VCO voltages for 160m band??

[Ron ZL1TW]

One for the experts........today I re-checked my VCO voltage readings for
each band ( they were fine), but I realized that the table lists all bands
except the 160m band.
Unless I am wrong, there is nothing in the 160m module instructions to tell
you what VCO voltage to expect, so I tried a few readings there and was
quite surprised at how little voltage I actually had.
At 1800KHz I read only 0.61v   and that rises to about 1.0v by about
1900KHz....still somewhat less than the 1.5v minimum suggested.
I can forget about the statement in the manual where it says" Receive-only
operation down to about 1.4MHZ is possible"......as my VCO drops to 0.0v at
1600KHz.
How does this compare with *your* K2 VCO readings?? My K2 is a pre-3000 set
with all the mods and up-grades to bring it up to latest series specs. It
is quite conceivable it is not "up to specs" on 160m :-(  but it appears to
work fine there even with low VCO voltages!
Cheers......Ron ZL1TW

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[Sverre Holm]

Quoting Ron W <[hidden email]>:

> At 1800KHz I read only 0.61v   and that rises to about 1.0v by about
> 1900KHz....still somewhat less than the 1.5v minimum suggested.

Ron,

I had a similar problem and had to add 33 pF in parallel with C75 (470 pF). See
http://www.ac6rm.net/mailarchive/html/elecraft-list/2003-04/msg00592.html

Sverre
LA3ZA
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[G3VVT]

 
I needed to open up my K2 serial no. 4168 to tinker with the AGC threshold  
setting so took the time to measure what the VCO voltages at R30 were on  160m.
The results are:
                        1800kHz  = 1.68V
                        2000kHz  = 3.83V
 
On my particular K2 on initial testing the lowest reading VCO voltage  
reading came out on 7000kHz rather than 3500kHz so made that the reference  setting
at 1.50V. This shifted up 3500KHz to 2.40V and 4000kHz to 6.85V. All  still
within the stated goal posts.
 
As a side issue the optimum AGC threshold seemed to be at 3.70V rather than  
the initial 3.80V on this K2. Another item noticed during testing was that
even  with the S LO and S HI correctly adjusted for the new threshold the signal
level  required for S9 reduced with lower threshold settings. On this K2 with
the  preamp off the settings for S9 came out as follows:
 
AGC threshold V.    uV PD for S9.
3.80V                        63uV  (-71dBm)
3.70V                        40uV  (-75dBm)
3.60V                        25uV  (-79dBm)
 
With the new setting of 3.70V the audible low level band noise  from AGC on
to AGC off is just reached the point of no change. This compares  with the
initial AGC threshold setting of 3.80v, where there was  a small increase in noise
when the AGC was switched off.
 
Bob, G3VVT
K2 #4168

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[Don Wilhelm-3]

Bob and all,

There is a difference in which frequencies will produce the lowest/highest
VCO voltage if the K60XV is installed.  Without the K60XV, the lowest
reading is usually 7 mHz, but after the K60XV installation, 1800 kHz and
4000 kHz become the more critical points.  With the K60XV added, it is good
practice to check all the band ends to be certain they are within range.

Your observations about the AGC Threshold are correct - there is some
variation for the proper threshold voltage from K2 to K2 (but normally not
as wide as you report).  However, be certain you are doing the AGC On/Off
check on a quiet band because even an S-1 noise level will alter your
adjustments from the norm.  For my own - if I had a high noise level, I
would want the AGC Threshold set so no AGC action occurs because of the
noise - even if it results in 'strange' value settings.  Bottom line, your
abnormal settings could be due to conditions present at your QTH.

