The AM Forum

Has anyone used a ceramic or mechanical filter on any of the surplus receivers such as the BC-342/312, TCS-14, or BC348? Surplus Sales of Nebraska has filters for a great price.

TNX Gary

Which filters? Ceramic resonators or something else... are those receivers all 455 KHz IF?

I'm interested in adding filters to my Command Set receivers. That 2830 KHz IF is just too wide, and even the 1415 KHz is not very selective!

How about a simple half-lattice crystal filter? 2 xtals and an IF can? Wonder what the insertion loss would be.


It's not often I see SSN and "great price" in the same sentence  ::)

-Charles

Check out the "TCS Broad as Barn" thread   

AFAIK there are no mechanical, ceramic, or crystal filters made for the BC-348's IF of 915 KHz.

    the BC348 and 312/342 both have crystal filters as delivered. the one in the 312/342 is actually quite good. the 348's is so-so. if the filter in you 348 is bad the crystal is likely n/g but before you give up, open crystal up, clean it with alcohol or napthta and reassemble it being careful not to get any finger grease/oil on the blank or it's plates. if you really wanna get down with a 348 you need an OUTBOARD SLICER as used by W8VYZ. that would be a broadcast band Command Set receiver coupled to the output of the mixer in the '348. it's quite selective, and if done properly there will not be a "sidebander in North America that can touch you"... i have both a '348 and '342, and they do what they were desinged to do very well. you can't polish a turd (ok that's a bit extreme), so if you want sharp selectivity your best bet is to find it in some other radio.

I have simulated a couple 455 KHz LC filters to see how hard it would be to match a crystal filter performance at am bandwidths. Take 4 IF transformers and lightly couple them. Carefully tune them and you can make a pretty fair filter around 10 KHz wide. As JN said no filters were made for these old receivers with odd IF frequencies.
Like Chris said not worth wasting time making a turd shine. Get a part time job and buy a good receiver.

     worst part of trying the outboard slicer system is these days the BC band ARC5 can run you more than a decent BC348... i also did it once with a Delco all tube car radio, one of the ones that used 12 volts on the plates of the tubes. i still think the stock crystal filters in those receivers are pretty good, the one in the 312/342 being quite sharp. the phasing control even notches out hetrodynes effectively.

So what your saying is, quit working on this WWII gear, get apart time job and turn into an Appliance Ham.

Most WW2 era receivers suck! Appliance operator---NEVER!! Just step a little further down the historical timeline and get some post WW2 stuff. R-390s kick ass and take names!!
                                      the Slab Bacon

or step out of the 50s and get a late model MIL RX. and have some real performance.
BTW they don't have many knobs to play with. 

WWII era and older receiver work just fine for 90% of AM applications. If conditions are so bad that you need some newer, high selectivity jobs, it's time to sign-off or find another frequency/band. AM is about wide bandwidths and good audio. Settling for anything less, and you might as well save the hassle and get on sideband.

I used to enjoy 3.885 while k1man was at on 90 he didn't bother me.
sometimes you feel like running battle mode but sometimes you don't
Save the old stuff for a Sunday afternoon ride in the park.

Yup - the TCS has that nice 455 kc IF.

My 348's crystal filter is off frequency a few kc but that is normal. I alligned the radio to match the filter's peak at 913 kc and it works great. The level barely goes down when it is switched in. I use the filter for CW only.

There was a good article on making a Q-multiplier for the 348 and other non-standard IF's in the early 1960's. I have a copy if you are interested and could probably find it. I built a nice Q-multiplier for a command set which had a 915 IF and it did wonders for AM selectivity. 

Mike WU2D

There is/was a method of home brewing Xtal Filts in a handbook?? seems like a few xtals  in the neighboorhood may be ground 'up' to cover the 'odd' IF freq..   klc

Hams used to roll their own AM and CW filters using surplus crystals. The half lattice filter was popular.

Mark WA1QHQ has a Super Pro (which is normally outfitted with a simple single crystal phasing filter) with an elaborate deck of beautifully contructed half lattice filters made from surplus crystals. Each filter uses two crystals. This arrangement gives his Super Pro several selectivity settings.

See:

http://books.google.com/books?id=rsdWstFvfSEC&pg=RA1-PA155&lpg=RA1-PA155&dq=crystal+filters+lattice&source=web&ots=iM-bNKhMyr&sig=0pT7YTyDjaabfFzbYVX-wD1Icys#PRA1-PA156,M1

Mike WU2D