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Characterized my new v6

 

I did some baseline measurements on my new V6 running Reed's FW before I start changing too many things.
The power's a good bit lower than expected and the third harmonics on both 15m and 30m are 4-5 dB over.

I've seen other references to low power, but I didn't notice anyone reporting issues with the third harmonic on 15/30m.
Not sure what I'll do about it yet.

John
K6JDS




Measurements are with 40dB attenuation before the SA with the ubitx in CW.
The SA is a fairly decent Agilent unit.

 

Try reducing power by a watt or two and see. If the harmonics drop significantly then I'd say the PA
is being over driven a bit.

The power you are getting at the low bands is less than I would expect and power at high end (10M) is higher
than my expectation.

An external 30MHz LP Filter should help.

Raj


At 20/06/2020, you wrote:
I did some baseline measurements on my new V6 running Reed's FW before I start changing too many things.
The power's a good bit lower than expected and the third harmonics on both 15m and 30m are 4-5 dB over.

I've seen other references to low power, but I didn't notice anyone reporting issues with the third harmonic on 15/30m.
Not sure what I'll do about it yet.

John
K6JDS


[]

Measurements are with 40dB attenuation before the SA with the ubitx in CW.
The SA is a fairly decent Agilent unit.
[]  

Ashhar Farhan
 

You dont have enough attenuation for proper measurement. The fundamental as fed into the spectrum analyser should be -30bdm. Which would indicate about 70 db of attenuation. 
Stronger signals can easily overload the spectrum analyzer leading to second order distortions (harmonics).
- f

On Sat 20 Jun, 2020, 5:25 PM Raj vu2zap, <rajendrakumargg@...> wrote:
Try reducing power by a watt or two and see. If the harmonics drop significantly then I'd say the PA
is being over driven a bit.

The power you are getting at the low bands is less than I would expect and power at high end (10M) is higher
than my expectation.

An external 30MHz LP Filter should help.

Raj

At 20/06/2020, you wrote:
I did some baseline measurements on my new V6 running Reed's FW before I start changing too many things.
The power's a good bit lower than expected and the third harmonics on both 15m and 30m are 4-5 dB over.

I've seen other references to low power, but I didn't notice anyone reporting issues with the third harmonic on 15/30m.
Not sure what I'll do about it yet.

John
K6JDS




Measurements are with 40dB attenuation before the SA with the ubitx in CW.
The SA is a fairly decent Agilent unit.
 

ajparent1/kb1gmx <kb1gmx@...>
 

Farhan,

Depends on the SA, the rigol and HP units I ahve that can be as high as 5 dbm
for the rigol and 10dbm (with out attenuator on the HP8568B.

You want to have the strongest signal near the base line (usually 0DBM)
so you can see the maximum useable dynamic range.

For others it can be lower but TX fundemental needs to be attenutated any
way as watts at the input  would kill most SAs.


Allison
---------------------------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

ajparent1/kb1gmx <kb1gmx@...>
 

I'm with Raj,

Overdrive the audio and the output gets dirty fast.   Drop the audio in small
steps and if the harmonics drop faster its over drive.

Allison
---------------------------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

Evan Hand
 

Allison,
The test was in CW mode, so the audio drive is not the issue.  I believe that Raj was talking about the RV1 adjustment to lower the drive to the finals.

Highest Regards,
73
Evan
AC9TU

Evan Hand
 

Is it not possible to verify the distortion of the SA input with a step attenuation on the input?  Drop the input by some amount (like 3 or 6 db) and verify that all signals are reduced by the same amount.  If all drop, then the input is not distorting.

Please let me know if this test is not valid, still somewhat new to SA use.
73
Evan
AC9TU

Dexter N Muir
 

As Sir Terry Pratchett's Discworld "Hex" thinking engine would say (in
cursive script): + + + Re-do from start  + + +

I rather like Discworld: it has an oddball similarity to the world of
Electronics (and Ham Radio!), its own sort-of logic, comprehensible to
those akin to Ponder Stibbons.

73 de ZL2DEX :)

 

That is in fact how I first characterized my attenuator when I built it.

My test equipment is:
   VNA:        Agilent E5071B
   SA:           Agilent E4407B
   SigGen:   HP 8648C
Really, it's my company's R&D test lab equipment, but I like to pretend it's mine :-)

The SA's max input is 30dBM, so with 40dB attenuation at 0dBM, I'm nowhere near saturating it.

I did spend some time with my  attenuator and VNA today to measure it on all
the ham bands and then every 5 MHz up to 400 MHz.  I should have done this ages
ago.

I didn't realize it was so far off. From 160 to 6m it varied from 40.2 to 37.1 dB.
From 50 to 300MHz it was pretty flat staying between 37.0 and 37.4
and then from 300 to 400MHz it went from 37.2 to 36.1.

Refiguring the numbers showed less power than before, but no wins for the third harmonics for 15 or 30m  (40.4 and 39.5 down).

My test procedure is:
  1. Set Tx frequency
  2. Set SA frequency to match & span 100K Hz
  3. Set trace hold
  4. Key Tx for 1 second
  5. Measure peak on held trace

Next time I get a chance, I'll try reducing the bias and fiddling with the LPF torroids.

I did install a kit-projects AGC Sunday.  I seemed to not have broken anything, but
It took about an hour to install.  I used two cuts in the RF line to get rid of
the stubs under the AGC PCB.
I don't notice any difference with it on or off yet.
I guess that's what the weekends are for. 

John
K6JDS

On 6/20/2020 7:46 AM, Evan Hand wrote:
Is it not possible to verify the distortion of the SA input with a step attenuation on the input?  Drop the input by some amount (like 3 or 6 db) and verify that all signals are reduced by the same amount.  If all drop, then the input is not distorting.

Please let me know if this test is not valid, still somewhat new to SA use.
73
Evan
AC9TU