Hi Mike, Hi Group,
Well I did the experiments and it was interesting. The best coax length I
found was 20 feet and I made the mistake of cutting it further back to 19.5
then 19 only to see things deteriorate but it was worth the $25 in cable
hihi. It didn't solve all the SWR issues but I think it is a fairly good
solution.
Bottom line:
10m has improved from SWR of ~2.0 to now 1.5
12m remains the same aroud 2.3
15m improved from 2.2 to 1.7
17m improved the most from 2.3 to 1.5
20m improved from 1.5-1.7 now its a flat 1.1 across the band
30m remains the same about 1.4
40m has improved form 1.3-1.5 now is 1.1 across the band
80m has worsened at the low end. 3500-3600 KHZ was 1.7 - 1.3 and now its
2.4 - 1.7. But I don't plan to use it for CW. While 3700-4000 Khz was
1.3-1.4 it's now 1.2
160m worsened from 1.5-2.0 it's now 2.2 across the band.
The other interesting comment from someone in the group was that the
measured SWR may not be an accurate reading if there is significant RF on
the shielding. I don't know why that would be the case in my well RF single
point grounded system setup but I tried by inserting a T4 line isolator by
Radio Works with a 6' coax on either side to the TS950SD and the 87a and I
repeated the experiment. Lo and behold, my SWR vastly improved and was only
1.1 across the bands on 10m, 15m, 17m, 20m, 30m and 40m. On 80m SWR was 1.5
or less from 3650 - 4000 Khz. Things improved on 160m with SWR 1.5-1.7.
However, I have found one remaining problem - a reproducible but
intermittent problem when switching to 80m and only to 80m. Sometimes the
SWR read by my Kenwood TS-950SD is > 5 and other times it is at < 1.5. When
it reads > 5 the power output from the TS-950SD folds back and I cannot get
more than 800w output on the 87a. This seems to happen more often when
switching from band extremes like from 15m or 17m to 80m. When it happens
that the SWR >5 I can usally get it back to a normal SWR by making smaller
band changes, e.g. go from 15m to 20m then to 40m then to 80m. I am certain
it is a problem with the 87a and not the TS-950SD because I can reproduce
the intermittent by keeping an 80m frequency on the Kenwood and then
selecting a different band on the 87a... on xmit when the 87a autotunes back
to the 80m frequency, the SWR sometimes will be > 5.
I've been told that this can sometimes be fixed by reprogramming the
microprocessor that controls the bandswitch position. Is there any way I
can do this at home without shipping the amp back to Alpha? I'm concerned
that with the problem being intermittent and only on 80m that it's more than
the bandswitch contact positioning but maybe a bad stepper motor that's
beginning to fail.
73 Jerry
K1JOS
CCA #11906
-----Original Message-----
From: Mike Schatzberg [mailto:cherokeehillfarm@earthlink.net]
Sent: Monday, January 01, 2007 2:44 PM
To: JOS Earthlink
Subject: Re: [Amps] Alpha 87a
ps....you are not matching impedances, they are already matched, each at 50
ohms. You are shifting the phase.
----- Original Message -----
From: "JOS Earthlink" <jsternmd@earthlink.net>
To: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>
Sent: Monday, January 01, 2007 2:33 PM
Subject: RE: [Amps] Alpha 87a
> Hi Mike,
>
> I found this intereting short dissertation on the use of 1/4, 1/2 wave
coax
> and variations to match impedances:
>
> http://www.wenzel.com/documents/swr.html
>
>
> I guess the big question for me now is whether this actually makes things
> "better' or just becomes an interesting exercise. Since the Alpha only
> require 40-60w for full output, even if my TS950 were seeing an SWR of 3
> into the Alpha 87a, that means the reflected power my TS950 finals would
> experience is around 25% or 12.5-15w. How harmful are 12-15w of reflected
> power? If the TS-950SD were running barefoot at 150w full output into an
> antenna with an SWR of 1.8 then the reflected power (~ 8%)would also be
> about 12.5w. So, overall, is it worth the time and effort to optimize the
> coax between the TS950SD and 87a??
>
> I dunno but it sure makes me think,read more and ask more questions
hihi.
