Re: Harmonics and Relay Replacement
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Jim I agree with you regarding the lowest number of turns.
My theory is that the relay contacts are acting as the primary of a current transformer inducing the RF current flowing in the contacts into the great number of turns of the relay coil which would explain the RF voltage found and posted by someone on the relay supply lines. It's like a normal current transformer but with the primary on the outside of the coils with the strong RF field inducing the voltage in the relay coli. Apart from the possible blowby from the contacts to the other contacts due to the strong RF field, the RF voltage on the relay coil would also induce a current in the other contacts reducing the isolation. It is true that one can say that the current in the relay contacts would cancel each other as one is going in one direction and the other in the opposite direction, but the intense RF field and the small spacing could lead to unexpected results. It could also be considered that the contacts are acting like a small loop inducing a current in the relay coil. Remember that a transmitting loop has a very strong field in its vicinity. This is why I asked earlier on whether someone had or intend to check whether the results are the same with the different relay coil inductance. The lower inductance ones would have a lower voltage induced in the relay coil due to the smaller number of turns which can be checked by the RF voltage on the relay supply lines and also leading to better isolation. This is just my theory. Regards
Lawrence
On Sun, Oct 14, 2018 at 1:39 PM Jim Sheldon < w0eb@...> wrote: Raj,
I thought the same thing, but maybe, even using sockets, just for the
experiment, I could get some relative comparisons between the types to
see if any were better than others.? I suspect the 500mw version, Arrow
part# V23105A5503A201 will be the best because they have the lowest coil
resistance, fewest turns on the coil.? The only thing that worries me
using that relay is it's current draw - I'm hoping it won't be too much
for the switching transistors in the uBITX.? ?The 400mW relays are
working and switching OK but the additional current from the lower coil
resistance may become a problem and I'm not sure yet.
I don't want to risk ruining the board by soldering and unsoldering the
relays several times so planned on using sockets but ONLY on the one
board I'm planning on setting up as a test station.? I'll build it up on
a board but use double shielded Teflon insulated COAX from the uBITX
boards 2 pin connector to the BNC output and make all digital and audio
wires twisted pair to the front panel jacks, encoder and switch.? The
construction will be open, no case but the uBITX board will be mounted
on a 16 gauge aluminum plate to give a good underside ground plane and
good low Z grounds for all connections.
I have some good, gold plated machined pin socket strips that are very
low profile and will use those to create the sockets.? Again, for these
tests I will only look for which of the 4 relay types gives the best
harmonic attenuation between types and then I will solder that set into
a uBITX for the final results.? Only way I know to test all 4 types
without possibly ruining a good board from too much
soldering/de-soldering of relays.? A repaired trace would negate the
original test results as it's characteristics would be different.
Hope people can understand what I'm trying to say here.
Jim
------ Original Message ------
From: "Raj vu2zap" <rajendrakumargg@...>
To: [email protected]
Sent: 10/14/2018 1:06:47 AM
Subject: Re: [BITX20] Harmonics and Relay Replacement
>Jim,
>
>My take on this relay business is that both contacts are being
>inductively coupled.
>
>Imagine the NC contacts on one side - it is a loop and will be
>inductive. The same goes
>for the other pair on the other side..
>
>By adding a socket we may not get the best rejection from Axicom
>relays. I have also
>socketed KT1/2/3 .. the relays have arrived and I am at the farm.. so a
>week more
>of suspense.
>
>If someone with a SA like 815 can feed in the tracking gen through a 47
>ohm resistor
>to one NC contacts in/out and take the Analyser input from the other NC
>contact set
>and then sweep say up to 100MHz, we get some enlightenment. I am
>eagerly waiting
>to try for myself.
>
>Raj
>
>At 13/10/2018, you wrote:
>>Looking at the differences between the original Hongfa relays -S (for
>>sensitive) version in my uBITX boards and the Axicom relays Mike Doty
>>and I installed in place of them, the Axicom had lower coil resistance
>>in the 400 mW coils vs the 200 mW coils fot the Hongfa relays.? That
>>means fewer turns of wire in the Axicoms and subsequently less
>>inductance.? That may be a huge factor in the isolation between the
>>two types.? The coil resistance for the Axicom that matches the Hongfa
>>in DC spec aldo has the exact same listed coil resistance.
>>
>>I'm going to order 5 each of the 150mW, 200 mW and 500 mW versions,
>>put sockets on my 3rd V4 board and see how much difference there is
>>between the 3 other types relative to the already installed 400 mw
>>version.? Hopefully that will give us some definitive answers.? Be
>>Monday before I can order them so it will be a few days before any
>>testing can be done.
>>
>>Jim Sheldon, W0EB
>
>
>
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