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KAT500 antenna port isolation

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ANDY DURBIN

KAT500 antenna port isolation

I've been using Alpha Delta model Delta-4 switches for manual antenna selection. I thought that having the ability to auto select the appropriate antenna with my KAT500 would be a significant improvement for my station. I don't have a K3 so I created a band decoder that drives the KAT500 band inputs and now have automatic antenna switching. However, I'm unimpressed by the isolation between antenna ports.

With the KAT500 switched to the dummy load I'm still decoding a local FT8 station on 6 m. The difference in the FT8 signal between dummy load and antenna is about 19 dB. I have not found a specification for KAT500 port isolation. Is what I'm seeing typical?

Thanks and 73,
Andy k3wyc

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ke9uw

Re: KAT500 antenna port isolation

If you have ever disassembled an alpha delta, you can see what it takes for an attempt at isolation.

Chuck Jack
KE9UW

Sent from my iPhone, cjack

> On Jul 7, 2018, at 2:13 PM, ANDY DURBIN <[hidden email]> wrote:
>
> I've been using Alpha Delta model Delta-4 switches for manual antenna selection. I thought that having the ability to auto select the appropriate antenna with my KAT500 would be a significant improvement for my station. I don't have a K3 so I created a band decoder that drives the KAT500 band inputs and now have automatic antenna switching. However, I'm unimpressed by the isolation between antenna ports.
>
> With the KAT500 switched to the dummy load I'm still decoding a local FT8 station on 6 m. The difference in the FT8 signal between dummy load and antenna is about 19 dB. I have not found a specification for KAT500 port isolation. Is what I'm seeing typical?
>
> Thanks and 73,
> Andy k3wyc
>
>
> ______________________________________________________________
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Chuck, KE9UW

Phil Kane-2

Re: KAT500 antenna port isolation

On 7/7/2018 12:27 PM, hawley, charles j jr wrote:

> If you have ever disassembled an alpha delta, you can see what it
> takes for an attempt at isolation.

Please elaborate. I use a AD Delta-2 here to switch the antenna
between the K2, GND, and the RigExpert antenna analyzer.

73 de K2ASP - Phil Kane
Elecraft K2/100 s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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k6dgw

Re: KAT500 antenna port isolation

In reply to this post by ke9uw

Andy,

From your explanation, it sounds like you've switched the active KAT500
antenna port to a dummy load on which you're hearing a local 6m
station. If that's correct, I don't believe you're looking at port
isolation, you're just receiving a local guy on your dummy load, which
wouldn't be at all strange. What did I misunderstand here?

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/7/2018 12:27 PM, hawley, charles j jr wrote:

> If you have ever disassembled an alpha delta, you can see what it takes for an attempt at isolation.
>
> Chuck Jack
> KE9UW
>
> Sent from my iPhone, cjack
>
>> On Jul 7, 2018, at 2:13 PM, ANDY DURBIN <[hidden email]> wrote:
>>
>> I've been using Alpha Delta model Delta-4 switches for manual antenna selection. I thought that having the ability to auto select the appropriate antenna with my KAT500 would be a significant improvement for my station. I don't have a K3 so I created a band decoder that drives the KAT500 band inputs and now have automatic antenna switching. However, I'm unimpressed by the isolation between antenna ports.
>>
>> With the KAT500 switched to the dummy load I'm still decoding a local FT8 station on 6 m. The difference in the FT8 signal between dummy load and antenna is about 19 dB. I have not found a specification for KAT500 port isolation. Is what I'm seeing typical?
>>
>> Thanks and 73,
>> Andy k3wyc
>>

ANDY DURBIN

Re: KAT500 antenna port isolation

In reply to this post by ANDY DURBIN

" From your explanation, it sounds like you've switched the active KAT500 antenna port to a dummy load on which you're hearing a local 6m station. If that's correct, I don't believe you're looking at port isolation, you're just receiving a local guy on your dummy load, which wouldn't be at all strange. What did I misunderstand here?"

