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KBPF3A switching frequencies and performance

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w4sc-2

KBPF3A switching frequencies and performance

Looking for details of switch over frequencies and expected performance of the KBPF3A in its various bands,

There is improvement in the BCB and below 500KHz with the KBPF3A enabled, however the other SW BCB bands I have tried are lacking.

Has anyone measured the performance of the KBPF3A?

Ben W4SC

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ab2tc

Re: KBPF3A switching frequencies and performance

Hi Ben,

Others with more knowledge may chime in, but here is what I know:

The crossover frequencies you can find in the K3S schematic file. Here is a
link to it:

https://ftp.elecraft.com/K3S/Manuals%20Downloads/E740323%20K3s%20Schematic%20Files.pdf

It is the first page in the "options" segment. You can search for "KBPF3A"
to find it (the file is *big*).

I have not been able to find any real specifications for it. The
installation manual has no specs. I also don't know if either ARRL or
Sherwood has collected any data outside of the regular ham bands. In
principle the K3(S) equipped with this filter should have nearly identical
sensitivity anywhere from 0.1 to 30MHz. Note: the KBPF3 version has L1
installed which limits the low end to 0.5MHz. If you have an unmodified
early K3 and want to use it below 0.5MHz you need to add add a bypass
capacitor as described in the installation manual. Without that the bottom
end is very noisy from power supply noise. I know many people are fascinated
by Non-Directional-Beacons (NDBs) which are generally in that low frequency
range.

I have it in my K3S and find plenty of sensitivity anywhere in the range
supported (0.1-29.7MHz). I don't do much SWLing anymore since the number of
English language SW transmitters have dwindled over the past 10 years. It's
all Internet radio these days. Are you sure you have good antennas for the
bands where you think sensitivity is low? I certainly have no problem using
a 102' G5RV anywhere from 0.5 to 29.7MHz for reception. I leave the tuner in
bypass.

Knut - AB2TC

w4sc-2 wrote

> Looking for details of switch over frequencies and expected performance of
> the KBPF3A in its various bands,
>
> There is improvement in the BCB and below 500KHz with the KBPF3A enabled,
> however the other SW BCB bands I have tried are lacking.
>
> Has anyone measured the performance of the KBPF3A?
>
> Ben W4SC
>
> Sent from Mail for Windows 10
>
> ______________________________________________________________
> Elecraft mailing list
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Re: KBPF3A switching frequencies and performance

In reply to this post by w4sc-2

Hi Ben:
You had me curious with your request. I started to check my KBPF3 (modified to the "A") and noticed something that now bothers me. I tried going down from 160M and it appears that the switch over to the AM broadcast band occurs precisely at 1700,000 Kc. When I tune to 1.699999 the relays click. But the anomaly(?) I am seeing at the switchover point is a big drop in the signal level. At my QTH during the daytime the nominal noise level at 1700.000 Kc is about S7. When I switch to 1.699999 the noise level drops to S2. At the high end the switchover occurs at 2109.999+ with a drop in the noise level from S9+10 to S3. I don't use the K3 for listening to AMBCB but only in the case of checking my 160M receiving loops with some stations high in the AM Band. I checked on 80M and got similar results. At the low side the switch occurred at 3299.999 with a drop in the noise level from S5 to S2. On the high side the switchover occurred at 4209.999+ but here the noise level increased from S4 to S6. I don't know if this helps you any on at least these 2 bands. If I get the time I'll try to check the rest. Now I'm bothered by the changes in signal levels at the switchover points (ignorance is bliss). I wonder if anyone else has ever noticed this or do I have an issue with my KBPF3?

Russ, N3CO
On Friday, April 16, 2021, 12:39:28 PM EDT, w4sc <[hidden email]> wrote:

Looking for details of switch over frequencies and expected performance of the KBPF3A in its various bands,

There is improvement in the BCB and below 500KHz with the KBPF3A enabled, however the other SW BCB bands I have tried are lacking.

Has anyone measured the performance of the KBPF3A?

