Re: {Collins} BFO x-tals off frequency



I used a HP 8640B signal generator with frequency counter HP 5316A and ‎ a HP 3586B Selective Level Meter . Measured inside the M2A.     Filter terminated per design.   Very little coupling on both sides.    Please give me couple of days to find the curve and to wait for others that may be interested.  
73 Art ve3pnd



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  Original Message  
From: Gary J FollettDukes HiFi
Sent: Wednesday, October 26, 2016 8:24 PM
To: mariusz
Subject: Re: {Collins} BFO x-tals off frequency

I’d like to see your plot of the response.

Did you do it in the radio or was it in a terminated external circuit.

Did you sweep it or tune across it with the PTO using the calibrator and plot the S meter readings?

Just curious because I have several filters I would like to check, and it would nbc nice to have a comparison.

Gary


> On Oct 26, 2016, at 7:21 PM, mariusz <mdg@xxxxxxxxx> wrote:
> 
> I have a M2A and couple of years ago I measured the passband of my filter with accuracy of within 10 Hz. Quite interesting ... . If anyone is interested I can email you the curve . It shows how non-symmetrical the lsb and usb are .. .
> 
> 73 Art ve3pnd
> 
> 
> 
> Sent from BlackBerry Passport on the TELUS network.
> From: Dave Bottom
> Sent: Wednesday, October 26, 2016 7:19 PM
> To: mariusz
> Cc: Collins Mailing List
> Subject: Re: {Collins} BFO x-tals off frequency
> 
> 
> Don't confuse PTO dial accuracy with BFO offset. 
> 
> The BFO should set approximately 20 dB down the Mechanical Filter's Pass Band Curve. This is critical because it determines the portion of Voice spectrum that is modulating your rig. For a new properly aligned 2.1 KHz Mechanical Filter this was 1.350 KHz. The offset would be greater with say a 2.9 KHz Mechanical Filter for some ESSB.
> 
> If you really want the BFO right, you might as well find out what your Mechanical Filter Pass Band looks like 50 years later and then choose the correct new frequency based on its current shape and then have International Crystal make appropriate crystals for your filter. Or maybe it is close enough not to worry about it?
> 
> Once this is done you can work on optimizing the dial accuracy. My current S-Line is as good today as my Dad's (W6LEH) S-Line was in 1959. I wish you luck as they all haven't been as good.
> 
> 73 Dave WI6R
> 
> On Wed, Oct 26, 2016 at 2:48 PM, mariusz <mdg@xxxxxxxxx> wrote:
> Well, a difference of a 100 Hz will quite substantially affect the tone of your voice‎ particularly with narrow and sharp Collins filter. 
> 
> 73 Art ve3pnd
> 
> 
> 
> Sent from BlackBerry Passport on the TELUS network.
> Original Message 
> From: Ted Hartson
> Sent: Wednesday, October 26, 2016 1:18 PM
> To: collins@xxxxxxxxxxxxx
> Subject: Re: {Collins} BFO x-tals off frequency
> 
> Good Morning, I guess that I am surprised that this error would make
> much of a difference. Especially when the PTO shift between R and T
> addressed by the Viet Nam Zener was typically an uncorrected 100 Hz or
> more, how do you see this manifesting an issue in operation? Ted WA8ULG
> 
> 
> On 10/26/2016 8:14 AM, Ken Kaae wrote:
>> International Crystal has them in stock.
>> 
>> ken
>> ke7yd
>> 
>> 
>>> On Oct 25, 2016, at 11:57 PM, Peter Ravn <fasan5@xxxxxxxxx> wrote:
>>> 
>>> In my KWM-2 the BFO x-tals are a bit off frequency. The USB x-tal is 456.370
>>> kHz, the LSB-tal 453.681 kHz, so the x-tals are 20 Hz off in USB and 31 Hz
>>> off in LSB. I tried to pull down the x-tals by mounting a small 10 pF
>>> trimmer across each x-tal. With the trimmers at absolutely minimum capacity
>>> I managed to pull the frequency a few cycles before the BFO stopped
>>> oscillating. Any other way of the pulling the x-tals?
>>> 
>>> Peter OZ8CTH
>>> 
>>> 
>>> 
>>> 
>>> 
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> 
> 
> -- 
> 73 Dave WI6R
> 
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