开云体育

Folks,

I have an old eBay Chinese flat pack that I put on the bench to tune for a temporary use repeater. I can notch it down to 90dB just fine. But the insertion loss is horrible. I'm getting around 5dB of loss. I thought something was wrong with the SA/Tracking Generator and plugged it in to the service monitor to test before/after power output and sure enough, 5.4dB insertion loss. SWR is horrible for the actual pass frequency.

I don't think this got dropped (at least not that I know of). I hate to bash a cheap mobile duplexer from China, but I wondering if this has been other's experience of these knock off brand mobile duplexers?

The split is the same as factory...just a few Khz down.

Both sides are within a dB of each other.

-J

I should add that if I increase the split, then things look better (although not great). If I go with a 7Mhz split, I can get the insertion loss down to about 2dB and the VSWR looks good.

The only other thing I haven't tried yet, is to change the High and low side. Maybe they miss labeled at factory? I don't see how that will make a different since these cans should be symmetrical.

-J

Could the high side and low side be reversed? Maybe it came wrong from China.

Looking at the photo, I think the sides are reversed. Compare the frequencies to the "High" and "Low" labels.

So I double checked, and I should have thought about this before, but the frequency response looks ok for which side is high and which side is low given the roll off of the 'pass' frequency. So the label with the frequencies was indeed incorrect, but the 'low' / 'high' label was ok, which is what I was using for the 'pass' reference.

Note the attachment of the 'low' side. Notice how much the notch is encroaching on my pass frequency.

If I go to 7Mhz split, then its not as bad. Its like this notch filter was not designed for this kind of split... yet it was sold for 5Mhz split.

-J

The only other thing I haven't tried yet, is to change the
High and low side. Maybe they miss labeled at factory? I
don't see how that will make a different since these cans
should be symmetrical.

If they're anything like any other non-Chinese flat pack UHF notch duplexer
I've ever worked on, they are not symmetrical...

--- Jeff WN3A

quote"I should add that if I increase the split, then things look better (although not great). If I go with a 7Mhz split, I can get the insertion loss down to about 2dB and the VSWR looks good.

The only other thing I haven't tried yet, is to change the High and low side. Maybe they miss labeled at factory? I don't see how that will make a different since these cans should be symmetrical.

-J"



Not to go off on a tangent, but Wow, the email coming into yahoo groups looks like its out of sequence. This above? email was from earlier today before I did the low/high swap and test.

-Jeremy

Jeff you are 100% correct. They are not symmetrical, I don't know what I was thinking since the frequency response swings up or down based on the side of the duplexer.

Here is a snapshot of the response when I put things back on the SA/TG. You'll see the insertion loss...

If I push the split up to 7Mhz, then its not bad. Its kind of like they designed this for a wider split but sold it as a 5 Mhz split.

Flatpack Duplexer Fun

quote"I should add that if I increase the split, then things
look better (although not great). If I go with a 7Mhz split, I
can get the insertion loss down to about 2dB and the VSWR
looks good.

I do a flatpack duplexer pre-alignment... With an example 452
& 457 MHz pair, (5 MHz offset) targeted. I might move all the
low notches all the way down, well below 450 and the converse
of moving all the 457 notches up well in to the high 460 segment.
This type of approach can help to minimize miss-adjusted interaction
of excessively (initial set) close spaced cavities or cells. You're
not tuning the notch cavities to any specific frequency well below
and/or above the desired new location, you're just getting them
out of the way to a known visually (test equipment) confirmed starting
point. Once you have the known starting point, each side can then
be "brought back" and aligned at the new, desired location.

The only other thing I haven't tried yet, is to change the High
and low side. Maybe they miss labeled at factory? I don't
see how that will make a different since these cans should
be symmetrical.

If the flat-pack was labeled for repeater service, the high and low
side will be different from the same duplexer marked for duplex
base-station and/or mobile telephone type of service. Trust no
labels and wash you feet at least twice a month.

The flat-pack duplexer might not be symmetrical and I wouldn't
expect it to be for reasons I right now care to deal with. In
theory, the inter-connecting coax lines and the internal probe
makeup will normally not be the same length.

Not to go off on a tangent, but Wow, the email coming
into yahoo groups looks like its out of sequence.

"Yahoo is now part of Oaf", I mean "Oath" the Verizon Group...
it's time to see how a large cell carrier can further ruin Yahoo
while trying to extract your personal information for sale.

