Posted on October 24, 2017
There are several things that will be big benefits from Son of Mod Bob:
- I will remove the center element which is way to close to my 40M vertical array. This will eliminate the distorted 40M pattern
- I will no longer turn on the Trane HVAC when I transmit at full power
- I get three antennas in one, a half square on 40, Inverted L on 160 and grounded loop on 80. 30 will be great on all three of these configurations
- I will have an automated remote antenna tuner. I never got around to mounting stepper motors on my Palstar BT1500A, which is a good thing. My uRAT prototype becomes my remote tuner
- I can sell the BT1500A
- Almost all of the wiring is already in place, meaning this is a one day project. I have 96 buried radials and tie points and even several wires that can be used as a solid grounded loop connection (instead of counting on buried radials that could be compromised over the years. I do have gophers under the radials
Its always good to assess the pros and cons of a project. There are absolutely Zero down sides – which is always nice – when you do a benefit analysis sometimes there are trade offs.
Pacificon and this blog have sparked this next phase of my low band antenna pursuit. The Mod Bob was up about 10 months, and I learned a lot, and now I take the next step.
A little creativity goes a long way!
Posted on October 24, 2017
Son of Mod Bob!
Page 14-7 from the ARRL ON4UN Lowband DX-ing book
Chapter 14 in the ON4UN Lowband DX-ing book is a gem. John shows how to take a 40M half square and feed it just like the grounded loop – and where it then is a close array on 80M with gain. The dimensions in the book call for 72′ wide and 34′ tall. I might drop the height down to 34′ – maybe 35′ since I only have 70′ max width to play with. I doubt it really matters.
The feed and switching is like what I mentioned in one of the last posts:
if I add an Inverted L in parallel with the element on the left and the top wire, I get the best 160M performance where the wires fit in my back yard:
I will have to build a fairly simple switching scheme . .
There is gain on 80M now – “close enough” to what John documents in his FB book . . .
On 40M, I would switch the bottom wire out and its a half square . . .
On 30M its close – but the 40M half square is kind to this band
So, besides my u.RAT remote L-C tuner, I would have an Inverted L parallel to the half square – and would need a high power relay to switch from one to the other. I would also need another relay to switch the right side to be a half square (un-ground the grounded loop), or ground the loop.
Because I have been building maker stuff, I’m more than happy to add couple relays and the u.RAT and make this project sing!
Posted on October 23, 2017
I would guess that the Inverted L and Grounded Loop would be about the same on 160M.
It has more gain and a better take off angle on 80M
It has about the same gain as the Inverted L, but better take off angle. Its a moot point though since I have 40M already covered
Same on 30M
I am not showing the Inverted U in the plots because the only band where the Inverted U looks good is on 40M – where it shows as a half square – which is 4.1 dBi gain. This is actually useful, because the plot of the broadside gain for the DX Engineering DV-40-P is only 1 dBi or so.
So I think I am going to use my Mod Bob end supports and convert it to a switchable grounded loop and Inverted U. This combination gives at least as good – or better – gain and take off angle than the Inverted L.
Since DX-ing has been abysmally boring lately – I’m glad I now have an interesting antenna project – and about 1 month before it starts raining in Northern California.
Posted on October 23, 2017
The feed is a simple L-C circuit, left, and the antenna can be switched between being an Inverted U or Grounded Loop, right
Jan, OM2XW, wrote and reminded me of an antenna that is in the ON4UN Lowband Book, and one I have never tried. AA7OK has a VERY nice write up with great references at his web site – http://litlisten.com/aok/ As I understand it – Jack Belrose, VE2CV originally proposed this antenna some years ago. I will look at the ON4UN book again when I get home tonight.
Thanks to Jan, I am now seriously considering an antenna that will very easily replace the Mod Bob, and the only thing I need to do is take down the center wire support (a big plus), and move the feed and matching unit farther away from the house and my Array Solutions switch (another big plus). The first plus is that it become s a simpler configuration, and more importantly, the center elements and feed of the Mod Bob are too close to the house, and when I transmit at full steam, the Trane heater turns on! In the past, when I had the feed for my single vertical, I had no such interference.
I will do some modeling and also check it against the Inverted L, which is even simpler yet, but one thing for sure – I will be replacing the Palstar BT1500A with my “u.RAT” remote tuner at the base. I have a Comet vacuum variable capacitor, and might even try experimenting with that.
The KPOD and the Raspberry Pi are in the shack . . .
An additional wire would be used to switch the far end for the Inverted U / Grounded Loop. The best thing is – I have everything in place, and this will be a very nice weekend project. I can even get the control box and u.RAT ready – knowing that the actual components at the base of the vertical with the feed could be any combination of Land C and air variable vs. vacuum variable.
Posted on October 23, 2017
Inverted U on 160, 80 and 30 and half square on 40M
Just for laughs, lets compare three antennas that I could have – against what I have now – the “Mod Bob”.
An Inverted L would be MUCH better than the Mod Bob. Its something I need to consider – because I could use the u.RAT to tune it.
On 80M, the Mod Bob seems to have the best take off angle by far, but the gain (loss) looks pretty bad.
On 40M, the inverted U is a half square and it is best out of the three
I had my friend Andreas, N6NU, model the Mod Bob vs. the Inverted L, and on 160M and 80M, the Inverted L is a clear winner.
