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Ten meters?

 

Has anyone built a 10m QCX?
 

Yep!? Currently in use for qrss.
 

Hello Richard,

I've built one, also, and have been using it for CW QSOs, including contesting (QCX+). Works great for that band, too.

73, Aki, JR1XKU
 

¿ªÔÆÌåÓý

Hello Aki,

For a 10M QCX, could?you please provide information on number of turns for L4 and T1?
I built a 15M QCX-Mini, and it works well on receive and WSPR.

73,
Ed? ?AA2L


From: [email protected] <[email protected]> on behalf of Akira Murayama <amurayam@...>
Sent: Wednesday, December 1, 2021 10:05 PM
To: [email protected] <[email protected]>
Subject: Re: [QRPLabs] Ten meters?
?
Hello Richard,

I've built one, also, and have been using it for CW QSOs, including contesting (QCX+). Works great for that band, too.

73, Aki, JR1XKU

 

Hello Ed,

I used:

18 turns for T1 (3 turns each for its 3 small windings)
7 turns for L4

For L4, I experimented 6 turns to 12 turns, and the lot of BS170s that came to me liked 7 turns best - 45.3Vpp into 50 ohm dummy load or 5.1W at 13.8V input (D3 protection diode bypassed).

I hope these will work for you, also.

73, Aki, JR1XKU
 

Hello Ed,

Just an FYI, with these number of turns, no heating of BS170s or MPS751 observed (by my finger) after sending messages at 22WPM for one minute. I have not tried WSPR.

73, Aki, JR1XKU
 

I wonder if there's an easy way to make the toroids "plug in".......boy, that would make adjusting/modifying them a breeze. ?
 

Before toroids there were coils and some plugged in like this British-supplied spy radio used by the Norwegian resistance.



That suitcase-sized radio was the rough equivalent of the QSX-mini.

¡ª²Ñ¾±°ì±ð Perry, WA4MP

On Dec 2, 2021, at 8:20 am, Keith Davis <islandpiper51@...> wrote:

I wonder if there's an easy way to make the toroids "plug in".......boy, that would make adjusting/modifying them a breeze.
 

But a QSX-mini does not invoke the very unpleasant, and probably terminal, consequences of being found in possession of, or operating, said spy radio during WWII.

73, Stay Safe,

Robin, G8DQX

On 02/12/2021 15:57, Mike Perry, WA4MP wrote:
Before toroids there were coils and some plugged in like this British-supplied spy radio used by the Norwegian resistance.



That suitcase-sized radio was the rough equivalent of the QSX-mini.

¡ª²Ñ¾±°ì±ð Perry, WA4MP
 

Quite right. I have a lot of respect for those in the resistance who had to travel on trains luging a heavy suitcase that was obviously not filled with clothes. And in France the Nazis took the resistance radios very seriously. In Paris, I am told, they had hundred of receivers, each monitoring a small slice of the HF spectrum, with cars and planes positioned to track the transmitter down. They would have loved to have something as compact and powerful as a QCX-mini.

¡ª²Ñ¾±°ì±ð

On Dec 2, 2021, at 4:17 pm, G8DQX list <list@...> wrote:

But a QSX-mini does not invoke the very unpleasant, and probably terminal, consequences of being found in possession of, or operating, said spy radio during WWII.
 

On Thu, Dec 2, 2021 at 08:20 AM, Keith Davis wrote:
I wonder if there's an easy way to make the toroids "plug in"
You probably could with something like this:

?
--
John AE5X
 

I still have some gear from long ago that uses those Molex connectors. Even if the company makes versions that mount to PC boards, they¡¯d still stick up quite a bit and might short to nearby components. That said, someone probably makes a connector that¡¯d work.

¡ª²Ñ¾±°ì±ð Perry, WA4MP

On Dec 2, 2021, at 5:36 pm, John AE5X <ae5x@...> wrote:

On Thu, Dec 2, 2021 at 08:20 AM, Keith Davis wrote:
I wonder if there's an easy way to make the toroids "plug in"
You probably could with something like this:
 

The idea would be to cut them to size.
--
John AE5X
 

I just finished building a QCX-mini for 10m.
I ended up with:
?
T1 T50-6 (yellow)
Primary: 4T
Secondary 1: 4T
Secondary 2: 4T
Secondary 3: 14T
?
L4 T37-6: 5T
L1 & L3 T37-6: 9T
L2 T37-6: 10T

On RX alignment, I can peak the BPF with the modified T1. Note that I swapped the supplied T1 T50-2 core for a T50-6. I also swapped supplied L4 T37-2 core for a T37-6.
On TX I get 5W out with supply of 14.4V (protection diode fitted).

So all good on TX. The only problem is that RX sensitivity a little low. Comparing it to my old Ten Tec Corsair 2, the QCX-mini is definitely a bit deaf and cannot hear weaker signals at all. I did read a post from Hans where he suggested power out on 10m may be lower and an RX pre-amp may be desireable.

