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Re: Hamtronics Preamps



Hamtronics preamps are a pretty good deal for the performance.

For VHF use I would not recommend the use of an SO-239.  It will work at 
VHF, but is not the best.  I'd go with BNC or N fittings.
For UHF, the PL-259/SO-239 is unacceptably bad, and you really need to 
use BNC, SMA, SMB, or N fittings.

For extremely over-the-edge low noise setups, you need to use SMA or N 
fittings, as BNC fittings are made to swivel, and the tendency of the 
connector to move around a little due to vibration or temperature 
changes will sometimes cause some annoying problems with shot noise (I 
suspect this will be true for SMB as well).  SMA and N fittings lock 
tightly in place and won't move about much so they are more 
desirable..Most people won't encounter this problem.

In general, the cheap BNC fittings are typically good to about 2 GHz, 
the good ones can go a lot higher.  For serious stuff, use SMA, or N 
fittings.

As to running a separate power cable goes, you might consider running a 
shielded twisted pair with the shield connected to the negative (ground) 
supply lead of the twisted pair at the power supply end.  Deliver the 
power supply voltage with the twisted pair and leave the shield of the 
twisted pair ungrounded at the preamp end. This will help reduce the 
tendency of the power cabling to pickup noise.

Downeast Microwave has an assortment of preamp kits that have rather 
nice die cast metal enclosures. I built one for UHF, and it works rather 
nicely.  Lastly, In the May/June 2004 Issue of QEX Magazine, there is a 
MAR-6 based preamplifier of my own design (yes a shameless plug).  It 
has an enclosure made entirely of copper clad circuit board material. 
 The performance is pretty good , and if you have some BNC fittings and 
some double sided pc board stock laying around, the project is a very 
cheap one to complete. Several people have reported building this preamp 
with good results.


Glen


hobergenix wrote:

>Thanks for all the suggestions. I have checked out the hamtronics preamps
>and they seem right for the price. They are 39.00 I also like the fact that
>they use surface mount as well. From what I gather they still need to be
>switched out of the line for transmit. They say in the info that they have
>diode protection but I think this is only for reverse polarity protection of
>power to the preamp.
>
>I plan on making my own enclosure but was wondering about connectors to use
>on the case. The enclosure they show uses bayonet connector. I plan on using
>pl259 chassis connectors. Should I consider another connector.
>
>I will just run a separate power and ground lead rather than trying to feed
>power up the coax and adding extra circuitry.
>
>Mike
>N6IMF
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>  
>

-- 
Glen E. Gardner, Jr.
AA8C
AMSAT MEMBER 10593



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