I don't think you misunderstood anything but I don't know how you decided the signal is through the dummy load rather than coupling in the KAT500 from the antenna port to the dummy load port. I don't remember hearing local stations on the dummy load when using the Alpha Delta switch.

I suppose the only way to get good isolation data will be to do a sweep of the KPA500 and Alpha Delta switch with the SA+TG. If I do that I'll share the results.

For now I'll enjoy the automatic antenna switching.

73,

Andy k3wyc
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jh3sif

Re: KAT500 antenna port isolation

In reply to this post by k6dgw

I have similar issue and was told in this mailing list that the issue came from antenna port isolation but it was within specification.
If you open the KAT500 box, you will find that lines between antenna ports and switch relay are close enough to cause inter-port cross-talk.

I wanted to switch 3 antennas with KAT500 but decided not. instead, I connected antenna 1 to port A, dummy load to port B and antenna 2 to power C. This improves isolation between antenna 1 and 2.

73 de JH3SIF, Keith

Kiichiro (Keith) Onishi
Sent from iPad

2018/07/08 7:08、Fred Jensen <[hidden email]> のメッセージ:

> Andy,
>
> From your explanation, it sounds like you've switched the active KAT500 antenna port to a dummy load on which you're hearing a local 6m station. If that's correct, I don't believe you're looking at port isolation, you're just receiving a local guy on your dummy load, which wouldn't be at all strange. What did I misunderstand here?
>
> 73,
>
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
>> On 7/7/2018 12:27 PM, hawley, charles j jr wrote:
>> If you have ever disassembled an alpha delta, you can see what it takes for an attempt at isolation.
>>
>> Chuck Jack
>> KE9UW
>>
>> Sent from my iPhone, cjack
>>
>>> On Jul 7, 2018, at 2:13 PM, ANDY DURBIN <[hidden email]> wrote:
>>>
>>> I've been using Alpha Delta model Delta-4 switches for manual antenna selection. I thought that having the ability to auto select the appropriate antenna with my KAT500 would be a significant improvement for my station. I don't have a K3 so I created a band decoder that drives the KAT500 band inputs and now have automatic antenna switching. However, I'm unimpressed by the isolation between antenna ports.
>>>
>>> With the KAT500 switched to the dummy load I'm still decoding a local FT8 station on 6 m. The difference in the FT8 signal between dummy load and antenna is about 19 dB. I have not found a specification for KAT500 port isolation. Is what I'm seeing typical?
>>>
>>> Thanks and 73,
>>> Andy k3wyc
>>>
>
> ______________________________________________________________
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k6dgw

Re: KAT500 antenna port isolation

In reply to this post by ANDY DURBIN

I did in fact misunderstand that a 6m antenna was still connected to one
of the other ports ... I read it that they were open. You could get a
rough idea by listening to the local and removing the antenna(s) from
the KAT500 and maybe terminating the unused ports in a PL-259 with a 47
ohm resistor. I don't know if the unused ports are shorted or grounded
by the relays, I never traced it out when I had my KAT500. I did like
the antenna selection capabilities however. [:-)

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/7/2018 3:32 PM, ANDY DURBIN wrote:

> " From your explanation, it sounds like you've switched the active KAT500 antenna port to a dummy load on which you're hearing a local 6m station. If that's correct, I don't believe you're looking at port isolation, you're just receiving a local guy on your dummy load, which wouldn't be at all strange. What did I misunderstand here?"
>
>
> I don't think you misunderstood anything but I don't know how you decided the signal is through the dummy load rather than coupling in the KAT500 from the antenna port to the dummy load port. I don't remember hearing local stations on the dummy load when using the Alpha Delta switch.
>
>
> I suppose the only way to get good isolation data will be to do a sweep of the KPA500 and Alpha Delta switch with the SA+TG. If I do that I'll share the results.
>
>
> For now I'll enjoy the automatic antenna switching.
>
>
> 73,
>
> Andy k3wyc
>

ANDY DURBIN

Re: KAT500 antenna port isolation

In reply to this post by ANDY DURBIN

"I suppose the only way to get good isolation data will be to do a sweep of the KPA500 and Alpha Delta switch"

Sorry - that should have read "I suppose the only way to get good isolation data will be to do a sweep of the KAT500 and Alpha Delta switch".

