[Lowfer] 630m overnight

[Michael Sapp]

Brian:  Thank you for the Maas reference.  Your 2005 Microwave Update paper 
"A Primer For Millimeter-Wave Multipliers and Mixers" is a very good read on 
diode mixer operation as well.

I tried the 3dB pad port matching when I first built the RAY6 based MF/LF 
converter a few years ago. As long as there were no consistent strong signal 
issues, the double-balanced mixer weak signal performance was noticeably 
better without the extra 3 dB attenuation on the IF port.

Since my LF/MF converter is modular and connectorized, it is relatively easy 
to try various building-block configurations. I built another 475 kHz 
diplexer to place on the RF input port yesterday afternoon and have it in 
service now. It will likely take a few weeks or months to determine how much 
of an improvement it does (or does not) make under various propagation and 
band activity conditions.

I am running a 475 kHz diplexer between the input filter and the 2N5109 
preamp on my LF/MF converter. The input filter is a 3 pole Butterworth 
Coupled Resonator with better than 20 dB of return loss in most of the pass 
band. Of course, for frequencies outside of the pass band, the match is 
expectedly terrible---so the 475 kHz diplexer on the input of the 2N5109 
preamp improves the broadband frequency matching of the filter output to the 
preamplifier input.  It also improves the attenuation of AM BC signals to a 
certain degree, up to several dB better than not having the diplexer after 
the coupled resonator filter.

Having built a SHF transverters for the 23cm through the 3 cm bands over the 
past 25 years, I get the impression this universal diplexer provides an 
improvement in block level system impedance matching for LF-MF-HF with 
relatively low loss that is similar to using an isolator at microwave 
frequencies (of course, the physics of isolator design and operation is 
different).

Thanks again for your insights.

73 Mike wa3tts

----- Original Message ----- 
From: "Brian, WA1ZMS" <wa1zms at att.net>
To: "Discussion of the Lowfer (US, European, & UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Cc: <wa3tts at verizon.net>
Sent: Thursday, December 28, 2017 11:14 AM
Subject: Re: [Lowfer] 630m overnight


Mike-

FWIW....
A diplexer on the input port of the mixer may not help much if the output 
match, S22 of the LNA looks like a reasonable load at 3MHz too.  If you have 
extra LNA gain to lose, a 3dB pad between the LNA and the mixer may be as 
good as a diplexer.

Mixer's impedance load at all ports is often overlooked until, as you do, 
want best dynamic range. Maas' book on mixers is a great reference text as 
well for those who don't have a copy.

-Brian, WA1ZMS
iPhone

> On Dec 28, 2017, at 10:36 AM, Michael Sapp <wa3tts at verizon.net> wrote:
>
> John (& the Lowfer Group):  Interesting observation overnight, I was able 
> to decode K9FD with another station reporting being on the same frequency 
> at the same time---although with some drift...
>
> This event occurred once over 10 K9FD decodes.  The other evening I saw 
> the same thing happen with the same stations when watching the waterfall 
> in real time. At the time I thought it was a
>
> fluke, but it has happened again last night, so I thought it may be 
> noteworthy.
>
> 10 spots:
> Timestamp Call MHz  SNR Drift Grid Pwr Reporter RGrid km az
> 2017-12-28 07:30   K9FD   0.475615   -20   0   BL11je   1   WA3TTS 
> EN90xn   7439   54