73,
Don W3FPR

----- Original Message -----

>
> I needed to open up my K2 serial no. 4168 to tinker with the AGC threshold
> setting so took the time to measure what the VCO voltages at R30 were on
> 160m.
> The results are:
>                        1800kHz  = 1.68V
>                        2000kHz  = 3.83V
>
> On my particular K2 on initial testing the lowest reading VCO voltage
> reading came out on 7000kHz rather than 3500kHz so made that the reference
> setting
> at 1.50V. This shifted up 3500KHz to 2.40V and 4000kHz to 6.85V. All
> still
> within the stated goal posts.
>
> As a side issue the optimum AGC threshold seemed to be at 3.70V rather
> than
> the initial 3.80V on this K2. Another item noticed during testing was that
> even  with the S LO and S HI correctly adjusted for the new threshold the
> signal
> level  required for S9 reduced with lower threshold settings. On this K2
> with
> the  preamp off the settings for S9 came out as follows:
>
> AGC threshold V.    uV PD for S9.
> 3.80V                        63uV  (-71dBm)
> 3.70V                        40uV  (-75dBm)
> 3.60V                        25uV  (-79dBm)
>
> With the new setting of 3.70V the audible low level band noise  from AGC
> on
> to AGC off is just reached the point of no change. This compares  with the
> initial AGC threshold setting of 3.80v, where there was  a small increase
> in noise
> when the AGC was switched off.
>

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[G3VVT]

K2 serial no. 4168 for which the tests were reported does not have the  K60XV
installed. The use of 5MHz frequencies in the UK are only available by  issue
of a special licence to a restricted number amateurs for experimental  
purposes on USB only.
 
4000kHz had the highest of the VCO control voltage measured  when completing
alignment at 6.85V with my particular K2. When meeting the  minimum
recommended VCO control voltage of 1.50V at 7000kHz, a watch  on the readings at 4000kHz
had to be considered at the same time. Bringing the  7000kHz VCO voltage much
above 1.50V resulted in the voltage at 4000kHz  exceeding the Elecraft K2
manual recommended maximum of 7.50V.
 
The AGC threshold adjustment was done after noting postings on the  reflector
on the subject a few months back pointing out the method of testing. I  found
my K2 exhibited the rise in background when switching the AGC off  compared
to that with AGC on (when testing under quiet band conditions).
 
Don, W3FPR in his reply has apparently misread the reason for testing at  the
various AGC threshold voltages.
 
The original new setting tried was 3.60V as on first observation this  
appeared to fulfil the AGC threshold requirement. However when tested with  the
bench signal generator at 7100kHz, I found that compared with the initial  AGC
threshold setting of 3.80V the level needed to give S9 on the K2 with the  preamp
off had dropped from 63uV PD to 25uV. This was after careful adjustment  of
the S LO and S HI required as per the K2 Alignment Instructions posted  on
Don's web site. (Very well worth keeping a copy of this with your K2 manual)  This
three fold increase in S meter sensitivity was not really welcome as I had  
tried to keep all my receivers at 50uV for S9 where practical.
 
A new start was made to find the optimum setting for the AGC threshold  
setting.
With this I adopted the following when testing:
1. The antenna input was terminated to prevent any external noise  
influencing the results.
2. The K2 preamp was switched on.
3. The receiver audio O/P was monitored by headphones to more easily detect  
the slight change of audio level AGC on to off. (probably a sensitive scope  
would have done the same test)
 
With these conditions in place it appeared with K2 #4168 that the optimum  
setting for the AGC threshold worked out at 3.70V. Again the S LO and S HI were  
reset to compensate for the changed AGC threshold voltage and a new test was  
done for S9. With the preamp off it came out at 40uV PD  (-75dBm) which much
closer at -2dB compared to the standard I use  of 50uV PD (-73dBm) for S9.
 
The changes to the readings noted for S9 are only given as an observation  to
the changes seen with the three AGC threshold voltages tested at, though  
could be significant where a disparity of S meter readings between various K2  
are noted. The absolute accuracy of my bench generator is unknown, though does  
compare favourably with a Marconi 2955 Communications Monitor which had  a
much later calibration date. Sending my test equipment for calibration is  a
luxury beyond my means these days now after joining the band of the  retired.
 
Bob, G3VVT
K2 #4168
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[David Pratt-3]

In a recent message, [hidden email] said....
>The use of 5MHz frequencies in the UK are only available by  issue
>of a special licence to a restricted number amateurs for experimental
>purposes on USB only.

