Hi Paul,
>What can I do?
See also my other mail.
Shielding and common mode choke.
73
Clemens
DL4RAJ
>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of N1BUG
>Sent: Thursday, December 28, 2017 9:57 PM
>To: [email protected]
>Subject: Re: R: Re: LF: TXing 2200m WSPR
>
>I was able to make a few more tests without getting frostbite. :)
>
>I disconnected the coax from the matching transformer (at the
>antenna) and put the coax into a dummy load. All OK, exactly the
>same as when the dummy load is in the shack. I guess the coax is OK.
>
>Next I connected the coax as usual to the primary of the matching
>transformer. I put the dummy load on the transformer secondary and
>set the transformer taps for 1:1 ratio. All OK, amp was completely
>happy. I did see a very small phase error between current and
>voltage on the scopematch, but nothing more than a couple of degrees.
>
>It seems the problem must be RF getting into something, RF current
>where it does not belong, but only when feeding the antenna.
>
>An important note: There is no such thing as complete isolation of
>antenna ground from shack AC power ground here. Both towers are
>grounded for lightning protection, one has an extensive radial field
>because I shunt feed the tower on 160m. All of the 160m - HF - VHF
>coax cables are grounded to antennas and towers, so the antenna
>ground is connected in the shack to other equipment. Of course that
>equipment is connected to the power ground through 3 wire cords.
>What can I do?
>
>73,
>Paul N1BUG
>
>
>
>On 12/28/2017 03:19 PM, N1BUG wrote:
>> Hi Clemens,
>>
>> Thank you for taking the time to run these simulations!
>>
>> My Ultimate 3S does have a LPF before the feed to the PA. I
>> understand some PAs prefer a square wave. Should I remove the LPF? I
>> have a function generator which can make the same power as the
>> Ultimate 3S with either sine or square wave. I could try that as a
>> test...
>>
>> Today I made some more tests. I can run a little more power before
>> trouble begins when I have the primary (coax) and secondary
>> (antenna) grounds tied together at the antenna! When I isolate the
>> grounds, the problem is worse! What does this tell us?
>>
>> I'm not sure how to make an effective common mode choke for this
>> frequency. I can try another transformer at the shack if I can find
>> a low power version that uses an inexpensive core. At this point I
>> don't want to buy 3 x FT-240-77 cores for a <20W test. Any
>> suggestions? I have some FT-144-JC cores. Any chance these could be
>> used for a test?
>>
>> Could I have some mistakes in my isolation transformer? I have
>> primary turns spread around the whole core, with the secondary turns
>> around almost the whole core placed between primary turns. But the
>> primary and secondary windings do not start at the same position on
>> the core. I thought this wouldn't matter. Maybe it does?
>>
>> 73,
>> Paul
>>
>>
>>
>> On 12/28/2017 08:00 AM, Clemens Paul wrote:
>>> Hi Paul,
>>>
>>>> I already have plans to build the big T type LPF.
>>>
>>> Out of curiosity I've done some spice simulations of your PA.
>>> They indicate that a T type LPF won't help at all.
>>> This was to be expected because your PA is not a class D
>voltage mode
>>> push pull PA like W1VD's or IK1HSS's or 2E0ILY 's.
>>> Indeed the T type LPF will cause considerably higher
>voltage spikes at the FET'S drain.
>>> In the attached screenshot you can see three
>simulations,each with a different output filter.
>>> A shunt C LPF,a series L LPF and even a diplexer filter.
>>> The red traces represent voltage at the drain,green is DS current.
>>> With the diplexer voltage spikes are lowest.
>>> But I obviously the filter is not your problem.
>>> It seems that the near field of the antenna is causing the trouble.
>>> I would suggest to try a second isolation transformer or a good
>>> common mode choke *at the shack* end of your coax run
>instead of building a T-type LPF.
>>>
>>> P.S. Has your Ultimate 3S a LPF installed before you feed
>it into the PA?
>>>
>>> 73
>>> Clemens
>>> DL4RAJ
>>>
>>>> -----Original Message-----
>>>> From: [email protected]
>>>> [mailto:[email protected]] On Behalf Of N1BUG
>>>> Sent: Monday, December 25, 2017 1:15 PM
>>>> To: [email protected]
>>>> Subject: Re: R: Re: LF: TXing 2200m WSPR
>>>>
>>>> Hi Marco,
>>>>
>>>> I don't detect any heat in the LPF but at this low power level it
>>>> could be difficult to detect it.
>>>>
>>>> I already have plans to build the big T type LPF. I have the
>>>> T-225A-2 cores and metal to make a compartmented box.
>Capacitors are
>>>> on the way, could arrive around 29 December. I still need to order
>>>> the wire and some kind of material for mounting the big inductors.
>>>>
>>>> I'm making that LPF because eventually I will also build the big
>>>> amplifier. I'm not sure when that will happen, probably a bit late
>>>> for this LF season.
>>>>
>>>> The most curious thing is what seems to be some
>measurement error or
>>>> impedance transformation but the cause remains elusive. I hope to
>>>> find the reason so I can be more confident about
>measurements when I
>>>> go go high power.
>>>>
>>>> 73,
>>>> Paul N1BUG
>
>
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