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Question for Joy
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At the Baylands a few months back, Barry and I tested a pair of the QRP Bandpass Filters made by Tactical Radio, one for 15m, one for 20m, which are spec'd to have >40 dB cross-band rejection. ?We found that with one bandpass filter inline with his mcHF and the other bandpass filter inline with my HL2, we could both operate at the same time, even with our two antennas only a dozen meters apart, without noticeable cross station interference. ?But with only one bandpass filter in use on the HL2, the HL2 picked up significant interference from operation on the other band. ?We hypothesized it was wide-band phase noise from the transmitter getting into other bands.
The Tactical Radio filters were expensive. ?It would be nice to find a less expensive kit-build-able solution with smaller connectors.
73, Ron, n6ywu |
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Plenty of opportunity but I haven't done it. It sounds ?from what Ron said others would also have to use a filter in order to reduce the interference. ?Am I correct Ron? I don't want to bother other people by asking them to use a filter. I'll continue to just switch to another band or wait until there is a pause in the interference. I still have the filter you made and can return it when I may see you at Pacificon.
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I am planning a trip to France to visit family in either September or October. The trip is kind of up in the air at the moment. ?So I may not make it to Pacificon.?
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Joy |
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Hi Joy,
If you use a bandpass filter, you are less likely to interfere with other operators nearby, anyone operating on a different band !
Needing bandpass filter on other transmitters is more of a problem for receiving with wideband direct sampling SDRs, such as the Hermes Lite 2. ?A superhet with a roofing filter, or a Tayloe IQ direct conversion design, seems less susceptible to unfiltered wideband phase noise than a direct sampling SDR.
73, Ron, N6YWU |
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Thanks Ron, I am hearing interference from other stations some of the time. I am transmitting qrp and doubt I am causing interference for others. I could be wrong. It was my misunderstand of what Doug's band pass filter does. Dave had told me it wouldn't work in my application so I am dropping it. I'll return Doug's filter the next time I see him which may be at Pacificon.?
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Thanks for the suggestions.?
Joy |
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Hi Joy,
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The issue is symmetric. ?If you hear noise when others transmit on other bands, you will be creating the same kind of RF noise to other nearby operators when you transmit (likely broadband transmitter phase noise and/or spurious intermodulation). ?If everybody (nearby) uses a bandpass filter, even on QRP radios, the noise level for everybody will be reduced; and more people will be able to use different bands at the same time far less interference to each other. ?Barry and already I tested that at the Baylands. ?So, for multi-operator sessions with adjacent antenna's, as is common at the Baylands, we should all make or buy and use bandpass filters (similar to multi-op Field Day and DX operations).
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73, Ron, n6ywu |
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Agree.? I tested the 20 meter band pass filter at Pacificon.? ?The Pacificon station was running 500 Watts on 40 meters.? Their antenna was 20 feet from my antenna.? ?With no BP filter, I was having interference from them.? I was on 20 meters.? Then I put the 20 meter bandpass Filter on.? The interference was GONE.? ?I couldn't believe it.? ?Darryl Swenson was with me and I took the Filter off.? As soon as I did, the interference was back.? So they were still on the air!!? I put the Filter back on, the interference went away.? So, yes, I am a fan of bandpass filters. |
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which filters were you using? You guys are convincing me I want to get a couple. Connie W6EFI On Thu, May 22, 2025 at 22:03, Doug Hendricks via groups.io <ki6ds1@...> wrote:
-- Connie KN2EFI |
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I am one of the folks that run the Pacificon station.?? This last year we had very good radios across the board with good? harmonic suppression?and no key clickers.? ? ? ?? ?We are transmitting through bpf's and a triplexer.? ? ? ?? That said, the second harmonic of the 40m station is still strong.? ? (Probably wasn't running 500 W into the filter, but 250+ W, sure...) I'm surprised?a 20m bpf did much since?the second harmonic is in band.? ? ? If we're splattering, I want to know. I have an HP spectrum analyzer at the event, so if you want to check something, please find me. 73 de AI6KG On Thu, May 22, 2025 at 7:03?PM Doug Hendricks via <ki6ds1=[email protected]> wrote:
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it looks like schematics and ?bill of materials are available as well. ? Thanks! On Thu, May 22, 2025 at 23:15, Doug Hendricks via groups.io <ki6ds1@...> wrote:
-- Connie KN2EFI |
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Hi Doug. I suspect we must have been?operating 40m phone.? ?? That would have put the second harmonic outside of the 20m and 15m bands but loud enough (obviously) that it would desense a receiver without enough selectivity.? A (tight enough) bpf would do as you described..? A BPF won't help in the same situation for?40m CW near the bottom of the band as? the second harmonic lands in-band on 20m and the third in-band on 15m.?? We have this issue? at the station itself (and we have decently sharp high Q BPF's for each band).? ? ? We keep the 40m antenna away from the 20m/15m/10m triband but we can only get so much separation at the site.? ? ?We've been discussing other ideas like a coaxial stub. It is worth noting that a single conversion receiver will struggle with strong adjacent signals much more so than a dual conversion receiver. Hope to see you folks in October.? ?Come on by if you'd like to work QRO for a change.? :-) 73. On Thu, May 22, 2025 at 8:11?PM Doug Hendricks via <ki6ds1=[email protected]> wrote:
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