Hi Everyone:
As some of you know, my AM operation has
been off for some time. I would like to get
it running again because I really think
(for me anyway) this is where the real fun
is.
Hi Everyone:
As some of you know, my AM operation has
been off for some time. I would like to get
it running again because I really think
(for me anyway) this is where the real fun
is.
The best outside AM Part 15 transmitting
antenna I had was a (slightly less than
3 meter) ground mounted copper pole
with a gigantic 4 radial top hat. Each top
hat radial was about 2 feet long.
The ground system was 16 radials buried
in the back yard.
The transmitter was an SS-Tran. Instead of
using the conventional coil approach, I did
things differently. I disconnected the internal
coils inside the SS-Tran and put in a much
larger coil. This coil was on the outside of the
SS-tran but was electrically connected on the
inside. It had a lot of taps and could be tuned
with a sliding ferrite (?) bar. I don't know if
the bar was really made from ferrite, though.
I just pulled it out of an old portable radio.
Audio and power went out to the transmitter
from the house.
As some of you know, my system changed
frequency at local sunset from 1690 kHz to
1700 kHz and back to 1690 again at local
sunrise. This was done with a timer in the
house, which actuated a power supply at
the correct time to power a relay out in
the transmitter to change from 1690 to
1700 and visa versa. This was done because
1690 was the clearest channel during the
day, but at night 1700 was the most vacant.
Local tests showed that the 1690 signal was
stronger than the 1700. In order to make 1700
stronger, I would have needed
a relay to change the tuning coil taps and I never
got that far.
Anyway, because of other things that were going on
(life stuff), my system was never really weather proofed.
It worked great at first. My most loyal listener (another ham
and local broadcast engineer) could drive around the center
of town and listen on his car radio. As he approached large
shopping centers, the signal improved greatly. We think
this was due to the fact that all the buildings (some more
than a mile away) were providing many good ground
returns. Because of intermittent performance, I dismantled
the system a year or two ago. To tell the truth, I can't
even remember when I shut 1690/1700 off.
Fast forward to now. I really want to get this thing back on
the air. I have wanted to for a long time, but life keeps
getting in the way.
There has been discussion about the legality of top hats.
I understand both the pros and cons. Just to be safe,
I do not want to use a top hat.
However, there has recently been discussion about fat
antennas. Downspout material has been mentioned.
That sounds interesting. Also, it has been said on
this board that an antenna that is fatter on top
will work better. I have a few ideas in mind, such
as using 4 fed copper poles that are joined together on the
bottom, and are spread apart on top. On top the poles
would be electrically joined together by something.
I'm not sure by what. But it seems this would provide
capacitance at the top without being a top hat. Also,
I'm not sure how far apart the poles would be on
top.
Another idea goes back to just a single copper pole
for the antenna. The idea is to have radials coming off the
antenna part way down one copper pole. The radials
would be supported by wires going to the top of the
pole and also supported by wires going down the pole
some ways. All of this would be electrically connected.
Again, it would not be a top hat. It would sort of look
like a diamond configuration and the antenna would
be fat on top and thin on the bottom. This second
idea, like the first, would be to pull the antenna current
up to the top of the stick.
So, if you guys have gotten this far, then maybe you
could tell me what you think. You guys are the
best there is in the Part 15 universe as far as I'm
concerned. If you feel like commenting on this,
that would be great.
Also, my other Part 15 projects, (the 13.560 MHz
transmitter, the Gates board restoration, and the
solar powered repeater) are still cooking on the
stove, although very slowly.
Best Wishes,
Bruce, MICRO1690/1700
I recall the sliding bar coil thing ... there was a lot of commentary. Hey, whatever works!! It kind of reminds me of North Country's VARIOMETER.
I can't really comment on diamond monopoles other than my general research which showed they once enjoyed some popularity, but precious few are in operation today. There wasn't and isn't enough evidence to say they do any better than a straight monopole, or as compared to using capacitive hats, which is one reason they kind of died out. I have other ideas I want to try, so it's unlikely, based on my current findings, that I personally will experiment with them, but I don't want to deter you.
Your idea about multiple pipes spread out at the top is intriguing, but I wonder if it complies, or would it be considered an array where each element has to be counted as part of the total 3m length?
Myself, I'm still intrigued by magnetic antennas because of ease of loading and less space requirement. Reminds me I should get back to working the formulas.
Thank you for your comments.
Your question about the different
antenna pipes adding up to be
more than 3 meters is a valid question.
I can see it both ways, it's OK or it's not
OK. Fortunately, for me, if I ever get this
AM transmitter back on, I will be trying
many different things. My operation is
very low key, because I really don't have
any programming to offer. If I did, I would
save up for one of the type accepted AM
transmitters.
By the way, your website is wonderful! I
haven't had a chance to listen to your
stream yet, but I am going to very soon.
I am familiar with North Country Radio, but
I don't remember seeing that variometer
picture so thanks for cluing me in.
I once built a variometer for my Part 15 AM
operation. (It didn't look as good as the
one in the picture.) The variometer I made
did tune, but I don't think it was very high
Q. If I was going to do it again, I would
change some things.
