[Milsurplus] ARR-15 IF bandwidth.

[Jim Whartenby]

Hue
I had a similar issue with oscillation in a hammified ARR-15 several years ago.  Turns out that the little aluminum cover was missing from over the IF area tube sockets.  Once a substitute cover was made and installed, the oscillation problem was cured.  Several years ago I modified two radios with reduced IF coupling caps and they worked well, with no issues.  The math verifies that the IF bandwidth is proportional with coupling capacitor value.  The equation can be found in RDH4th, page 418, Figure 9.12.

IMHO, the ARR-15 is an under appreciated receiver.  First Collins designed receiver to cover a large portion of the HF band.  First Collins receiver using an autotune mechanical memory.  Uses the second and third PTOs designed by Ted Hunter for Collins, one for RF and another for BFO,  Both will hold a frequency setting to within 250 cycles after several autotune cycles.  The RF and IF stages are permeability tuned.  The variable IF allowed for the crystal calibrator to tune the receiver to any frequency covered by the receiver without auxiliary equipment.  

I can see the heritage between the ARR-15 and the 51J.   Everything is there in the ARR-15 except for double conversion and all was done by 1946.
Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy

-----Original Message-----
From: Hubert Miller <Kargo_cult at msn.com>
To: milsurplus at mailman.qth.net <milsurplus at mailman.qth.net>
Sent: Mon, Feb 27, 2023 7:20 pm
Subject: Re: [Milsurplus] ARR-15 IF bandwidth.

 <!--#yiv5961173117 filtered {}#yiv5961173117 filtered {}#yiv5961173117 p.yiv5961173117MsoNormal, #yiv5961173117 li.yiv5961173117MsoNormal, #yiv5961173117 div.yiv5961173117MsoNormal {margin:0in;font-size:11.0pt;font-family:"Calibri", sans-serif;}#yiv5961173117 span.yiv5961173117EmailStyle18 {font-family:"Calibri", sans-serif;color:windowtext;font-weight:normal;font-style:normal;}#yiv5961173117 .yiv5961173117MsoChpDefault {font-family:"Calibri", sans-serif;}#yiv5961173117 filtered {}#yiv5961173117 div.yiv5961173117WordSection1 {}-->“Someday” i will revisit this. I decreased the capacitance by i don’t remember how much, and the IFs took off. As in, oscillation. I think there will be a practical lower limit which wouldn’t enter into a fixed frequency IF: the trueness of the tracking of the individual tuned circuits. This is assuming you want to retain the variable IF feature; but it seems from my reading here that most ? users leave it set to 500 kHz. I like the “incremental tuning” feature kind of like on the Eddystone 830.      I have wondered the same thing about the ARC-2. This radio has a very odd design, 2 or is it 3 RF amps. I came to the conclusion that this is because the radio was intended for remote control operation only, and applying AGC to these multiple stages was the way to control, even out gain when subjected to signals of greatly varying strength. I am wondering how well those stages will track when the coupling caps are lowered. ( ARC-2A models only, for the cognoscenti. ) I thought about also a q multiplier with negative resistance without tuned circuits, using only the transceiver’s tuned circuit, and using maybe a spare fuse opening on the front panel with a small knob so that the overall effect looked pretty much original. Maybe. -Hue Miller ______________________________________________________________
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