Re: Tracing receive signal for low signal

Jack, W8TEE

 Interesting. I checked the one-price for the relay at Digikey, Mouser, Arrow, and Newark and all but Arrow were the identical price, $2.81. Arrow is $2.67. I've been pleased with Arrow in terms of prices, service, and low shipping costs (sometimes, zero).

Jack, W8TEE

On Tuesday, January 15, 2019, 9:25:48 AM EST, Evan Hand <elhandjr@...> wrote:

I go the relays at Mouser:

I believe you can do better on price if you go through ebay, though the lowest cost may take awhile in shipment.

I am not sure that I would trust my RTL-SDR to accurately measure for the harmonics/spurs.  I got different results when compared to my RF Explorer WSUB1G+, and the front end of the RTL-SDR seems to overload easily, giving strange results.  Again, I am not sure which one to believe.  They both do agree that there is a 3rd order harmonic at 21mhz that is higher than the -43db that is required in the US.

I would also read the following threads:

There are more and the net of all of this is that there is not total agreement on the fixes that are required.

My interpretation is as follow (please understand that I am NOT and expert.  I have just read a LOT of the emails related to the uBitx)
1 - The relay replace is minimum and may not totally fix the harmonic issues.  The true fix is an external low pass filter board linked to the uBitx switching relays, or possible loss in receiver sensitivity if left in and manually switched when the band is changed.

2 - If you can fix the harmonics, then operation on bands 20m and lower in frequency  should not have the IMD issue.  You can reduce that with both Ashhar's and Raj's fixes combined.

3 - without the major modifications that are suggested by the v5 board changes, the v4 and earlier should NOT be used as the exciter to a PA, UNLESS you have the equipment and skill to verify the spurious radiation is under control.

I have been told in this group that in the "old days" spurious emissions where tested using another receiver located far enough away to not overload the front end.  In other words, have a friend that can hear your signal verify no spurious emissions.  This would involve scanning for them.  I am sure that was state of the art then, not sure the FCC would agree now.  We are responsible for our transmissions.

It has also been pointed out that with the normal power levels of the uBitx, that as long as you were close, the spurs would be so far down that it would not really cause interference or be noticed.  One of the reasons for me abandoning the PA until I know what to do to the uBitx.

As always, take my input with a grain of salt.

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