Insertion loss can change a bit with the drive level which is more likely with CW bandwidths. An SSB filter loss should be under 4 dB at a -10 dBm level. A 250 Hz filter may have 10 dB insertion loss. I do not recommend driving filters over +10 dBm.
Rob, NC0B
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On Mar 6, 2024, at 1:23?PM, Jerry Kessler <N4JL.cw@...> wrote:
?Jim,
Any guidance as to maximum signal level for sweeping these Drake filters?
Thanks,
Jerry, N4JL
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Jim Shorney
Sent: Wednesday, March 6, 2024 12:22 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] Drake SL-2300 2.3-5645kHz Filter Testing
Wes,
Comments inline below.
On Wed, 06 Mar 2024 07:03:50 -0800
"Wes Winkler via groups.io" <wewinkler@...> wrote:
I got a couple of Drake SL-2300 2.3-5645kHz Filters at a swap meet and am
contemplating testing them with a NanoVNA. I have three concerns.
1) Can I directly connect the filter to the Nano VNA? I am mainly
concerned about damaging the filter due to the signal input signal level.
Yes. I have done it with several TR7 filters with both a NVNA and a Midnight
SNA. They both agree closely with sweeps done with two different HP 8594E
spectrum analyzers with the tracking generator option. You could use an
inline 50 Ohm attenuator on the NVNA output if you are really worried about
the signal level but I have had no issues.
2) I reviewed the TR-7 manual but it not immediately obvious which is the
input, and which is the output of the filter.
The filters are symmetrical. It doesn't matter. If you really want to know
you can trace the signal path on the block diagram and the schematics to
figure out which port is which by visually inspecting the filter board.
3) An idea of what the input/output impedance termination should be? I
may need matching transformers for the Nano VNA test.
50 Ohms. You can directly connect to the NVNA.
Attached are some samples done within the past couple of months of NOS eBay
filters. One is a screen cap of an Inrad 4 KHz, the other two are sweeps of
a late production Drake labeled SL2300 done with nanovna-saver software in
Linux.
You can also bench test the filters from your radio without taking them off
the filter board. All you need is a source of around 10 volts to activate
the filter you want to test and a source of -4 or so to bias off the unused
filters. I used by bench supply for the + voltage and a 18650 lithium-ion
cell for the - voltage.
73
-Jim
NU0C
Rob Sherwood