They do have excellent notch rejection, but very poor
bandpass qualities. If you look at a wide-band
spectrum plot, say from 0 to 1000 MHz, you'll find the
two notches, and many peaks, but the majority of the
signal gets through with nearly no attenuation. It's
almost flat from 0 to maybe 400 MHz, and flat from 500
to 1000 MHz, with perhaps 5dB loss. I've seen other
duplexers that have two notches and two peaks, and
everything else is attenuated a considerable amount
(over 60dB). Not so with the Celwave/PD 526 series.
Call or write to Celwave (now RFSystems) and ask them
for the cutting chart for units using RG400. Last time
I tried that, every technician I spoke with told me,
in no certain terms, that they NEVER used RG400 or
RG142, yet I have seen photos and one actual unit that
was factory fresh and had that unmistakeable tan
colored, RG58-size teflon coax that I know is not
RG214. Maybe they finally realized that they DID make
them that way.
I've never been able to figure out the actual lengths
of the coax jumpers on these things. Of course, the
coupling loop inside the cavity probably has something
to do with the length too. Since I don't want to drill
the rivets to find out what's inside, I'll stick with
the cables the factory sends out.
By the way, my first unit had RG8 with clamp-on male N
connectors. Every one had been twisted so much that
pieces of braid were shorting out the center pin and
there was no longer a good electrical ground circuit.
So I bought one brand new set of cables for 440-450
MHz for $250. When I had to do this the second time, I
built my own; 6 ft of RG214 and a dozen crimp-on male
N connectors cost a whole lot less than $250.
Bob M.
==
--- mdnosliw <[EMAIL PROTECTED]> wrote:
> --- In Repeater-Builder@yahoogroups.com, "mdnosliw"
> <[EMAIL PROTECTED]>
> wrote:
> >
> > I recently picked up a Phelps Dodge 526-5 on
> e-bay. The auction
> stated
> > that it would work in the ham band. When I
> received it I discovered
> > that it was a 470 to 512 mhz model.
> >
> > If I replace the cables can I get it to tune down
> to the 440 segment
> > of the band.
> >
> > Thanks
> >
> > Mark
>
> Thanks for the info Bob. I know that there are
> different versions of
> the notch filter, but I think that relates to filter
> bandwidth.
>
> Yes I have the cable length chart, but I think I
> prefer to use RG-
> 400.Should not be a big deal to do the math.
>
> I have 3 526's and think it is the best Uhf duplexer
> that can be had.
>
>
> Thanks
> Mark
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