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QMX PCB Rev 2 low output 20-10M #qmx

 

I have just finished assembly of my 20-10M QMX. Although it's always terrifying when power is first applied, no magic smoke was released this time. All went well but the output on some bands seems low. Here's what I measured.

20 M = 4.22W
17M? = 5.14 W
15M? = 2.15 W
12M? = 3.74 W
11M? = 4.22W
10M? = 2.81W

I am curious what others are seeing at 1st power up?

Any suggestions on improving things on 15M, 12M and 10M?

Thanks and Happy New Year to all!
--
73, Rick
VE7TK

Website:

 

Hi Rick,

These are roughly the values that I also had after the build. After a bit of tinkering, I get 4.5 to 5 watts on all bands.?
What I have observed is a noticeable RX insensitivity on the 10m band. Have you noticed anything?

73!
Simon
 

I get 3.2 to 3.4v on all bands 20-10m. My input is a 9v buck converter whose actual out is 8.8v. What adjustments might i make if I wanted to tweak it?
Thanks
Scott
K1SMK
 

An update:

Here are my readings with an estimate of the efficiency and current @12VDC and output per band. RF output varies slightly from yesterday's values. The current draw on 17M seems high as well.

??????????? POut?????????? I @12VDC??? Efficiency
20M??? 4.32 W out???? 0.72 amp???? 50%
17M??? 5.12?????????????? 1.04???????????? 41%
15M??? 2.20??????????????? 0.5????????????? 37%
12M??? 3.65 ????????????? 0.92???????????? 40%
11M??? 4.38?????????????? 0.82???????????? 46%
10M??? 2.84?????????????? 0.6?????????????? 39%

I have looked at the Hardware Tests and they seem in line with what Hans has posted. Also, I have added a through-hole 1N4148 at Q508 as suggested by Hans (thanks for the heads-up!).

Like others have posted I'd be interested in what "tweaks" have been tried? In my case, manipulating the windings on L401 had little impact.
--
73, Rick
VE7TK

Website:

 

Hi Simon.

I put the QMX on the air today and had a 1st QSO on 10 metre FT8 with 3.5 watts. The receive sensitivity was excellent with signals of -22 dB received.
--
73, Rick
VE7TK

Website:

 

Scott I was able to make some minor adjustments by adjusting the LPF coil winding spacing. In particular L510 and L513. I was able to improve 10 metres in particular.

The same can't be said for adjusting L508 and L512. These are for the 17/15 metre bands and moving the spacing seemed to be of little value.
--
73, Rick
VE7TK

Website:

 

Using PuTTY and Hans' diagnostic software I think I'm zeroing in my new QMX.

My main issue was the 17/15m LPF. After spreading out the L512 windings I was able to improve the 15m output. A little work may still be needed to tweak the 12/11/10m coils but for now I'm a happy camper. The output with a 12 VDC power supply is:

20m??? 4.09 watts? 48% Efficiency
17?????? 4.45??????????? 46%
15?????? 3.56??????????? 46%
12?????? 3.08??????????? 31%
11?????? 4.25??????????? 41%
10?????? 3.68??????????? 43%

In all cases the current @12 VDC is now less than 0.9 amps.

Thanks to all for the bandwidth and thanks to Hans for another great little rig!
--
73, Rick
VE7TK

Website:

 

To prove the law of YMMV, here are my results from some extensive tweaking of the LPFs. I'm a happy camper too... I added 30M instead of 11M as you can see.

QMX high band rev 2
RWTST transformer
12V
1_00_014
Power measured as DC over a 50Ω dummy

30M 3.3W 0.47A 59%
20M 3.9W 0.60A 54%
17M 5.2W 0.78A 56%
15M 5.4W 0.83A 54%
12M 3.9W 0.76A 43%
10M 4.1W 0.70A 49%

Good luck all builders!!

Anders

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