Topband: TX/ RX Antenna Switching

[Tom W8JI]

> Forgot the link to Array Solutions
>
> RF Limiter / Front Load Protector   (Helps to know what they call these 
> items so you can search for them :-)  i.e..  "Front End Protector".
>
> http://arraysolutions.com/Products/as_rxfep.htm

That's a terrible protection system. It would deteriorate almost any 
receiver, unless you are using a super regenerative.

Back-to-back diodes by themselves are a poor enough system. They generate 
significant intermod with a sum of all signals at .5 volts RMS, which is a 
sum of signal power (from all signals) of only 7 dBm at 50 ohms or 5.2 dBm 
into 75 ohms. Back-to-back diodes even deteriorate performance below that 
threshold with most small fast signal diodes, some fast small signal diodes 
start to create unwanted mixing products at 0 dBm or less.

Back-to-back diodes driven by minicircuits type transformers would be worse 
yet. I can't use minicircuits transformers on my Beverages here, because of 
IMD.

A properly designed clamp would have no effect up to about 20-23 dBm, where 
it would clamp hard, and would not include easily-saturated very small core 
transformers.

Be careful with anything that uses back-to-back diodes.

73 Tom