Topics

low output only on 40m

Curt
 

a run through all the bands with a dummy load - my uBITX is now outputting about 2 watts on 40m - when it is strong on all the other bands.  sounds like the LPF is out of tune - anyone seen this before?  (no I haven't finished my PHSNA yet -- but maybe I can manually check it with my DDS somehow)

73 Curt

Ted
 

Yes, I reported this symptom a week or two ago and was told something to the effect of, "wiggle the torroid chokes around a bit, they're not embedded in stone" or some such.  No resolution as of yet, and I'm working on a greater problem at present [ something stupid I did, while looking at the aforementioned as it haopens]  and I look forward to anything you hear about this where where to look. Good luck.

Ted
K3RTA

Curt
 

Ted

thanks for communication - I know slightly more about symptom now --

first, it likely can't be what I thought - LPF - as this LPF also is used on 30 meters!  my 30m power is okay. 

I just ran a sweep across all the bands into a dummy load -- every band except 40m is producing a lively output (my power meter is reading 10 watts on 160m * down to 4 watts on 10m -- its got a QRP scale, but it was calibrated a couple decades ago).  So I am convinced I have a substantial dip (reading less than 2 watts now on 40m). 

since I am using a dummy load - I will get some data on the width of this notch.  it is almost like a choke isn't working around 7 MHz. 

brief history: my ubitx has always been weaker on 40m.  I will confess it has one modification - an extra 45 MHz xtal filter placed on the other side of its IF amplifier.  this network made the 40m outage worse.  I saw a tip from Farhan to reduce R26 from 470 to 220 ohms to compensate for this filter loss - I made this mod.  but I can't blame it directly -- I got nice output on all other bands. 

we have 22 other ubitx from the same or recent lot in our club -- maybe mine is acting different that the population -- we are still gathering data from builders. 

the funny thing - these kind of problems always increase education, getting 'me' to examine places I would not be compelled to examine.  let's see if I can learn anything, and get this thing fixed. 

* yes I realize I have no low pass filtering of the second harmonic when operating at 1.8 MHz ... but my 160m vertical presents a dreadful match at 80m.  a nearby RBN receiver conveys I got at least 40 dB rejection by its non-report on 80m!  know your antenna before doing this - but several of us in NA operating a stock ubitx on top band. 

73 Curt

ajparent1/kb1gmx
 

Its not the first time I've seen the wrong toroids installed and 40 was messed up.

Make sure the toroids have something like 15 turns of wire on them.
Last one I'd seen had the same number of turns as the 10m toroids (about 9 turns).

Also of a cap in the circuit gets cracked it will have a similar effect.

Allison

Evan Hand
 

This 40m output is very low compared to others, however ALL reports that I have seen always seem to have the 40m output much lower than 20m.  Does anyone know the reason for the drop on 40m compared to 20m?  Is it related to spurs being measured as part of the power out?

Trying to learn and understand.

Evan
AC9TU

Bill Cromwell
 

Hi,

Did you run this sweep through the filters with a spectrum analyzer or a wobbulator> Or did you just use the transmitter itself? Just because the filter labeled 40 and 30 meters works on 30 meters does NOT mean the attenuation curve is right for 40 meters. I think Allison mentions counting the turns in her latest post. She has posted about this exact thing before.

73,

Bill KU8H

On 1/15/19 11:41 AM, Curt via Groups.Io wrote:
Ted
thanks for communication - I know slightly more about symptom now --
first, it likely can't be what I thought - LPF - as this LPF also is used on 30 meters!  my 30m power is okay.
I just ran a sweep across all the bands into a dummy load -- every band except 40m is producing a lively output (my power meter is reading 10 watts on 160m * down to 4 watts on 10m -- its got a QRP scale, but it was calibrated a couple decades ago).  So I am convinced I have a substantial dip (reading less than 2 watts now on 40m).
since I am using a dummy load - I will get some data on the width of this notch.  it is almost like a choke isn't working around 7 MHz.
brief history: my ubitx has always been weaker on 40m.  I will confess it has one modification - an extra 45 MHz xtal filter placed on the other side of its IF amplifier.  this network made the 40m outage worse.  I saw a tip from Farhan to reduce R26 from 470 to 220 ohms to compensate for this filter loss - I made this mod.  but I can't blame it directly -- I got nice output on all other bands.
we have 22 other ubitx from the same or recent lot in our club -- maybe mine is acting different that the population -- we are still gathering data from builders.
the funny thing - these kind of problems always increase education, getting 'me' to examine places I would not be compelled to examine. let's see if I can learn anything, and get this thing fixed.
* yes I realize I have no low pass filtering of the second harmonic when operating at 1.8 MHz ... but my 160m vertical presents a dreadful match at 80m.  a nearby RBN receiver conveys I got at least 40 dB rejection by its non-report on 80m!  know your antenna before doing this - but several of us in NA operating a stock ubitx on top band.
73 Curt
--
bark less - wag more

