TESTING KVG FILTER WITH VNWA

I found on eBay a PCB with 3 quartz filter for 34 $ :
here

The PCB comes with 3 KVG filters and some MC1496

S42 9 MHz AM
S43 8.998200 MHZ (LSB)
S44 9.001800 MHZ (USB)

With a little fixture, I have tested the USB filter with my VNWA.
Because the impedance of the filter is about 560 ohms with 25 pF in parallel, I needed 2 LC circuits to adapt the filter to 50 ohms.

The fixture with vertical PCB screen not really necessary :

The results after tweaking the capacitors for minimum ripple (very important) :

Bandwith :
3.22 kHz @ -3 dB
3.43 kHz @ -6 dB
5.15 kHz @ -60 dB
shape factor 6/60 dB = 1.5, not bad for the price

TEST OF DX WIRE SNAP ON FERRITE

I plan to build a instrument to measure from 1.8 to 50 MHz the common mode current that may exist on antenna feeder. It consist of a transformer, a diode detector and a moving coil meter.

References :
Owen Duffy : http://owenduffy.net/module/icm/index.htm
GM3SEK : http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

For example, without balun a dipole antenna may exibit this type of current and thus produces RF in the shack. In RX mode, noise radiated by a nearby computer or house wiring will induce non desired signals that will reach the receiver.
Search IZ2UUF on Youtube to see the videos that demonstrate the phenomen.


The hearth of the instrument is a clamp-on ferrite used as a transformer. Several types exist, a model named K13 is available on DX WIRE web site.
K13 : http://www.dx-wire.de/lng/en/soft-ferrites-toroid-cores/snap-on-ferrites/snap-on-ferrite-k13-id-130mm.html

With 13 mm inner diameter, it is compatible with 11 mm coax. 2 holes on the plastic case allow the clamp-on ferrite to be fixed with screws.

Because I have no idea of the RF specs of the K13, I made some measurements.

First, I have connected a coax between the tracking generator and the input of my E4402B spectrum analyser in order to make a calibration (0 dB).
Second, I have cut 40 mm of braid of the coaxial and soldered a wire between the 2 extremities of the braid.
Thus, the center conductor of the coaxial go thru the ferrite, forming the primary of the transformer. The external conductor pass outside the ferrite.
Then, 10 turns of wire are wound around one half of the ferrite and form the secondary. It is connected to the input of the spectrum analyser.


The measurement setup :

Details :

Results :

As you can see, reponse is very flat.

∆ is only 0.42 dB from 1.8 to 55 MHz. The K13 is good for my project.