[Moon] [Moon-Net] Antenna, 8877 amp SWR

Dominique Dehays f6dro at wanadoo.fr
Mon Nov 5 17:46:41 CET 2018


hi ,


yes , that was my feeling too. Old timers will remember from the past 
where eme was really eme , an article in the 2m eme newsletter which 
title was " fluidic diode" , describing a similar symptom

73

Dom


Le 05/11/2018 à 16:22, Roger via Moon a écrit :
> Serge,
> That sounds like a slight amount of moisture vaporizing on initial high
> power transmission and condensing again when allowed to cool. Probably at a
> low spot or loop in the feedline.
>
> 73, Roger
> W7TZ
> CN83ia
> Grid Busters
> w7tz.webs.com
>
>
> On Mon, Nov 5, 2018 at 6:47 AM Serge Szpilfogel via Moon <
> moon at moonbounce.info> wrote:
>
>> Thank you Gaby & all for detailed information's. As soon I get a dummy load
>> I will find out FIRST if the problem is in the radio room or at the
>> antenna.
>>
>> What makes it difficult it only happens on the first transmission of the
>> day
>> for less of a minute then it is ok for hours.
>> My MFJ analyser for VHF does not tell me anything since you need high power
>> going through the system to create the problem.
>> Thank you to all with good suggestions.
>> Serge VE1KG
>>
>>
>>
>> -----Original Message-----
>> From: Draskovits Gábor HA1YA [mailto:ha1ya at isiscom.hu]
>> Sent: November 5, 2018 07:41
>> To: 'Serge Szpilfogel'
>> Subject: RE: [Moon-Net] Antenna, 8877 amp SWR
>>
>> Hi Serge,
>>
>> Leif has right!
>>
>> The cause of your problem 99% high level spurious or harmonics level in
>> output power.
>>
>> Easy way to check it:
>>
>> Put with short cable 50Ohm dummy to the PA and check the VSWR.
>>
>> If you have spectrum analyzer you can see the harmonics or spurious sigs in
>> the output power.
>>
>> If you’ve tetrode amplifier and its self oscillating anwhere:
>>
>> Check the G2. If the G2 grounded  capacity is broken or not enough the tube
>> can generate similar problem.
>>
>> For example at GU87B or GU84B if only one connecting plate on G2 part
>> dosn’t
>> connecting  to G2 body the tube
>>
>> will self oscillate!
>>
>> If everything is OK around the socket:
>>
>> At tetrode amplifiers put pre-dummy to G1 to ground.( 100 Ohm 50W, non
>> inductive serial with 1..2nF capacitor.
>>
>> It will helps a lot. The input stage will little bit wider  and it give
>> stability for the amplifier..
>>
>> …after few 100 amplifier building, with 73,
>>
>> Gabi HA1YA
>>
>> www.ha1ya.hu
>>
>>
>>
>>
>>
>> From: Moon-net [mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of
>> Serge Szpilfogel via Moon-net
>> Sent: Sunday, November 4, 2018 10:19 PM
>> To: moon-net at mailman.pe1itr.com; moonbounce reflector <
>> moon at moonbounce.info>
>> Subject: [Moon-Net] Antenna, 8877 amp SWR
>>
>>
>>
>> Hello I have not resolved my 1.5 SWR at the beginning of a TX first time
>> for
>> 30seconds.
>>
>> I changed some connectors & adapters but no results. I am know focusing on
>> the amp & the brick & the transceiver & am looking for a dummy load which
>> can stand a Kilowatt.
>>
>> Question: could it be a spurious frequency generated by the TX or brick or
>> Amp???
>>
>> When I get the dummy load I will be able to check the amp & the brick & the
>> transceiver.
>>
>> I have a DCI 145  Band pass filter which I could put between the brick &
>> transceiver
>>
>> Or the brick & the amp input I guess. Or simply put up with it???
>>
>> Your suggestions are always appreciated.
>>
>> Thank you
>>
>> Serge VE1KG
>>
>>
>>
>> <
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>>
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