Hi Andy,

I agree with Alan on RF being the issue.? I had the problem with an off-center fed dipole where 40 had no issues, and 20 had a lot of RF on the feedline.? Installed an ugly choke (6 turns through a toroid) or clamp-on ferrites.? Both could cut down the RF enough in the shack to allow FT8 operation.? Ferrites on the USB cable worked on my first attempt also.

73
Evan
AC9TU

On 04/08/2022 04:40, Andy AA0AM wrote:

20m recieves fine but when I try to transmit the led on the Qdx flashes 2 times indicating a sound problem and wsjtx loses cat control of Qdx all together.

Andy,

Typical symptoms of RF getting in.
Some manage with ferrites on the USB cable but best to reduce the amount of RF in the shack. (Consider antenna configuration.)

73 Alan G4ZFQ

Hi,?
up to 150 mA is ok with v.3.

73 Bojan S53DZ

I have built my QDX all is working fine. But it taking 150 mA on RX.
The spec said 100 mA.

Philip G7JUR

I struggle with low output power on some of the bands.?
80m: 5W - OK
60m: 5W - OK
40m: 2W - not OK
30m : 3.8W - not OK
20m: 2W - not OK

I did reduce the L4, and L10 (LPF3) also L3 L8 (LPF2) inductors by one turn. Still it is too low on 20,30,40m bands. I am running on 12 Volts. T1 output transformer is quite worm. Supposed to have 2:3 rate.

Would you have a suggestion? I am dreaming 5W on each of the bands.... Could it be that one of the BS170 is broken down? Does anyone experience with losing one of them?
?
73 de Béla HA4BM

开云体育

Hi Folks,?

is there anyone here who is thinking about adding a bluetooth interface for QDX??
This could improve the portability of it. QDX could be deployed very close to the antenna with some battery and no need for long USB cable. Quite ideal for field operations. I think.?
It is just an idea.?

73 de Béla HA4BM

Hi,

On wsjtx..40m band works great, 20m recieves fine but when I try to transmit the led on the Qdx flashes 2 times indicating a sound problem and wsjtx loses cat control of Qdx all together.

Works fine on 40m though. I could work 40 all day but as soon as I try to TX on 20, mayhem ensues.

All my volumes are @100% per the manual. Tried on raspberry pi 4 and a windows machine as well.

Any thoughts or similar experiences? Thanks- Andy

I cut the track on two Rev. 3A units last night, receiver problem has gone, now works perfectly.? A blade was used and the result checked with a magnifying glass. These are a great little radio.
Bob VK2RG / AK2RG

Hi Dan,

did you manage to find out??

I am asking as I am having the same curves as on your 80 band, but I have it on all just not on 20.
I think it could be something wrong with my low-pass filters, I am going to check the toroids and capacitors.

Is there a specific/recommended ptt cable to use between the QDX and the amplifier??

Andy: I am with you 100% on Anritsu menus!
73, Don N2VGU?

I don't think that you are going to get to your answer with this approach. The key thing that I see is that the reflected power from the mismatched antenna is again reflected by the low output impedance of the transmitter when it arrives back at the transmitter, the transmitter doesn't have a 50 ohm output impedance. It is designed to drive a 50 ohm impedance, but if the model is a zero impedance generator with a series 50 ohm resistor for the transmitter, that would result in half the output power being dissipated in the resistor, this would mean you could never have better than 50% efficiency, no matter what class amplifier, goodbye class C, D, E, etc.

I was trying to show the effect of both the DC dissipation AND reflections.

If there are reflections in the case of 2:1 VSWR for example, does that power get dissipated along with the DC power from the inefficiency?

John
KC1IDN

I am using a DROKK switching buck/boost DC to DC converter.? It seems to work well, and I can adjust the voltage easily to allow for lower power output for things like the WA2EBY amp that I use to boost the power out.

Here is what I am using:


You could use a fixed, smaller converter if you wanted to mount it in the case.

73
Evan
AC9TU

开云体育

Hi Dan & Randy,

I copied Dan's Solution with a 7809. However, as the rig still got quite hot, I added a heatsink on top of the case (see pic) ... But still I do develop Temperatures around 50°C in continous FT8 operation ... It seems that the 7809 radiats a lot of heat, especially with a 13.8V shack power supply. If I run the QDX on 12V batteries, it's more relaxed. - But I'm still not 100% happy with this ...

Vy73

STefan.

Randy,
Problem with that approach is heat. Putting the regulator on the PCB foes not allow for much heat diffusion to environment.?

But here's a solution for you. Look at msg #79293 where I explained my solution to this problem. Also, here are a couple of pictures. ?

--
73, Dan? NM3A

-- 
Stefan U. Hegner    <db4st@...>
              * * *
DB4ST --- German Ham Radio Station
D-32584 L?hne ----- Locator JO42IE 
              * * *
GPG-Key | C3CC 23A4 FBA8 622B 48AE
F-Print | 4F19 D0EE E39E ABDC 2BCE

John, I'm not sure that's correct. The 5 W out is not the issue, it's the 3.3 W not produced as RF due to the 40% (or maybe a bit less) inefficiency as class D. The 5 W out is only an issue when or if some of it is reflected back. I think the 3.3 W is the culprit as it is dissipated as heat in the finals.?
--
73, Dan? NM3A

Thanks Hans, and everyone else, for your replies. I guess I was tempted by a less complex build.? The reality is that this is my biggest project to date, and you have all helped me to realise, to coin a phrase, "It would be a shame to spoil the ship for a ha'porth of tar!" I have the full ten LPF and BPF filters and boards from Hans anyway, so why not use them and make the best transceiver I can? I will try to post the finished article here in a few months time.

Daimon.
G4USI

So Daniel, as an example. If we produce 5W RF, and 0.56W is reflected (2:1 VSWR), we have 5.56W RF to deal with, in addition to the DC dissipation.

Let's say we DO dissipate 3.3W across all four BS170s, then at 2:1 VSWR, that's 8.86W across all four transistors, or, 2.215W per transistor!

As you said, very little room for reflected power. But that contradicts what you said! HOWEVER, you said LESS than 5W of RF, and reducing RF means reducing Vcc and thus the DC dissipation too, a double whammy in either direction.

So your QDX is perfectly happy at 2:1 under these circumstances.

John
KC1IDN