R1155 IF Idea - UK Vintage Radio Repair and Restoration Discussion Forum

GW3OQK Andrew · 23rd Jun 2014, 5:03 pm

I noticed 560 KHz ceramic resonators now on sale on ebay at low cost and bought some. A crude test for parallel resonance showed 6db down points about +/- 2kHz from 564 centre. A series test showed a very sharp attenuation notch, i.e high impedance at resonance. Should I decide to "improve" my radio they could be well worth investigating further.

The one thing that lets the R1155 down, being a CW buff, is it's barn door IF. When it was my main rx when I was 15 I turned a DF valve into Q multiplier I recall and it worked great but the one I have now has no single-signal capability. Should be OK for 160m AM net.

73
Andrew

turretslug · 24th Jun 2014, 11:56 am

I recall noticing 560kHz resonators a few years back and thinking "R1155 IF" but not having an R1155, didn't get round to trying anything. Wonder what the original motivation behind producing this frequency resonator was? Sometimes, the availability of the frequency drives other applications, eg. cheap, plentiful NTSC subcarrier crystals being divided down for tone-dialling but 560kHz doesn't ring obvious bells here. Someone on here is sure to know!

Would be interesting to know how this works out- and they're small enough that they should fit in even in this application.

G6Tanuki · 24th Jun 2014, 1:07 pm

I've thought of doing something similar with my Eddystone 840A (which has a more-traditional IF).

One thing to be wary of is that a lot of the smaller ceramic filters do not like being subjected to high standing DC voltages - it excessively biases their piezo-electric bits. So while it's probably OK to wire a ceramic filter from the secondary of an IFT to the grid of the next valve (where it will only see a few AGC-volts) I'd recommend not applying HT directly across a ceramic filter's terminals.

GW3OQK Andrew · 4th Jul 2014, 7:32 pm

I tried the idea and it is spectacular.

I hadn't realised how wide was the bandwidth of my R1155. At -20 db it was 10kHz wide and the skirts just broadened out below -20db so a crude plot looked like the Sugarloaf near Abergavenny or Mount Fuji.

Its too crowded in the coil box to do it there so I fitted my filter between 2nd IFT and grid of 2nd IF amp. (1M from grid to AGC line.) With my filter its now 3 kHz wide at -20 db, 5 at -40 and the skirts drop rapidly, not measurable to me. I'm mostly interested in CW so it a fantastic improvement.

For AM/SSB I tried stagger tuning the 2 resonators and the nose broadens out with skirts similarly dropping away. Should be great on AM.

Best of luck if anybody else wants to try it. It uses 2 of the resonators, top coupled with 2.2 pF and 2.5-22 pF trimmers in parallel with each resonator. The centre is 562 kHz. Perhaps I'll try 3 resonators. No loss measurable either. Yes Tanuki I expect it works well on 455 IFs too.

73 Andrew

turretslug · 5th Jul 2014, 12:20 pm

That's most encouraging- there must be quite a few languishing R1155s- diminishing BC station material worth listening to and less than ideal for SSB but if a fortuitous bit of modern technology conbined with the v-e-r-y slow motion drive gives some of them a new lease of life for CW, it can only be a good thing. And no chopping up of the set: what's not to like?

23rd Jun 2014, 5:03 pm	#1
GW3OQK Andrew Pentode Join Date: Apr 2011 Location: Swansea, Wales, UK. Posts: 144	R1155 IF Idea I noticed 560 KHz ceramic resonators now on sale on ebay at low cost and bought some. A crude test for parallel resonance showed 6db down points about +/- 2kHz from 564 centre. A series test showed a very sharp attenuation notch, i.e high impedance at resonance. Should I decide to "improve" my radio they could be well worth investigating further. The one thing that lets the R1155 down, being a CW buff, is it's barn door IF. When it was my main rx when I was 15 I turned a DF valve into Q multiplier I recall and it worked great but the one I have now has no single-signal capability. Should be OK for 160m AM net. 73 Andrew

24th Jun 2014, 11:56 am	#2
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: R1155 IF Idea I recall noticing 560kHz resonators a few years back and thinking "R1155 IF" but not having an R1155, didn't get round to trying anything. Wonder what the original motivation behind producing this frequency resonator was? Sometimes, the availability of the frequency drives other applications, eg. cheap, plentiful NTSC subcarrier crystals being divided down for tone-dialling but 560kHz doesn't ring obvious bells here. Someone on here is sure to know! Would be interesting to know how this works out- and they're small enough that they should fit in even in this application.

24th Jun 2014, 1:07 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	Re: R1155 IF Idea I've thought of doing something similar with my Eddystone 840A (which has a more-traditional IF). One thing to be wary of is that a lot of the smaller ceramic filters do not like being subjected to high standing DC voltages - it excessively biases their piezo-electric bits. So while it's probably OK to wire a ceramic filter from the secondary of an IFT to the grid of the next valve (where it will only see a few AGC-volts) I'd recommend not applying HT directly across a ceramic filter's terminals.

4th Jul 2014, 7:32 pm	#4
GW3OQK Andrew Pentode Join Date: Apr 2011 Location: Swansea, Wales, UK. Posts: 144	Re: R1155 IF Idea I tried the idea and it is spectacular. I hadn't realised how wide was the bandwidth of my R1155. At -20 db it was 10kHz wide and the skirts just broadened out below -20db so a crude plot looked like the Sugarloaf near Abergavenny or Mount Fuji. Its too crowded in the coil box to do it there so I fitted my filter between 2nd IFT and grid of 2nd IF amp. (1M from grid to AGC line.) With my filter its now 3 kHz wide at -20 db, 5 at -40 and the skirts drop rapidly, not measurable to me. I'm mostly interested in CW so it a fantastic improvement. For AM/SSB I tried stagger tuning the 2 resonators and the nose broadens out with skirts similarly dropping away. Should be great on AM. Best of luck if anybody else wants to try it. It uses 2 of the resonators, top coupled with 2.2 pF and 2.5-22 pF trimmers in parallel with each resonator. The centre is 562 kHz. Perhaps I'll try 3 resonators. No loss measurable either. Yes Tanuki I expect it works well on 455 IFs too. 73 Andrew

5th Jul 2014, 12:20 pm	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: R1155 IF Idea That's most encouraging- there must be quite a few languishing R1155s- diminishing BC station material worth listening to and less than ideal for SSB but if a fortuitous bit of modern technology conbined with the v-e-r-y slow motion drive gives some of them a new lease of life for CW, it can only be a good thing. And no chopping up of the set: what's not to like?