More power to you with the Elecraft PXA100

When 5 watts is not enough

Gasp!  My blog is called "HamRadioQRP"... so what sort of heresy would lead me to post a topic on using more than 5 watts...

Will I have to turn in my QRP card?

I bit the expensive bullet and bought a used PXA100 amp for my KX3 this past week. There, I've got it off my chest.  I've come out of the closet. Go ahead and unfriend me and unsubscribe from my blog...

Normal Elecraft KX3 -- Notice the RF scale goes from 1w up to 12 watts

Elecraft KX3 with a PXA100 -- note the RF scale now goes up to 110 watts

OK, for those still reading...

This is my first time into the bottom of a solar cycle running QRP

If you've been operating for the past 6 months I'm sure you've noticed the band conditions have been getting pretty poor, and while I continue to try and make contacts and have ragchews using QRP power levels sometimes I feel bad for the other fella who is not QRP struggling to copy me.

I enjoy the challenge of making contacts at QRP levels but I also enjoy exchanging more than my call and an RST.  When the other station gives me a 559 or worse, or the QSB is getting bad I want to give them a few more dB to work with.  

I've written before that QRP operators can be compared to certain persons with dietary habits.  Sometimes vegetarians will eat dairy but if your vegan then you're abstain from anything that didn't grow from a root.  Well I'm more of a QRP vegetarian who will occasionally put a slice of bacon on my sandwich if I think it will improve the taste.  I'm certainly no vegan when it comes to operating QRP alone.   I've used my TenTec Eagle and TenTec C21 to go beyond 5w when the mood struck and in the case of SSB I've rarely operated at QRP levels with success so there I'm usually running well over QRP levels but I'd pretty much stuck to QRP for CW until recently.

Elecraft PXA100

Elecraft makes some very elegant equipment.  The KX3 by itself, running on internal batteries and with a built-in auto-tuner is an amazingly portable and full featured QRP rig.  With the newest version of firmware (MCU 2.70 / DSP 1.49, 2-27-2017) the KX3 will produce up to 15 watts of output on 80m, 40m and 20m when used with an external 13.8v power source, but if you want more than that you need an external amplifier.

I've been reading lots about the Hardrock 50 external amp and had even bid on a couple of Ten Tec 405 QRP amplifiers (which I lost) recently.  The Hardrock 50 was compelling for the price because it could be built with a full QSK option, whereas the old TenTec 405 did not have a full break in option but both would get my output up to 50 watts which is about 3-5 dB more output than the KX3 on it's own. 

But my normal operating mode is to begin at QRP and if that's insufficient I turn up my power.  In the case of most external amplifiers I would be over driving them if I kept the KX3 at 5 watts input to the amp.  It would require dropping my KX3 input power to the amp and fiddle with the output until I was at the power level I wanted.

On the other hand, the Elecraft PXA100 is fully integrated with the KX3 and I can simply turn up the power knob of the KX3 and when the power exceeds what the KX3 is capable of on its own the PXA100 electronics take care of adjusting the KX3's input into the amp to give me a smooth power output up to 100 watts.  Additionally, when using the internal tuner option with PXA100 I can use two antenna outputs from the PXA100 and switch between them using the ANT button on the KX3 while the PXA100 tuner maintains independent tune memories for each antenna. It is a very slick package but an expensive one.  Purchasing a used KX3 and PXA100 together puts you well over the $2k mark which you can certainly find more full featured 100w desk radios in that price.  So for price conscious hams this is not a sensible option.  I won't argue that this makes sense from a financial aspect, but I did it anyway.  Given the vibrant used market for ham equipment I wouldn't pay new prices for these but it still comes out to be a pricey desk rig even when purchased used.

OK, back to the PXA100.  One absolutely brilliant aspect of the PXA100 when using the internal tuner option is that its tuner seems every bit as good as the KX3's internal tuner.  I think it will tune a spoon on 160m (admittedly I haven't tried that).  It has no trouble tuning my ladder line fed attic Doublet which has some serious impedance mismatches on certain bands, so being able to quickly switch between my attic doublet and my outdoor Windom has been a real boon that I don't think other desk rigs can match with their internal tuners.  I could be wrong, but Elecraft's tuners and super fast matching algorithms are pretty much legendary in the industry.

