10MHz WWV reciever IF transfromer help? - Page 1
Forum section: electronics / projects

author: croyleje
author_rank: Regular Contributor
timestamp: December 18, 2014, 07:39:02 pm
content: Hello Everyone,I want to build a WWV receiver and found a nice schematic and parts list and have also been able to find the parts needed to build the unit. The problem I am having is with the IF transformers I have attached a copy of the schematic and parts list but I have been unable to find information on the transformers T1-T3 and T4-T7. There is supplied part numbers but I cant find cross reference data on them. My question is does anyone know if there is a way to figure out what type of transformers they are either by reverse engineering it or some other way. I asked the company Ramsey Electronics and got a reply of 10.7Mhz and 455KHz if transformers but when looking for them you find many different turns ratios? Any help would be greatly appreciated.Thank you,Jason

author: Paul Rose
author_rank: Regular Contributor
timestamp: December 18, 2014, 08:33:57 pm
content: Almost certainly one of the Xicon IF transformers at Mouser will do the trick:Part 42IF-10x for 455KHz unitsPart 42IF-12x for 10.7MHz unitsThe trick ( as you already noticed ) is figuring out which primary / secondary impedance you want.Most of them have high-ish ( 15K - 50K ) primary impedance, and either low ( 300 - 600 ohm ) or medium ( 4K -6K ) secondary impedance.From the schematic, 10MHz transformers are connected primary to primary, so I think you will be good either way.Two of the 455KHz units have the secondaries floating ( only using the primary for its inductance ), so I don't the secondary impedance matters.The other two 455KHz units are feeding the (ancient) Harris 3088 receiver chip ( where did you find one of these? ). The data sheet for this seems to indicate that the input impedance is in the 2K range.If I were to have a go at this, I'd try:Xicon 42IF102-RC for the 455KHz units for its lower secondary impedanceXicon 42IF123-RC for the 10.7MHz units for the lower turns ratio on the "back to back" connected T2 & T3I think you could probably get any of them going.Good luck.

author: German_EE
author_rank: Super Contributor
timestamp: December 18, 2014, 08:41:38 pm
content: And 10,7 MHz transformers will tune down to 10,0 MHz.

author: croyleje
author_rank: Regular Contributor
timestamp: December 18, 2014, 09:02:22 pm
content: Thanks Paul I really do appreciate the help and information the Harris 3308 was not to hard to find got some out of Greece for 3USD each. I think i will give it a try one other question if you don't mind T1 appears to be hooked up as a step up transformer or as they call it an antenna transformer any thoughts on this, am i reading that correctly or are they just doing it to filter the 10MHz. I also managed to get alignment procedure from them also so that should help a lot after i get it build up. I know nothing about RF just want to be able to receive 10MHZ signal so i can calibrate a few things at home if you were wondering why I want to build it.Again thank you very much,Jason

author: Paul Rose
author_rank: Regular Contributor
timestamp: December 18, 2014, 09:21:17 pm
content: T1 is primarily being used as a front end filter, using the built in capacitor on the primary ( here connected as a secondary ). This is to protect Q1 from amplifying too much out of band stuff.The impedance transformation is probably worthwhile too, but certainly not any kind of exact match with the antenna.

author: edavid
author_rank: Super Contributor
timestamp: December 18, 2014, 11:28:26 pm
content: Quote from: croyleje on December 18, 2014, 09:02:22 pmIf you bought a CA3308, that's the wrong chipYou need a CA3088.