[ARC5] Bandwidth for IF Transformers

[Sandy]

Hi all,

I haven't kept up with the traffic about then "command set" selectivity 
curves until now.  Been having some heart pulse rate difficulties and 
got fitted today with a "reveal LINO" heart monitor to study whether or 
not a pacemaker would be my solution to my troubles.

Anyway I gather there is some argument about selectivity curve 
information of the series.  Firstly the lower two IF
cans are the only ones that have the variable selectivity function. The 
one for the 85 khz. cans do get the narrowest and are excellent as an 
"IF unit" from a higher frequency receivers, especially where the 
bandwidth is rather "brioad as a "barn door".  The BC-453 was a very 
nice radio for what is in it considering the 1940's technology at the 
time and are really quality.

I played around with these back in the 1946-1950's "era" and were good 
providers for use provided what was expected of them.

I am sure the "HF receivers" would have been unsuitable for a pilot to 
tune in if the selectivity was better than it actually was as designed.  
Namely the 3-6 and 6-9.1 sets!

The beloved BC453 lives on even today!  Back in those days when I was a 
kid, I wanted a BC-946 (the broadcast band
set) was always very expensive and scarce in those days.  I wanted a 
better "rear end" IF strip for my Gonset "Tri-band" and Gonset "Super 6" 
converters!  Transmitters is this case was the usual ARC-5/SCR-274N 
transmitters that covered 80 and 40 meters!

Don't expect really super sharp selectivity from the BC-453 series. They 
were great and cheap before the Collins mechanical filter units that 
were often used in quality receiving gear.

I would have had no decent ham receivers if I the BC-453 hadn't 
existed.  Some of you "young bucks" probably don't know that the BC-453 
was used as an Exciter unit for an SSB transmitter with added circuitry 
for 75 and 20 meter SSB "output" exciters before the days of the phasing 
rigs before the Central Electronics 10A, 10B and 20A were available.
They made fairly good SSB exciters for what the BC-453 transformers 
offered.  (No 40 meters WAS NOT a phone band back then.)

Have fun and 73,

Sandy W5TVW
Got my ticket in 1951 after "bootlegging" CW for a couple of years!

On 3/16/2016 9:32 PM, Kenneth G. Gordon wrote:
> On 16 Mar 2016 at 18:12, Bill Cromwell wrote:
>
>> Hi Phillip,
>>
>> The specs say the 85 kc cans are (depending on source) 2 kc, 1.5 kc or 1
>> kc. I saw where somebody reported less than 1 kc. The 2 kc I found in
>> one of the "official' manuals and 1.8 kc in yet another "official"
>> manual.
> According to the Navy's manual on ARC-5 maintenance, the following
> selectivities are listed.
>
> IF Freq.                              Selectivity.
>
> 85 KC       1.1 KC at 6 dB down. 4.5 KC at 60 dB down.
> 239 KC     2.1 KC at 6dB down.  8 KC at 60 dB down.
> 405 KC     3.2 KC at 6dB down.  13 KC at 60 dB down.
> 1415 KC   7.3 KC at 6 dB down.  26 KC at 60 dB down.
> 2830 KC   13 KC at 6 dB down.   56 KC at 60 dB down.
>
> HOWEVER!!!!
>
> Since these figures are the "width" of the selectivity curve measured from the
> "nose" of the curve to ONE SIDE ONLY, the actual width of the selectivity
> curve is double those figures above.
>
> Furthermore, the Navy manual states that for those two receivers which have
> two-position IF coils, i.e., 85 KC and 239 KC, ALL three rods must be pulled
> up to their "undercoupled" position before alignment is begun.
>
> I have not yet checked the Army manuals, but I can see no reason they
> would be any different.
>
> Ken W7EKB
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