TMGS?

73,

Andy k3wuc

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ANDY DURBIN

Re: KAT500 antenna port isolation

"I have similar issue and was told in this mailing list that the issue came from antenna port isolation but it was within specification."

Ok, but where is the specification? I don't see it in the specifications in the KAT500 Owners Manual (page 2).

If I browse the DX Engineering catalog I do find several antenna switches that do provide a specification for port isolation.

73,

Andy k3wyc
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K7TV

Re: KAT500 antenna port isolation

In reply to this post by ANDY DURBIN

Anyone who has looked inside a good coaxial relay or switch knows that for
that level of isolation the mechanical construction one needs to provide a
more or less complete shield around the chosen signal path, that re-forms
around the new path when the swich is operated. This is complicated and
expensive. I would not expect to find it in a normal HF amateur transceiver,
tuner, or amplifier. Maybe in some specialized equipment for multiradio
operation, SO2R or otherwise. It is certainly something to be hoped for in
future equipment. However, one should not be very confident that a switch
with high isolation numbers would always prevent the sort of signal leakage
mentioned in this thread. "Transmitting on a dummy load" is a common
expression, but I guiess it is seldom representationve of what is actually
going on. More likely, some signal is flowing as on the outside of shields,
and needs common mode chokes for suppression.

This point is well known to high-end competition stations that depend on
separate receive antennas for the low bands. The job of such a receive
antenna is generally not to pick up as strong as possible version of the
wanted signal, but to pick up an adequate sampling of that signal along with
less noise covering up that wanted signal. This involves avoiding noise
pickup where the feedline runs through a high-noise environment (read: the
shack building), as well as long distance signals coming in from the back of
the receive antenna. (A conventional "front-to-back" number is not much
help, one must rather use a complicated measure of back side rejection over
all applicable "back" direction angles.) Noise pickup on the outside of coax
will generally nullify the performance of a well-designed receive antenna
that looks good on paper, unless the installation includes liberal
common-mode choking and grounding of coax shields. I seem to remember one
report that said the grounding was so critical that a ground connectied only
to one side of the coax was markedly infererior to one that completely
encircled the coax. Installations normally include running the coax through
metal conduits, not just for mechanical protection, but for blocking noise
pickup. If it is not already obvious to the reader, I am referencing noise
pickup on receive antenna feedlines as something that corresponds to
transmit capability as well, allowing transmission "on a dummy load" even if
the dummy load is perfectly shielded. Bottom line: Leakage and crosstalk is
a system characteristic that results from more than the performance of a
given component such as a switch.

73,
Erik K7TV

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of ANDY DURBIN
Sent: Saturday, July 07, 2018 3:54 PM
To: [hidden email]
Subject: Re: [Elecraft] KAT500 antenna port isolation

"I suppose the only way to get good isolation data will be to do a sweep of
the KPA500 and Alpha Delta switch"

Sorry - that should have read "I suppose the only way to get good isolation
data will be to do a sweep of the KAT500 and Alpha Delta switch".

TMGS?

73,

Andy k3wuc

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K8TE

Re: KAT500 antenna port isolation

I'm curious why significant (you pick the level) isolation is necessary. The
unwanted rf level is down so far that I have not noticed it causing any
issues. If there were two radio ports, then I might be concerned for radio
2 if I were transmitting on radio 1. This is a big concern with a 6x2 or
8x2 antenna switcher. Can someone count the angels on this pinhead for me?

BTW, I have made a 75m QSO on a dummy load. I think I was using Radio Shack
coax back then (in the 1970's when I worked for the company).

