Well, that looks pretty good to my inexperienced eye! Thanks for running that 300Ohm! I'm going to give that a try...

back 10 channels to cover the ch 18-48 range.
Yeah, it looks like an increase of about a good 1 dbi Net Gain in that range. :)

The SWR going down with the whisker length increase was a bit surprising.

I've never seen a graph of the CM4228 with the upshift trick applied but from anecdotal evidence over the years it was apparently a very simple and clear shift up the band and left the channels below 30 somewhat weaker and below 20 noticeably weaker.

Heres the graphs with the upshift trick applied. I ran the graphs to 890 mhz, old channel 83, to see if that was significant.
(frequency between each point is 6 mhz, ie one channel)


Raw Gain:
http://img695.imageshack.us/img695/2879/cm4228minus1inchrawgain.jpg

SWR:
http://img843.imageshack.us/img843/7149/cm4228minus1inchswr.jpg

The SWR going up with the whisker length decrease is not now surprising.

A quick way to look at the SWR figures to subtract from Raw Gain to get Net Gain :
Code:

SWR Mismatch Loss dBi
----- -----------------
1.0 0
1.5 .18
2.0 .51
2.5 .88
3.0 1.25
3.5 1.60
4.0 1.94
4.5 2.25
5.0 2.55
6.0 3.08

Hi there. According my blue print:D whiskers aperture 80mm ,,,420mm from side tu side.....30 mm space,,whiskers are 1844mm =1 1/4" long

Extending the whiskers 1 and 5/8th inches, whisker length 9 and a half inches, is physically doable. Extending to 10 inches isnt, as the whiskers would touch.

Raw Gain:
http://img691.imageshack.us/img691/2444/cm4228plus1625inchesraw.jpg

SWR:
http://img691.imageshack.us/img691/9306/cm4228plus1625inchesswr.jpg

Yeah, it looks like an increase of about a good 1 dbi Net Gain in that range. :)



Well, as a follow up to this, I went ahead and added 1 1/8" whisker length to my 4228 to bump up the lower channels. My high tech mod involved taping 1/8" solid aluminum rod onto the ends (wanted a quick, easy trial...).

The bottom line is that it really worked. Bearing in mind that I am in an extreme fringe area and every decibel counts, my readings increased on average about 30-50%. This was for my only 3 receivable channels on RF 20, 22 and 33, so it is not a large sample size. And the readings went up from 30-40% (frequent breakup) to 45-65% (solid lock on all three).

Overall, I am quite happy that the theoretical finally seems to match the real world results for me anyway. Thanks again 300ohm...