[1000mp] Improving IM3 DR with Mark V and Inrad Roofing Filter

[Mike Schatzberg]

Hello 1000MP Fans:

I wanted to update this thread with some additional information from Milan,
OK1VWK,  a member of OL7R multi contest team.  Milan has just recently
emailed me regarding his experiences with the W2AJI modifications for the
Mark V Inrad Roofing Filter Board.  He has given permission to post his
comments here on our 1000MP Reflector.

There have been several questions lately regarding the mod.  I hope that
this will help a little towards answering them.  Perhaps W8JI will reinstall
the modified Inrad board, and make before and after mod data available.

Milan has also made a photo available of the mod, the way he performed it,
using three parallel 470 ohm resistors for R6, as he did not have a 150 ohm
resistor in his spare parts box.

He goes on to say that his colleague, Mirek, OK1UFE,  tried to install the
IC756PRO2 Inrad Roofing Filter in an IC718, as they both have the same 1st
IF.  Mirek's data is presented in the correspondance below.

73 and Happy DXing,

Mike
W2AJI

Hi Mike,

I would like to inform you about my experiments with Inrad roofing filter.
I have aplied your roofing filter IMD mod in my FT1000MP with good results.
It seems to be quite better than original solution from Inrad. I had big
problem with RX IM overload mainly on 40m. After reduction LNA gain, which
is installed on the roofing filter board is my RX more quiet than before.
No problem with space on 40m band now. No problem listen weak signal on
crowded band. I absolutely agree with your idea about this problem. I dont
understand why is Inrad still standing on the RSGB and ARRL measurements.

There is some picture form my modification:
http://bp2.blogger.com/_JwUR_jrJq74/R4igQ71BB6I/AAAAAAAAAFE/X1i3xJ5X-nA/s1600-h/ft1kroofing_mod1.jpg
http://bp2.blogger.com/_JwUR_jrJq74/R4il871BB7I/AAAAAAAAAFM/bX5eTh8QaTA/s1600-h/ft1kroofing_mod2.jpg

73 de Milan, OK1VWK


Hello Mike,

> I see that you used about 157 ohms, the parallel sum, by replacing R6 with
three
> resistors.  Was this because you did not have a 150 ohm resistor?

Absolutely right.

> Did you test
> the 150 ohm verses the 157 ohm resistor and find a better solution?

No, it was only my problem with R6 value and my spare parts for use. I
wanted to try your mod and I had 3x470 only, hi.

> Several people have had big issues like you on 40 meters,
> particularly during CW contests.

It was terrible during last CQWWCW. I am member of OL7R contest team and we
had backup TRX TS850 also there. The TS850 seemed better than my FT1000MP
with Inrad roofing filter without your mod. I was thinking "It isnt normal
situation".

> Maybe you know someone who could
> make the measurements?

Grrr, thats problem. I am sorry but I dont have any idea now. But see text
below.

My job coleague Mirek OK1UFE said to me, that he tried to install IC756PRO2
Inrad roofing filter into the IC718, because both TRXs have the same first
IF and why doesnt try it. After instalation Mirek measured original filter
loss and LNA gain . Filter loss was 2,5dB and LNA gain 6,5dB. He had to
reduce LNA gain and his new value is 1,7dB. I asked him if he aplied your
roofing filter IMD mod and he confirmed it. It seems that after your mod has
LNA 1,7dB gain. His roofing filter was purchased two or three months ago.

Absolutely agree. LNA gain is designed for first VHF filter series with
highier loss than current production line and thats difference between ARRL
and RSGB test and real situation on the band. Inrad changed only filter loss
without LNA gain re-design. Inrad says highier filter LNA gain is good for
lower third IF gain. I think its total mistake. The major problem is total
radio system gain distribution on each IF. Inrad solution causes first IF
overload only and poor IMD results. Nothing else.

> Would you mind if I share your results with our 1000MP Reflector members?

Absolutely no problem. You may publish my info.

Also thanks and nice to see you ...

73 de Milan,OK1VWK