73, Bill, K8TE

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Phil Kane-2

Re: KAT500 antenna port isolation

On 7/9/2018 7:12 PM, K8TE wrote:

> BTW, I have made a 75m QSO on a dummy load. I think I was using Radio Shack
> coax back then (in the 1970's when I worked for the company).

When I lived about three miles away from Mt. San Bruno south of San
Francisco, I routinely worked all of the VHF and UHF repeaters there
using a dummy load! Amazing what a clear eye-ball path can do.

73 de K2ASP - Phil Kane
Elecraft K2/100 s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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Bob McGraw - K4TAX

Re: KAT500 antenna port isolation

All this doesn't speak well for the quality of the dummy load or coax jumpers.

Bob, K4TAX

Sent from my iPhone

> On Jul 9, 2018, at 10:01 PM, Phil Kane <[hidden email]> wrote:
>
>> On 7/9/2018 7:12 PM, K8TE wrote:
>>
>> BTW, I have made a 75m QSO on a dummy load. I think I was using Radio Shack
>> coax back then (in the 1970's when I worked for the company).
>
> When I lived about three miles away from Mt. San Bruno south of San
> Francisco, I routinely worked all of the VHF and UHF repeaters there
> using a dummy load! Amazing what a clear eye-ball path can do.
>
> 73 de K2ASP - Phil Kane
> Elecraft K2/100 s/n 5402
>
> From a Clearing in the Silicon Forest
> Beaverton (Washington County) Oregon
> ______________________________________________________________
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Dave-7

Re: KAT500 antenna port isolation

In reply to this post by Phil Kane-2

One time, a few years ago, when I was living near Mobile, AL, I was
testing an MFJ-949E tuner. It was switched to the internal dummy load.
There was an antenna connected to the balanced line binding posts but,
with it switched to the internal dummy load, these were open
internally. I ran a test at 5w into the dummy load and looked at RBN.
My signal had been picked up by a skimmer in NM.

73 de dave
ab9ca

On 7/9/18 11:01 PM, Phil Kane wrote:

> On 7/9/2018 7:12 PM, K8TE wrote:
>
>> BTW, I have made a 75m QSO on a dummy load. I think I was using Radio Shack
>> coax back then (in the 1970's when I worked for the company).
>
> When I lived about three miles away from Mt. San Bruno south of San
> Francisco, I routinely worked all of the VHF and UHF repeaters there
> using a dummy load! Amazing what a clear eye-ball path can do.
>
> 73 de K2ASP - Phil Kane
> Elecraft K2/100 s/n 5402
>
>>From a Clearing in the Silicon Forest
> Beaverton (Washington County) Oregon
> ______________________________________________________________
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Jim Brown-10

Re: KAT500 antenna port isolation

In reply to this post by Bob McGraw - K4TAX

Yep. When you're trying to get 50-60 dB down, EVERYTHING has to be done
very well. Several years ago, I was not achieving the harmonic
suppression I thought I should, so I bought a spool of BuryFlex (RG8
with a robust copper braid shield) and replaced every piece of coax
inside my shack. I didn't measure the result (not easy to do), but
suppression was 10-15 dB better. Another important component of
minimizing crosstalk is having a good ferrite choke at the feedpoint of
every antenna.

73, Jim K9YC

On 7/9/2018 8:19 PM, Bob McGraw K4TAX wrote:

> All this doesn't speak well for the quality of the dummy load or coax jumpers.
>
> Bob, K4TAX
>
>
> Sent from my iPhone
>
>> On Jul 9, 2018, at 10:01 PM, Phil Kane<[hidden email]> wrote:
>>
>>> On 7/9/2018 7:12 PM, K8TE wrote:
>>>
>>> BTW, I have made a 75m QSO on a dummy load. I think I was using Radio Shack
>>> coax back then (in the 1970's when I worked for the company).
>> When I lived about three miles away from Mt. San Bruno south of San
>> Francisco, I routinely worked all of the VHF and UHF repeaters there
>> using a dummy load! Amazing what a clear eye-ball path can do.