Topics

QCX for 2m VHF? #chat #qcx #vhf #mods


Dick PA3CW
 

Hi,
I am very much enjoying the QCX plus!  Recently we are more active with a group doing CW on 144.070 vhf.  I was looking for a nice VHF CW only tcvr design but here are none.  Would the QCX design not be able to make an VHF version?  Would love that!  Any ideas also welcome.
Dick PA3CW


Jim Mcilroy
 

Hi

Nice idea!

Maybe a QCX+ for the 17m band which is quiet, and an add on development board configured as a simple transverter.

Playing with numbers the L.O. could be 125.962 to 125.945

That would give a tuning range of 144.030 to 144.113 down converting to 18.068 to 18.168

Mixer could be ADE-1 or SBL-1

Jim  G4EQX

On 07/02/2021 12:59, Dick PA3CW wrote:
Hi,
I am very much enjoying the QCX plus!  Recently we are more active with a group doing CW on 144.070 vhf.  I was looking for a nice VHF CW only tcvr design but here are none.  Would the QCX design not be able to make an VHF version?  Would love that!  Any ideas also welcome.
Dick PA3CW


KEN G4APB
 

Hi Dick,
there is supplier called Transverters-store on ebay that sell a 2m to 10m board. I bought one for 4m and managed to fit it in a box a little bigger than the qcx- mini. The preamp should easily overcome the loss of sensitivity of the qcx, and the transverter only needs 25mw to drive it, so i bought the attenuator board too but you probably could leave out the finals in the qcx to achieve this.
Just a thought.
Ken g4apb 


Jim Allyn - N7JA
 

You seem to be assuming that Dick was asking about a transverter.  I don't think he was.  I think he was asking about a 2 meter QCX.  Dick, the limiting factor on receiving would be how fast the FST3253 can switch on and off, and a quick glance at the specs suggests it probably won't work well if at all at 2 meters.  According to Dan Tayloe in his paper, "Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier":

"The product detector’s upper frequency limit is set by the ability of a FET to be turned on for only a quarter cycle of the incoming RF being converted to baseband."

I don't think the FST3253 is fast enough for 2 meters.  It seems to me I read that somebody used one at 6 meters, and I think that is pretty much the upper limit.  However, if you have some fast switching FETs, the sky's the limit!


Jim Mcilroy
 

Not quite, Jim

I worked on the basis that the 17m band was the top limit of what Hans offered and went from there, which introduced the term transverter.

To design for 2m CW without the use of the QCX range is a different thing: thought provoking nevertheless  :)

Jim  G4EQX



On 7 Feb 2021, at 21:33, Jim Allyn - N7JA <jim@...> wrote:

You seem to be assuming that Dick was asking about a transverter.  I don't think he was.  I think he was asking about a 2 meter QCX.  Dick, the limiting factor on receiving would be how fast the FST3253 can switch on and off, and a quick glance at the specs suggests it probably won't work well if at all at 2 meters.  According to Dan Tayloe in his paper, "Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier":

"The product detector’s upper frequency limit is set by the ability of a FET to be turned on for only a quarter cycle of the incoming RF being converted to baseband."

I don't think the FST3253 is fast enough for 2 meters.  It seems to me I read that somebody used one at 6 meters, and I think that is pretty much the upper limit.  However, if you have some fast switching FETs, the sky's the limit!


ajparent1/KB1GMX
 

From my perspective....

Doing even 6M using QCX as a foundation is not without issues.
However doing 2M  is wishful thinking and the only way is a
transverter as then you keep all the QCX features.

The major issues,  Board layout for TX and RX are not aimed at VHF.
The FST switch is not anywhere near fast enough.  The class E output
stages are extremely difficult at VHF and requires parts and layout that
would not easily be done as a kit.  To meet VHF requirements (FCC-PTT)
is more difficult.  Also a RF amp [lna] for RX is needed to keep RF
leakage from the mixer from the antenna and insure adequate RF
sensitivity for VHF use.  Also the 5351 will be pushed hard to do 
the required quadrature LO signals if its possible at all.  

Building 2M gear is a whole other level, I do it but experience and
willingness to fail is assumed.  Also I have a bench of test gear
needed to tune, adjust and test the performance.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Jim Allyn - N7JA
 

On Sun, Feb 7, 2021 at 03:27 PM, Jim Mcilroy wrote:
I worked on the basis that the 17m band was the top limit of what Hans offered and went from there, which introduced the term transverter.

Not what the original poster asked.  He asked if the QCX design could be used at VHF. I commented on one aspect of doing so.


Jim Mcilroy
 

Fair comment.

I must confess that I assumed that most hams would know the distinct differences between HF and VHF design and construction.

On 8 Feb 2021, at 16:29, Jim Allyn - N7JA <jim@...> wrote:

On Sun, Feb 7, 2021 at 03:27 PM, Jim Mcilroy wrote:
I worked on the basis that the 17m band was the top limit of what Hans offered and went from there, which introduced the term transverter.

