I and WW2Y built a couple pre-amps for topband a couple of years ago.
He and K2WI used them with considerable success in topband contesting,
( not due to the pre-amp ) but at least the pre-amp didn't hurt.
The design was based on a medium power bipolar NPN in order to achieve
a very high dynamic range for a pre-amp. One of the complaints that
we were aware of was that some commercial pre-amps suffered from
being driven into distortion from broadcast and other sources nearby
in frequency.
BCNU DE N2LO
DF2PY wrote:
>
> hi reflectees !
> In the past weeks the question about preamps for low gain rx antennas came up
> frequently. Although there are a few units avialable commercially, i think
> homebrewing is the appropriate step for any avid topbander.The ARRL handbook
> has
> numerous designs and the basic knowledge every ham has, should be sufficient
> to
> nail a gadget like that together in a jiffy. As noise figure is not of concern
> one can go for readily available simple bipolar transistors like the famous
> 2N2222 or any small signal type/medium to high gain type transistor.
> One can put in as many LC-type filters in front of the stage to meet his own
> needs for Out-of-band rejection,nearby AM-stations are nicely suppressed and
> one
> can even put in "attenuation-poles" in case he sits "fence-to-fence" with a
> 100kW AM transmitter. I built filters like that with Arne/N7KA in ABQ and he
> neighbors a few hi pwr AM stns there. One will be surprised how nice and easy
> the filters are adjusted and he will receive a great deal of satisfaction if
> he
> can include each and every extra function that he needs.Amplification can be
> switched or smoothly adjusted just the way You like it. I strongly recommend
> homebrewing here as no special test equipment is needed and only the stuff
> already in the shack does the job. For my own needs i have a homebrew
> filter/preamp autoswitched gadget that fully satisfies me with each and every
> QSO i run thru it. Good luck homebrewing !
> 73 de wolf -df2py-
>
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