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Broadcast band Interference Filter for Cricket 80A


Bryan Nehl
 

In this video I demonstrate a 4SQRP Cricket 80A picking up a nearby AM broadcast station. By adding a filtering circuit, the broadcast station interference (BCI) can be greatly reduced. https://www.youtube.com/watch?v=ODTVDoc8Ya8&feature=youtu.be
I built my filter based on this schematic included with the kit here: http://qrpme.com/?p=product&id=BCI
  

72 de Bryan k0emt


WA0ITP
 

GM Byan,

This is a great little filter circuit, glad you found it on Rex's web site. It's been my goto hipass for many years. I first saw it in the original Rockmite's group files, it was posted by NE4LS. There is a similar design in the '86 (?) Handbook, #60 I think. I live close to two kilowatt bcb stations and have needed a hipass filter on every dc receiver I've ever built. This is the one I've used.

Thanks for posting

On December 26, 2017 at 8:07 AM Bryan Nehl <k0emt@...> wrote:

In this video I demonstrate a 4SQRP Cricket 80A picking up a nearby AM broadcast station. By adding a filtering circuit, the broadcast station interference (BCI) can be greatly reduced. https://www.youtube.com/watch?v=ODTVDoc8Ya8&feature=youtu.be
I built my filter based on this schematic included with the kit here: http://qrpme.com/?p=product&id=BCI
  

72 de Bryan k0emt


Dennis Gaskill
 

Here in Augusta Kansas we are about 20 mi from Wichita .
The Cricket picked up a loud CW station (Country and Western )  and the digital band quite handily .
After digging out the old MFJ-971 Tuner all was well .
Not perfect, but the Cowboys and Cowgirls were gone  .

Hope you all had a Merry Christmas and have a Happy New Year

Dennis KC0IFQ


Curt
 

Have read notes from various ops experiencing BCI with the Cricket, and recall there being similar issues with other simple rigs like the Rockmite and Pixies of various flavors.  Seem to recall that the crystal on the RM input was originally to deal with BCI not adequately suppressed by LC network.

I personally have very minor issues with BCI despite living near a large city with many AM broadcast stations.  Use a tuner and balanced antennas.  Can someone describe the station attributes that make BCI more of a problem with DC receivers?

72, Curt KB5JO (Cricket #005)


Wayne Steury
 

My biggest problem is that it receives a very low tone type of signal. I think it is tuned low because I can hear signals one to two kHz higher than my transmit crystal. W1AW is loud and clear with my 3580 crystal   

But I have made 22 initial contacts so far. 

N9EGT Cricket #4
Wayne 


On Feb 2, 2018, at 5:58 PM, Curt <rhulett1@...> wrote:

Have read notes from various ops experiencing BCI with the Cricket, and recall there being similar issues with other simple rigs like the Rockmite and Pixies of various flavors.  Seem to recall that the crystal on the RM input was originally to deal with BCI not adequately suppressed by LC network.

I personally have very minor issues with BCI despite living near a large city with many AM broadcast stations.  Use a tuner and balanced antennas.  Can someone describe the station attributes that make BCI more of a problem with DC receivers?

72, Curt KB5JO (Cricket #005)


Curt
 

I built a Hi Pass filter with two inductors and three capacitors.  I ended up wih 1000pF/1.6uH/560pF/1.6uH/1000 pF.  According to Elsie, the knee is at 3.1 mHz.  At 3.58 loss is 0.3 dB.

Tested with a dummy load, the Cricket failed.  Output without the filter was 600 mW, with the filter was 200mW.  Trying the filter on an NE4040, output without was 900 mW, with was 800 mW.  Testing on an SST-20, without was 2W, with was 1.9W.

Not understanding how the loss on 20M and 40M is 5-10% but on 80M is 67%. 

What have others experienced using a simple high pass filter for BCI reduction on a Cricket.  What was the architecture?  What was the power loss?

72, Curt KB5JO (Cricket #5) Chirp Chirp


Jeff Peters <k9jp.radio@...>
 

Hello Curt,

Is it easy to replace any of the parts (caps. or inductors) on your built filter?  I guess, I would have picked a design frequency of 1.8 or 1.9 Mhz and then the knee might have moved to 2.0 or 2.5 MHz.  If my guess is correct, then you should have nearly the same output with or without the filter.

Hope this might help.

72/73 Jeff K9JP

On Tue, Feb 27, 2018 at 6:04 PM, Curt <rhulett1@...> wrote:
I built a Hi Pass filter with two inductors and three capacitors.  I ended up wih 1000pF/1.6uH/560pF/1.6uH/1000 pF.  According to Elsie, the knee is at 3.1 mHz.  At 3.58 loss is 0.3 dB.