Has anyone had the same issue with lower RX sensitivity on 10m? Has anyone got any suggestions for a pre-amp circuit? Alternatively, any suggestions for improving sensitivity?

If I go down the pre-amp route, I am thinking that an external amp with bypass on TX could be tried. I could get 5V power and T/R switching for the pre-amp from the PTT socket. Maybe a common gate FET pre-amp circuit could be used? I suspect that only 12dB of gain might be enough. As the QCX-mini is in the little QRP enclosure, it might be a struggle fitting an amp inside. Hence, the thinking to go for the external option.

Despite the low RX sensitivity, I have made a few QSOs and, as with the other QCXs I have built, really enjoy using this rig. In fact, before I "tweaked" the various inductors as above, it was only putting out about 1.25W and I manged a couple of QSOs with NA ?.
 

Hi Steve. That's a very interesting issue. I was thinking that if you haven't fitted the AGC option in there, then you might take that little circuit board included?with the kit for the purpose?of doing the SSB modifications, or cut a small board of equivalent shape and size and maybe build?a little preamp on that with SMD parts. Electrically it would?need to fit between Q5 and the input winding of T1, with DC continuity to ground on the input of the amp to allow A DC path for the switching?function of Q5. That might be as simple as a 1:1 transformer on a tiny ferrite toroid.?

You are right that it is a tight fit?for anything?added to a Mini. But an external amp would require you to forgo the full break-in keying of the mini.... unless you could connect the amp internally between Q5 and T1 via a modification to the CAT and PTT jacks in case you aren't planning to use those features on this rig.?

Interesting possibilities... Good luck with this project ... 73 ... Ron

On Sat, Feb 4, 2023 at 5:58 PM GM0HUU Steve <gm0huu@...> wrote:
I just finished building a QCX-mini for 10m.
I ended up with:
?
T1 T50-6 (yellow)
Primary: 4T
Secondary 1: 4T
Secondary 2: 4T
Secondary 3: 14T
?
L4 T37-6: 5T
L1 & L3 T37-6: 9T
L2 T37-6: 10T

On RX alignment, I can peak the BPF with the modified T1. Note that I swapped the supplied T1 T50-2 core for a T50-6. I also swapped supplied L4 T37-2 core for a T37-6.
On TX I get 5W out with supply of 14.4V (protection diode fitted).

So all good on TX. The only problem is that RX sensitivity a little low. Comparing it to my old Ten Tec Corsair 2, the QCX-mini is definitely a bit deaf and cannot hear weaker signals at all. I did read a post from Hans where he suggested power out on 10m may be lower and an RX pre-amp may be desireable.

Has anyone had the same issue with lower RX sensitivity on 10m? Has anyone got any suggestions for a pre-amp circuit? Alternatively, any suggestions for improving sensitivity?

If I go down the pre-amp route, I am thinking that an external amp with bypass on TX could be tried. I could get 5V power and T/R switching for the pre-amp from the PTT socket. Maybe a common gate FET pre-amp circuit could be used? I suspect that only 12dB of gain might be enough. As the QCX-mini is in the little QRP enclosure, it might be a struggle fitting an amp inside. Hence, the thinking to go for the external option.

Despite the low RX sensitivity, I have made a few QSOs and, as with the other QCXs I have built, really enjoy using this rig. In fact, before I "tweaked" the various inductors as above, it was only putting out about 1.25W and I manged a couple of QSOs with NA ?.
 

On Sun, Feb 5, 2023 at 12:58 AM, GM0HUU Steve wrote:
Has anyone got any suggestions for a pre-amp circuit?
A MAR-xx device.

Even your grannies cat could build one ;-)
?
--
- 73 de Andy -
 

On Sun, Feb 5, 2023 at 12:58 AM, GM0HUU Steve wrote:
Has anyone got any suggestions for a pre-amp circuit?
Steve,

If it has to fit inside then Andy's suggestion is probably the easiest.
I am intending a larger version of a QDX, I favour Nortons. Look here down to High Dynamic Range RF Amp.
I've built quite few of these, they seem to work well. In my high power VHF signal area a LPF may help - but the QDX has one..

73 Alan G4ZFQ
 

Thanks, this looks good. I just ordered some MAR-6 monolithic amps. Around 20dB gain with 3dB noise sounds good. Also, the circuit may be small enough to fit inside the case in the RX chain only?
 

I have the AGC module fitted which limits space a little. Trying to maintain the nice break-in feature is a good point. It would be desireable to have the pre- amp inside withing the RX chain. It's not like I need the pre-amp for the QCX's I have for 40/20/17m. Therefore, will give G0FTDs monolithic amp a try and see if it can be shoehorned in somewhere.
 

Thanks G4ZFQ. I found AC0Cs common base High Dynamic Range RF Amp. This is very broadly similar to a common gate FET circuit I was considering (http://www.ham-radio.com/n6ca/50MHz/50appnotes/U310.html).
I am thinking will give the MAR-6 monolithic a go but may try a prototype common gate/base circuit as a lash up in RX only just to see how much gain might fix the sensitivity issue.

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