Another nice thing about the KX3/PXA100 combo is that full break-in QSK is maintained and there are no fans. My shack stays very quiet (I hate fans).  The amp has a massive finned heat sink on top that while getting quite warm to the touch has not become overheated even on extended transmissions at 100w into non-resonant loads.  I still haven't delved into digital modes but I'm confident that while the KX3 struggles to maintain its cool when used for full cycle modes at 5w and above, when used with the PXA100 this combo avoids that problem because the KX3 is only running between 2-3w intput into the amp and can dissipate its heat at that level with no problem.

So for the past week I've been using this combo and I'm quite pleased.

Here is a video that I made today in a contact on 30m where I started at 5w and moved up to 25w and switched antennas during the QSO.

So lower your power and raise your expectations, but when expectations fail, use an amp

Richard AA4OO
http://hamradioqrp.com

Non-resonant versus resonant antenna for receive only use

Well... that's not what I expected

I've been playing around with my SDRPlay and have been thrilled with its sensitivity when connected to my attic antenna.  My attic antenna is a 68 foot doublet that weaves around my attic and is fed with 450 ohm ladder line.  I use a 1:1 balun connected to the ladder line and a short run of coax with the RF-front-end-protection  to feed my SDR.  

My Doublet antenna is not resonant on any ham band and requires matching to bring the impedance in line with something my transceiver wants to transmit into.

My outdoor antenna is an 80m OCF Dipole (aka Windom) in the 1/3 configuration, meaning that the short side of the dipole is 1/3 the length of the long side.  Its been a good performer for me and is resonant on 80m, 40m, 20m, 17m, 12m and 10m .  While using the indoor Doublet antenna as a receive antenna for the SDR (with front-end protection and a relay to switch out the SDR during transmit) I use the Windom connected to my transceiver.

This configuration has worked well and the SDR feeding HDSDR as a panadapter has been a real boon to finding stations quickly as well as being a wideband audio feed to CWSkimmer.

HDSDR fed by my SDRPlay

For grins I wondered how much better the Windom would be as a receive antenna for the SDR on the resonant Ham bands... Well it was between 6dB to 10dB down on reception on most bands when used with my SDR.  I tested this by alternately connecting the Windom and the Doublet to the SDR for repeated tests.

This doesn't make sense to me.  I assumed that a resonant antenna (and one that's much longer) would be a better antenna than the Doublet for the SDR but it's not working that way in my case.  

When I use the Doublet with the transceiver it is used with an autotuner.  In general my A/B tests using my transceiver between the Doublet and the Windom are about 3dB to 6dB weaker for the Doublet on receive but I often get better RBN signal reports using the Doublet by a few dB on transmit.

I'm really perplexed.  I expected the Windom to be a better receive antenna for the SDR.

I have a lot more to learn about antennas.

That's all for now...

So lower your power and raise your expectations

Richard, AA4OO

http://hamradioqrp.com

Spruce up a basic transceiver with an SDR

Using SDRPlay as a panadapter for the Ten-Tec Eagle

SDRPlay produces a nice middle of the line Software Defined Radio (SDR)

SDRs are a lot of fun to play with simply as broad band receivers.  I've used the regenerative receiver I built for some shortwave listening but that isn't even in the same universe of capability as a good software defined receiver.  SDRPlay is significantly better than what you'll find with simple RTL-SDR dongles but costs around $150 as compared to $25 for the dongles.  Since there are other reviews of SDRPlay out there so I won't go into details other than to mention that it offers continuous coverage from 10kHz to 2 GHz, has a 12-bit ADC rather than the 8-bit ADCs in dongles and provides up to 10 MHz bandwidth at a time.

One of the ADCs on the SDRPlay board

Using SDRPlay as a panadapter

In addition to using SDRPlay as an incredible broadband receiver, I wanted to use it as a panadapter for my Ten-Tec Eagle.  My Eagle is an early run model that does not provide an IF output or the circuitry to drive a panadapter.  It is possible to splice into the Low Pass filter line of the Eagle with some minor surgery to provide receive antenna input to the SDR but if I did that the SDR could only be used when the radio is turned on and its receive bandwidth is limited to the Low Pass filter switched in the Eagle at the time.  I didn't want that limitation or to have to keep switching the receiver's antenna inputs when I switched back and forth.  So I decided to keep the receive antenna external from the Eagle. 