>
> 73 Jerry
> K1JOS
> CCA #11906
>
>
> -----Original Message-----
> From: Mike Schatzberg [mailto:cherokeehillfarm@earthlink.net]
> Sent: Monday, January 01, 2007 1:29 PM
> To: JOS Earthlink
> Subject: Re: [Amps] Alpha 87a
>
>
> Hello Jerry:
>
> I searched my archives, and I see that my memory is a little off. The
> optimal length on average is about 20.5 feet for the jumper solution. I
had
> suggested this experiment to Win W0LZ, and he published his experiment on
> the Yaesu reflector. His starting SWR was about 2:1 on 15 meters which
was
> his worst band. Please see his data below:
>
> OK, Mike, and anyone else that is interested, I started with 23 feet
> > of RG8X Premium Low Loss, FV 78% Center # 16, 1.2 db per 100' at 15
> > MHz coax from Radio Works. Drive was 30 watts on 15 meters into a old
> > SB-220 that is somewhat modified for QSK and 10 meters,among other
> > things.
> >
> > At 23 feet the SWR was 1.75:1 into the Amp - !,2:1 to the antenna
> > At 20.5 feet the SWR was 1.15:1 into the Amp _ 1.2:1 to the antenna
> >
> > The readings in between I am leaving out because I was tired and don't
> > trust my notes.
> >
> > With the 20.5 foot cable SWR on 20 and 10 meters into the amp was
> > 1.2;1 into the amp and 1.2:1 to the antenna.
> >
> > It works for me. Thank you very much.
> >
> > Win
>
> The solution is dependent upon the networks involved, and the type of
cable
> being used to adjust the phase shift, that is why I asked Win to publish
the
> details about the cable he used to obtain his solution. Win is a great
guy,
> with a long amateur history since 1960, and will gladly share his
experience
> with you. I have learned over the past 46 years in this hobby that not
too
> many amateurs are familiar with this solution, Win was no exception.
>
> 73 and Happy DXing,
>
> Mike
> W2AJI
>
> ----- Original Message -----
> From: "JOS Earthlink" <jsternmd@earthlink.net>
> To: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>
> Sent: Monday, January 01, 2007 12:21 PM
> Subject: RE: [Amps] Alpha 87a
>
>
> > Hi Mike,
> >
> > On which band should I be doing this pruning? I assume I should I do
the
> > pruning on 15m as that had the highest mismatch. How will this effect
my
> > SWR on the other higher bands which aren't too bad right now?
> >
> > 73 Jerry
> > K1JOS
> > CCA #11906
> >
> >
> > -----Original Message-----
> > From: Mike Schatzberg [mailto:cherokeehillfarm@earthlink.net]
> > Sent: Monday, January 01, 2007 10:41 AM
> > To: JOS Earthlink
> > Subject: Re: [Amps] Alpha 87a
> >
> >
> > Hello Jerry:
> >
> > The antenna tuner in the radio introduces a phase shift as do all
antenna
> > tuners, and this will create and odd multiple of 90 degrees, which again
> > causes problems for you.
> >
> > Do not use the autotuner when you start to prune the coax back to the
> > optimal length. You can coil the coax up after you have finished. It
> will
> > not act as a line isolator, you will need a pretty good chuck of ferrite
> > around the coax to make one of those. The line isolator does not
prevent
> > ground loops, it prevents RF currents on the shield of the coax from
> > reaching your transmitter. This will avoid RF distortion on your audio,
> or
> > microphone burns from RF on the grounds.
> >
> > Solder one connector to the jumper before starting your pruning tests,
the
> > other end does not need to be soldered, but the cable must make contact
> with
> > both the center conductor as well as the connector shell. You can do
this
> > without a connector with a clothespin attached to the SO 239 input
> > connector, or you can just tack the center connector to a PL 259 and use
a
> > force fit with the braid. When you are done, solder both connections
> > properly, using considerable heat on the shield to connector shell.to
> assure
> > a good bond. I am assuming that you have a SO 239 input connector, as
> Alpha
> > has used a BNC jack on some of its amplifiers.
> >
> > The connector does not add anything to the SWR if properly connected, it
> > does not change the SWR on or off the cable end. There is little or no
> loss
> > at HF frequencies.
> >
> > Don't let this small task cause you any concern, it is easy to do. You
> can
> > use low power while driving your amp to achieve the lowest input SWR.
You
> > can check later at full drive, but nothing should change.
> >
> > You can not harm anything if you use reasonable care connecting the
cable.
> > Listen first on your receiver to make sure the connection is proper and
> > nothing has shorted from your work. Then use low power and transmit
> > briefly, using a string of high speed dits on CW, not SSB. to check SWR
> > with the built in meter in your transceiver. Do not use an outboard
> meter,
> > what matters is the apparent SWR seen by the output of your transceiver.
> >
> > Whether your input circuits are tuned, as in your case, or broadband
> > torroidal input, like the Alpha 76A, this method should lower the input
> SWR
> > when done carefully.
> >
> > 73 and Happy DXing,
> >
> > Mike
> > W2AJI
> > http://home.earthlink.net/~cherokeehillfarm/id2.html
> > ----- Original Message -----
> > From: "JOS Earthlink" <jsternmd@earthlink.net>
> > To: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>
> > Sent: Monday, January 01, 2007 10:14 AM
> > Subject: RE: [Amps] Alpha 87a
> >
> >
> > > Hi Mike,
> > >
> > > My inexperience will show in the next few questions...but I will pick
up
> > an
> > > antenna book and start reading.... until then:
> > >
> > >
> > > 1) so I can determine the correct length by only having the coax
> attached
> > to
> > > the 950SD and add a unsoldered connector to the end? Does the
connector
> > > contribute much... I would have thought it's only determined by the
coax
> > > characteristics.
> > >
> > > 2) Once right length is found can I coil the coax between the exciter
> and
> > > amp? Would that help make it act like a line isolator to prevent
ground
> > > loops?
> > >
> > > 3) What I find weird is that when I have tried the 950SD antenna tuner
> to
> > > bring down the SWR, the efficiency of the RF transfer between the
950SD
> > and
> > > 87a goes down appreciably. For example, on 15m at an SWR of 2.5 at
> 21.000
> > > Mhz I find that 22w output will drive about 1Kw on the 87a. When I
set
> > the
> > > 950SD autotuner and it gives me an SWR of 1.3 without any reflected
> power
> > > then I need 54w to drive 1Kw on the 87a. Maybe I'm overthinking all
of
> > this
> > > but when something doesn't make sense it drives me nuts hihi. Any
> > thoughts?
> > >
> > >
> > > 73 Jerry
> > > K1JOS
> > > CCA #11906
> > >
> > >
> > > -----Original Message-----
> > > From: Mike Schatzberg [mailto:cherokeehillfarm@earthlink.net]
> > > Sent: Sunday, December 31, 2006 6:49 PM
> > > To: JOS Earthlink
> > > Subject: Re: [Amps] Alpha 87a
> > >
> > >
> > > Yes Jerry:
> > >
> > > That is 21.5 feet. The coax will act as a transformer, and shift the
> > phase
> > > of the input, moving what maybe a node at the input of your amp.
> > >
> > > They also claim it will produce the lowest intermod for the
combination
> as
> > > well.
> > >
> > > I can't say what the shorter length will do for you, but if you
haven't
> > > tried the six feet, you could give it a go.
> > >
> > > If you want to see how the length acts as a transformer, start with
say
> 25
> > > feet or so, and prune about 6 inches at a time, watching the SWR as
you
> > go.
> > > You should see the SWR decrease as you cut back the length.
> > >
> > > It is not necessary to actually even have a connector at the amp end
on
> > the
> > > coax. You can carefully trim the end, and place the center conductor
> into
> > > the center of the SO 239 connector, and hold the braid in place with a
> > > clothespin while you measure. When you are done, you can solder the
PL
> > 259
> > > onto the end of the coax jumper.
> > >
> > > Pruning will allow you to reach the optimal solution for the jumper
> > length.
> > >
> > > 73,
> > >
> > > Mike
> > > W2AJI
> > > ----- Original Message -----
> > > From: "JOS Earthlink" <jsternmd@earthlink.net>
> > > To: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>
> > > Sent: Sunday, December 31, 2006 4:51 PM
> > > Subject: RE: [Amps] Alpha 87a
> > >
> > >
> > > > Hi Mike,
> > > >
> > > > Is that 21.5 feet or inches ?? I noticed that the Alpha manual says
> to
> > > use
> > > > a 72" coax between the exciter and the amp but 21.5 feet??
> > > >
> > > > 73 Jerry
> > > > K1JOS
> > > > CCA #11906
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: Mike Schatzberg [mailto:cherokeehillfarm@earthlink.net]
> > > > Sent: Sunday, December 31, 2006 4:49 PM
> > > > To: JOS Earthlink
> > > > Subject: Re: [Amps] Alpha 87a
> > > >
> > > >
> > > > Hello Jerry:
> > > >
> > > > Before you adjust anything, I would use the old Collins standard of
a
> > > length
> > > > of high quality RG 8 Type cable, 21.5 feet in length, between the
> > exciter
> > > > and the amp.
> > > >
> > > > Measure the input SWR once again with this longer length of cable in
> > > place.
> > > > I'll bet that you will see a lower SWR this time.
> > > >
> > > > 73 and Happy DXing,
> > > >
> > > > Mike
> > > > W2AJI
> > > > ----- Original Message -----
> > > > From: "JOS Earthlink" <jsternmd@earthlink.net>
> > > > To: <amps@contesting.com>
> > > > Cc: "JOS Earthlink" <jsternmd@earthlink.net>
> > > > Sent: Sunday, December 31, 2006 4:38 PM
> > > > Subject: Re: [Amps] Alpha 87a
> > > >
> > > >
> > > > > Oops, I forgot to mention that all measurements were made with the
> 87a
> > > > into
> > > > > a 50 ohm dummy load and the reflected power LEDs on the 87a stayed
> at
> > > zero
> > > > > through the testing I described.
> > > > >
> > > > > 73 Jerry
> > > > > K1JOS
> > > > > CCA #11906
> > > > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: JOS Earthlink [mailto:jsternmd@earthlink.net]
> > > > > Sent: Sunday, December 31, 2006 4:35 PM
> > > > > To: amps@contesting.com
> > > > > Subject: Alpha 87a
> > > > >
> > > > >
> > > > > Hi All,
> > > > >
> > > > > I just got an ETO Alpha 87a with Alphamax and it seems to work
very
> > > > nicely.
> > > > > I only see one problem with the amp - I'm almost certain that the
RF
> > > input
> > > > > coils for many of the bands need to be adjusted. I noticed that
> the
> > > SWR
> > > > > out of the TS-950SD was running high into the 87a on a few bands.
> To
> > be
> > > > > absolutely certain I placed my Powermaster powermeter between the
> > > TS-950SD
> > > > > and the 87a. I think the 87a RF input circuits are out of whack:
> > > > >
> > > > > At 28.0000 - 29.7000 Mhz SWR into the 87a is from 1.5 - 2.0
> > > > > At 21.0000 - 21.4500 Mhz SW goes from 2.3 - 1.8
> > > > > At 18.068 - 18.168 Mhz SWR goes from 1.7 - 1.4
> > > > > At 3.5000 - 4.000 Mhz SWR starts at 1.3 but goes 2.2 above 3.700
> Mhz.
> > > > >
> > > > > I tried this with other tranceivers instead of the TS-950SD and
all
> > show
> > > > the
> > > > > same. On my Collins 30L-1 it's a piece of cake to adjust the RF
> coil
> > > for
> > > > > each band by looking at Reflected power between the exciter and
amp
> > > tuning
> > > > > the RF coil for minimal Reflected power but the 87a is a new beast
> for
> > > me
> > > > > plus I don't have any schematics. Any advice appreciated.
> > > > >
> > > > > Have a Happy and Healthy New year to All !
> > > > >
> > > > > 73 Jerry
> > > > > K1JOS
> > > > > CCA #11906
> > > > >
> > > > > _______________________________________________
> > > > > Amps mailing list
> > > > > Amps@contesting.com
> > > > > http://lists.contesting.com/mailman/listinfo/amps
> > > >
> > > >
> > >
> > >
> >
> >
>
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