[Hallicrafters] Substitute antenna coils

[Dr. David Knepper]

I don't pretend to be an authority on the SX-71 but it has been my
experience that the poor performance of these general coverage receivers,
particularly, on the BC band was the result of not having a matched antenna.
I know that the performance on the BC band is down when using a dipole cut
to 75 meters, for example.

If transmitters have to be matched to a 75 ohm output impedence, would it
follow that a receiver's front-end must be matched to the "correct"
impedence?  What is the difference except one transmits and other receives!


David Knepper - W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
CRA website:  http://www.collinsra.com

-----Original Message-----
From: hallicrafters-admin at mailman.qth.net
[mailto:hallicrafters-admin at mailman.qth.net]On Behalf Of Philip Atchley
Sent: Saturday, April 27, 2002 9:02 PM
To: hallicrafters at mailman.qth.net
Subject: Re: [Hallicrafters] Substitute antenna coils


> There's another thing, though as applies to the MW band on the SX-71.  I
> see no mention of it in the manual, but it looks to me on the schematic
> that a wafer on the bandswitch bypasses the first mixer on band one.  Is
> it single conversion on BCB and dual on the top four bands?

Barry
Yes, the set is single conversion on the lower 2 bands.  But that shouldn't
really affect sensitivity any as you still have an RF amplifier, then a
mixer followed by 3 IF amplifiers.  A decent tube line-up in any set.  I
suspect the gain reduction on the bcb is done in the front end coils.  If it
was done intentionally they may have got carried away (though I won't know
for sure until I remove/inspect and replace that coil).

73 de Phil  KO6BB
Loving home provided for wayward Boatanchor Receivers
k06bb at elite.net
Merced, Central California
37.18N  120.29W  CM97sh




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