Not what the original poster asked.  He asked if the QCX design could be used at VHF. I commented on one aspect of doing so.


Jim Allyn - N7JA
 

Well there, now we have a list of the difficulties in building a 2 meter QCX.  All that remains is to tackle and overcome those difficulties.

I don't think building 2 meter gear is terribly difficult, lots of hams have done it.  Heath made several VHF/UHF kits, probably the best known of which was the HW-2036/2036A.  I have designed and built receivers operating up to 929 MHz; it does start getting difficult there.


Jim Mcilroy
 

To follow from my last post, and my errors for ambiguity as I see and agree with Allison’s comments.

I guess the original question could be read as ‘wouldn’t it be great if….’  and the answer is that it wouldn’t be possible for the QCX design to stretch that far.





On 8 Feb 2021, at 17:51, Jim Mcilroy via groups.io <gts53@...> wrote:

Fair comment.

I must confess that I assumed that most hams would know the distinct differences between HF and VHF design and construction.

On 8 Feb 2021, at 16:29, Jim Allyn - N7JA <jim@...> wrote:

On Sun, Feb 7, 2021 at 03:27 PM, Jim Mcilroy wrote:
I worked on the basis that the 17m band was the top limit of what Hans offered and went from there, which introduced the term transverter.

Not what the original poster asked.  He asked if the QCX design could be used at VHF. I commented on one aspect of doing so.



Jim Mcilroy
 

Beat me to it, Jim  :)

On 8 Feb 2021, at 18:14, Jim Allyn - N7JA <jim@...> wrote:

Well there, now we have a list of the difficulties in building a 2 meter QCX.  All that remains is to tackle and overcome those difficulties.

I don't think building 2 meter gear is terribly difficult, lots of hams have done it.  Heath made several VHF/UHF kits, probably the best known of which was the HW-2036/2036A.  I have designed and built receivers operating up to 929 MHz; it does start getting difficult there.


Mont Pierce KM6WT
 

On Mon, Feb 8, 2021 at 08:29 AM, Jim Allyn - N7JA wrote:
Not what the original poster asked.
He ALSO asked:

On Sun, Feb 7, 2021 at 04:59 AM, Dick PA3CW wrote:
Any ideas also welcome.

km6wt


Jim Allyn - N7JA
 

If ideas are welcome, then let's give him some.  A full transverter wouldn't be needed. The Si5351 would generate a 2 meter transmit signal easily enough, so you'd only need a receive converter. The BS170 wouldn't give you much power at 2 meters (basically none I suspect), and would be nigh unto impossible to drive as is currently done in the QCX, but you could use one or more TO-92  transistors that would give you some power output at 2 meters.  Next?


HF
 

Next:  Agreed, BS170 won't work at 2m.  You should be able to get some signal at 144 MHz out of a BSN20-7 MOSFET or others.  But driving it with the QCX's 74ACT00 might not work.  I've inserted a similar device into the PA on my U3S.  It improves drive a bit on 6m but nothing gets through on 2m.  2m works, albeit weakly, without the inserted ACT gate.
A potential solution:  Drive the
BSN20-7 from the Si5351a via a capacitor as is done with the U3S, leaving the 74ACT00 out of the chain.  Have the TX line supply gate bias via a variable resistor.  See the U3S schematic diagram.
Could a good receive converter be simpler, cheaper, and faster (time between order and receipt) than an inexpensive, full transverter?  I haven't worked with transverters yet, though one I ordered almost a year ago awaits.
Halden VE7UTS


Jim Allyn - N7JA
 

On Mon, Feb 8, 2021 at 09:51 AM, Jim Mcilroy wrote:
I must confess that I assumed that most hams would know the distinct differences between HF and VHF design and construction.
I don't know why you would assume that.  Clearly the original poster didn't know the differences between HF and VHF design and construction, else he wouldn't have asked, "Would the QCX design not be able to make an VHF version?"  Maybe things are different where you live, but here in the United States, it seems to me that a significant number of hams, perhaps a majority, don't know the difference between HF and VHF.  I have heard lots of US hams admit that they know basically nothing: in their own words, they just memorized enough questions and answers to pass the test, then promptly forgot everything.  An example of how much some hams here (don't) know:  within the last year or so, I heard a discussion on one of the local repeaters about baluns.  One of the guys wanted to know what kind of balun he needed: "I see there are one to one baluns, and four to one baluns, and nine to one baluns.  How do I know which one I need?"  The answer he received was, "If you want to operate on one band, you need a one to one balun.  If you want to operate on four bands, you need a four to one balun.  If you want to operate on nine bands, you need a nine to one balun."  I looked up the gentleman who gave that answer on QRZ.com, and he holds an Extra Class license.  I'll leave it to you to consider whether that gentleman is likely to know much about the differences between HF and VHF design and construction.

