Topband: W7IUV Preamp from Low Band DXing

[Steve Ratzlaff]

>From: "Dan Zimmerman N3OX" <n3ox at n3ox.net>
>To: <topband at contesting.com>; <john.devoldere at pandora.be>; 
><w7iuv at yahoo.com>
>Sent: Saturday, January 13, 2007 11:20 PM
>Subject: Topband: W7IUV Preamp from Low Band DXing


> Just a heads-up to the flag, pennant, and K9AY builders-to-be out there.
>
> I built a W7IUV-design preamp using the 2n5109 tonight.  I built it
> from the 4th ed. Low Band DXing so I'd have the schematic in front of
> me.  When I hooked it up, it amplified, and I was happy, but I
> measured the gain and it was only about 8dB.
>
> I found the problem.  The schematic in Low Band DXing lists the
> unbypassed part of the emitter resistor as 47 ohms instead of 4.7
> ohms.
>
> And there's my missing 10dB.
>
> Just thought I'd let everyone know.  It's a nice simple project and
> I'd imagine a lot of people are building from ON4UN's book.
>
> 73,
> Dan


Very coincidentally, I made a W7IUV preamp recently as well, except I used
the latest version on Larry's webpage, with the correct values. My 2N5109
must be a little different, as current draw was much higher than the stated
nominal 75mA--mine was about 90mA, and runs very hot to the "finger test".
But bench tests give very good performance. Using 3/4 MHz output tones at 0
dBm each gave +40 dBm OIP3, +60 dBm OIP2. Gain is +21.3 dB. Using 20 bifilar
turns on an FT37-75 core had the -1dB response from about 220 kHz---27 MHz,
and only -1.2 dB at 30 MHz. (I used 1 uF monolithic ceramic caps for
coupling and emitter bypass.) This is an excellent broadband preamp, not
just for 160M!
73,
Steve AA7U
NE Oregon

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