Re: Ver066_9_3_22_25
开云体育Yeah exactly right… everyone is use to having a BPF in transmit to clean up the signal before transmitting…. ? But what many SDRs are missing is a preselector… a band filter mechanism in receive that only allows the band you are listening through (Hence two BPFs for dual receive… because you could be on different bands).? And because SDRs (and particularly this SRD that can operate from about 400kc up to almost 150 mhz), receiving a very loud signal pretty much anywhere in its receive range can desensitize the front end/ mixer to the point that you hear nothing!? We fixed that with the BPF in the T41 operating in Receive too…. ? So when at Field Day operating with friends on different bands… you won’t see any interference in the receiver from them. ? That’s the reason we used a 5 pole filter…the skirts are very sharp so all the trash outside of the TX and RX frequency is greatly attenuated. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ VP2EHZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: ? Moderator: North American QRO Group at Groups.IO. Moderator: Amateur Radio Builders Group at Groups.IO. ? email:? bill@... ? ? From: [email protected] <[email protected]> On Behalf Of Oliver KI3P via groups.io
Sent: Wednesday, April 2, 2025 4:09 PM To: [email protected] Subject: Re: [SoftwareControlledHamRadio] Ver066_9_3_22_25 ? Bill can comment further, but the BPF should be in the signal path in both RX and TX mode.? ? In TX mode it cleans up the signal before it goes to the PA. This means that higher-order harmonics of the signal produced by the exciter -- copies of the signal at multiples of the transmit signal -- are filtered out and not amplified by the PA. These would be removed by the LPF anyway before they could hit the antenna, but removing them before the PA helps with signal quality because the PA isn't having to amplify signals at multiple bands simultaneously. ? In RX mode the BPF keeps the other bands away from the input to the mixer. If you didn't have the BPF in place you would expect to get a higher noise level in the audio at best, and distortion from strong signals in other bands at worst. ? ? On Wednesday, April 2nd, 2025 at 3:54 PM, epif18 via groups.io <epif18@...> wrote:
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K9HZ