Re: [amsat-bb] Pre-Amp?

["hasan schiers" <schiers@xxxxxxxxxx>]

Tony is correct, it is highly likely that even with the SSB SB-7000 preamp,
you will need a front end filter, and the duplexor is an excellent solution.
It only introduces 0.25 dB loss, so it's impact on the following gasfet is
minimal for the kind of work we are doing.

I found with my FT-847, even setting the power to absolute minimum (no
deflection on the Bird 43), that broad band noise and desense was terrible
with the SB-7000 until I put my comet duplexer in front of it...at which
point it was perfectly quiet w/r to desense/overload/broadband tx noise.

Admittedly my tx and rx feedpoint are only about 6 inches apart, being
nested 4 and 8 element quads on the same boom. There is nothing wrong with
the SB-7000 preamp, in fact many consider it to be the elite of RF
switchable preamps. However, it does have an input protection diode that can
be caved in rather easily in the face of high rf. This can be modified, but
I wouldn't suggest it. The simple solution (as has now been pointed out at
least a dozen times) is to put a good quality, readily available,
inexpensive duplexer in front of the preamp, and terminate the unused 2m
port (if it is unused) with a 50 ohm resistor.

This is all nicely laid out on the amsat site...drawings, et al.

It is possible that one might not need the diplexer as filter...but not
likely, so don't be disappointed if you have any of the above mentioned
gasfet preamps and find that they are trashed by your tx (uplink) signal.
The solution is cheap, simple and effective.

73,

...hasan, N0AN
----- Original Message ----- 
From: "Anthony Monteiro" <aa2tx@comcast.net>
To: "Glen Gardner" <Glen.Gardner@verizon.net>
Cc: "'amsat-bb'" <amsat-bb@AMSAT.Org>
Sent: Thursday, August 19, 2004 11:53 PM
Subject: Re: [amsat-bb] Pre-Amp?


> Hi Guys,
>
> Just a little clarification:
>
> I have ARR, SSB and DEM preamps. All of
> them need input filters.
>
> The SSB preamps have NO filtering on the front end.
> The 2 7000 model has a helical filter on the
> output which is good for weak signals but does nothing
> for strong signal overload. I use a comet duplexor and this
> works pretty well.
>
> The DEM preamps are actually better all around preamps
> (probably the best NF) but they also need an input filter
> and have no TX switching so if you want to use your antenna
> to TX also, you have to provide your own switching.
>
> ARR preamps are a good bargain and work fairly well
> but not as good as DEM.
>
> 73,
> Tony AA2TX
>
>
> At 08:20 PM 8/19/2004 -0400, Glen Gardner wrote:
>
> >The SSB electronics preamps are about as good as they come. They have
> >*substantial*  filters and are beautifully made.
> >The ARR preamps have no filtering, and while the gain and noise figure
are
> >very good, I'd suggest putting a DCI filter *after* the ARR preamp, with
> >nothing between the preamp and the antenna. (mount the preamp right at
the
> >antenna). That way you get the best options possible for noise figure and
> >low IMD.
> >
> >If you go with the SSB electronics preamp, you won't need an external
> >filter, but it won't hurt if you add one.  The same applys here, put the
> >preamp at the antenna. Anything between the preamp and antenna will add
to
> >the noise figure of the preamp. Also, coax losses apply to noise as well
> >as signal, so having some gain ahead of the lossy coax can actually
> >improve your S/N ratio if you have a good low noise preamplifier to begin
with.
> >
> >
> >Glen
> >
> >
> >Greg Greenaae wrote:
> >
> >>I'm going to try this 440 preamp on the Arrow:
>
>>http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=PR
-S
> >>ERIES
> >>
> >>The specs look close to the SSB preamps.  Not sure about intermod
rejection
> >>on the unit.  Anyone know if the SSB units have a Helical filter or
> >>something fancy for intermod rejection?
> >>
> >>-----Original Message-----
> >>From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org] On
Behalf
> >>Of Danny Monge
> >>Sent: Wednesday, August 18, 2004 9:21 PM
> >>To: amsat-bb
> >>Subject: [amsat-bb] Pre-Amp?
> >>
> >>
> >>I know this has been asked about before but I didn't see any reply's so
here
> >>goes again. Does anyone have a recommendation for a pre-amp to use with
a
> >>tripod mounted arrow antenna? Thanx.....
> >>
> >>
> >>
> >>Danny Monge - AD6SJ
> >>IRLP Node # 5040
> >>EchoLink # 152401
> >>CM97dx
> >>----
> >>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not
> >>an AMSAT member? Join now to support the amateur satellite program! To
> >>unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >>----
> >>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> >>Not an AMSAT member? Join now to support the amateur satellite program!
> >>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >>
> >>
> >
> >--
> >Glen E. Gardner, Jr.
> >AA8C
> >AMSAT MEMBER 10593
> >Glen.Gardner@verizon.net
> >
> >
> >http://members.bellatlantic.net/~vze24qhw/index.html
> >----
> >Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> >Not an AMSAT member? Join now to support the amateur satellite program!
> >To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
> >
> >
> >
> >---
> >Incoming mail is certified Virus Free.
> >Checked by AVG anti-virus system (http://www.grisoft.com).
> >Version: 6.0.737 / Virus Database: 491 - Release Date: 8/11/2004
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org