My squadron is in need of a new DF unit and we are considering the Sniffer, however this will require an antenna. It would be great to use old resources but we are also willing to buy a specialty antenna too. From what I understand, the MARK4 operates best with 3 element antennas, the L-per is only 2, will this affect the search? Thanks!!
They do not work very well together at all. It has nothing to do with the number of elements - though more is always better - but more with the design of the L-Per's antenna.
I'd recommend a handheld beam antenna. Arrow Antennas makes a decent one cut for 121.5:
http://www.arrowantennas.com/arrowii/121.5-3ii.html
You could also make one (the "tape measure" antennas is inexpensive and popular, if somewhat aesthetically unpleasing).
If you are going to buy a Sniffer, then consider picking up a mobile antenna as well for use in the vehicle. L-Tronics used to sell an excellent one, but alas, no longer. The Larsen "Larsen-MB-1-4" antenna here would seem to be a reasonable substitute:
https://www.cumulus-soaring.com/larsen.htm
I've DF'ed tons of ELTs with the Sniffer and both handheld and mobile antennas in the past and would be happy to discuss techniques with any interested units.
We got the purpose-built antenna from RD4.
It's well-made and you can be sure it will work.
http://www.rdfantennas.com/index.php
(http://www.rdfantennas.com/images/flabob4.jpg)