Guy,
Re.
I read your Rationale as well about the filters...it is the QSE BP filter that has me a bit confused.. Do you have a design with different plug in filters?
I see that my write-up is not clear on this. It is necessary to remove the standard bandpass filter that follows the TX mixer (which restricts operation to e.g. 80-40m) so that the RXTX will work on all bands. If this BP filter is simply replaced with a jumper then that will work. However, the level of the IMD spurs is higher than desirable (and at least on some bands higher than the FCC specified limit of -43 dB down from the main signal). See the Note 1 measurements. I am recommending that low pass filters be installed after the TX mixer, which requires that there would be several of them so some means of plugging them in or switching among them would be needed.
I provided the values for two filters, a 30 MHz one that would work for 20m thru 10m (see Note 1), and a 14.3 MHz one that works for 40m thru 20m. Values were not provided for lower bands. If you are only going to run 1 W output from the RXTX, or to a low power amp, maybe 20W, the IMD spurs will be so low as likely never to cause problems. If you plan on running 100W plus, then I would strongly encourage having low pass filters on the TX mixer output.
I have a set of 6 low pass filter that are relay switched in. That many would not be needed, I happened to have access to a board with the necessary circuitry.
Does this help Guy?
Roger
On Sep 29, 2020, at 7:10 AM, Guy Mengel <guy@...> wrote:
Hi Roger;
I have your document before me and I am putting together a BOM for the build of the 160-10 Meter Mods.
In your document you state: " iii) replace the old filter with a set of switched or plug-in filters that will cover all bands. Andy, YL2QN, has designed and built a switched filter for his RXTX mod. "
For the External Filters
I have looked everywhere in the forum (its huge) for YL2QN's switched filter. I would love to see what he built. (these (BP?)filters between the QSE mixer and driver... Do you have a link?
I have your switched filter as well (the link to the 3 pole 6 Position Switch has expired) It actually pointed to a 1 pole 6 pos, 3 stack switch.. This is actually the external LPF. These switches are pricey. Unless I wait for the slow boat from China...
I read your Rationale as well about the filters...it is the QSE BP filter that has me a bit confused.. Do you have a design with different plug in filters?
I am enjoying this greatly. Thank you again Roger..
PS.. I wonder why the 6.3 design with the plug in filters was discontinued by Tony.. perhaps I have not read enough..
PSS. Thanks for the patience for a VERY latecomer to use these Softrocks..
Guy