Ben W4SC

Sent from Mail for Windows 10

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ab2tc

Re: KBPF3A switching frequencies and performance

Hi Russ,

Your response made *very* curious so I checked out my own K3S. I can confirm
the two switchover frequencies you mention (1700 and 3300kHz), but observe
at most a couple of dB change when crossing the boundaries. I use an
external panadapter (LP-PAN/NaP3 connected to IF-OUT) so I can easily see
the same stations and noise while tuning across the boundaries. On the
1700kHz boundary the signals are a couple, maybe 3dB stronger when below
1700kHz. So it sounds to me that the filters in your KBPF3A are not being
switched in when it is supposed to be used. The KBPF3 needs to be enabled
(set to "nor") in the configuration menu. Have you checked that?

Hmm, I neglected to carefully read the last part of your post. It sounds
like your KBPF3A might be working above 4210kHz so may be just the 2 lowest
bands are defective. If you look at the schematic you see that those two
bands use the same filter but with some components switched in and out by
another relay (K2). So that could narrow the problem down to one relay (K1)
not operating. Is this a *new* problem or has it been like this since you
got the K3 or installed the KBPF3A?

Knut - AB2TC

Elecraft mailing list wrote

> Hi Ben:
> You had me curious with your request. I started to check my KBPF3
> (modified to the "A") and noticed something that now bothers me. I tried
> going down from 160M and it appears that the switch over to the AM
> broadcast band occurs precisely at 1700,000 Kc. When I tune to 1.699999
> the relays click. But the anomaly(?) I am seeing at the switchover point
> is a big drop in the signal level. At my QTH during the daytime the
> nominal noise level at 1700.000 Kc is about S7. When I switch to 1.699999
> the noise level drops to S2. At the high end the switchover occurs at
> 2109.999+ with a drop in the noise level from S9+10 to S3. I don't use
> the K3 for listening to AMBCB but only in the case of checking my 160M
> receiving loops with some stations high in the AM Band. I checked on 80M
> and got similar results. At the low side the switch occurred at 3299.999
> with a drop in the noise level from S5 to S2. On the high side the
> switchover occurred at 4209.999+ but here the noise level increased from
> S4 to S6. I don't know if this helps you any on at least these 2 bands.
> If I get the time I'll try to check the rest. Now I'm bothered by the
> changes in signal levels at the switchover points (ignorance is bliss).
> I wonder if anyone else has ever noticed this or do I have an issue with
> my KBPF3?
>
> Russ, N3CO
> On Friday, April 16, 2021, 12:39:28 PM EDT, w4sc <

> w4sc@

> > wrote:
>
> Looking for details of switch over frequencies and expected performance
> of the KBPF3A in its various bands,
>
> There is improvement in the BCB and below 500KHz with the KBPF3A enabled,
> however the other SW BCB bands I have tried are lacking.
>
> Has anyone measured the performance of the KBPF3A?
>
> Ben W4SC
>
> Sent from Mail for Windows 10
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:

> Elecraft@.qth

>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to

> erusst@

>
>
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Re: KBPF3A switching frequencies and performance

Hi Knut:
I couldn't tell you if this is a new problem as I didn't notice anything amiss until I started checking switchover frequencies to answer W4SC's question. I verified that the KBPF3 is enabled in the config menu. I bought the used KBPF3 about 4-5 years ago from another ham and don't remember who it was. It came with the instructions to modify it to the "A" version. I can't remember if it was already modified or if I did it myself. I do know that I did install the 220uF capacitor on the main board of the K3. Arrrgh, I guess I'll have to tear everything apart to check if the mods were done correctly before proceeding. Thanks for your information.
Russ, N3CO
On Monday, April 19, 2021, 09:04:58 PM EDT, ab2tc <[hidden email]> wrote:

Hi Russ,

Your response made *very* curious so I checked out my own K3S. I can confirm
the two switchover frequencies you mention (1700 and 3300kHz), but observe
at most a couple of dB change when crossing the boundaries. I use an
external panadapter (LP-PAN/NaP3 connected to IF-OUT) so I can easily see
the same stations and noise while tuning across the boundaries. On the
1700kHz boundary the signals are a couple, maybe 3dB stronger when below
1700kHz. So it sounds to me that the filters in your KBPF3A are not being
switched in when it is supposed to be used. The KBPF3 needs to be enabled
(set to "nor") in the configuration menu. Have you checked that?