Tested with a dummy load, the Cricket failed.  Output without the filter was 600 mW, with the filter was 200mW.  Trying the filter on an NE4040, output without was 900 mW, with was 800 mW.  Testing on an SST-20, without was 2W, with was 1.9W.

Not understanding how the loss on 20M and 40M is 5-10% but on 80M is 67%. 

What have others experienced using a simple high pass filter for BCI reduction on a Cricket.  What was the architecture?  What was the power loss?

72, Curt KB5JO (Cricket #5) Chirp Chirp




--
Not all of me will die - - - The good I do for others will live on forever.  <><


Curt
 

QSL.  That results in 1500pf/2.2uH/820pF/2.2uH/1500pF.  Knee 2.5MHz.  I will replace the parts and test again.

Curt KB5JO chirpchirp


nm0s_qrp <ai9e_qrp@...>
 

A quick test you can run, if you have an antenna tuner that uses two variable Cs and a switched L (like the 4SQRP Tuner), this is a high pass filter type circuit by itself.  Just put the tuner in line, you should drop the BCB interference by 30 - 40 dB, and be able to tune it to keep your power output from being affected.


Chip Stratton AE5KA
 

The BCI filter from QRPMe does a good job for the Cricket. At 3580 it is just about transparent to the Cricket. It uses3 caps and 2 toroids.

72
Chip
AE5KA

On Wed, Feb 28, 2018 at 3:36 PM, nm0s_qrp via Groups.Io <ai9e_qrp@...> wrote:
A quick test you can run, if you have an antenna tuner that uses two variable Cs and a switched L (like the 4SQRP Tuner), this is a high pass filter type circuit by itself.  Just put the tuner in line, you should drop the BCB interference by 30 - 40 dB, and be able to tune it to keep your power output from being affected.



Curt
 

Well my High pass duplicates the QRPme architecture and uses very nearly the same values.  I am going to check this out varying some of the component values.

Thankfully I have no problems with BCI, maybe because use a tuner.

72, Curt KB5JO


Bryan Nehl
 

Curt,

I didn't have the parts available to get to the values that you mentioned.
So, I used parts on hand to end up with 1300pF/1.8uH/820pF/1.8uH/1300pF.
Cricket Pout to dummy load ~1000mW
Cricket Pout to "stock" BCI ~400mW
Cricket Pout with filter spec above ~600mW

Also, looked much better when checking through a signal generator.

I got to ~1300pF by putting a 820pF in parallel with a 470pF.  (Parts from building the stock design.)

72,

Bryan - k0emt


On Tuesday, February 27, 2018 6:40 PM, Curt <rhulett1@...> wrote:


QSL.  That results in 1500pf/2.2uH/820pF/2.2uH/1500pF.  Knee 2.5MHz.  I will replace the parts and test again.

Curt KB5JO chirpchirp



Chuck Carpenter
 

Curt, Bryan and All,

Attached a drawing comparing two HP filters.  One that Bryan suggested and one that was worked up using Elsie.  Compare the characteristics.  If you can get parts as close as possible to the Elsie model,  I think the transmission loss will be much less than Bryan found.  Mainly because the impedance and RL are much better.
--
Chuck Carpenter, W5USJ
EM22cv Rains County, TX


Chip Stratton AE5KA
 

My testing of the QRPme BCI filter with a 50 ohm termination on one end, and my AA-230 antenna analyzer on the other end, revealed an SWR of 1.04 at 3580 kHz, vs 1.01 with the 50 ohm termination without the BCI filter.

I don't recall my analyzer  measurements at BCB frequencies, only that attenuation increased rapidly below the 80m band.

I also found no significant effect on the 800 mW output power of my Cricket 80a.when the BCI was in circuit, my Elecraft W1 wattmeter 0.8 watt LED remained lit either way.

I'm certainly not trying to push any vendor's BCI filter - the circuit is easily duplicated and there is nothing special about QRPme's implementation, but it does work.

Chip
AE5KA

On Wed, Mar 7, 2018 at 4:07 PM, Chuck Carpenter <w5usj@...> wrote:
Curt, Bryan and All,

Attached a drawing comparing two HP filters.  One that Bryan suggested and one that was worked up using Elsie.  Compare the characteristics.  If you can get parts as close as possible to the Elsie model,  I think the transmission loss will be much less than Bryan found.  Mainly because the impedance and RL are much better.
--
Chuck Carpenter, W5USJ
EM22cv Rains County, TX