开云体育

I found a copy of a 1998 Murata databook for these sorts of filters. One set of graphs shows the effect of having source/load impedances which diverge from 330 ohms. Higher impedances seem to create the sort of effects we can see in my most recent graphs above... gain droop on the high-frequency side of the curve, and a group delay curve where the low-frequency peak is higher than the high-frequency peak.

I don't know yet whether the filter is seeing an impedance with an R that's too high, or one with an X that's too far from zero... could be both of course.

I've moved the case over to Cults for a paltry donation($2) to help with my time and costs. You can print this in any material you want. TPU is a softer material with a cushion.

I have the Murata data sheet here, and for a 180 ceramic filter, your group
delay plot looks normal. Murata does not show data beyond +/- 150 kHz, though,
and the y axis scale is 1 dB / divison, 6 dB total, so be careful making
comparisons to other plots not scaled the same. I can post that pdf page for
the GDT filters, showing a small version of all the plots, in you want.
PS thanks for the heads up to see what's going on here Dave.

I'd very much appreciate postings of the PDFs of the filter data sheets, Bob. A lot of the information on the older parts is getting hard to locate.

I have a few Model 18s and a Model 19 receiver. The Model 19 schematic is

attached; note no transformers. What do you make of it?

The 18 has a BJT input stage vs. the 19's JFET, and the 18 has no AGC for its
passive front end.

Oh, that's a beauty! Individual IF filters tunable inductors and caps - five adjustments per section, each. That really is something.

I wouldn't personally want to try fiddling with those filters without a _lot_ of careful thinking up front... the alignment procedure is probably a whole cave-full of hungry bears. Mark the starting positions carefully!!!

The good news is, this is going to be pretty easy to drive and measure, I think, as long as you look at the whole IF strip as a unit, because you're not actually driving any of the filters directly. The input side of each filter bank is driven from its own transistor amp and isolated from whatever you might do outside, and all but the last of the filter bank outputs is also isolated from the outside.

Take a look at the "IF input from front end". This has a very high input impedance... 470 kOhms, in parallel with the input impedance of the Q301 JFET (which will be extremely high at DC, and somewhat capacitive at 10.7 MHz). The L332 input inductor (between the jack and the gate of the JFET) might be there to cancel out the capacitive reactance... I haven't crunched the numbers to see.

Anyhow, I suspect that the best way to drive this input is to use a simple three-way T connector - NanoVNA drive port on one leg, the tuner's IF input connected to the other, and a good 50-ohm resistor connected to the third to terminate the drive signal. This will give you a high S11 return loss, and provide plenty of signal to drive the JFET. You _might_ need to pad down the NanoVNA drive signal to keep from overloading the JFET and saturating the whole IF chain.

On the output side... well, this may be a bit trickier. R317 (coming out of the last filter) is 2.7k, so the filter won't see less than that. When I look at the next stage of the schematic (the limiter assembly) I see this signal driving right into the base of a BJT, whose emitter is AC-bypassed to ground... so, the input impedance of the limiter is going to be quite low (a few tens of ohms at a guess - I'd have to evaluate the limiter schematic and figure out what sort of current they're running through its first transistor). So, odds are, you could just run this output into the 50-ohm input of a NanoVNA's second port, and the impedance would be OK.

A safety "gotcha" here, though... this IF strip has some gain in it due to the input and interstage-buffer transistors! The signal coming out of the output will probably be larger than the signal going in - I'm not sure how much. You don't want to risk overloading the bridge and mixer in your NanoVNA's second port. It would probably be wise to stick something like a 20 dB 50-ohm attenuator pad between the IF strip output and the NanoVNA input at first... do a sweep and see what your peak gain is. Then, consider reducing the amount of padding until you're close to a 0 dB insertion loss.

Fortunately there isn't any DC imposed on either the input or output of this IF strip (according to the schematic) so you don't need to worry about that... I don't think any of the +/-12 can get through to the analyzer in either direction...

... unless you've got a fault on the board. Wouldn't hurt to isolate both the input and the output from the NanoVNA with .1 uF caps, just to be safe.

This receiver really is a beautiful example of a fully-discrete transistor design from its era.

Do you know a Marantz receiver/tuner model number? Is a schematic available?
or part numbers for the transformers?

