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Yup, and after opening up one of the original relays that I removed from a V4 board in prep for putting new ones on (they should be here within the hour) it was extremely obvious that those relays were not designed with RF in mind.? There is no shielding of the relay coil at all and all the contacts are on movable arms that run parallel to each other and the full length of the relay as well as close to the relay coil itself.? The armature is mostly made of plastic so doesn't provide much (if any) shielding between the coil and the movable contact arms.? The movable arms are each made up of 2 parallel, approximately 2mm wide strips of metal that are separated in the middle of the top of the relay by about 1 mm. ?(Pictures not possible as the relays were pretty much destroyed in the dissection.) ?I believe the parallel arm construction was for current carrying capability (not needed in small signal RF relays) as the contacts are rated to 125V @ 60 watts (their designation) in the data sheet.? The width & placement of these contact arms would allow a whole lot of coupling between both sets of contacts and I really believe it's one of the culprits though not necessarily the entire problem. ?

Changing the relays to an RF rated set with proper isolation certainly can't hurt and may just wind up being the simplest fix for the problem.

The Postman just delivered the new relays from Digi-Key so off to install them and run some tests to see if I can prove or disprove Mike Doty's data. ?

I do believe my results will corroborate his after chopping up one of the old relays to see what was in it.

Jim Sheldon

------ Original Message ------

From: "Arv Evans" <arvid.evans@...>

To: [email protected]

Sent: 10/10/2018 12:20:51 PM

Subject: Re: [BITX20] Harmonics and Relay Replacement

Jim

Sorry for the "blindly changing relays" comment.? That was not intended to be derogatorily in

any way.? Thinking when I said that was about those who follow what we say, assuming that

we have performed all the necessary testing and evaluation.? Some have measured the

capacitance between relay armatures and between relay contacts, but I have seen little

said about capacitance between RF carrying parts of these relays and the windings.? My

point was about the possibility of relay windings acting as RF chokes, thus allowing the DC

traces between relays to be coupling agents with respect to RF.?

Arv

_._

On Wed, Oct 10, 2018 at 11:02 AM Jim Sheldon <w0eb@...> wrote:

Arv and others,

#1 I really believe it's capacitive coupling within the relay itself and between the contacts, as well as from contacts to coil.? The original relays in the uBITX are inexpensive (read CHEAP) Chinese power relays that are not (I have their spec sheet) rated for RF and there are no RF parameters in their data sheet such as capacitance between contacts, from coil to armature and coil to contacts at all.? I had already bypassed the coil terminals to ground with .1uF SMD capacitors and didn't notice an appreciable difference.

#2, After this came to light, I don't consider myself "blindly" changing relays.? I'm investigating the cause and effect of changing these relays.? My two version 4 uBITX boards DO barely meet spec with the strongest harmonic(s) being -49 dB below the carrier level on MY (calibrated last year) spectrum analyzer.? Others' results will surely vary depending on the precision and how well and when calibrated their spectrum analyzers are.? I do not have the test equipment to measure inter contact/coil, etc. capacitance so I have no choice but change the relays as part of my experimentation.? It's an expense I am willing to undertake to attempt to improve MY uBITX rigs and if it helps others, so be it.? If others chose to ignore the results (good or bad) then the consequences are on them, not me as I am only sharing the information out there with the caveat "For What It's Worth!" ?

Looking at the construction of the original relays after dissecting one, I can certainly see the wire to the far end of the coil runs parallel to the contacts along that same side of the relay and not very far away either.? Even though it's smaller than 30 gauge wire, the internal capacitance between the coil and at least one set of contacts is going to be a factor in these relays not to mention there is no shielding of the coil so inductance and capacitance could also be playing a part in the "blow-by". ?

The new ones are too expensive to disect one as far as I'm concerned, but at least TE Products (Axicom) saw fit to publish the RF parameters (isolation by frequency) and inter contact/coil capacitance. ?

Jim Sheldon, W0EB?

------ Original Message ------

From: "Arv Evans" <arvid.evans@...>

To: [email protected]

Sent: 10/10/2018 11:16:53 AM

Subject: Re: [BITX20] Harmonics and Relay Replacement

Kees, and others....

Blindly changing relays may fix the problem, but are we missing something here?

What is the real problem with the original relays?? Is it capacitive coupling between

RF carrying parts and the activation conductors, or is it that the relay coils might

be acting as RF chokes and allowing RF to be coupled between relays via the

RF-isolated traces of DC relay control leads?? Has anyone measured how much

is being carried by the DC control leads?? Has anyone tried bypassing the relay

control leads for RF?

Arv

_._

On Wed, Oct 10, 2018 at 8:56 AM Kees T <windy10605@...> wrote:

Thanks for dissecting an AXICOM relay and the pictures. The coil mounted over the contacts is a definite difference to the ones I dissected.

The other thing which may effect results is that most of the larger (16 pin) relays offer up to 4 different "coil sensitivity" options .....which will effect coil resistance and inductance. The resistance for a given 12V relay coil varies between about 960 ohms and about 320 ohms. That may well effect the coupling also.

I don't have enough different relays to compare but I do have some series inductors to evaluate. The thing to watch out for there is the inductor self resonance effect.

73 Kees K5BCQ