Varactor diodes KB127 - anyone know of them?

Admin wrote:Hi all,
...
At the moment I am trying to make a variable BW IF stage. While looking for ideas I saw a published design using 9MHz crystals. The second BPF is "shiftable" using varactor diodes.
...
BR Harry

Hi Harry

Possible common varactor (at aliexpress) that could be used. The varactors that are commonly used for (ancient) LW, MW tuners: 1SV149 490-25pF 1-8V (or KV1236Z, BB212, SVC383).

Have you seen or considered these variable crystal based filters?:

.

Very interesting variable ladder MF-filter - both CW and SSB:
Amateur Radio (G3TXQ) - Cub II:
https://web.archive.org/web/20190717212858/http://www.karinya.net/g3txq/cubii/filter.jpg
https://web.archive.org/web/20200215001501/http://www.karinya.net/g3txq/cubii/

.

I suspect that if you put capacitors/varactors in both crystal paths, you can both vary center frequency and passband bandwidth, but the cascade half-lattice filter will loose some of the widest bandwidth. But less than 300Hz bandwidth should be possible, because the two paths can be tuned much closer together.

SSB Exciter with IF-Clipper for QRP.
DL6ZB, Rolf Heine:
https://www.dl6zb.de/SSB%20EXCITER/SSB%20Exciter%20with%20IF-Clipper.html
Backup:
https://web.archive.org/web/20180515052354/https://www.dl6zb.de/SSB%20EXCITER/SSB%20Exciter%20with%20IF-Clipper.html
Citat: "...
This is a description of a simple but effective single side band exciter for 10.7 MHz with a built-in if-clipper.
...
I developed a special 50 ohms SSB (USB/LSB) crystal filter for this exciter in a so-called bridge design [actually cascade half-lattice filter]. This filters are more suitable for SSB generation for me than ladder filters since bridged filters can be tuned very easy without significant change of impedance. Just change the 33pF capacitors to change the bandwidth of the filters. This filters can also be used for if-stages of receivers. Just cascade it for higher filter orders. The bandwidth depends on the capacitors (see C1/C2) only. The greater the value the narrower the bandwidth. This filters can be tuned from 6000 downto 300 Hz bandwidth within a 2.5:1 VSWR bandwidth (50 ohms). The sideband is changed by tuning the carrier oscillator crystal. The crystals needn't be selected or matched, although I recommend to use crystals from the same type (manufacturer).
..."

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More info:

High-frequency crystal filters for s.s.b.
Design procedure plus a high-performance unit using surplus crystals.
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1960/10/page35/index.html
https://web.archive.org/web/20200503113829/https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1960/10/page35/index.html
Quote: "...
[important note:]
The leakage reactance between the two halves of L2 and L3 is tuned out by the capacitors connected in series with the center taps of these coils.
..."

Surplus-crystal high-frequency filters
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1959/01/page24/index.html
https://web.archive.org/web/20200502101536/https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1959/01/page24/index.html

How-to make a crystal filter slide show:
http://pages.suddenlink.net/wa5bdu/crystal_slide_show.pdf
https://web.archive.org/web/20190418131120/http://pages.suddenlink.net/wa5bdu/crystal_slide_show.pdf

A History of Crystal Filters:
https://ieee-uffc.org/about-us/history/uffc-s-history/a-history-of-crystal-filters/
https://web.archive.org/web/20190911171837/https://ieee-uffc.org/about-us/history/uffc-s-history/a-history-of-crystal-filters/

Hi Ivan,
I didn't realise you could still get such items! Thank you for the links.
I may get one for playing, but not for this project: I need something a lot smaller, such as this:

https://www.aliexpress.com/item/33030545570.html?spm=a2g0o.productlist.0.0.35c25adeaIHU8h&algo_pvid=164db45b-83b4-4070-93a8-43213e121f56&algo_expid=164db45b-83b4-4070-93a8-43213e121f56-0&btsid=0b8b15cb15992495396751905e08f8&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

I have a stock of those. For a Bandwidth know I do not need much - 0 to 3kHz - mounted sideways, two caps coupled by a band. Should be good enough.

But the links you gave are the answer to a prayer for a different HF project I gave up due to heavy mechanics. It would only be a tracking/tuning exercise, after the calculation exercise (using LC index method).

Thank you very much.

Goodnight - Harry - SM0VPO

Hi Harry,
if you want to save the effort of 3D printing, this may be of some interest for you:
https://www.aliexpress.com/item/32823772316.html
https://www.aliexpress.com/item/10000366672573.html

VBR from Ivan

Hi Ivan,
Thank you for the response. I did reply last week but I found it unsent this morning.
I have found data on the KV127 and I see that it was used in the Klopic radio. The circuit I googled was probably a clip from that project. The other circuits I found used the V149 and that is more easy to find both data and sources.

I think that my variable IF filter will be better built using a 4-gang variable capacitor. I have some miniature 375pf dual-gang variable capacitors and a 3D printer, so I can easily make a small assembly with one knob and a zero-backlash belt-drive. But for variable IF it does not need to be that accurate.

The only problem will be switching for TX/RX, but due to the small signals I think diode switching will make a good solid-state bypass circuit.

The KV127 has a capacitance at 1V of about 250pf but the V149 is 500pf. My 375 X2 caps should be more than man-enough to give me a 3kHz filter shift. It is just to experiment a bit with the crystals I have.

Very best regards, and thank you for the comments.

One thing I have learned is that there are 100's of ideas found on Google, but most seem to come from the same source, but re-drawn ;-)

Best regards from Harry

Hi Harry,
the varicap is KV127 and it comes from Russia. The character "B" is bee in Latin, but vee in Russian alphabet. Some basic data are e.g. KV127 here. It was probably designed for tuning MW radio receivers. The Klopik filter uses KV127B (in Latin transcription).

KB107 / KV107 seems to be a typo.

VBR from Ivan

Hi all,
Don't get much time on the bench (again). Sold the house in Spain ad all our stuff from Spain is now in this little house in Sweden. Boxes everywhere!!

I have been spending my lunch breaks on a little design work. Have a coupe of finished projects to add to the homepages, and a couple to update.

At the moment I am trying to make a variable BW IF stage. While looking for ideas I saw a published design using 9MHz crystals. The second BPF is "shiftable" using varactor diodes. The project using them is written in Russian, and I guess the diodes KB107 are some Russian type. Does anyone know anything about them? Capacitance at 1V and capacitance at 10V?

BR Harry