I have a few Model 18s and a Model 19 receiver. The Model 19 schematic is attached; note no transformers. What do you make of it?

The 18 has a BJT input stage vs. the 19's JFET, and the 18 has no AGC for its passive front end.

--
I_B_Nbridgema

I have the Murata data sheet here, and for a 180 ceramic filter, your group delay plot looks normal. Murata does not show data beyond +/- 150 kHz, though, and the y axis scale is 1 dB / divison, 6 dB total, so be careful making comparisons to other plots not scaled the same. I can post that pdf page for the GDT filters, showing a small version of all the plots, in you want.
PS thanks for the heads up to see what's going on here Dave.
Bob

There is for sure a problem with this measurement. When the two GD-peaks in
pass band looks like this something is wrong. That is confirmed by the pass
band curve that is too un-symmetric - rolling off in pass band.

Thanks, SJ - I rather suspected something of the sort.

Something that's certainly going on here, is that the measurement plots are for the test-jig-plus-filter, not just for the filter... I calibrated the "through" signal using a direct connection between the two cables. So, the behavior of the filter, and the behavior of the jig with its L-match and pad, are being conflated together.

I rather strongly suspect that reactance from the L-match is at least partly to blame. The match might be perfectly resistive at the design frequency, but with a Q of around 2.8 it's going to be significantly capacitive off to one side and signlficantly reactive to the other side. This is very probably affecting the phase quite a bit and could account for the asymmetries we see.

As a short-term tweak I'll try re-running the calibration, over a narrower frequency span, with the "through" cal being done through the whole test jig (with the filter position shorted). Then, see what a measurement of the filter looks like. It may be better but I don't expect really great results.

Although the L-match looks good enough for coarse sorting of these filters (to find the center frequency) a better matching arrangement is going to be required for reliable phase measurements. It'll need to be a broader-band match.

My next thought is to grab a couple of ferrite beads and some magnet wire, and wind up a couple of bifilar 4:1 broadband transformers and make another jig. One of these on each end, plus a 130R in series with each, ought to let the filter look into the impedance it wants without significant reactance appearing in the pass-band. The S11 return loss won't be wonderful, but probably not terrible either (about 1.55:1 SWR) and likely not enough to seriously affect the measurement.

Great to hear it works for you!
OTG cables, which are typically microUSB, always have pins 4 & 5 connected at the micro plug end.
Pin 5 is GND and when 4 is pulled to low on a device that supports OTG, its interface switches to USB host mode and supplies +5V at 500mA max.
As for the USB-C socket on your Nano - there have been a number of comments about the quality of the part and my unit has the same issue.
One user found it was the cable that was shipped with the unit - they bought a good cable and the problem went away.
Cheers,
Larry

UPDATE

Got it working. Looks like the usb-c socket on the nano may be a
little sloppy.

First, I used the USB Serial Console app and was able to send
commands that worked such as "help" and "pause" and resume". So OK
this is communicating.

Then I opened the NanoVNA android "webapp" app, and it indicated it
was connecting but wouldnt respond, moving the unit I noticed it
asking to connect again, and figured out that (I think) the usb-c port
on the nano, or possibly cable end, is sloppy.

Played with it and now the android app runs the nano.

INTERESTINGLY, the web site "app" approach still generates the "fail
to claim interface". But, who cares since the android app now works.'

I'll try another USB cable before exchanging the nano itself.

Lessons learned: mainly, the OTG cable must be on the phone, not the
nano. They dont work both ways. also, the console is a big help to
test communications because u know instantly if it is responding.


thanks to all who helped

I'm not sure whether this filter was specified to be linear-phase, but I believe that was probably part of its goals. It's an IF filter specified and sold for use in FM stereo tuners. In these signals, the peak FM signal deviation is 75 kHz. The baseband signal extends out to about 53 kHz (L+R audio bandwidth is nominally 15 kHz and there's a double-sideband-modulated L-R subcarrier centered at 38 kHz). So, Carson's Rule suggests that we'd want at least 128 kHZ of bandwidth on either side of the carrier. More bandwidth and more-linear phase behavior results in better demodulation of the FM signal, and thus lower distortion (particularly in the stereo L-R signal).