Curt
 

Evan

learn - yeah me too! 

if you convert the spurs to absolute power, relative to the carrier power - you can add them all up and see they are quite small.  power in dBm is 10 log (power in mw).  and convert something like a spur that is 20 dB down to a ratio of 0.01  (factor of 100).  so a 1 watt signal with 2 spurs 20 dB down, the power in the spurs is something like 0.02 watts ! 

but keep asking yourself and others questions - and not latching onto your first thought on what may be causing an issue [don't research the web to see how I have resembled this in the past on several projects!]

Allison

thanks for what to look for.  I never did build that RF probe or PHSNA yet (I will get the built someday and may not need them then ....) -- but I can do a simple sweep with my power meter and dummy load to see what is going on (I would be doing it except for being at work).  it seems that issue is after (on transmit) the two sets of 45 MHz filters it now has.  [yeah I cracked 2 SMT caps making this mod - but they were tombstone installed - so I realize they are delicate - I may have used leaded ones if my friend who kitted the filter told me the cap value ... our spur fix is this xtal filter (with 2 matching transformers) + Gordon's board of relays - we will have data on 23 units some day]

other than the response of the LPF, the only other thing I see that offers potentially narrow bandwidth are those chokes feeding the PA transistors - and that seems highly unlikely unless a hole bunch of turns were added to it. 

out of the box my ubitx was weaker on 40m - and I just brought it down further.  its nice on every other band.  [yes I blamed it on the xtal filter before I checked all the other bands.  ditto for snow and ice on my elevated vertical coil -- always check with a 50 ohm dummy load, or a simpler antenna not impact by ice's dielectric loading!] 

73 Curt

Bill Cromwell
 

Hi Evan,

Here is a contrary report for you. The forty meter output on my uBitx is close to the same as 80 amd 30 meters and close to 10 watts. I have the red and brown power supply wires connected together and run all of my radios on 12 volt batteries (~13 volts at no-load, full charge). Due to tolerance stacks among all the various parts used each of these radios will be at least a little different from all others. If any parts are out of tolerance that is going to be more so.

Mine is a V3 with the non "WX" audio IC socketed. I am running the CEC software but that has nothing to do with RF power out. Board version might.

73,

Bill KU8H

On 1/15/19 12:10 PM, Evan Hand wrote:
This 40m output is very low compared to others, however ALL reports that I have seen always seem to have the 40m output much lower than 20m. Does anyone know the reason for the drop on 40m compared to 20m?  Is it related to spurs being measured as part of the power out?
Trying to learn and understand.
Evan
AC9TU
--
bark less - wag more

jim
 

Couple 'o questions ...SSB or CW  and How is power being measured?  broadband watt meter ?

If so ..All emissions from the xmitter are being summed together (dc to daylight) ie fundamental + harmonics + spurs + ?

Jim

On Tuesday, January 15, 2019, 9:30:55 AM PST, Bill Cromwell <wrcromwell@...> wrote:


Hi Evan,

Here is a contrary report for you. The forty meter output on my uBitx is
close to the same as 80 amd 30 meters and close to 10 watts. I have the
red and brown power supply wires connected together and run all of my
radios on 12 volt batteries (~13 volts at no-load, full charge). Due to
tolerance stacks among all the various parts used each of these radios
will be at least a little different from all others. If any parts are
out of tolerance that is going to be more so.

Mine is a V3 with the non "WX" audio IC socketed. I am running the CEC
software but that has nothing to do with RF power out. Board version might.

73,

Bill  KU8H

On 1/15/19 12:10 PM, Evan Hand wrote:
> This 40m output is very low compared to others, however ALL reports that
> I have seen always seem to have the 40m output much lower than 20m. 
> Does anyone know the reason for the drop on 40m compared to 20m?  Is it
> related to spurs being measured as part of the power out?
>
> Trying to learn and understand.
>
> Evan
> AC9TU
>

--
bark less - wag more



Curt
 

Okay here is my CW measurement into a power meter - yes broadband.  My rig was measured, I have usual spurs for a stock uBITX - nothing to impact this measurement.  I think my LPF might be shifted up - maybe - not sure what this response is across 40m as a LPF does not do that! 

X axis is frequency and Y axis is power in watts.  sure my instrument isn't high quality but I trust the trend it conveys. 

