I did try this on the bench but the loss in gain seemed pretty severe
for the modest bandwidth improvement I could get. Maybe with a more
methodical approach I could make it work.
Steve WD8DAS
[EMAIL PROTECTED]
http://www.wd8das.net/
------------------------------------------------
Radio is your best entertainment value.
------------------------------------------------
-----Original Message-----
From: Jim Wiley <[EMAIL PROTECTED]>
To: [email protected]; [EMAIL PROTECTED]
Sent: Tue, 22 Jan 2008 10:49 pm
Subject: Re: GB> 75A-2 project
It might be possible to "stagger tune" the IF stages to increase
bandwidth. Use of a sweep generator (or a manually swept signal
generator) will let you know how you are doing when trying this. As a
general rule, you can trade gain and selectivity for increased
bandwidth. You might be able to get as much as a doubling of the IF
bandwidth by this method.
I am not familiar with the 75A-2, but if it includes more than one IF
transformer between the IF amplifier stages, it would be a excellent
candidate for this modification. I have a 51J-3, but the two might not
use the same design inside the IF section. With luck, the 75A-2's IF
system might have some excess gain that you could sacrifice to get more
bandwidth. Might be worth a try, at least.
The advantage here is that this is a non-intrusive modification - in
other words, easily reversible, requiring no component changes, extra
parts, etc.
Lacking a sweep or signal generator, you could experimentally try
turning the IF transformer slugs or capacitors a bit each way (keep
track of the original positions!!) to see if it gives you what you
want. If the trimmer capacitors or slugs are the multi-turn type,
then
they can probably be detuned a full turn or more without losing too
much
gain. Try small steps, such as a 1/4 or 1/2 turn at first. Half-turn
trimmer caps are more difficult, and you will probably need to use a
series of pencil marks on the can to try and get fractional turn
indicators.
There are fancier ways to do this, such as by using double tuned
circuits and/or over-coupling, but then you are into the realm of
parts
changes and not so easy to reverse modifications.
YMMV
- Jim, KL7CC
************ The Glowbugs E-mail List Website is: ***************
*********** http://www.mines.uidaho.edu/~glowbugs/ **************
*** Send subscribe and unsubscribe requests to this address: ****
************** [EMAIL PROTECTED] **************
Steve WD8DAS
[EMAIL PROTECTED]
http://www.wd8das.net/
------------------------------------------------
Radio is your best entertainment value.
------------------------------------------------
-----Original Message-----
From: Jim Wiley <[EMAIL PROTECTED]>
To: [email protected]; [EMAIL PROTECTED]
Sent: Tue, 22 Jan 2008 10:49 pm
Subject: Re: GB> 75A-2 project
It might be possible to "stagger tune" the IF stages to increase
bandwidth. Use of a sweep generator (or a manually swept signal
generator) will let you know how you are doing when trying this. As a
general rule, you can trade gain and selectivity for increased
bandwidth. You might be able to get as much as a doubling of the IF
bandwidth by this method.
I am not familiar with the 75A-2, but if it includes more than one IF
transformer between the IF amplifier stages, it would be a excellent
candidate for this modification. I have a 51J-3, but the two might not
use the same design inside the IF section. With luck, the 75A-2's IF
system might have some excess gain that you could sacrifice to get more
bandwidth. Might be worth a try, at least.
The advantage here is that this is a non-intrusive modification - in
other words, easily reversible, requiring no component changes, extra
parts, etc.
Lacking a sweep or signal generator, you could experimentally try
turning the IF transformer slugs or capacitors a bit each way (keep
track of the original positions!!) to see if it gives you what you
want. If the trimmer capacitors or slugs are the multi-turn type,
then
they can probably be detuned a full turn or more without losing too
much
gain. Try small steps, such as a 1/4 or 1/2 turn at first. Half-turn
trimmer caps are more difficult, and you will probably need to use a
series of pencil marks on the can to try and get fractional turn
indicators.
There are fancier ways to do this, such as by using double tuned
circuits and/or over-coupling, but then you are into the realm of
parts
changes and not so easy to reverse modifications.
YMMV
- Jim, KL7CC
************ The Glowbugs E-mail List Website is: ***************
*********** http://www.mines.uidaho.edu/~glowbugs/ **************
*** Send subscribe and unsubscribe requests to this address: ****
************** [EMAIL PROTECTED] **************
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