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Hi Fred,

Any chance of an English version please? This looks very interesting and a possible good use of the developer board for the QCX+.?

73 Ian

For changing bands I had considered making plug in board with the tuned parts, at one point Hans had sent me a mechanical drawing of the hole locations for the transformer and filter parts.?

Justin N2TOH?

Working on a translation, should soon be ready.
Paul DJ0CU

I saw and wondered about doing something similar.

we used the LPF and BPF Kits from Hans and they are fine.

Martin
DK3UW

Hi Ian,

A translation has been uploaded to the files section. "Multiband_QCX_V2.pdf"

Paul DJ0CU.

"In the

simplest case, the QCX is operated without any modification on bands below the cutoff frequency

of the TX lowpass filter"?

?re... QCX ... band mods...

Thanks Fred,
?Outstanding thread with documentation


Follows here a suggestion for ta1db

I went for three bands 20, 30, 40

Since? L4? is band sensitive I chose the 30m kit to mod then not mod L4 on other bands
Note There is also a no T1 MOD (my second image) that worked very well for me

I bypassed the onboard LPF and mounted all LPFs external to main PCB

72 73
John
N3AAZ

As John’s post with its picture of external low-pass filters illustrates the problem with multi-banding a QCX. A 40 meter QCX absolutely has to have a filter to block its second harmonic and that’s 20 meters. That is doable but adds complexity. I’ve sometimes wondered if a 60/40 or a 40/30 QCX might be possible with the low-pass filter set above the higher band, but I’ve not looked into the matter since neither 60 or 30 interests me. I opted for the QCX mini for 40 since its a day/night band less dependent on sunspots. That keeps matter simple and the QCX is all about simple.

—Mike Perry, WA4MP

On Fri, Nov 5, 2021 at 05:48 AM, Mike Perry, WA4MP wrote:

Dear Mike, John,
Thanks for your kind and informative answers.

A 40 meter QCX absolutely has to have a filter to block its second harmonic and that’s 20 meters.

I should have thought of that, I'll consider it!

I bypassed the onboard LPF and mounted all LPFs external to main PCB

@John , I understand that you've ordered a 30 meter QCX and 2 extra LPFs for 20 and 40 meters from here??, right? How did you mount 30 meter LPF components externally; did you make a pcb for 30 meter LPF components, did you mount the components on a breadboard, did you order a pcb from QRP Labs for 30 meter or did you omit the 30 meter? In the picture I see an extra pcb something like a mother board for 5 LPFs, what is it? Did you make by you own or did you buy it from somewhere?

Greetings Murat ta1db

All components purchased from QRPLabs

Filters sell in all band kits or buy for single band

Bandpass
?https://qrp-labs.com/bpfkit.html

Lowpass
?https://qrp-labs.com/lpfkit.html

"Mother board" seen in my image
?https://qrp-labs.com/ultimatelpf.html

You can place an order for one 30m QCX kit, it will ship with one 30m LPF included in price

The other filters sell as seperate items

The "Mother board" and relay kit sell as seperate item

...Side note...
...I just read specks? from website....

Ed W3NQN (mentioned below) now SK and I worked in the same lab for 20 years? I retired 1997

"..." This Low Pass Filter (LPF) kit is based on the G-QRP technical pages design by Ed Whetherhold W3NQN. Kits are available for 16 bands 2200, 600, 160, 80, 60, 40, 30, 20, 17, 15, 12, 10, 6, 4, 2m and 222MHz. The kit uses a high-quality double-sided PCB with silk-screen, solder-mask and through-hole plating. The capacitors supplied with the kit are high-quality low-loss RF ceramics of the NP0 type (near-zero temperature coefficient). Designed for the U3 & U3S kits, U2 kit, relay-switched LPF kit, Arduino shield, or your own projects! "qrplabs "

TNX AGN Fred

72 73
John
N3AAZ

Murat,

There are two answers to your question.

RX:
In our prototype with the wideband input transformer the RX sensitivity is nearly constant from 80m up to 10m.
The mixer, however, detects signals not only on the RX frequency, but also on its harmonics. For example, the RX set to receive at 3.5 MHz will also hear singnal on 2 x 3.5 MHz = 7 MHz, 3 x 3.5 MHz = 10.5 MHz etc.
While signals on even harmonics are suppressed by more than 50 dB, those on odd harmonics are attenuated by just 10 to 15 dB. Fortunately the TX lowpass filters come to the rescue here. They provide enough attenuation to fix this problem.

TX:
The lowpass filters can be used on adjacent bands (40m filter for 40m and 60m, 20m filter for 30m and 20m; see pg. 4 and 5, and Table 1 and Figure 6). The harmonic suppression on the lower band, however, is just 35 dB which is not enough to meet spectral purity requirements. A suitable tuner can provide the missing harmonic attenuation.

73 Wolfgang DK4RW

On Sat, Nov 6, 2021 at 09:09 AM, Wolfgang DK4RW wrote:

Fortunately the TX lowpass filters come to the rescue here.

Murat,

BTW is there any suggestion about how to make a 35 uH wide-band choke a L4 ?

Just 10 turns on a FT37-43 core. See Figure 5. Wire size is not critical.

73 Wolfgang DK4RW