[ARC5] ARC-5 Mods

[Kenneth G. Gordon]

On 1 Jan 2009 at 16:39, Bob Macklin wrote:

> Consider that these receivers were made for a few pilots to
> communicate with each other not for a million hams trying to operate
> in a 100KC segment!

Yes!

> In 1958 I also had a BC-312 or BC-342 as my main receiver. Even it was
> difficult to use on the ham bands in those days.

My first "ham" receiver, was a Heathkit AR-3...in which the 
BFO didn't work.

My next, much "better", receiver was a Hallicrafters S-41-G 
that a plumber-friend of my step-dad's found in his 
basement when he and his wife moved into a "new" home.

The filter cap was shot, but I fixed that. At least it had a real 
BFO that worked, although it WAS an AC/DC set.

And talk about selectivity! The entire 20 meter band took up 
all of 3/16" of dial space on band three. Yet I worked some 
DX on 20 with that thing. I doubt if I could do it today.

Any selectivity I had available was between my ears.

That receiver was totally unusable on AM phone in those 
days. All the phone bands were simply one gigantic 
heterodyne. So, I spent all my hamming on CW for years 
afterwards.

My first GOOD receiver was a BC-348 with an attached 
broadcast band R-24/ARC-5 (?) as a "Q-5er" since the BC-
348 has a 915 Khz IF.  I was amazed at the selectivity!

I traded that for an RAL-7 because the RAL had 15 meters 
and the BC-348 didn't. I never regretted the trade. The 
RAL-7 was far more stable, and plenty selective enough for 
me.

I am saying all this to give a little idea that the selectivity of 
a receiver kinda depends on the operator and what he is 
used to.

I was able to use the S-41G and other receivers of like 
"quality" (essentially non-existent) simply because I didn't 
know any better.

I find the BC-454 to have very much better selectivity than 
the BC-455. The BC-454 is fully usable on 80 meters. The 
selectivity of the BC-455 is marginal, even for people like 
me. :-)

But it is STILL usable on 40 meters CW. I wouldn't want to 
attempt to use one on 40 meters AM phone though...

Now, just for fun, we can look at the ARC-5 maintenance 
manual and find some selectivity figures for the various 
receivers.

BC-453 or R-23: min bandwidth = 1.1 Khz, max= 4.5 Khz
BC696/R-24: min = 2.1 Khz max = 8 Khz
R-25: min = 3.2 Khz, max = 13 Khz
BC-454/R-26: min = 7.3 Khz, max = 26 Khz
BC-455/R-27: min = 13 Khz, max = 56 Khz. (!)

So, yes, the BC-455 is quite broad.

I used to make the 1st IF stage regenerative, and added a 
pot between the cathode to ground to vary the 
regeneration. It made a big difference on weak signals, but 
didn't really help on strong ones.

Ken Gordon W7EKB