On the other hand, one could argue that there is no difference between HF and VHF design and construction.  The principles are the same: keep all component leads and signal paths as short as possible, minimize the loop area circumscribed by the signal paths and their return paths, keep different types of signals (analog and digital, for example) away from each other, ensure that bypass capacitors have a low impedance at the design frequency, and so on.  The differences are in the details.  Practically speaking, an inch of wire doesn't exist in a circuit designed for 80 meters, at 70 centimeters that same piece of wire is a fairly large inductor.


Jim Allyn - N7JA
 

I like the idea of practicing CW with the local hams on VHF.  A couple of hams locally have been practicing CW with each other on 20 meters.  For a good portion of the day, they can be head over a considerable area.  CW practice on 2 meters avoids that.  A small, inexpensive, low power 2 meter CW transceiver would be great for code practice with the locals.


Evan Hand
 

An off-topic idea (not based on QCX) might be to convert a cheap (Baofeng) FM transceiver to CW.  They can be had for less than $30 US.  Could be as simple as a code practice oscillator input into the mic.  Could be to modify the modulator to not deviate the frequency and supply a local IF level oscillator to get the tone.

Just an out of the box (and again OFF-TOPIC) thought.

Please excuse the message, I just could not help myself.
73
Evan
AC9TU


Jim Mcilroy
 

Jim

When I got my ticket back in the 70s everybody I knew at my local club knew how to build and use stuff, and was very interested in doing so. The exam was a written one, and as far as I can recall there were few multiple choice questions, and various questions about valves.

I do recognise these days at my local club that there are a significant number of hams who are only interested in operating gear and their eyes glaze over a bit when backs get taken off radios and soldering irons get fired up. One hopes they will grow out of their fears and get more out of their respective ham worlds.

Nevertheless everyone had to do an exam and surely some of that knowledge must get taken on board. I can see you have reservations about that.

I am generally in agreement with your last paragraph and it is much easier to build at higher frequencies these days. A good quality BNC connector will work up to about 3.5 GHz. I used to work at a microwave components factory and would measure anything I could get my hands on. Prior to that I cut my teeth on GAT-5 and GAT-6 transistors working at 8 GHz for satellite comms and they were tricky to match and easier to blow up. Had steadier hands then.

So, yeah, we agree on some things.

I noticed your other post about a simple 2m CW rig. Good idea. Not so simple for many to do a prototype but double sided copper sheets would be your friend.

I also have a Datong PC1 in my junk box that I bought in a lot as scrap. I intended just to use the box but I notice that it has a parametric mixer and a 144MHz filter. I'm sure I could have some fun with that.

Also have a couple of Avala PCBs which were the forerunners for the Genesis SDRs. They are intended for HF but they are easy to work on and could possibly be integrated with 2m VHF components. That would have to be a downconverter design as the mixer chips are 74HC4066s. Not as good as the QCX design but probably pretty good at 40m. Later on we'll see.

Jim

On 10/02/2021 08:41, Jim Allyn - N7JA wrote:
On Mon, Feb 8, 2021 at 09:51 AM, Jim Mcilroy wrote:
I must confess that I assumed that most hams would know the distinct differences between HF and VHF design and construction.
I don't know why you would assume that.  Clearly the original poster didn't know the differences between HF and VHF design and construction, else he wouldn't have asked, "Would the QCX design not be able to make an VHF version?"  Maybe things are different where you live, but here in the United States, it seems to me that a significant number of hams, perhaps a majority, don't know the difference between HF and VHF.  I have heard lots of US hams admit that they know basically nothing: in their own words, they just memorized enough questions and answers to pass the test, then promptly forgot everything.  An example of how much some hams here (don't) know:  within the last year or so, I heard a discussion on one of the local repeaters about baluns.  One of the guys wanted to know what kind of balun he needed: "I see there are one to one baluns, and four to one baluns, and nine to one baluns.  How do I know which one I need?"  The answer he received was, "If you want to operate on one band, you need a one to one balun.  If you want to operate on four bands, you need a four to one balun.  If you want to operate on nine bands, you need a nine to one balun."  I looked up the gentleman who gave that answer on QRZ.com, and he holds an Extra Class license.  I'll leave it to you to consider whether that gentleman is likely to know much about the differences between HF and VHF design and construction.

On the other hand, one could argue that there is no difference between HF and VHF design and construction.  The principles are the same: keep all component leads and signal paths as short as possible, minimize the loop area circumscribed by the signal paths and their return paths, keep different types of signals (analog and digital, for example) away from each other, ensure that bypass capacitors have a low impedance at the design frequency, and so on.  The differences are in the details.  Practically speaking, an inch of wire doesn't exist in a circuit designed for 80 meters, at 70 centimeters that same piece of wire is a fairly large inductor.


Daniel Walter
 

Check out the Ultra PicoKeyer. It can interface to an FM (or SSB) rig to do MCW. Makes it easy for 2m 'CW' (Morse). Here in western Pennsylvania we have a lot of hills so direct 2m QSOs are very limited in area. We have taken to using a repeater for scheduled CW on-air practice. It works well. 
--
73, Dan  NM3A