[Milsurplus] Military Receiver R105A/ ARR 15 question

[Jim Whartenby]

Have you seen:

http://k6jca.blogspot.com/2010/01/improving-selectivity-of-r-105a.html

Personally, I would lower the value of the IF coupling capacitors by half or more to reduce the IF bandwidth (KISS), but that said, the test data k6jca presents IS impressive.

I agree with Al, it is a curious radio, single conversion with a variable IF.  But it works very well and you can both see the heritage in this design and see the influence to future Collins designers on the radios to follow for the next 30 or so years.


I have to admitt that I am a bit jealous or even envious; k6jca has much better test equipment then I!
Jim

 


----- Original Message ----

Good description of the radio.  Biggest problem for ham use, though,  
is the tunable IF strip required to accommodate the calibrate/autotune  
cycle which results in about a 20 kc receiving bandwidth.  Myself and  
others have considered a mod to switch a 500kc mechanical filter in  
line at the conclusion of the cycle but have heard no reports on  
anyone having actually done this.

Dennis D. W7QHO
Glendale, CA



On May 1, 2010, at 9:47 AM, Al Klase wrote:

> Hi Greg,
>
> Nobody else spoke up, so I'll see what I can do.
>
> This receiver uses the Collins Autotune system to accommodate 10  
> preset
> channels.  With the wing nuts on the tuning and bandswitch knobs
> loosened, it can be tuned manually.  In this mode there is no  
> detente on
> the band switch, so the half-way-in-between condition in the picture  
> is
> probably OK.
>
> The small window on the upper left is the "BFO-Calibrate" indicator.
> The knob below tunes the entire IF and the BFO +/- 50KC form the 500KC
> IF.  When this control is turned away from it's center detente, the
> antenna is disconnected and a 100KC calibrator is turned on.  If for
> instance if you want to tune the set accurately to 3520 KC, you set  
> the
> BFO-Calibrate control to +20 and zerobeat using the main tuning  
> control
> in the vicinity of 3500 KC.  Then when  BFO-calibrate is returned to
> zero, the set is on the air at 3520.
>
> I have one of these in storage.  It strikes me as more of a curiosity
> for the Collins collector who wants one of everything, and you might  
> be
> happier with an BC-348 for everyday use.  Of course it will coordinate
> with the autotune in the ART-13 and it's kinda cool to watch it click
> and whir it's way to the next frequency.
>
> 73,
> Al