But to do that I had to protect the front end of the SDR from the transmitter or it would be overloaded and destroyed.

WARNING: Input to the SDRPlay cannot exceed 0dBm without causing damage so be very careful when using your SDR with a transmitter

Front end protection

There are a number of designs for protecting receivers from overload used in multi-station events.  A common circuit is a bulb with two reversed diodes to shunt off extra energy.

I considered building one but when I priced out the parts and a metal enclosure I decided to just buy one.  I found one made by a ham in Slovenia (Aleš S59MA) that was reasonably priced and available on a famous auction site.

This allows me to use a receive antenna connected to the SDR with this protector in-line while I transmit on my outdoor antenna.

That works but the panadapter display really lights up when I transmit and while the specs say everything should be safe I'll feel better switching out the receive antenna on transmit.  I ordered a kit from OK1RP.  The kit requires some extra parts (2x2N2222 transistors and 4x4k7 resistors) to complete that most hams already have but my junk box is pretty shallow so I ordered the 2N2222 transistors from DigiKey.  The part specs are listed on OK1RP's page.

Simple receiver switching circuit can be built in 30 minutes

Note that this relay defaults to the receiver output being switched off when there's no power supplied to the relay.  The relays are so quiet I have to hold it up to my ear to hear it operate.

A bit of extra armor

The SDRPlay RSP1 comes in an unshielded plastic enclosure but I wanted to keep noise and near-field RF at bay.  So I added layer of protection from near field RF by putting it in an aluminum enclosure.  

Original plastic enclosure to the right

$20 aluminum enclosure

Making it work as a panadapter

Bring in the CAT - Computer Aided Transceiver 

SDRPlay feeds IF/IQ to software defined receivers like HDSDR. That provides a way to view and listen to all that can be received by the SDR, not just ham bands but any signal from 10kHz up to 2GHz.  But to use it as a panadapter for my Eagle I needed a way to control both HDSDR and my transceiver.

OmniRig is CAT control software that simplifies software control of receivers and transceivers.  It communicates through COM ports.  The Eagle has a USB to serial interface that uses a hardware COM port but HDSDR is software with no physical COM port.  HDSDR can be CAT controlled as well using either a Virtual COM port or DDE interface.  

So I created a Virtual serial port using VSPE software to create a virtual serial port "pair".  The first COM port is considered the INPUT from HDSDR.  The second pair of the COM ports is the OUTPUT to be used by the listening application (OmniRig).  OmniRig needs to know the "type" of "radio" it's talking to.  HDSDR uses the Kenwood CAT protocol so I chose Kenwood when configuring OmniRig.

HDSDR also provides the ability to synchronize the CAT traffic between two OmniRig connected radios.  This ability to sync two rigs is the key to making this work.  It syncs with the transceiver so that changes made in HDSR are sent via CAT control to the Eagle and vice-versa.

SDRs have huge bandwidth

SDRPlay can send up 10MHz of bandwidth to the SDR software receiver.  That much bandwidth isn't terribly useful other than at the macro scale of seeing if there are signals.  More typically I set the IF bandwidth to 2MHz which easily covers an entire ham band and use the zoom control in HDSR to narrow it even further.  What's further, I can feed IF audio from what's being received by the SDR to programs such as CWSkimmer.  CWSkimmer has an interface for the SoftRock SDR to receive up to 192kHz.  The issue was how to get the audio output from HDSDR to the CWSkimmer application.

To accomplish that I use VB-Audio virtual audio cable to route 192kHz bandwidth of audio from HDSDR to CWSkimmer's SoftRock IF/IQ interface. CWSkimmer also has an OmniRig interface so that is configured to read the second virtual COM port pair from HDSDR.  Thus I can control the Eagle from either HDSDR or from CWSkimmer and vice-versa, changing the VFO on the Eagle commands HDSDR and thus CWSkimmer to follow it.

It's a thing of beauty.

Video Demonstration

That's all for now

So lower your power and raise your expectations

Richard AA4OO

http://hamradioqrp.com

All keyed up

Sometimes I can't decide which CW key to use

As I've been posting videos I've received requests to display the translation of the CW as it's received and sent.  I have tried narrating a bit in some of the videos but that doesn't cut it.  So I did this little video test to see how FLDIGI would translate the code and capture that translation from my computer screen then display it in the video at the bottom.