I must correct you on that, Bob, to prevent any misunderstanding. The
"Notice of Variation" to the UK Amateur Licence allows use on five
min-bands as follows:

5258.5 to 5261.5 kHz
5278.5 to 5281.5 kHz
5288.5 to 5291.5 kHz
5398.5 to 5401.5 kHz
5403.5 to 5406.5 kHz

The permitted types of transmission are: Morse, Telephony, RTTY, Data,
Facsimile and SSTV. There is a "maximum power level" of 200W PEP (23dBW
relative to 1W).

Because of the small bands, the use of narrow modes is particularly
recommended. When telephony is used, the reference to USB is merely a
recommendation, a sort of band plan, because military use USB and we are
permitted to communicate with military and military cadet organisations
using those bands. Needless to say, when USB is used the centre carrier
frequency should be positioned towards the LF end of the band in use.

The K60XV on the K2 works very well on 60 metres and I can highly
recommend it.

73 de David G4DMP
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[Sverre Holm]

Quoting [hidden email]:
>  
> I found that compared with the initial AGC
> threshold setting of 3.80V the level needed to give S9 on the K2 with the
> preamp
> off had dropped from 63uV PD to 25uV. This was after careful adjustment  of
> the S LO and S HI required as per the K2 Alignment Instructions

I would recommend that you do this the other way around: adjust AGC setting
first for no decrease in level on a quiet band and then the S-meter settings
for approximately S9=50 uV. Otherwise you will mix the receiver's sensitivity
to quiet bands with S-meter sensitivity. My experience is that the following
works well:

1. First set CAL S LO as per the manual

2. Then adjust CAL S HI by setting RF GAIN to the 9 o'clock position
(instead of fully CCW) and set parameter so that right-most bargraph is
barely turned on. I have played with various other setting such a 10, 11
o'clock, but found the 9 o'clock position to be fine. It also agrees
reasonably well with 50 uV from my generator to give S 9.

If the AGC-setting is changed, the S-meter calibration has to be redone.


Sverre
LA3ZA
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[G3VVT]

In reply to my posting on the subject of 5MHz in the UK  
[hidden email] said:
 
In a recent message, [hidden email] said....
>The use of 5MHz  frequencies in the UK are only available by  issue
>of a special  licence to a restricted number amateurs for experimental
>purposes on USB  only.

I must correct you on that, Bob, to prevent any misunderstanding.  The
"Notice of Variation" to the UK Amateur Licence allows use on five  
min-bands as follows:

5258.5 to 5261.5 kHz
5278.5 to 5281.5  kHz
5288.5 to 5291.5 kHz
5398.5 to 5401.5 kHz
5403.5 to 5406.5  kHz

The permitted types of transmission are: Morse, Telephony, RTTY,  Data,
Facsimile and SSTV. There is a "maximum power level" of 200W PEP  (23dBW
relative to 1W).

Because of the small bands, the use of narrow  modes is particularly
recommended. When telephony is used, the reference to  USB is merely a
recommendation, a sort of band plan, because military use  USB and we are
permitted to communicate with military and military cadet  organisations
using those bands. Needless to say, when USB is used the  centre carrier
frequency should be positioned towards the LF end of the band  in use.
 
------------------------------------------------------------------------------
--------------------------
 
Oops, shot myself in the foot with the statement of USB only!
 
The UK "Notice of Variation" does allow the other modes as mentioned and  
even the use of LSB apparently. I had avoided using the term Notice of variation  
and used the "special licence" as the term of NOV may not be understood
outside  the UK.
 
Notice of Variation is a mechanism where the holder's main amateur licence  
is modified to add extra categories from normal. This is used as stated for the
 5MHz experimental work, repeaters, internet gateways, data nodes and I
believe  beacons. I hold the licence for the two local FM repeaters by this method.
 
There are restrictions placed on our 5MHz allocation by NOV that a  
relatively small percentage of the UK amateurs hold. Most significant  reading the
notices on the RSGB website appears it is still primarily for  experimental
purposes only and that at present they are not allowed to  communicate with others
outside the UK using the allocated 5MHz  frequencies such as amateurs in the
USA.
 
Bob, G3VVT

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