Thanks.? Good news is I am using their low pass filters actually not their band pass filters, so should be ok.
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On Sun, Jan 27, 2019 at 11:50 PM, AndyH wrote:
Don't use these Band Pass Filters as a transmitter output filter!
The filters are designed for receiver input band pass filtering. They have a quite narrow response. The double-tuned circuit with transformer match results in an impedance step-up from the 50-ohms input/output. As a result the voltage in the centre section will be higher. In a receiver this is Ok but if you are using it in a transmitter, the higher voltage will exceed the rating of the capacitors and could lead to failure.?
Furthermore, the filters have around 2dB of insertion loss. You will not want to be losing that much power from a transmitter output. And the lost power will be dissipated in the BPF as heat and also likely lead to failure.?
It may be Ok to use the band pass filter in an early stage of a transmitter output signal chain where power levels are very low. For example you may wish to use a Band Pass Filter after a mixer to eliminate unwanted mixing products above and below the wanted output.?
At a transmitter output always use a?, whose purpose is to attenuate harmonics of the output frequency. The??are designed to handle at least 10W power and the attenuation at the operating frequency should be very low.?
73, Andy, KG5RKP/AE
On Sun, Jan 27, 2019 at 08:10 PM, Dave Space wrote:
Do you have the link to the reference?
Thanks.
On Sun, Jan 27, 2019 at 01:46 PM, Timothy Fidler wrote:
There is a warning on the QRP labs site NOT to use the BPFilters on LPF? Power amp clean up duty......?
Timothy E. Fidler : Engineer BE Mech(1) Auckland , NDT specialist AINDT UT /RT3 , MT2 CB #2885,?
Telephone Whangarei?? 022? 691 8405
e: Engstr@...
?
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Sun, 27 Jan 2019 13:29:29 -0800
Subject:
Re: [BITX20] Spurs/Harmonics fixes for v4 based on v5 board design?
I'm hoping that we can find a cheap way to measure for spurs.? I built the 7mhz band pass filter based on the QRP labs kits one and put it on the antenna for testing.? I think it cleaned up some of the spurs/harmonics but it's still showing one when transmitting at 7.15MHZ at about 28MHZ range that is only -30db on the scope FFT - since its only 8bit ADC not sure if it's accurate or not.
I wish I knew if the? scope FFT amplitude was accurate.? I love the frequency range on it, can view huge swaths of spectrum
