On 8/9/2010 11:59 AM, Jim Brown wrote:
> On Mon, 09 Aug 2010 00:47:48 -0400, Roger (K8RI) wrote:
>> Any thoughts and suggestions?
> Hi Roger,
> Several thoughts. First, my amps are manual tuned (Ten Tec Titan 425), and
> I use manual tuners (Ten Tec 229, 238).
As are mine.
> I write down all the settings for
> each antenna and band so I can go to those presets when changing bands.
I have them in a spreadsheet, so I just look up the band, frequency, and
> That gets me close, then I tune the tuners with exciter power, usually
> about 40W, then fire up the amp and tweak it for maximum smoke as indicated
> on the SWR meter. That minimizes distortion in the amp. With practice, I
> can do this in a couple of seconds for the tuner with exciter power,
> another few seconds with the amp (because the antenna is already matched).
> Many years ago, I tried what you want to do, and what I do now works better
> and faster.
My hands just aren't steady enough for a "spot on" quick tune up.
I was 47 when I went to college, graduated at 50. I had two classes
where the information came so fast and furious I could take notes or pay
attention, but not both. I haven't been able to write well, or "find
tune" with that hand since. I'd come out of those classes with writer's
cramp every time but I wasn't the only one. <:-)) It really ruined my
> Here's one of the problems that may be affecting your situation. If you
> look inside most antenna tuners (including mine), you'll find switching for
> antennas with single wires running to a rotary switch, depending on the
> chassis for a return.
This was my original opinion.
> That is LOUSY PRACTICE, and it puts a big
> discontinuity in the line that may be no big deal on 160 and 80, but can
> create significant mismatches on the higher bands. Interior wiring SHOULD
> run on coax between the SO239 connectors, the switch(es), and the tuning
I think I can get around this by adding a coax switch (Alpha Delta - 2)
between the amp and tuner, so instead of selecting the dummy load on the
aux position, I just use the coax switch. It means two switches instead
of one and I've been trying to keep it simple. The original Alpha Delta
- 2 switch between the exciter and amp that allows selecting the exciter
or antenna analyzer would stay in place. I've had very good luck with
> Ah, you say, the chassis is a complete enclosure, and it has low
> resistance. Yes, BUT the wires to/from the switch and components have
> inductance, and that path forms a inductive loop through the circuitry to
> the chassis and back to the SO239. If you replace the wire with coax, the
> return current all flows on the wire, not on the chassis, and there's
> almost no inductance, only the coax, which is an extension of what's on the
> SO239s. The way that EMC guys look at it, LOW frequencies and DC follows
> Ohm's Law (the chassis). High frequencies follow the path of least
> inductance (the braid of the coax). In this case, LOW frequencies are audio
> and below. I continue to be amazed that folks will ignore BIG, REAL issues
> like this while fixating on the imagined difference between an N connector
> and a UHF connector that only matter above 500 MHz.
I use UHF connectors and bore them out on a mill. <:-))
> If you look inside the Ten Tec 425 amp, you'll find coax from input
> connector to relays, and from output connector to relays. Done right. But
> if you look in Ten Tec tuners, you'll see wires. Could that be part of your
> antenna switching problem?
Yes, which is what I believed from the start. Although the length of
the coax also comes into play. The tuner just throws in the reactance to
keep the user from getting bored. Although the manual recommends using
the AUX position for a dummy load, the person I talked to did not
recommend taking that approach on the higher bands.
> At Dayton, I saw this same problem in PalStar
> tuners that were on display, and pointed it out to a guy who said he was
> the design engineer. He looked at me like I was crazy.
BTW Palstar does use coax with compensating caps in the DL5K dummy load
and it works very well.
I may try rewiring the Aux as an experiment if this turns out to be the
case. The coax bypass positions seem to work well.
> Same problem with ICE bandpass filters, which may be part of why their
> performance isn't that good. And you can't just go re-wiring with coax,
> because that will change their tuning.
Using the shortest leads/coax I can get this to work nicely up through
20, but the reactance makes it difficult above 20.
I need to install a long shaft to the switch handle so I can stay in
front of the rig and the switch can be located at the rear. <:-))
> 73, Jim Brown K9YC
> TowerTalk mailing list
TowerTalk mailing list