It worked reasonably well for this short message but I think when I have my next video QSO I'll need to capture the entire FLDIGI translation window and include it as a video insert.  This was just a test for me to see how to use iMovie to overlay a video within a video.

Hopefully you'll enjoy this little test... No QSO, just me rotating sending different words across each type of key I had on the desk.

That's all for now

So lower your power and raise your expectations

72/73

Richard AA4OO

http://hamradioqrp.com

First Down Under contact

The bands aren't dead yet

Still relatively new to the HF CW scene I have a bit over 1400 contacts and I've found that more than half my calls now are with stations I've previously worked.  Don't get me wrong, that's not a problem, and I enjoy the camaraderie of frequent chats.  But even so, I want to expand my reach and begin working some DX stations on a more regular basis.

My 80m OCF Dipole (Windom) is resonant (below 2:1 SWR) on 80m, 40m, 20m, 17m, 12m, 10m and 6m.  So I've been spending time on 17 and 10 meters, trying to work beyond my normal circle of CW contacts.  Yes the solar cycle is definitely on the wane but I am pulling in a few contacts on 17m and each one is a new call for me. 

This afternoon, after about 10 minutes of fruitless calling on 18.080 I spun the VFO and behold, I heard a VK station (VK2DX) calling on 18.074.  I had to send my call a few times but he copied me and we exchanged reports and names.  

A QSO with Australia, I was psyched!  

My first VK contact with VK2DX in Australia -- 9636 miles

RF is indeed magic

Now for you old timers with thousands of contacts in the log and dozens of VK's in the log you're thinking no big deal, but if you're new to this and started on the downside of the solar cycle you may be thinking, like me, that 10,000 mile DX is rarer than hens teeth.  

So, if you're still new to HF and you think you'll need to wait until the solar cycle 25 for a CW contact with the other side of the world, because your using a low power radio and a wire antenna; just keep plugging along and you'll probably find the RF pixies are smiling at you.

So give those higher frequencies a shot even when they sound dead and RBN shows nary a spot.

EDIT:
Just checked my RBN spot page (spots for AA4OO) and I did indeed get picked up by a RBN station in Australia but on 20m rather than 17m.  So maybe it's not so surprising that I was able to work him today.  I need to pay more attention to my RBN spots.

73/72

Richard, AA4OO

http://hamradioqrp.com

Over the waterfall

Situational awareness 

After reading all the hoopla surrounding the ICOM 7300 with its nice touch screen and waterfall/spectrum display, it got me to thinking that I was missing out on something.

HDSDR display on 40m tonight

When I first got my Electraft KX3 I hooked it up to HDSDR running on my PC and played around with the panadapter display. I admit it is very cool to visualize signals on the band.  That 44kHz view shown in HDSDR covers a large portion of the commonly used CW band segments.  I'd click on a signal and bam there it was tuned right in. I'd listen for a while and click another, and another. It was like shooting fish in a barrel (although I admit I've never tried shooting fish in a barrel).  After a while the novelty wore off and I went back to just tuning around the band.

There seemed to be more magic in stumbling upon someone calling CQ than looking at the bandscope and choosing the strongest signal.

Taking it all in

But I'm starting, just starting, to be more interested in working DX and potentially doing some contesting this year and for that I can definitely see an advantage to using a panadapter with the radio to see what's around me at a glance. 

However, as you may have read, I prefer using my TenTec Eagle over my KX3 at the desk.  But my Eagle is an older model made before the panadapter output came standard and even before they offered a provision for hooking one up.

My friend AA4XX uses a separate SDR with a input splitter and a DX Engineering RTR-1A receive interface to switch the SDR out of the chain when transmiting. The advantage of his solution is that it works with any transceiver but the relay in that unit is quite noisy and I appreciate the quiet full QSK offered by my radios.

Using a SDR as a receiver
protected during transmit by a DX-Engineering RTR-1A

One option for an older Eagle like mine is to take the input for a SDR straight from the input of the Low Pass Filter. That line is switched out on transmit by the Eagle to protect its own receiver so no separate switching circuit is required.  There's a tiny coax that would need to be spliced into which Paul assures me is doable mod with the right equipment. I would still need to buy an external SDR and it should be a good quality one or there's little point.

