Topics

K5BCQ uBITX Relay Switched LPF/BPF board

Kees T
 

In the interest of avoiding any confusion, I break this out to a separate thread.

73 Kees K5BCQ

Kees T
 

Since most keep talking about the need for BPFs for certain bands, I "guess" the 80m-10m uBITX direction should be a board with 6 filter capability. How about a basic dual relay switched filter board (3-1/4" x 3-7/8") with up to 6 pluggable filters, all manually selected with a 6 position rotary switch --AND-- you can add a small mux board with 2N3904 relay drivers for the filters and a CD4028B mux to go from the 3 Raduino pins to the filters. Start with the existing 111,110,100,000 and add two others when you have the code modified.

73 Kees K5BCQ 

Kees T
 

Here is what all 4 uBITX LPFs look like as plug-ins. Note that the 6x LPF board is arranged to where you can cut off 1 or 2 of the LPF/BPF positions with no ill effect.

73 Kees K5BCQ

Kees T
 

 W0PWE
Sep 2   

Kees - With 6 filters is the plan as follows?
LPF1 = 80M
LPF2 = 40M and 30M
LPF3 = 20M and 17M
LPF4 = 15M
LPF5 = 12M
LPF6 = 10M

Kees T
 

You can assign the filters to any LPF/BPF you want. Your list looks good to me, maybe combine the 12m/10m LPFs and make the 15m a BPF.

73 Kees K5BCQ

 

Kees & Group:

 

Please Clarify: I thought I was told some time ago on this post that only passband filters would address the uBitix issues. If that earlier statement was correct, why are people working on solutions using lowpass filters???

 

David A Posthuma, WD8PUO

1 (616) 283-7703

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Kees T
Sent: Monday, September 03, 2018 10:23 AM
To: BITX20@groups.io
Subject: Re: [BITX20] K5BCQ uBITX Relay Switched LPF/BPF board

 

 W0PWE

Sep 2   

 

Kees - With 6 filters is the plan as follows?
LPF1 = 80M
LPF2 = 40M and 30M
LPF3 = 20M and 17M
LPF4 = 15M
LPF5 = 12M
LPF6 = 10M

 

Kees:

 

Why manual band switching? Could not the code select the proper filter according to frequency the user selects on the uBitx? Could not the RF Switching be done using pin diodes or FET switching? I’m just trying to learn, thanks.

 

David A Posthuma, WD8PUO

1 (616) 283-7703

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of Kees T
Sent: Monday, September 03, 2018 10:13 AM
To: BITX20@groups.io
Subject: Re: [BITX20] K5BCQ uBITX Relay Switched LPF/BPF board

 

Since most keep talking about the need for BPFs for certain bands, I "guess" the 80m-10m uBITX direction should be a board with 6 filter capability. How about a basic dual relay switched filter board (3-1/4" x 3-7/8") with up to 6 pluggable filters, all manually selected with a 6 position rotary switch --AND-- you can add a small mux board with 2N3904 relay drivers for the filters and a CD4028B mux to go from the 3 Raduino pins to the filters. Start with the existing 111,110,100,000 and add two others when you have the code modified.

73 Kees K5BCQ 

ajparent1/KB1GMX <kb1gmx@...>
 

On Mon, Sep 3, 2018 at 12:10 PM, David Posthuma wrote:

Why manual band switching? Could not the code select the proper filter according to frequency the user selects on the uBitx? Could not the RF Switching be done using pin diodes or FET switching? I’m just trying to learn, thanks.

 

David A Posthuma, WD8PUO

First there are two issues one being poor harmonic filtering and Kees is addressing that here.

The other is spurs from inadequate filtering above 17M,  That requires band pass filters before
the power amp.  The tail end low pass filter cannot fully try to address that.

I doubt the band pass filters he sells can stand 10W in that location.   Kees comment please?

Allison

Kees T
 

The QRP Labs LPF filters are rated at 10W according to Hans Summers, the BPF filters he sells are not, probably because of the series current the capacitors have to handle or larger inductors required. No reason you can't make up BPFs which CAN handle 10W. The filters you see in the pictures are blank boards I made up and you add what components you need to add, and design your own. Could come out with a different BPF filter layout if needed. With those little 1.5" x 0.5" boards you can get 16 per 100mm x 100mm panel .....that's 160 boards per 10 prototype panel order for only $2 plus $5? for scoring plus shipping.

73 Kees K5BCQ  

Kees T
 

David,

Manual switching is only one of the options. There is also a small board you can add which can mux the 3 bits from the Raduino to all 6 sets of relays......but it would require a small code change. I was suggesting to use the codes 111,110,100, and 000 which the existing Raduino code supplies via TxA, TxB, TxC to select the 4 LPFs as today and add the remaining 2 when you get around to it. There is also no magic to 6x filters....it could be 5x or 8x filters or 12x filters if you add another select bit. 6x happens to fit readily on a 100mm x100mm panel.

The 4x LPF board version decodes the existing TxA,TxB, and TxC drivers just like the uBITX does today (and I have to reinstall K3). Those boards should be here next week.

73 kees K5BCQ

Kees T
 

You can also see, in the picture with the uBITX board, that the 2N3904's have already been pulled, waiting for the 2N2222A's ..............and other incremental improvements.  

73 Kees K5BCQ

Kees T
 

You can also  modify the existing filter for a faster roll-off which MAY catch enough of the 15m spur .....for instance. The plot labeled "1" is the original LPF, the other plot is the modified LPF.

