I have the EF Johnson Low Pass filter from decades ago. It is the model with adjustable air caps at each end of a cylindrical aluminum tube. I spent some time setting it up yesterday. I drove it with an FT-891 at 6w connected with two, 12" lengths of RG-8x patch cords into a dry DL.
I could get flat SWR from 10-40 but not 10-80. I could adjust the caps to get flat SWR on 80 but then 10-40 suffered. The SWR on 80 (3.8) when adjusted for best SWR 10-40 was 'a hair under 2'.
I dug it out from storage because I use the MRF422 amp on occasion and suspect it's not the cleanest device. Given that I do not have an SA, I'll leave it in. I would like to see a YouTube video by someone with an SA showing a filter in action.
After adjustments were finished, I noted some power drop. Not a lot but noticeable when watching meter (Dentron ATU meter which is general at best so it's hard to quantify the decrease). I can say that the drop is more of a dampening of peaks on syllables or a drop in responsiveness on SSB. On AM carrier I'll estimate 10% decrease?. In use, I never drive amp over 20-25w, the efficiency noticeably drops-off with more than 25/30w drive. In any event, the PO drop tells me it's working.
.
neil, NYC
n2eye
I could get flat SWR from 10-40 but not 10-80. I could adjust the caps to get flat SWR on 80 but then 10-40 suffered. The SWR on 80 (3.8) when adjusted for best SWR 10-40 was 'a hair under 2'.
I dug it out from storage because I use the MRF422 amp on occasion and suspect it's not the cleanest device. Given that I do not have an SA, I'll leave it in. I would like to see a YouTube video by someone with an SA showing a filter in action.
After adjustments were finished, I noted some power drop. Not a lot but noticeable when watching meter (Dentron ATU meter which is general at best so it's hard to quantify the decrease). I can say that the drop is more of a dampening of peaks on syllables or a drop in responsiveness on SSB. On AM carrier I'll estimate 10% decrease?. In use, I never drive amp over 20-25w, the efficiency noticeably drops-off with more than 25/30w drive. In any event, the PO drop tells me it's working.
.neil, NYC
n2eye
Last edited: