[Amps] Alpha 87a High SWR between Exciter and Amp vs Bad Bandswitch
Dick Green WC1M
wc1m at msn.com
Wed Jan 3 00:22:51 EST 2007
Jerry,
Did you try just a 6' length of coax between the TS950S and the 87A? I'd be
curious to know how that works, as it's the length originally supplied with
the 87A.
There could be a number of causes for the 80m problem. It could be a dirty
or faulty input bandswitch. Or, it could be that your bandswitch needs
recalibrating -- the contacts may be landing just on the margin in the 80m
position. If you can hook up a PC to your 87A, you can test whether the
bandswitch needs recalibrating on 80m and can patch a new calibration factor
into the firmware. Contact me directly and I'll walk you through the
procedure.
73, Dick WC1M
> -----Original Message-----
> From: JOS Earthlink [mailto:jsternmd at earthlink.net]
> Sent: Tuesday, January 02, 2007 10:52 PM
> To: Mike Schatzberg; Amps at contesting.com
> Subject: [Amps] Alpha 87a High SWR between Exciter and Amp vs
> Bad Bandswitch
>
> 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 at 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 at earthlink.net>
> To: "Mike Schatzberg" <cherokeehillfarm at 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 at 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 at earthlink.net>
> > To: "Mike Schatzberg" <cherokeehillfarm at 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 at 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 at earthlink.net>
> > > To: "Mike Schatzberg" <cherokeehillfarm at 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 at 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 at earthlink.net>
> > > > To: "Mike Schatzberg" <cherokeehillfarm at 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 at 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 at earthlink.net>
> > > > > To: <amps at contesting.com>
> > > > > Cc: "JOS Earthlink" <jsternmd at 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 at earthlink.net]
> > > > > > Sent: Sunday, December 31, 2006 4:35 PM
> > > > > > To: amps at 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 at contesting.com
> > > > > > http://lists.contesting.com/mailman/listinfo/amps
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
>
>
>
>
More information about the Amps
mailing list