73 Kees K5BCQ

MadRadioModder
 

Let’s do it…

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Kees T
Sent: Monday, September 3, 2018 3:26 PM
To: BITX20@groups.io
Subject: Re: [BITX20] K5BCQ uBITX Relay Switched LPF/BPF board

 

The QRP Labs LPF filters are rated at 10W according to Hans Summers, the BPF filters he sells are not, probably because of the series current the capacitors have to handle or larger inductors required. No reason you can't make up BPFs which CAN handle 10W. The filters you see in the pictures are blank boards I made up and you add what components you need to add, and design your own. Could come out with a different BPF filter layout if needed. With those little 1.5" x 0.5" boards you can get 16 per 100mm x 100mm panel .....that's 160 boards per 10 prototype panel order for only $2 plus $5? for scoring plus shipping.

73 Kees K5BCQ  


Virus-free. www.avg.com

--

…_. _._

Guy WB7SZI
 

Forgive me if this is way over simplified. I’m not an RF designer, 
but couldn’t you manually just insert an appropriate LPF from your ant. connection to the antenna to reduce harmonics on that specific band? I agree that a six band LPF system would be great but I for one only use one or two bands most of the time. Is that doable? 
73,
Guy WB7SZI 

ajparent1/KB1GMX <kb1gmx@...>
 

Kees,

Before you remount K3 remove the audio switching path from it.  Many get 
feedback from that path.  Also it can be inserted form the bottom.

Also the big issue is all the spaghetti traces. The LPF are good as is, just
the switching is a fail and its all layout.  Too many intereleaved lines.  The real
trouble maker is that all RF in to the filter and out from the filter go by was
of KT1.

In the drawing 3.jpeg The red is new wires yellow are bad wires.
This was built with relays on bottom and works well for 80 through 17m.
KT3 switches antenna to filter outptu or through coax direct to KT1 pin12.
Coax is under board.

In drawing 1jpg  The enclosed in red are the troublesome areas.
Yellow bad, green is audio mod, black means cut!, blue is the spaghetti to be removed/altered

That parallel DC lead (tx relay power) is parallel to RF line from KT3... If it looks like a
directional coupler it works like one. Its why there is a ton of RF on the switched 
DC+ line during TX.  Very bad!

If you don't care for above 17M the fix is messy but easy once the
relays are out.  Use one relay per band from 80/40/20 and it works.
RF goes in via KT1 and out via KT3.  Also modify the relays power
path to avoid that parallel line.  

Allison

ajparent1/KB1GMX <kb1gmx@...>
 

Now if one does all that and really wants 20 and up spurs and all....

Simple add an inline (between radio and antenna jack) 28mhz low pass filter.
and leave it there.  If it well made it will be invisible (low loss) and at worst
it catches harmonics like the old school TVI filter.  It does not fix the spur
Issue.

So the deal for the relays then is:
           
KT1 selects 20m filter via TXA
KT2 selects 40m filter via TXB
KT3 selects 80m filter Via TXC
none selected is straight through
and the external always inline 28mhz LPF is doing the work.

 **
 * Select the tx harmonic filters
*/  
void setTXFilters(unsigned long freq){
  
  if (freq >= 20000000L){ 
    digitalWrite(TX_LPF_A, 0);
    digitalWrite(TX_LPF_B, 0);  // 10m straight through
    digitalWrite(TX_LPF_C, 0);
  }
  else if (freq >= 14000000L){ 
    digitalWrite(TX_LPF_A, 1);
    digitalWrite(TX_LPF_B, 0);  // 20M
    digitalWrite(TX_LPF_C, 0);
  }
  else if (freq >= 7000000L){  
    digitalWrite(TX_LPF_A, 0);
    digitalWrite(TX_LPF_B, 1);  // 40m
    digitalWrite(TX_LPF_C, 0);    
  }
  else {
    digitalWrite(TX_LPF_A, 0);
    digitalWrite(TX_LPF_B, 0);  // 80m
    digitalWrite(TX_LPF_C, 1);    
  }
}

Kees T
 

Close.......

What I am doing on the 4x board (the one compatible with the existing uBITX) design point is:
#1) it fits in the space I cleared on the uBITX board picture,
#2) it selects 3 of the relay sets with the TxA, TXB, and TxC uBITX drivers for 80/60m, 40/30m, 20/17/(15)m,
#3) if any one of those 3 drivers is picked it selects the TXD driver (on the 4x board) which is driven by a 3 input diode dot-OR from the TXA,TXB, TXC inputs. The TxD driver has the 4th 10/12m filter on  the NC contacts so you don't have to have 1 LPF relay energized at all times and may not require K3 if it's the highest band LPF, like on the present uBITX. .....haven't decided yet). 
#4 yes, disabling audio M1/M2 with the same RF relay is strange.

73 Kees K5BCQ

Glenn
 

I had a problem long time back with K1 not operating correctly. Some others have had this problem too. Took the cover off, might be interesting to see construction.

Its hard to see in the pictures but one contact was restricted in movement by the adjustment of the other NO contact.



Lawrence Macionski <am_fm_radio@...>
 

Kees-
Modern rigs, use diode switching to engage filters. I suggest using just 1 relay for positive switching and the output of each filter be run through diodes to a commonality. It would reduce current flow to the relays by 50%.. My thought is simple- steering up front, but where the output goes is always the same..

Years ago, I did some modifications on solid state switching VHF amplifier for VHF Engineering in Binghamton, NY.. We could drive 40 watts at 146Mhz though 4 1N914's in parallel, 25 watts through 2 of them. Experimenting required --but 2-4 1N914's are cheaper than a relay. Smaller foot print too..

Kees T
 

The 4x LPF/BPF boards have arrived and I need to get one in Warren's hands for testing (in addition to the other 6x LPF/BPF boards).

A little more layout tweaking will make the interface leads even shorter now that I know these guys will put a notch in the board for no additional charge.

Picture shows where it's installed on the uBITX board after removing the uBITX LPF parts and putting them on the individual plug-in LPFs.

73 Kees K5BCQ