Adjustment advice

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mojoe
 

Posts: 9
Joined: 17 Jul 2022, 00:16

Adjustment advice

Post by mojoe »

My assembled radio arrived today. I tested it on my HP 8920B Communication Analyzer. I did have to adjust the frequency a bit. I was using a bench supply set to 12.0 V. On receive, I measured 82 mA.

The transmit power measurements don't track with what the radio displays. Here are my readings:

Band -- Disp Power -- Meas Power -- Current mA
80 --------- 6.12 ---------- 3.21 ----------- 768
60 --------- 6.20 ---------- 4.32 ----------- 736
40 --------- 4.98 ---------- 4.15 ----------- 617
30 --------- 6.25 ---------- 6.11 ----------- 763
20 --------- 6.11 ---------- 6.46 ----------- 803

Edit: one band was 78% efficient, the others were > 80%.

Before I change anything, I'd like to know if adjusting the coils will fix the discrepancies, or is there something else I should look at.

On a side note, the radio still uses the 7:1 windings on T1. It also has the occasional oscillation/microphonics problem. I'll look at replacing caps later.
mojoe
 

Posts: 9
Joined: 17 Jul 2022, 00:16

Re: Adjustment advice

Post by mojoe »

No one has any advice on this? I could start tweaking on the coils, but the very non linear nature of the difference in power readings make me wonder if there isn't something else I should look at.
N4XTL
 

Posts: 24
Joined: 08 Jul 2022, 01:44

Re: Adjustment advice

Post by N4XTL »

The measured power readings on 80 and 60 seem low, especially given those current readings, and assuming 80% efficiency is remotely accurate. I'm not familiar with the 8920B, is it accurate down at those frequencies?

40m is certainly low in power. You should be able to fix that by fiddling with L31.

20m is slightly high in power, you may want to increase the inductance on L11 a little.

The 2nd harmonic notches should be verified on all bands.

You may also want to characterize the top of each band, if you are interested in voice. Power will generally decrease as you go up in frequency, so you can adjust the series inductor in each band filter to have the output power curve across the band where you want it. Either favoring CW/Digital, or bringing up power on the voice portion.

T2 is the transformer that gets the mod. I just did it on one of my radios yesterday, 28 AWG wire worked great.

Once you get the coils dialed in, you can adjust the Rshunt setting to bring the efficiency measurements on the radio closer to real world, but it's a hand-wavey type of change that just improves the displayed reading as much as possible. It won't be perfect.

Just my 2 cents from playing with my radios.
mojoe
 

Posts: 9
Joined: 17 Jul 2022, 00:16

Re: Adjustment advice

Post by mojoe »

Thanks for the suggestions. I was very concerned about the fact that the difference between the measured output and the displayed output is wildly different on some bands (almost 2:1 on 80m), especially given the reported efficiencies, and my measured currents. I guess I'll try adjusting the coils and see if things fall in line.

As for the HP8920B, the default configuration is spec'ed from 10 MHz to 1 GHz. I have the Option 055 which goes down to 400 kHz. Although it hasn't been officially calibrated in a few years, I check it periodically against other gear to make sure that it's measurements are still very close.

I'll report back after my coil tweaking.
N6MG
 

Posts: 3
Joined: 09 Aug 2022, 14:20

Current draw?

Post by N6MG »

Mojo, or N4XTL...Can either of you learned Gentlemen give me an "estimate" of how much current I should be drawing on my (tr)uSDX on receive, and on trasmit?
I've only had my radio for a few days, and I'm amazed at the bells and whistles!
I want to fuse the power cord and choose a small battery.
Thanks in advance for your replies.
Milt.
N6MG
N4XTL
 

Posts: 24
Joined: 08 Jul 2022, 01:44

Re: Current draw?

Post by N4XTL »

N6MG wrote: 18 Aug 2022, 20:53 Mojo, or N4XTL...Can either of you learned Gentlemen give me an "estimate" of how much current I should be drawing on my (tr)uSDX on receive, and on trasmit?
I've only had my radio for a few days, and I'm amazed at the bells and whistles!
I want to fuse the power cord and choose a small battery.
Thanks in advance for your replies.
Milt.
N6MG
Transmit current is anywhere from ~350 mA to ~750 mA depending on how the filters are tuned. I use a 1A fuse on my power cords.

I use a small 3S LiPO battery for my (tr)uSDX that I take into the field and it works great. If you don't mind a battery about as big as the radio then a Bioenno 3Ah LiFePO4 or something similar would be a good option too. The LiFePO4 chemistry has a bit higher voltage so you will get a little higher transmit power as well.
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