeff DePolo WN3A <jd0@...>
Sent: Tuesday, September 21, 2021 5:55 PM To: [email protected] <[email protected]> Subject: Re: [repeater-builder] Filter Cavity Question ?
? ? Every one I've tuned went down into the ham band.? When stretching the tuning of cavities lower in frequency, aside from running out thread the concern is as the plunger gets closer and closer to the bottom end of the cavity, there is more capacitive coupling which begins to degrade the Q.? Whether or not the extra half inch (or whatever the difference is between resonance at 144 MHz vs 148 MHz) is going to make enough of a change in C to worry about I can't say, but would easy to determine via measurements. ? On the opposite end of the scale, I also ended up with a large quantity of aircraft-band (108-136 MHz) DB4001 cavities, and those went UP to the 2m ham band no problem as well. ? ??????????????????????????????????????????????????????????????????????????????? --- Jeff WN3A ? |
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One will find most cavities will tune well outside the limits spec'd.? One issue though the cables on the cavities are usually cut for specific frequencies.? So might not get exactly the spec'd performance.
Many cavities I have used were for out of band I needed, but they tuned to the point they worked fine. 73, ron, n9ee/r |
Chris Baldwin