Yes, I plan to re-sweep these filters with a narrower bandwidth, and multiple sweep segments in order to get a more accurate look at the passband behavior.

I played around with a spreadsheet copy of one sweep's S2P data last night - wrote the formulae to plot the amplitude, and much of the math to calculate the group delay. I need to implement the phase-unwrapping step next... less easy in a spreadsheet than in something like Python. In any case I should soon have a package put together to go from an S2P file, to a nice dual-axis Gnuplot PNG file.

There is for sure a problem with this measurement. When the two GD-peaks in pass band looks like this something is wrong. That is confirmed by the pass band curve that is too un-symmetric - rolling off in pass band.

Hi David.
I understand and it is often the case when measuring with Network analyzers. In the first setup you find all the flaws and the second is much better. I have experienced it so many times, but on the same time it is where the experience really builds up. Sounds good about your new thoughts.

About plot and S2P file. You can easily import the S2P file in fx LTspice and do your plots there. I fully agree with you that this is a good way to move forward, because when you can also add additional components and immediately see the impact. In the end you can then simulate the complete circuit around the filter before building anything. And of cause if perfect, you also extract a S1P of the passives you intend to use and use that in the simulation also.

My experience is for the ceramic filters, that if Group delay or attenuation in stop-band is bad, it is often a filter impedance matching problem. Matching problems does often not affect pass-band.

My H4 arrived today. Although I didn't pay for it, it looks like it shipped by DHL on the 15th of Feb, arrived YYZ on the 20th, and spent the rest of the time clearing customs and taking the slow boat from YYZ to YOW to my QTH...

Tnx Maggie & Hugen.

N-connectors at full legal limit: I exclusively used N-connectors when
doing EME at 1.5 kW on 2-Meters. No problem. A short run of RG-8 coax to
the Bird meter got warmer than the connectors in that application on 144
MHz. N-connectors have no problem taking full legal limit on HF.

Dave - W?LEV

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*

This reader operates in the 13.56 MHz ISM band. The reading range is very
close-in, roughly to 1 cm. While the RF link is established by an
"antenna" of sorts, it is not an antenna in the usual sense of the word.
"Antennas" for these RFID applications consist more of a printed planar
inductor in a parallel resonant LC circuit. So design a spiral planar
inductor, model or measure the resulting inductance and choose an
appropriate capacitance to resonate the circuit at 13.56 MHz.

Here is a reference for calculating the inductance of printed spiral planar
inductors:



From there, you can calculate the required lumped capacitance from:
2
LC = 25330 / F

where: L in microhenries
C in picofarads
F in MHz (that's F squared in the above formula)

The combination of these will, then, form a parallel resonant circuit
"antenna".

Dave - W?LEV

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*

Pl-259 was invented in the 1930s as a form of shielded "banana plug."Sent from my Galaxy Tab? S2

It's interesting how the focus or center of discussions drifts. This started about testing filters with UHF connectors, so obviously they would have to be used in this case.. The discussion of N connectors has happened often, and in fact I'd read some time ago that, as well as 'inertia', one strong reason for using UHF connectors on ham gear was power handling. Someone in that discussion said that N connectors wouldn't handle ( or maybe just wouldn't be reliable) for high-power ham rigs. The main reason given was the small center pin of the N connector. (I suppose if that's the case, BNC's might have the same problem.)

It would be good to know how much improvement was gained by the folks who have changed their HF station connectors from UHF to the N series, both in transmitting and in reception measurements.

Somewhat related to this (but not the NanoVNA) has anyone researched the development of the UHF (SO-239/PL-259) series and what it's original purpose might have been?

Doug, K8RFT

Hi Daniel,I have no idea what you are building (HI), but I Googled "mfrc522 antenna" and got LOTS of sites, including construction pages.Good luck.Ed? KB8ESVSent from my Galaxy Tab? S2

A simple google search:
yields:
check page 20 for details.
Hopefully, this helps.

Hi Everyone,

I'm trying to develop my own rfid antenna for mfrc522. It's my first one, so... it's very difficult. Do you know the procedure to properly tune my antenna ? Or a good tutorial to help me use my NanoVNA properly ?

Any help will be very appreciated

Thanks