TopBand: High Input Intercept SMD Devices

[Tom Rauch]

> Date:          Wed, 08 Apr 1998 13:58:14 -0500
> From:          Peter Sears <w5ps@airmail.net>

> I saw a note from Carl, KM1H talking about how bad surface mount devices
> can be for intermodulation products.

Hi Peter,

I'd be careful using MMIC's, since the intercept ratings can 
sometimes be misleading. I have to use MMIC's almost monthly in 
new designs, and they are pretty poor performers compared to what a 
standard bipolar CATV transistor can provide in cases like low noise 
high intercept amplifiers for HF. 

The advantage MMIC's offer is they are "plug and play", the lack of 
external components simplifies the design. The disadvantage is they 
hog a lot of current for the IMD specs they provide, they have 
limited output power, and you are generally stuck with the gain they 
are preset at. 

A few dB of amplifier noise figure isn't important at all, even in 
the quietest location, unless you use a *very* small antenna for 160.

My noontime noise level, on a 3/8 wl omni vertical, is about S-2. 
Despite that low noise level, my Beverages only require a five dB 
noise figure amp for plenty of head-room at noon time. At 
night time, a 20 dB NF amp is good enough (even on a quiet winter 
night).

Theres no reason to mount the amp outside either, unless the system 
has some sort of problem. I have over 1000 feet of RG-11 cable here, 
and there is absolutely no difference with the amp in the house or at 
the antennas.
73, Tom W8JI
w8ji.tom@MCIONE.com

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