XV144 - further lesson learnt, experience sharing

[johnny-52]

Hi Group,

Further to my earlier email about trouble shooting of my XV144 transverter,
I would supplement the following observations:

1.  When I used a transceiver as a signal tracer, I needed a step-by-step
RF attenuator ahead of the front end of the transceiver.  My attenuator is
a 80dB one but made in China.  I have no idea about its frequency response
and SWR under 50 ohm.  Having said that, it should be Ok under HF frequency
spectrum.   Therefore, it would be good if Elecraft considers getting a kit
of RF attenuator which will be a valuable tool in casual RF repair works.

With a suitable RF attenuator, your rig can be used as a very good signal
tracer.  You can read both the level of signal and frequency.  Clearly, if
you have a IC781, IC756 families with band scope spectrum, you can turn
your rig into a specturm analyser for casual repair works.  DON'T blame me
if you accidentally blow up the front end of your rig.

2.  K2 (without K60XV) does not produce a stable RF power output below say
0.5 watt even you turn the POWER knot fully CCW.  However, in the SEC
Manual, if you set the maximum power output for TRN at 0.1 watt, you will
get a stable power output well under 0.5 watt.  I do not have any RF power
meter which can measure anything below 1 watt.  I have no idea about the
exact power output from K2.

However, under this configuration, I have to use the lowest input selection
of my XV144.  For that selection, the maximum allowable input level for
XV144 is about 1 mW.  The next higher input level for XV144 is 251 mW.  
Based on the above observation, I would suspect the minimum power output
from K2 should be well below 0.2 watt.

Through this exercise, I think I need a RF power meter which can measure RF
power around 10 mW level, as a tool in my shack.  Any suggestion from the
Group will be the most welcome.

3.  Noise generator was used in tuning the RX section of the XV144.  The
N-gen of Elecraft is a very useful tool.  Bearing in mind its low cost, I
think you should have one if you haven't brought yet.  N-gen is also useful
in aligning the filters of your K2.

Do I think XV144 (together with the crystal oven) is expensive? Yes, it is
expensive indeed because IC910H V/U all mode transceiver is only sold at
USD1100 in Hong Kong.  HOWEVER, if you are looking for exceptional RX
performance, the survival among nearby S9+60 stations, a transverter with a
HF rig could be the only choice.

73

Johnny Siu VR2XMC


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[Don Wilhelm-3]

Comments in-line below:

73,
Don W3FPR

> -----Original Message-----
>
> 1.  When I used a transceiver as a signal tracer, I needed a step-by-step
> RF attenuator ahead of the front end of the transceiver.  My
> attenuator is
> a 80dB one but made in China.  I have no idea about its frequency
> response
> and SWR under 50 ohm.  Having said that, it should be Ok under HF
> frequency
> spectrum.   Therefore, it would be good if Elecraft considers
> getting a kit
> of RF attenuator which will be a valuable tool in casual RF repair works.

-------------
There is an alternate method of reducing power - use a 20 or 30 dB coupler,
the Elecraft CP1 is a good tool.  A 30 dB coupler followed by a 60 dB step
attenuator can provide up to 90 dB signal reduction with less possibility of
overloading the step attenuator.  Yes, the high power side of the coupler
must be terminated in a good dummy load.

I too would like to see a well designed step attenuator kit, but the
shielding requirments for an RF tight enclosure would elevate such an
attenuator kit beyond the class of the current Elecraft mini-kits.
-----------------
>
> With a suitable RF attenuator, your rig can be used as a very good signal
> tracer.  You can read both the level of signal and frequency.
> Clearly, if
> you have a IC781, IC756 families with band scope spectrum, you can turn
> your rig into a specturm analyser for casual repair works.  DON'T
> blame me
> if you accidentally blow up the front end of your rig.
--------------------------------
Again, the directional coupler helps (but does not prevent) overload of the
receiver front end.

The major problem with attenuators is signal isolation (as well as power
handling capability).  An 80 or 90 dB attenuator must have considerable
attention to signal leakage to allow good measurement of the level reaching
the receiver.

For narrow-band spectral analysis, Spectrogram can be a very useful tool
when coupled with a receiver - it can actually be more useful than a
spectrum analyzer for narrow-band analysis because of the fine resolution
available (and the price is much less than a high resolution spectrum
analyzer).  See "Experimental Methods in RF Design" for additional
information on the uses of FFT spectrum displays.
--------------------------------
>
> 2.  K2 (without K60XV) does not produce a stable RF power output
> below say
> 0.5 watt even you turn the POWER knot fully CCW.  However, in the SEC
> Manual, if you set the maximum power output for TRN at 0.1 watt, you will
> get a stable power output well under 0.5 watt.  I do not have any
> RF power
> meter which can measure anything below 1 watt.  I have no idea about the
> exact power output from K2.
---------------------------------
An oscilliscope with down to a 50 mV scale and a precision dummy load (1% or
better) will allow power measurement to 6 microwatts with 10% or better
precision.  Measure the peak to peak RF Voltage across the dummy load and
use the formula P = (Vp-p)^2/8R (or plug the peak to peak reading into
'Mini-dB Calculator' a free program from DL5SWB -
http://www.dl5swb.de/html/mini_db_calculator.htm ).  The precision realized
depends on your ability to properly interpolate the peak to peak voltage on
the 'scope and the precision of the dummy load - I figure I can get 5%
results or better for power levels of 0.1 mW and higher with my 'scope and a
1% dummy load.
---------------------------------

>
> However, under this configuration, I have to use the lowest input
> selection
> of my XV144.  For that selection, the maximum allowable input level for
> XV144 is about 1 mW.  The next higher input level for XV144 is 251 mW.
> Based on the above observation, I would suspect the minimum power output
> from K2 should be well below 0.2 watt.
>
> Through this exercise, I think I need a RF power meter which can
> measure RF
> power around 10 mW level, as a tool in my shack.  Any suggestion from the
> Group will be the most welcome.

--------------------------------
See 'scope method above.

73,
Don W3FPR
>

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[Andrew Moore-4]

My apologies for the slightly off topic ad, but I did run my K2 on this...

For Sale: Astron RS-20M power supply, under a year old, orig owner, works
perfectly, beautiful condition.

Ran my K2/100 on it with no problems.  Now going QRP.

USD $75.00 plus $10 to ship, and I'll chip in any additional shipping.

US shipment only please.

http://www.photogs.org/out/rs20m.jpg

73,
--Andrew, NV1B


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