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swr bridge diodes

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Brett gazdzinski-2

swr bridge diodes

Anyone have any idea what sort of diodes
would work best in the swr bridge of a high power
antenna tuner?
What is normally used, fast switching or what?

Thanks for any info,
Brett
N2DTS

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Don Wilhelm-3

Re: swr bridge diodes

Brett,

Choices abound - 1N34s are common, 1N5711s work well. It mainly depends
on the directional coupler design. See chapter 27 of the ARRL Antenna
Book for additional information and projects.

73,
Don W3FPR

Brett gazdzinski wrote:
> Anyone have any idea what sort of diodes
> would work best in the swr bridge of a high power
> antenna tuner?
> What is normally used, fast switching or what?
>
>
> Thanks for any info,
> Brett
> N2DTS
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John, KI6WX

Re: swr bridge diodes

In reply to this post by Brett gazdzinski-2

Use a 1N5711. Breakdown voltage is 70 volts and voltage drop across the
diode is only a few tenths of a volt at low current. It makes a reasonable
detector up to 500 MHz.
-John
KI6WX

> Anyone have any idea what sort of diodes
> would work best in the swr bridge of a high power
> antenna tuner?
> What is normally used, fast switching or what?
>
>

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Brett gazdzinski-2

RE: swr bridge diodes

In reply to this post by Don Wilhelm-3

I looked at the ones in the K2 antenna tuner,
but was not sure about the power rating.

My heathket tuner has blown out its diodes for the 2nd time,
and they are not identified in the diagram.

I suspect my roller inductor goes open (its worn out)
and allows a voltage spike to take the diodes out.
500 watts of carrier into a G5RV generates some voltage!

I was thinking about higher voltage diodes, I have 1n34a's,
had 1N270's in, tried 1n914's last night but they don't
give enough output...

1N34a's are rated to 60 volts, but I guess it does not
matter if the inductor opens up.

I was just curious as to what is important in the circuit,
switching speed?, low voltage drop?

Thanks for the info,

Brett
N2DTS

> Brett,
>
> Choices abound - 1N34s are common, 1N5711s work well. It
> mainly depends
> on the directional coupler design. See chapter 27 of the
> ARRL Antenna
> Book for additional information and projects.
>
> 73,
> Don W3FPR
>
> Brett gazdzinski wrote:
> > Anyone have any idea what sort of diodes
> > would work best in the swr bridge of a high power
> > antenna tuner?
> > What is normally used, fast switching or what?
> >
> >
> > Thanks for any info,
> > Brett
> > N2DTS
>

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Don Wilhelm-3

Re: swr bridge diodes

Brett,

The voltage rating and the forward voltage drop are the two most
important. The 1N5711 diodes seem to have a flatter output vs.
frequency characteristic than the 1N34s.

There are 2 cures to the blown diode problem - first is to do any tuning
at low power levels, and second is to disconnect or ground the antenna
when not in use so static surges from the antenna are not coupled back
to the diodes.

Clean the contacts on that roller inductor <G>.

73,
Don W3FPR

Brett gazdzinski wrote:

> I looked at the ones in the K2 antenna tuner,
> but was not sure about the power rating.
>
> My heathket tuner has blown out its diodes for the 2nd time,
> and they are not identified in the diagram.
>
> I suspect my roller inductor goes open (its worn out)
> and allows a voltage spike to take the diodes out.
> 500 watts of carrier into a G5RV generates some voltage!
>
> I was thinking about higher voltage diodes, I have 1n34a's,
> had 1N270's in, tried 1n914's last night but they don't
> give enough output...
>
> 1N34a's are rated to 60 volts, but I guess it does not
> matter if the inductor opens up.
>
> I was just curious as to what is important in the circuit,
> switching speed?, low voltage drop?
>
> Thanks for the info,
>
> Brett
> N2DTS
>
>
>
>> Brett,
>>
>> Choices abound - 1N34s are common, 1N5711s work well. It
>> mainly depends
>> on the directional coupler design. See chapter 27 of the
>> ARRL Antenna
>> Book for additional information and projects.
>>
>> 73,
>> Don W3FPR
>>
>> Brett gazdzinski wrote:
>>> Anyone have any idea what sort of diodes
>>> would work best in the swr bridge of a high power
>>> antenna tuner?
>>> What is normally used, fast switching or what?
>>>
>>>
>>> Thanks for any info,
>>> Brett
>>> N2DTS
>
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> Elecraft web page: http://www.elecraft.com
>

rrkrr-2

Re: swr bridge diodes and roller inductors

In reply to this post by Brett gazdzinski-2

The 1N34 is a Germanium diode and will have a lower forward voltage drop
than a standard PN junction Silicon diode - so will work better on small
signals.
Low barrier Schottky diodes designed for small signals, like the 1N5711
should have performance similar to the 1N34, but will usually have
higher reverse leakage currents.

You might try a little silver loaded silicone grease on the roller
inductor: http://www.2spi.com/catalog/msds/msds04993.html

Bob K4ERR

Brett gazdzinski wrote:

> I looked at the ones in the K2 antenna tuner,
> but was not sure about the power rating.
>
> My heathket tuner has blown out its diodes for the 2nd time,
> and they are not identified in the diagram.
>
> I suspect my roller inductor goes open (its worn out)
> and allows a voltage spike to take the diodes out.
> 500 watts of carrier into a G5RV generates some voltage!
>
> I was thinking about higher voltage diodes, I have 1n34a's,
> had 1N270's in, tried 1n914's last night but they don't
> give enough output...
>
> 1N34a's are rated to 60 volts, but I guess it does not
> matter if the inductor opens up.
>
> I was just curious as to what is important in the circuit,
> switching speed?, low voltage drop?
>
> Thanks for the info,
>
> Brett
> N2DTS
>
>
>
>
>> Brett,
>>
>> Choices abound - 1N34s are common, 1N5711s work well. It
>> mainly depends
>> on the directional coupler design. See chapter 27 of the
>> ARRL Antenna
>> Book for additional information and projects.
>>
>> 73,
>> Don W3FPR
>>
>> Brett gazdzinski wrote:
>>
>>> Anyone have any idea what sort of diodes
>>> would work best in the swr bridge of a high power
>>> antenna tuner?
>>> What is normally used, fast switching or what?
>>>
>>>
>>> Thanks for any info,
>>> Brett
>>> N2DTS
>>>
>
> _______________________________________________
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> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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>
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> Elecraft web page: http://www.elecraft.com
>
>

Ron D'Eau Claire-2

RE: swr bridge diodes and roller inductors

I've never had a problem with roller inductors IF they are clean.

They don't have to be shiny silver. Silver oxide (the dark black stuff that
forms on real silver) is an excellent conductor! If it offends your
sensibilities, use a tiny bit of silver polish to clean it up, but it has
nothing to do with the performance of the inductor.

One end of the inductor usually connects through a rotating contact near the
shaft. If that's dirty it can be intermittent too. Unless you take the
roller to bits - often not practical - the best way to deal with that is to
put a DROP of suitable contact cleaner on the contacts. I prefer Caig DeOxit
for such things.

Sometimes the mechanism that presses the roller against the turns gets
sticky. Some designs use little coil springs. Others have leaf springs that
might also serve as the end supports for the rod on which the roller
travels. A bit of dirt or old, gummy lubricant in the supports or guides can
keep the rod from moving freely to hold the roller snug against the coil as
it turns.

I'd avoid any conductive lubricants, including any lubricant that contains
metal. Lubricants, especially silicon types, have a habit of migrating over
time into places where they aren't wanted - such as across the turns of a
roller inductor.

Ron AC7AC

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