This above email was from earlier today before I did
the low/high swap and test. -Jeremy

My last RB Group post took more than than 24 hours to
show up in the listings.

cheers,

Pearl Jam

On 9/19/18 12:29 AM, jeremy_georges@... [Repeater-Builder] wrote:

quote"I should add that if I increase the split, then things look better
(although not great). If I go with a 7Mhz split, I can get the insertion
loss down to about 2dB and the VSWR looks good.

The only other thing I haven't tried yet, is to change the High and low
side. Maybe they miss labeled at factory? I don't see how that will make a
different since these cans should be symmetrical.

I'd try that next. Those Chinese duplexers are hit or miss, they could have
very easily run out of 5mhz units and given you a 10 mhz split one.

At 7.5 db you could use two circulators a duplexer with less loss.


--
Bryan Fields

727-409-1194 - Voice

I think you're right on this Bryan. I can't get a 5Mhz split to tune on this thing, no matter what I try. But if I get close to a 10Mhz split, it looks okay.

Many notch filters are not symmetrical.

If you discuss the bare notch filter or cavity response without any
other tricks or compensation, by nature of electronics theory, it
will probably be non-symmetrical in most cases where the physical
hardware or construction actually adds some additional reactance
on one side of the notch.

It can be compensated for in many cases, but the basic animal
(notch cavity) will normally not have a truly symmetrical response.

If you look at some of them, one side will have just a T connector
between the cavities and the other side will have what looks about
like a 1/4 wave of coax(hardline) comming from the middle of the T
to the cavity.

To learn a little more about notch filter placement and operation...
based on a real world example. The below article in this Groups
Files Section can be very informative.



Scroll down and select the:

Optimizing Notch Filter Matching DRAFT.pdf

Enjoy...

cheers,

Hand me down shoes
(Burton Cummings)

On 9/19/2018 9:02 PM, skipp025@... [Repeater-Builder] wrote:

If you discuss the bare notch filter or cavity response without any
other tricks or compensation, by nature of electronics theory, it
will probably be non-symmetrical in most cases where the physical
hardware or construction actually adds some additional reactance
on one side of the notch.

This is plainly seen in many band-pass cavities, and BPBR duplexer configurations because of the commonality of inductive coupling loops.? Many of these filter systems use a closed loop (inductive) coupling method.? This causes a defined difference in symmetry between the response of a cavity tuned to high-pass as compared to one tuned to low-pass.? The same happens with a band-pass cavity with two identical coupling loops.

In the band-pass cavity, if you trade one of the inductive coupling loops for a capacitive probe, a good bit of the asymmetry will be 'compensated' out.? In the case of a duplexer, some companies like TX-RX have added inductance on one 'side' which is placed somewhat out of the magnetic plane to minimize coupling.? This added inductance serves to balance the coupling method and attempts to make the duplexers response symmetrical.

Kevin

If you discuss the bare notch filter or cavity response without any
other tricks or compensation, by nature of electronics theory, it
will probably be non-symmetrical in most cases where the physical
hardware or construction actually adds some additional reactance
on one side of the notch.

If you look at it in the simplest sense, a 1/4 wave notch cavity is just an
open stub 1/4" long that is loosely coupled to the thru-line. In the same
manner as if you teed in the stub directly (rather than loosely coupling
it), it's going yield a shunt reactance across the line. In other words,
there's no such thing as a notch cavity that does NOT have some effect on
the thru-line at frequencies other than only at the notch frequency.

The tighter you couple the resonator to the line, the more pronounced the
deleterious off-channel effects will be. That should be obvious. Of
course, the tighter you couple, the more notch depth you get, so there's an
inherent tradeoff when designing/adjusting the coupling.

You can often correct for the adverse effects in the passband by adding a
reactance to compensate. You can also stand the resonator off the thru-line
with a length of cable to change the effect and/or to optimize the response
(either with or without stubs or other compensation) at the pass frequency.

Scroll down and select the:
Optimizing Notch Filter Matching DRAFT.pdf

Yahoo doesn't seem to be working at the moment (browser hangs and I get an
"Activity Timeout" page from Yahoo) when I click that link, but I think that
file you're referring to is something that I wrote while back to demonstrate
some of the effects we're talking about.

--- Jeff WN3A