I wasn't sure where to ask this question, but since I found the problem using my NanoVNA, I thought I'd ask here.
Our club has a multi-band Bandpass filter from ICE, Model 419 that we want to use on Field Day. This unit covers 160, 80, 40, 15 and 10 meters.
Complete Unit:
Internals: !Ats-2fm84F1OgaUfhmHlYIjlktAx5g?e=JcS9i3
I tested the unit with my NanoVNA and found that the loss varies greatly by simply tapping the unit. Through DC testing, I have determined that the unit has a bad 15m relay where it should be passing the signal directly through (bypass the 15m coils) through the Common to NC contacts.
It¡¯s the relay in the upper left corner, next to the small green cap. I¡¯m seeing anywhere from 3 or 4 dB loss at BEST and up to 30 dB loss through the NanoVNA. The loss varies as you tap the unit.
When I measure the loss using my transmitter (tune position, 10 watts, into a dummy load with a wattmeter) I¡¯m seeing:
160m -.432 dB loss..
80m -.414 dB
40m -.914 dB
20m -.801 dB
15m -.964 dB
10m -1.10 dB
The faulty contact is only a problem at lower signals, such as the NanoVNA and receive signals.
The way the circuit works is that the signal comes in on the input coax connector, and when all relays are disabled (NC position) the signal goes through the NC connections of each relay. When you switch in any one band, that relay is pulled in (NO Contacts) and the signal goes through the Band Pass coil/capacitor network.
So, it appears that the 15m relay is intermittent. I tested across each relay in the NC position with an digital multi-meter, looking at the voltage drop across the contacts.
Because of the construction practices used, it¡¯s impossible to remove the relays to clean the contacts.
My ideas are:
1. Drill a hole in the plastic and spray (lightly) some contact cleaner
2. Remove the coil/capacitors on that relay and try to get the relay out, clean the contacts and replace everything, hoping that the band pass tuning doesn¡¯t change.
I¡¯ve been trying to find a way to clean the contacts by passing current through them, but I haven¡¯t come up with much.
I tried to contact the manufacturer, but they haven¡¯t built this unit for over 12 years and they have no idea what to do.
Anyone have any ideas?
--
Mike, W0IH