I also have a North Country Radio MPX-96
FM transmitter. I run it in mono at the
Part 15.239 level. I can tell you more about
the MPX-96 if you are interested.
Well, thanks again. It's late here in Connecticut.
A few chores and it will be time for some ZZZZZs.
I think I'll listen to your station right now!
Best Wishes
Bruce, MICRO1690/1700
Say, thanks ... but I hope you weren't listening when iTunes auto-played a mixdown from a Christmas benefit concert which interrupted the running program.
That's what I get for trying to edit and mix down a set of recordings on the same computer where I'm broadcasting my stream. I've tried everything, but I've failed to reconnect my backup broadcast computer through the main via Ethernet ... it keeps telling me Ethernet has a self-assigned IP address and can't connect to the Internet 🙁
I generally do a couple back-to-back Sherlock Holmes mysteries at 9:00pm PST on Mondays, between the playlists of all local musicians and the Classic Jazz set at 10:00pm PST.
I do a lot of recording of local music, sometimes I air live broadcasts from local venues and record (archive turned on) at the same time. For me, live music is a big deal around here. I'm also working an idea script for a pilot I call "Charlie Suspenders", local humorous wisdom from a fictitious old islander.
Here's a Halloween Intro from last year, my first on-air attempt. I thought it worked pretty well, but I'll never sound like that homeless guy 😉 What say?
Hi Ken!
Your station sounds great! I listened from
midnight to 1:30 AM my time. (Connecticut,
EST.) I heard the Sherlock Holmes episode
(radio drama is always fun) and the jazz.
Jazz has a very special meaning in our family.
My son is a jazz musician and I used to be
a pretty good jazz piano player years ago.
Anyway, you have another listener!
Great job!
Best Wishes!
Bruce, MICRO1690/1700
Ken! Nice job with the Halloween
intro! Aside from the creepy feel
of the production work you did,
I also got a real feeling of being
out in the miserable cold rain when
you opened the door and looked out.
I'm glad I'm in here.
Best Wishes,
Bruce, MICRO1690/1700
Hi Bruce MICRO1700:
I think the multi-pipe transmitter you are describing is a "cage-monopole" type antenna, and I have an experimental one right now operating at 107.1 FM with 4-elements.
According to some literature each element of a cage monopole added in parallel does not increase the wavelength of the antenna, but it serves to lower the impedance, which of course requires re-tuning.
I also notice that the FCC rules for AM and FM band do not limit the number of "elements" an antenna can employ. This becomes significant because in some bands the number of transmitting antenna "elements" are specified, as for example 15.235 Operation in the band 49.82-49.90mHz (3) The antenna shall be a single element, etc.
Based on those observations I take the position that adding parallel elements to an AM or FM transmit antenna does not exceed the rules.
By the way, one thing I notice with my 4-element cage-monopole is that the FM signal is very stable indoors, no interference is caused by my moving around within the field.
Hi Carl!
I have been following your tests with the
cage monopole on the FM band.
Thank you for noticing the 49 MHz part
15 rule that stated that the antenna
has to be a "single element." Great point,
great reference! So one could infer that
at FM BCB lengths or AM BCB lengths,
a monopole made of different elements
next to each other is OK. The FCC does
not say that is isn't OK, on those bands.
But on 49 MHz, it is NOT OK. OK?
OK.
Bruce, MICRO1690/1700 (Actually AM is
not on the air, but might be if everything
works out OK.)
Bruce MICRO1700
One special thing I am looking forward to with your antenna experiment is what will happen because of the "wider at the top" aspect.
Do you know anything so far about what you expect to find? Is there a theory about "wider at the top?"
The inverted conical monopole has, for some time, been the concentrated area of research in broadband vertical antennas. Patents have been applied for and granted on the design. Here is the link to one such patent:
http://www.freepatentsonline.com/5216436.pdf
Shortwave and spread spectrum military communications have used these antennas for years.
What advantage is expected from the inverted conical monopole?
Not much else to say ... I'm inspired to get back into creating more custom SFX.
The research and development writings say that the primary advantage of the conical monopole is the broadband or wide pass-band characteristics of the antenna. The length and angle of the cone determine the operating impedance of the device. The geometric median diameter of the cone helps determine the bandwidth. These antennas are used primarily for multiple frequency shortwave broadcast and military spread spectrum data transmission where the object of the communications path is reception over the horizon (sky wave propagation). There have been several conical antenna designs over the years. Amateur Radio has used conical antennas for vhf and uhf for decades, as well as 10 through 20 meter SSB. Inverted conical antennas also exhibit increased efficiencies when designed for special service, supposedly due to the increase in radiation resistance. This helps to overcome, only slightly, ground losses. The inverted conical monopole still requires some kind of matched ground radial system to work properly.
From comments and references made so far, it would appear that the inverted cone monopole
A.) Offers a very wide bandwidth at HF (high frequencies), but by this we mean bandwidth over a wide-range of frequencies, far more than simply bandwidth on a single channel;
B.) I have seen nothing said about the expected near-ground or upward thrusted signal throw, that is, the "shape" of the pattern expected from an inverted cone monopole.
C.) Nothing has been said about use of the inverted cone monopole at MW frequencies, i.e., AM Band. Will there be an expected advantage on these low frequencies?