Hmm, I neglected to carefully read the last part of your post. It sounds
like your KBPF3A might be working above 4210kHz so may be just the 2 lowest
bands are defective. If you look at the schematic you see that those two
bands use the same filter but with some components switched in and out by
another relay (K2). So that could narrow the problem down to one relay (K1)
not operating. Is this a *new* problem or has it been like this since you
got the K3 or installed the KBPF3A?

Knut - AB2TC

Elecraft mailing list wrote

> w4sc@

w4sc-2

Re: KBPF3A switching frequencies and performance

In reply to this post by w4sc-2

A little back ground,,

The effort started as a result of my using WWV at 15.000000 MHz for calibrating the reference oscillator. Tuning from 14.999999 to 15.000000 MHz I noticed a 9 to 12 Db drop in signal strength of WWV.

I could hear relays’ switching at the 14.999999 to 15.000000 MHz boundary. This lead to making a list of (“suspected”) switching points by tuning from low 1MHz through 30MHz listening Looking at schematics of the KBPF3/A I heard switching at some points that did not make sense, with the 14.999999 to 15.000000 MHz boundary being one.

It is not easy to probe the KBPF3A in my K3S-100 to check which relays are bein set/reset because of the installed KRX3A. I have a K3S-10, but will need to install a KBPF3/A to check the 14.999999 to 15.000000 MHz boundary and gather the information. (PENDING)

de Ben W4SC

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w4sc-2

Re: KBPF3A switching frequencies and performance

In reply to this post by w4sc-2

Russ,

Unfortunately, it appears you may have a defective KBPF3A. (Modified KBPF3). I actually see a slight increase in band noise below 1.7MHz with my K3S-100, which has KBPF3A installed.

Ben W4SC

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Brian Hunt

Re: KBPF3A switching frequencies and performance

In reply to this post by w4sc-2

This thread also got my curiosity up. Several years ago I upgraded my
K3 #41xx with the KBPF3 including the 'A' mod of the capacitor on the RF
board. I never really checked it out except for the 630 meter coverage
and transmit capability - both were as advertised.

Using a wideband noise generator (QRP Guys K7QO Noise Bridge) I tuned
from about 500 kHz up to 30 Mhz and was able to identify the filter
switch-over points (most of them anyway). I measured the received noise
level using the P3 dBm scale. At none of the switch points was the
noise level more than about 5 dB different from one side to the other.
By continuously tuning and watching the display, it was apparent that
the differences were mainly due to roll off of one filter segment or the
other. The gain was uniformly consistent across each of the ham bands
but sometimes rolled off at the KBPF3 switch points. The area between
7.41 MHz and 8.4 MHz is kind of no-man's land due to the first IF being
there. At the IF frequency the gain was down >50 dB.

73,
Brian, K0DTJ

On 4/20/2021 08:57, w4sc wrote:
> A little back ground,,
>
> The effort started as a result of my using WWV at 15.000000 MHz for calibrating the reference oscillator. Tuning from 14.999999 to 15.000000 MHz I noticed a 9 to 12 Db drop in signal strength of WWV.
>
> .......
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Re: KBPF3A switching frequencies and performance

Brian,Thanks for your information which got me thinking again about my situation. I went back and set the config for the KBPF3 to "not inSt" and found no difference at the signal levels at the switchover at 1700 Kc. Toggling back and forth between "not inSt" and "nor" I verified that there is no change in signal levels. On the surface it appears that I purchased a broken used KBPF3. Now I really have to take things apart to figure out what's wrong.
Russ, N3CO
On Tuesday, April 20, 2021, 07:23:37 PM EDT, Brian Hunt <[hidden email]> wrote:

This thread also got my curiosity up. Several years ago I upgraded my
K3 #41xx with the KBPF3 including the 'A' mod of the capacitor on the RF
board. I never really checked it out except for the 630 meter coverage
and transmit capability - both were as advertised.

