K2-XV222 RFI Susceptibility Problems - a solution found

[Steve Kavanagh]

A couple of weeks ago I posted here regarding a problem whereby transmitting on my 6m rig cause my XV222 (connected to K2/K60XV) to key up.

It appears that if any moderate amount of stray RF ends up on the tranmit IF line (probably due to imperfect shielding of the transverter rear panel jacks), this power is then detected by the power detector diode on the K60XV board, which then apparently triggers the K2 to switch the state of the 8R line.  This then keys the transverter.

No word yet from those in the know as to whether this firmware behaviour in the K2 is to be expected or not.  Id be interested in hearing the results if anyone else wants to try injecting up to 1 mW of RF (HF or VHF...it shouldn't matter much) into the K2/K60XV XVTR OUT jack (while receiving) and checking to see what happens.

I have found a solution which works at my home station.  That is to put a filter in the transmit IF line which passes 28 MHz but does not pass 50 MHz.  At present I have it mounted in an external box with a short coax cable to the XVTR OUT jack on the K2.  I think it still needs a little tweaking to give a good match so that the K60XV will give full output in transmit, but the odd effects when I transmit on 6m have completely disappeared.

I may still work on improving the XV222 shielding in case the problem is worse in my rover setup.

73,
Steve VE3SMA


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[wayne burdick]

Hi Steve,

Minicircuits makes a 30 MHz in-line (BNC) low-pass filter that should  
do just as well, for those who don't want to roll their own: their  
model #BLP-30+. See:

     
http://www.minicircuits.com/cgi-bin/modelsearch?
search_type=info&model=BLP-30%2B

I would recommend this filter if anyone has similar RFI problems with  
any transverter, used with either a K2 or K3.

73,
Wayne
N6KR

> From: Steve Kavanagh <[hidden email]>
> Subject: [Elecraft] K2-XV222 RFI Susceptibility Problems
>
> A couple of weeks ago I posted here regarding a problem whereby
> transmitting on my 6m rig cause my XV222 (connected to K2/K60XV) to
> key
> up.
>
> It appears that if any moderate amount of stray RF ends up on the
> tranmit
> IF line (probably due to imperfect shielding of the transverter rear
> panel
> jacks), this power is then detected by the power detector diode on
> the
> K60XV
> board, which then apparently triggers the K2 to switch the state of
> the
> 8R
> line.  This then keys the transverter.

> I have found a solution which works at my home station.  That is to
> put
> a
> filter in the transmit IF line which passes 28 MHz but does not pass
> 50
> MHz.


---

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[Steve Kavanagh]

That filter has pretty much the same attenuation at 50 MHz as my homebrew one, so yes, it should work fine.  Mine has better match at 28 MHz, at the expense of not as good match at lower frequencies.  I ended up with the following, after some tweaking....

My filter is a two section low-pass pi-network.  The two inductors are both 7 turns #22 AWG enamelled wire on T30-6 cores.  The capacitors to ground at the input and output are both 166 pf (91 pF and 75 pF dipped silver-mica caps in parallel).  The capacitor to ground at the junction of the two coils is 309 pF (270 pF and 39 pf dipped silver-mica caps in parallel).  Measured > 30 dB return loss and < 0.5 dB insertion loss over 27-30 MHz (mind you my measurement setup probably isn't really accurate enough to reliably measure 30 dB return losses).  Also > 30 dB attenuation at 50 MHz.

When I try modelling the filter with SPICE I get only a fair agreement with measurements.  I think the lead length and other strays are not insignificant.  So if anyone else builds one, be prepared for some tweaking if you want best performance.

The K2/K60XV now (after tweaking) likes the impedance it's seeing and can provide full 1 mW output with the filter mounted right at the output of the K60XV and a few feet of 50 ohm cable to the transverter.

73,
Steve VE3SMA


--- On Thu, 2/12/09, wayne burdick <[hidden email]> wrote:

> Minicircuits makes a 30 MHz in-line (BNC) low-pass filter
> that should do just as well, for those who don't want to
> roll their own: their model #BLP-30+. See:
>
>  
> http://www.minicircuits.com/cgi-bin/modelsearch?search_type=info&model=BLP-30%2B
>
> I would recommend this filter if anyone has similar RFI
> problems with any transverter, used with either a K2 or K3.
>
> 73,
> Wayne
> N6KR

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