Curt


jim
 

Ok thanks ..just trying to get some references to establish some sort of  rational base-band ..High accuracy is not needed,  just something "close"

this one 5 watts from 8 to 10 Mhz on CW ..Previous quoted from you was SSB? right?

Jim


On Tuesday, January 15, 2019, 2:57:13 PM PST, Curt via Groups.Io <wb8yyy@...> wrote:


Okay here is my CW measurement into a power meter - yes broadband.  My rig was measured, I have usual spurs for a stock uBITX - nothing to impact this measurement.  I think my LPF might be shifted up - maybe - not sure what this response is across 40m as a LPF does not do that! 

X axis is frequency and Y axis is power in watts.  sure my instrument isn't high quality but I trust the trend it conveys. 

Curt


Curt
 

Jim

most of my data is CW, as that plot.  all bands but 40m are okay CW output.  using a dummy load after the wattmeter, a TT1202 that is decently designed. 

SSB seems to be doing same, weak on 40m per needle response.  our local build leader did request I take some SSB data -- I need to see if my audio test source has enough drive. 

I cannot fathom what is doing the above.  originally I was getting around 4 or 5 watt CW - weaker than other bands.  I don't see any visual damage on the LPF that serves 40m.  since 80m and 160m do fine -- I can't fathom what is happening here. 

Saturday I hope to take rig to our club building session - for careful evaluation. 

73 Curt

jim
 

Ah good ..More eyeballs make for better results

Jim

On Tuesday, January 15, 2019, 5:24:39 PM PST, Curt via Groups.Io <wb8yyy@...> wrote:


Jim

most of my data is CW, as that plot.  all bands but 40m are okay CW output.  using a dummy load after the wattmeter, a TT1202 that is decently designed. 

SSB seems to be doing same, weak on 40m per needle response.  our local build leader did request I take some SSB data -- I need to see if my audio test source has enough drive. 

I cannot fathom what is doing the above.  originally I was getting around 4 or 5 watt CW - weaker than other bands.  I don't see any visual damage on the LPF that serves 40m.  since 80m and 160m do fine -- I can't fathom what is happening here. 

Saturday I hope to take rig to our club building session - for careful evaluation. 

73 Curt

M0OOZ
 

Same horrible problem!
I have good output on all other bands - the best is 20 meters. However, the 40 meter band is really low!

I have shelved this project (as this has dun my head in) for a while until I can face looking at it again as the problem does not seem to have an obvious solution. 

M0OOZ
 

Note: I have, like others, injected RF and manually swept the frequency through from 1 to 30 MHz. There is a horrible dip at the lower end i.e. 40 MHz is really low compared to 20 MHz. Yes I realize that this uses different filters. I even made a 'software tool' from modded code. 

The software tool allows me to 'manually' (via arduino serial monitor), change the filter switching, so I can see exactly what is switched in and out, while testing. I did this because at one point I noticed RF appearing on two filters at the same time, which did not seem good, and would have accounted for the apparent attenuation @ 40 Meters. (two filters being connected together would necessarily present a different load and produce characteristics that are non desirable.)

 

I love the idea of the uBITX, but it has actually really dun my head in!

Jim
 

Curt,

Did you ever get resolution on this?

MVS Sarma
 

Can jim and curt  check the inductorcwinding turns for L17, 18 and 19 thatcwerectentatively used for 40m.

Old boards i remember overwinding thereby blocking 40m 
These coils should have 14 or max 15T

If more , make it 14, 40m improves.

On Wed, 5 Feb 2020, 9:33 am Jim, <n0oct@...> wrote:
Curt,

Did you ever get resolution on this?

Jim
 

I removed L17 from the board, and measured it with my nanoVNA -- 745 nH, right about where the schematic says it should be.  The other three inductors have the same number of windings as L17.

MVS Sarma
 

Kim, try to trst the cut off point of theclpf and loss at say 40m mid range. 


On Wed, 5 Feb 2020, 7:22 pm Jim, <n0oct@...> wrote:
I removed L17 from the board, and measured it with my nanoVNA -- 745 nH, right about where the schematic says it should be.  The other three inductors have the same number of windings as L17.

MVS Sarma
 

Sorry Jim to have mis spelt tou name. 


On Wed, 5 Feb 2020, 7:43 pm MVS Sarma via Groups.Io, <mvssarma=gmail.com@groups.io> wrote:
Kim, try to trst the cut off point of theclpf and loss at say 40m mid range. 

On Wed, 5 Feb 2020, 7:22 pm Jim, <n0oct@...> wrote:
I removed L17 from the board, and measured it with my nanoVNA -- 745 nH, right about where the schematic says it should be.  The other three inductors have the same number of windings as L17.