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Reviews For: INRAD Roofing Filter ICOM Pro III

Category: Filters, RF: bandpass, duplexer, lowpass, highpass, RFI/EMI

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Review Summary For : INRAD Roofing Filter ICOM Pro III
Reviews: 12MSRP: 200
Description:
This roofing filter can help reduce the third order Intermodulation from multiple strong signals in the 2 to 20 kHz region either side of the tuned frequency. Please see our document titled "A Few Words About Roofing Filters" for more details.


Product is in production
More Info: http://www.inrad.net/product.php?productid=225
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00124.9
K8AC Rating: 2008-05-22
Difficult installation - minor scope effects Time Owned: 0 to 3 months.
I chose to install this roofing filter after experiencing the IMD problem during the CW SS in 2007. While I don't have any way to test the results (until next contest season), I trust the info provided by I1ODP regarding the measurements. If you're not confident of your ability to work with the tiniest of surface mount devices, you probably want to avoid doing the install yourself. You need to remove a resistor and connect a discrete capacitor and resistor to the pads left after the removal, and you'll need some good magnification to carry that out. Mechanical work includes the removal of a shield can from the board, drilling two small holes in it and attaching two small coax cables to the shield. The filter board is completely assembled and it is placed in an open space just to the right of center behind the front panel display. The board just sits in the space and can move around if you happen to ship your Pro III, so if you plan to do that you might consider forcing a piece of foam plastic between the board and the frame to hold it in place.

I had heard that the filter had some effect on the spectrum scope display, but observed only a minor effect on signals. At a point approximately 3.3 KHz on each side of the center frequency, I found that the displayed signal peaked about 3 dB over a small range and I determined that by tuning across the calibrator signal while watching the signal height with the vertical scale. The effect isn't noticeable unless you're looking for it with the calibrator or other stable signal source.

The filter reduces the bandwidth enough to affect the fidelity of AM broadcast signals as you'd expect, but it's in the signal path for the main receiver only. If you want to listen to AM with the same fidelity as before, you can use the subreceiver in dual watch mode and adjust the balance control so you don't hear the main receiver.

My rating of 4 considers the difficulty (and high risk) of the installation and the fact that the filter board is not secured in the mounting space. I would not recommend the installation unless you are bothered by the IMD problems of the stock receiver.
I1ODP Rating: 2008-02-24
A great performer Time Owned: 0 to 3 months.
I just measured my Pro III with Inrad roofing filter (nominal 3kHz BW) :
Noise Floor -135 dBm
MDS -132 dBm
Dynamic Range with
2 interfering signals spaced 5kHZ -------------> 95 dB (9+35 on the Smeter) about
2 interfering signals spaced 4kHZ -------------> 92 dB (9+30 on the Smeter) "
2 interfering signals spaced 3kHZ -------------> 82 dB (9+20 on the Smeter) "

Without the roofing filter I measured years ago my Pro III see

http://www.ab4oj.com/icom/ic756pro3/i1odp.html

and close-in Dynamic Range results where :

2 interfering signals spaced 4,4 kHZ -------------> about 80 dB.

Conclusion:
Using narrow VHF roofing filters you improve your Pro III DR (2 sigs spaced 4 kHz) by more than 12 dB .