His models are a little different than mine, but I needed to have this “peer review”.
The Mod Bob seemed to perform better than the models suggest, which show the Mod Bob as a cloud warmer. However, not all DX angles are low, especially during sunrise and sometimes at sunset.
I wish I could do an A-B test, but I can’t.
I think it’s time to convert the Mod Bob to an Inverted L, because 160M is the one band I really need, and both his model and mine match and tell the same story. I will use the u.RAT to control the tuning now that it will be an unbalanced vertical feed.
I do remember that when I had a Cushcraft MA160v that I feed it with just one variable capacitor and that’s all it took to tune it on 160M. I did this to avoid tuning the stinger at the top.
Ok, lesson to remember – ask a friend to peer review your antenna modeling!
Posted on October 22, 2017
Its amazing how different this weekend is from last.
Fall colors in Orinda are mostly from landscape trees – where people planted trees that would give color.
Chinese pistachio trees are popular and have all of the fall colors in one tree
Because we have two Japanese maples that are at the end of their life – I planted two Nyssum Salvatica trees – or Tupelo. They are perfect for our area.
I planted the second one this morning and the hole was deep and a lot of work. This one has crimson and orange fall colors – the other one seems to be mostly crimson.
This Spring, Summer, and now Fall have been three seasons where I revamped our front yard and it looks great going into Fall and Winter.
Posted on October 22, 2017
Autumn colors are fleeting . . . as is life . . .
It was fun presenting at Pacificon in the Antenna Seminar, and for the first time in more than 10 years of presenting there, I arrived early and stayed for the entire seminar. Its always interesting to see how we all just keep aging – at Pacificon and at Visalia.
The presenters included several people whom I’ve presented with over many years, the one I miss is Dean Straw, N6BV, and who has been a real mentor – from when I first got back into ham radio in 2001 until the last time I saw Dean – a few years ago at Visalia. I haven’t seen Dean in person for a while.
This was a “tongue in cheek” photo op – where I had special “Team HFTA” caps made for Dean and I – Visalia 2013
I staged a photo of Dean and I – with Dean “presenting” my Honor Roll plaque to me. The “inside joke” was that Dean’s fantastic HFTA program was the software and technique that helped me (literally) get “over the hump” and make Honor Roll from my Orinda QTH – and where my station and antennas are down in a bowl. Dean appreciated the gesture, and we had fun staging this. It ended up in QST and on several DX web sites.
Carl Smith, N4AA just passed at age 77, and I had been a long time subscriber to his wonderful DX Magazine. VK0EK had an issue dedicated to our DX-pedition, and now that Carl is SK, I reflect on my DX-ing years going back 16 years. It has made me think of all of the characters who made DX-ing what it was along those years. I remember working Chuck Brady, N4BQW on many semi rare and even rare locations.
VK0EK at the 2017 Dayton DX Dinner
Rather than get morose about how time marches forward and how things have changed (for better or worse), I’ve been thinking that there are “eras” that occur with anything that you participate in for any length of time. When I was WN2QHN and WA2QHN, I was only active from 1973 – 1977, and so being a ham as a teen was a real little “blip” in time – so much so it was almost inconsequential.
When I got back into ham radio in 2001 – I picked up an Icom 756ProII, which was a revolutionary new rig. I then moved to a Ten Tec Orion I and then II:
Ten Tec is pretty much dead, but in their zenith, they created one of my very favorite rigs. There are days I still wish I had mine.
Elecraft beat Ten Tec at its own game, and I switched back in 2008 if I remember right
I have an Elecraft KPA-500 in the closet and use my new SPE Expert 1.3K FA amplifier instead. It will be the very last amplifier that I own – once I work the last 12 on 160M and last 2 for Top of DXCC Honor Roll – I will sell the SPE and go back to the KPA-500
There are several threads in my ham radio epoch. There was the WA2QHN years, and now the more modern 2001 – 2017 period. This more modern period started when my oldest boy was 10 and youngest was 6. They are now 26 and 22, which is hard to believe.
The thing that helps me still feel young at heart is that technology keeps changing – and I am already behind. Flex Radio is the new shiny penny, but since I am at the end of my DXCC chase, I am not motivated to jump to the new shiny penny. In fact, I am much more likely to head backward to simpler home brewed rigs – especially if they are Arduino and or Raspberry Pi based. I am sure that soon enough, we will be assembling radios from such boards and they will be very configurable and customiz-able. With FT8, and whatever follows it – we also will no longer need 1500 watts.
There are DX-pedition teams that will come and go – some mega DX-peditioners will retire soon – ending that thread in my “epoch”, and I guess my epoch will be defined as closed when I finish my DXCC counters. I expect that will be around 2020, so I will have worked 19 years on it. That’s how long the activations were between Heard Island – VK0IR and VK0EK, and while it was theoretically possible for me to have completed DXCC Top of Honor Roll in 2016 – with VK0EK (because I missed the two that I need), if I make Top of Honor Roll by 2020 I will feel like that is well within “fast”. For some its a lifetime pursuit.
There is overlap – the end of my DXCC epoch is so slow – almost painfully so – that I’ve taken up with the new Maker Ham stuff – and at Pacificon, that went over VERY well. It was encouraging to see that so many old dawgs are as interested in the new tricks that we have at our fingertips.
Time waits for no man – onward!