[HBQRP] [mkars80] Digest Number 137

[Arnie Grubbs]

Hi Group!

There are several members of this list that have MKARS-80 kits and 
I thought that this info might be of interest to them. ( Dar, Joe?)

I have not gotten started on my MKARS-80 yet, but I hope that this
holiday season will find that I have time to work on some kits...
If things go good I should have 3 weeks off around the holidays to
work in my 'lab! :)

73 - Arnie KA0NCR


 ________________________________________________________________________
> > 1.1. MKARS80 VFO Stability - A significant improvement?
> >     Posted by: "Steve Drury" g6alu at tiscali.co.uk
> > hamlab3
> >     Date: Fri Dec 5, 2008 8:39 pm 
> > 
> > Evening all..
> > 
> > Following the modifications posted by Brian G8DIU I thought
> > I would check out his modification of replacing the 1nF
> > polycarbonate capacitors with polystyrene types, these were
> > kindly donated by Ray G4TZR.
> > 
> > Firstly I logged the drift from start-up to a stable
> > operating frequency, this took about 30 minutes and drifted
> > a total of 7kHz - mainly in the first few minutes after
> > switch on.
> > 
> > I replaced the capacitors, adjusted the orange trimmer for
> > correct coverage, re-assembled the radio and allowed it to
> > rest un-powered for about 2 hours. Next step was to plot the
> > drift over a 30 minute period from switch on... it
> > didn't! At least the huff and puff held the radio around
> > the centre of its range during this period. I then
> > transmitted for several minutes into a dummy load and was
> > pleased to find the huff and puff still held it on tune.
> > 
> > The test needs repeating once the radio has been switched
> > off for a longer period but the results do look encouraging
> > - this came as a surprise as I had tried polystyrene
> > capacitors on the first prototype when they gave similar
> > results to the specified polycarbonate types.
> > 
> > If this mod does provide a significant improvement (and it
> > looks likely) it leaves me with a problem, 1nF polystyrene
> > capacitors are around 1 UK pound each, this cost can't
> > be absorbed in the kit price so I have two choices: Sell the
> > kit as is and offer the capacitors as an up-grade or
> > alternatively increase the cost of the kit.
> > 
> > I will provide an update when the radio has been run from
> > cold and air tested.
> > 
> > Thanks to Brian and others who have experimented with VFO
> > stability.
> > 
> > Steve G6ALU
> > 
> > [Non-text portions of this message have been removed]
> > 
> > 
> > 
> > Messages in this topic (3)
> > ________________________________________________________________________
> > 1.2. Re: MKARS80 VFO Stability - A significant improvement?
> >     Posted by: "John YAHOO" v321uk at yahoo.co.uk
> > v321uk
> >     Date: Sat Dec 6, 2008 9:16 am 
> > 
> > If you can use surface mount then 18p from Farnell for 50V
> > or 23p for 100V
> > 1nF COG/NPO
> > 
> > http://uk.farnell.com/kemet/c0402c102j5gac-7867/capacitor-1nf-npo-50v-0402/dp/1535558
> > 
> > http://uk.farnell.com/kemet/c0402c102j1gac-7867/capacitor-1nf-npo-100v-0402/dp/1535563
> > 
> > John G3UGY
> > 
> > 
> > > Following the modifications posted by Brian G8DIU I
> > thought I would check
> > > out his modification of replacing the 1nF
> > polycarbonate capacitors with
> > > polystyrene types, these were kindly donated by Ray
> > G4TZR.
> > >
> > > Firstly I logged the drift from start-up to a stable
> > operating frequency,
> > > this took about 30 minutes and drifted a total of 7kHz
> > - mainly in the
> > > first few minutes after switch on.
> > >
> > > I replaced the capacitors, adjusted the orange trimmer
> > for correct
> > > coverage, re-assembled the radio and allowed it to
> > rest un-powered for
> > > about 2 hours. Next step was to plot the drift over a
> > 30 minute period
> > > from switch on... it didn't! At least the huff and
> > puff held the radio
> > > around the centre of its range during this period. I
> > then transmitted for
> > > several minutes into a dummy load and was pleased to
> > find the huff and
> > > puff still held it on tune.
> > >
> > > The test needs repeating once the radio has been
> > switched off for a longer
> > > period but the results do look encouraging - this came
> > as a surprise as I
> > > had tried polystyrene capacitors on the first
> > prototype when they gave
> > > similar results to the specified polycarbonate types.
> > >
> > > If this mod does provide a significant improvement
> > (and it looks likely)
> > > it leaves me with a problem, 1nF polystyrene
> > capacitors are around 1 UK
> > > pound each, this cost can't be absorbed in the kit
> > price so I have two
> > > choices: Sell the kit as is and offer the capacitors
> > as an up-grade or
> > > alternatively increase the cost of the kit.
> > >
> > > I will provide an update when the radio has been run
> > from cold and air
> > > tested.
> > >
> > > Thanks to Brian and others who have experimented with
> > VFO stability.
> > >
> > > Steve G6ALU
> > 
> > 
> > 
> > Messages in this topic (3)
> > ________________________________________________________________________
> > 1.3. Re: MKARS80 VFO Stability - A significant
> > improvement!!
> >     Posted by: "Ron" pa0rcl at planet.nl pa0rcl
> >     Date: Sat Dec 6, 2008 11:22 am 
> > 
> > Hello all,
> > 
> > After reading Brian's post I switched on my soldering
> > iron and rushed 
> > off to my local electronics store to buy a few of the
> > miracle 
> > capacitors. And... they work, indeed!! No more retuning, no
> > more lost 
> > QSO's and this for only 5 Euro's and 10 minutes of
> > work. 
> > Thanks very much Brian (and Steve)!
> > 
> > 73's Ron de pa0rcl
> > 
>