Using a wideband noise generator (QRP Guys K7QO Noise Bridge) I tuned
from about 500 kHz up to 30 Mhz and was able to identify the filter
switch-over points (most of them anyway). I measured the received noise
level using the P3 dBm scale. At none of the switch points was the
noise level more than about 5 dB different from one side to the other.
By continuously tuning and watching the display, it was apparent that
the differences were mainly due to roll off of one filter segment or the
other. The gain was uniformly consistent across each of the ham bands
but sometimes rolled off at the KBPF3 switch points. The area between
7.41 MHz and 8.4 MHz is kind of no-man's land due to the first IF being
there. At the IF frequency the gain was down >50 dB.

73,
Brian, K0DTJ

On 4/20/2021 08:57, w4sc wrote:
> A little back ground,,
>
> The effort started as a result of my using WWV at 15.000000 MHz for calibrating the reference oscillator. Tuning from 14.999999 to 15.000000 MHz I noticed a 9 to 12 Db drop in signal strength of WWV.
>
> .......
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w4sc-2

Re: KBPF3A switching frequencies and performance

In reply to this post by Brian Hunt

When setting installed/ NOT installed, make sure you reboot….
Ben

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Re: KBPF3A switching frequencies and performance

Thanks Ben, I didn't think of that. Now when the KBPF3 is not inst There is no difference in signal level when transitioning from 1.700 to 1.699999. And when I set the KBPF3 to nor (and reboot) there is a definite drop of 5-7 S units at the 1.700 transition point and also at the the 2.11 to 2.10999 transition. So there is definitely something in the low band signal path that is attenuating the signal. I'll also do some checking at the other freqs. I guess it's time to drag out the scope for some signal tracing which should be fun with SMDs and my old eyes.
Russ, N3CO
On Thursday, April 22, 2021, 09:09:47 AM EDT, w4sc <[hidden email]> wrote:

When setting installed/ NOT installed, make sure you reboot….
Ben

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Re: KBPF3A switching frequencies and performance

In reply to this post by ab2tc

Just an FYI, I found out what the problem is with my modified KBPF3. I removed the added caps and signal levels returned to somewhat normal levels. Adding a cap to C2 didn't make sense and attenuated the signals. But Fig. 14 shows adding a cap to C4. Apparently the ham I bought this from used Rev. A1, June 24, 2015 instructions which have an error. Figure 13 shows adding the 0.1uF caps to C2, C3 and C6. I downloaded Rev. A2 June 29, 2015 which correctly shows in fig. 13 to piggyback caps on C4, C3 and C6. Problem solved!
Russ, N3CO
On Monday, April 19, 2021, 09:04:58 PM EDT, ab2tc <[hidden email]> wrote:

Hi Russ,

Your response made *very* curious so I checked out my own K3S. I can confirm
the two switchover frequencies you mention (1700 and 3300kHz), but observe
at most a couple of dB change when crossing the boundaries. I use an
external panadapter (LP-PAN/NaP3 connected to IF-OUT) so I can easily see
the same stations and noise while tuning across the boundaries. On the
1700kHz boundary the signals are a couple, maybe 3dB stronger when below
1700kHz. So it sounds to me that the filters in your KBPF3A are not being
switched in when it is supposed to be used. The KBPF3 needs to be enabled
(set to "nor") in the configuration menu. Have you checked that?

Hmm, I neglected to carefully read the last part of your post. It sounds
like your KBPF3A might be working above 4210kHz so may be just the 2 lowest
bands are defective. If you look at the schematic you see that those two
bands use the same filter but with some components switched in and out by
another relay (K2). So that could narrow the problem down to one relay (K1)
not operating. Is this a *new* problem or has it been like this since you
got the K3 or installed the KBPF3A?

Knut - AB2TC

Elecraft mailing list wrote

> w4sc@