Not true. Build for your particular impedance matching needs. the TT
product and most made for hams are designed to attempt to match
everything because that's what most hams what, the mythical do
everything matching network. The reality is that you have to have
various matching networks depending on your feedlines, and range of
load Z at the point you want to do the transformation, usually to 50
j0 unbalanced. Since no one makes EF Johnson grade inductors and
variable Cs in manufacturing order quantities at a wholesale price
that will make a product affordable for hams, the commercially
manufactured component quality suffers. At least Ten Tec is honest
about the current handling level of their RMC N1500 disc ceramic caps
(or whatever they use now) on 160 m.
Go to hamfests--troll through eBay....you can find gems like a Gates
10 A roller inductor I picked up on eBay last year; get a bunch of
Russian 470 pF RF doorknobs, or get the 1 MHz tx micas from Fair
Radio--240 pF 6 KV for $8.75 each. You don't need a high v. air
variable for a low Z unbalanced L network. Look for a 900 pF 2 KV
Cardwell; put everything on a board with copper strap and brass
hardware -- I never use a cabinet--it is much better to see the
components so you can head off any signs of trouble, or see where the
inductor is or how much the air variable is meshed. Look for knobs,
porcelain standoffs, shaft decouplers and a few aluminum L pieces for
mounting UHF jacks and a ground lug. you can manually clip in extra
fixed value capacitance by mounting a capacitance buss bar made of
copper strap held up with standoffs. Surplus sales has silver plated
knife switch clips you can buy for 25 cents each and use as clips to
add capacitance on the buss bar--don't bother with a ceramic rotary
switch unless you want to get fancy. you can use clips on standoffs
and a copper bar to switch the caps (which I always shunt to ground)
between input and output with the inductor always in series.
don't bother with vac. variables--PITA and unnecessary. OTOH fixed
vacuums are a bargain on eBay--I use them not for the v. rating but
for the current handling.
For less than 500 bucks you can build a tuner that will take a kw bc
rig that would turn your palstar into a charcoal brickette.
73
rob
K5UJ
On Fri, May 4, 2012 at 4:13 PM, Jim Barber <audioguy@q.com> wrote:
>
> The TenTec L-network design is interesting and has lower losses than
> most, but when I called them about it they wouldn't stand behind QRO
> AM/CW/digital operation on 160M even with a 50-ohm resistive load. (with
> my current workload I ended up buying a PalStar AT5K rather than
> home-brewing - only minor repair needed out-of-the-box)
>
> So - anyone want to build a L-network with enough capacitance to handle
> lots of power at most impedances and phase angles? I have one of those
> football-sized Russian vacuum caps that might work, but I can't think of
> much else that would be economical or practical.
>
> 73,
> Jim N7CXI
>
> On 5/4/2012 1:59 PM, Rob Atkinson wrote:
>> I wouldn't touch a T network. High pass = no pass here
>>
>> 73
>>
>> Rob
>> K5UJ
>>
>> On Fri, May 4, 2012 at 8:37 AM, Tom Thompson<tlthompson@qwest.net> wrote:
>>> Kevin Schmidt, W9CF, has a nice Java app where you can study the losses
>>> in a T-network tuner at http://fermi.la.asu.edu/w9cf/tuner/tuner.html
>>>
>>> Tom W0VJ
>>>
>>> On 5/4/2012 7:22 AM, Carl wrote:
>>>> The first series of tests even had the MFJ coils catching on fire in the
>>>> ARRL lab at well under power ratings on 160.
>>>>
>>>> Tuners with 250pf max on 160 will always be inefficient, a High C tuner
>>>> with
>>>> 500pf will be very efficient and require proportionally less L. The higher
>>>> Q
>>>> results in less bandwidth so there is no free lunch.
>>>>
>>>> Its so much easier to modify an amp to be able to do the matching and toss
>>>> the tuner in the dumpster.
>>>>
>>>> Those with autotune amps are left swinging in the wind and need autotune
>>>> tuners (-;
>>>>
>>>> Carl
>>>> KM1H
>>>>
>>>>
>>>>
>>>> Carl
>>>> KM1H
>>>> ----- Original Message -----
>>>> From: "Roger (K8RI)"<k8ri@rogerhalstead.com>
>>>> To:<amps@contesting.com>
>>>> Sent: Friday, May 04, 2012 3:32 AM
>>>> Subject: Re: [Amps] Antenna tuner loss
>>>>
>>>>
>>>> On 5/3/2012 12:32 PM, Dan Hearn wrote:
>>>>> ARRL tested some popular commercial antenna tuners and reported the
>>>>> results in QST as follows. They covered 160-10 and various loads. All were
>>>>> quite lossy on the low bands with low Z loads.
>>>> And there are people out there that didn't expect this? They are
>>>> running into low impedance loads which means high currents and high
>>>> losses. I believe the Palstar manual even mentions this. Also the
>>>> power handling capability drops off substantially with low Z loads
>>>>
>>>> 73
>>>>
>>>> Roger (K8RI)
>>>>> February, 2003
>>>>> Product Reviews
>>>>> High Power Antenna Tuners:
>>>>> • AMERITRON ATR-30
>>>>> • MFJ-986
>>>>> • PALSTAR AT1500CV
>>>>> • TEN-TEC 238A
>>>>> • VECTRONICS HFT-1500
>>>>>
>>>>
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>>>>
>>>>
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