So I've been operating my KX3 at the desk this week using its built in RX/IQ to feed HDSDR to see if I like the idea enough to spend the money on doing this for the Eagle.  It's been over a year since I had this setup and I've switched computers so I had to go throuth the setup again and I thought it was worth documenting in case there are others that want to do this with their KX3's.

HDSDR is a really nicely done program, doubly so because it's free. It can be fed from an SDR or from your sound card. It interfaces to the control the radio using Omni-rig software.

So the setup is in two parts, configuring Omni-rig and secondly configuring four your sound card.

Omni-rig

Omni-rig is freeware CAT control software.  In the case of the KX3 it interfaces using the USB control cable that comes with the KX3.  Simply choose the serial port that your computer assigned to the KX3 and match the baud rate settings in the KX3. 

omni-rig settings for my KX3

HDSDR configuration

Download HDSR.

Configuration for the KX3 is mostly straightforward. Click the options button HDSDR.  The only part that trips me up each time is configuring the CW offset in [RF Front end configuration]. Make note of your side tone Hz setting on your KX3 by pressing and holding the CMP/PITCH button. Also be sure that you haven't inadvertently set CW reverse on some bands because that will really have you pulling your hair out as you try and figure out why the signals line up on some bands but not others.

So to set your CW offset correctly put your sidetone Hz as a negative number in CW_L and subtract your sidetone from 1000 Hz and put that value in CW_U as shown below.  Everything else should be set as shown.

RF-front end configuration screen

Choose the Omni-rig configuration as shown below to match your station settings.

CAT to radio settings

Lastly make sure RX/IQ output is turned on in your KX3 by setting MENU: RX I/Q to ON.  Run the KX3 RX/IQ cable to your mic input on your PC.  Then  choose your sound card bandwidth setting in HDSDR.  I'm not sure what the available bandwidth from the KX3 RX/IQ actually is but on all the PCs I've tried it with a bandwidth of 44100 seems to work best.

soundcard bandwidth

That's basically all there is to it. If you see a bunch of "lines" in the waterfall display that do not correspond to signals and if there is a thick signal line right at your input frequency then your station grounding is insufficient.  See my article on grounding.  When I first set this up I had insufficient station grounding and saw a lot of artifacts in HDSDR that were due to bad grounding between my PC and the radio.  So it will let you know if you have grounding problems.

So if you're lusting after that pretty display in the IC-7300 and don't want to shell out for another shiny toy, you can at least get a pretty display out of your KX3 without buying a PX3.  Just use HDSDR and the built-in RX/IQ.


That's all for now...

So lower your power and see the signals in technicolor

72/73
Richard AA4OO

http://hamradioqrp.com

Hard fought SKCC QSO using the Ten-Tec Century/21

Sometimes you need to move your QSO

My ever changing station configuration
Left to right - Elecraft KX3, Ten-Tec Century/21 with Ten-Tec Eagle on top, the MFJ 493 keyer on the right
4 keys - Navy Flameproof, Kent Hand Key, Vibroplex Bug, N3ZN QRP paddle
The Elecraft AF1 audio filter is sitting unused in front of the Century/21

After starting our QSO the ARRL QST program started right on top of us causing QRM that forced us to move to another frequency

My old Ten-Tec Century/21 is a lot of fun to use and its direct conversion receiver makes CW sound beautiful. But the frequency dial is fairly imprecise so when I asked the station to QSY up 1kHz finding him again was a bit of a challenge.  When I heard him I had to zero-beat him again to make sure I was on the correct side of the direct conversion receivers passband.

Enjoy the QSO and the QRM dodging...

Shooting this video

This video was a bit harder to shoot than what I normally do.  I usually place my camera to one side but I wanted to use my fisheye lens and shoot the QSO from above.  

While shooting I was straddling the tripod with the camera right in front of my face so I was reaching around the tripod to use my keys and get to my keyboard for logging.  It was a bit awkward, and in the video you'll see me bump the VFO while trying to operate the radio because I couldn't really see what I was doing.  It's always fun to add a level of difficulty while making these videos.

That's all for now...

So lower your power and raise your expectations

72/73

Richard AA4OO

http://hamradioqrp.com