Modifying a TV “bunny ears” antenna for 2m and 70 cm use

Hey there! I haven’t been posting for a really, really, long time now. Been so busyyy~ T^T

On one of the amateur radio chat groups I am in, someone asked if they could make use of a TV “bunny ears” antenna for 2m and 70 use.

http://flowjournal.org/wp-content/uploads/2008/12/ill12.png

I was initially skeptical of the idea, and was wondering if the idea would actually work. Of course, what better way to find out than to actually modify one? So I went out and bought myself one, and got to work.

After calculating what the lengths of each “ear” should be, trimming them and taking more measurements, I wound up with this VSWR graph:

I obtained a VSWR of 1.3 on VHF and 1.5 on UHF! That ain’t bad at all, for such a quick modification! =D
So I decided to test it out by making some contacts. I was able to reach the repeater from my place, which is about 11.47 km away.

I was also able to make a contact with another ham on UHF, simplex.

So the antenna seems to be working fine so far! But in this state…

the antenna probably won’t last that long in the elements. =P
Let us make this into a more proper build! With a little help from my dad <3, here’s what I came up with:

I then mounted the antenna out of the window.

This is the final measured VSWR plot:

VSWR 1.2 on both frequencies! ^^

As you can see, modifying/making an antenna suitable for use on the ham bands is not a difficult task. This antenna “build” cost me about $10 SGD. Maybe one should try building and experimenting with antennas, and see what results they get, and make a few contacts with people on the air! There are many resources like the “Practical Antenna Handbook” by Joseph Carr and the “ARRL Antenna Book” which are comprehensive and handy guides, even for beginners.

Until next time! =)

Lucky Find! A Kenwood TS-670 Quad Band Transceiver

Hi there! If you reside in Singapore, you would be aware that at Sungei Road, lies a flea market, also known as the “Thieves Market”. Here’s how it looks like:

Taken from Wikipedia article: “Sungei Road”

Well I like to drop by there time to time. Who knows? One might find something quite interesting over there. That was the case for me when I made an interesting find over a month ago.

Being someone who is fascinated by electronics and radio, I would lookout for devices such as valve amplifiers and such. At the time, I was in need of a cheap microwave oven, so that I could re-use the high voltage transformer for a valve amplifier project. I scoured around, looking for one, but I didn’t find one (at least not for cheap! =P). Disappointed, I left the area. But as I did, my eyes lit up! Something interesting caught my attention! What could it be? This:

 

 

 

 

 

 

 

A Kenwood TS-670 Quad Bander! I knew I just had to grab it, and so I did (Impulse buying… That’s why I am broke! XD). The unit is in a very good shape when I got it. For something that could have been lying around in the flea market for at least a few days, it was relatively clean, scratch free and dust free, even inside!

Taking it to Blazer (Radio store), Mr Phua let me use his power supply, and we did the smoke test. It worked! I took it back home and verified that it could receive and transmit. I noticed though, that the dial is a little on the fritz now. I can get the frequency to go up, but when I spin the dial the opposite direction, the frequency still increments! Well, it is a small problem, and I’ll fix it when I have the time.

What surprised me is that the seller provided me with the instruction manual (albeit in Japanese), schematic diagrams and an external SWR/power meter to go along with it. All for $80 SGD. I will probably take it out on field day or one of our QSO nights.

Thanks for reading!

73,
Joyce (9V1AN)

RF Dummy Loads – Observations and experiments

Hi there! I have been busy and haven’t got the chance to post anything for quite a bit. Well, I’d like to share my observations that I made when I was experimenting with RF dummy loads. Loads and impedance matching itself is very interesting, but quite a broad field on their own, so more on that in future articles.

Well, a dummy load is meant to allow transmitters to perform on-air tests, simulating an antenna, without radiating much power out. A dummy load is essentially, made out of resistors. As you know, a perfectly matched dummy load would have its impedance match the transmitter’s. An ideal transmitter for amateur radio would have an output impedance of 50 ohms, with no imaginary component (50 + j0).

I have been asked questions like: “Hey! Can I use wire-wound resistors for use as an RF dummy load?”. So, to answer that, I’ll be showing you my observations with various RF dummy loads. Let us start with a commercial RF dummy load. Pictured here is one that I use for quick tests.

 

 

 

 

 

 

 

 

And here’s the corresponding measurement data:

I’m sorry for the lower resolution on this image. For most of the amateur frequencies, say up to 500 MHz, the VSWR is lower than 1.5:1. That’s quite okay! Now let us look at another load. This time, it was constructed by Mr Jeff, out of axial resistors. Here’s it is:

 

 

 

 

 

 

And of course, the measurement data.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As you can see, the VSWR is at 3.76:1 on the UHF band. The performance is not as great as the commercial dummy load.

At the start of the year, I asked myself a question: “Why can’t we use wire-wound resistors for a RF dummy load?”. After all, wire wound resistors have high power ratings, and a few could easily dissipate 100 watts from a transmitter. Being curious, I decided to build one myself. Here’s my completed load:

 

 

 

 

 

 

 

 

 

 

And here is the measurement data:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Totally not good! The vector network analyzer doesn’t lie! The load performs very terribly! Not a good idea to begin with. Why is that so?

The name itself tells us why! Wire-wound! You see, they are made by coiling a resistive wire! It behaves like an inductive load! A little computer model shows similar (kind of) results:

 

 

 

 

 

 

 

 

 

Just a tiny, tiny amount of inductance is enough to make the VSWR very high, especially on the VHF and UHF band. Just so you know, this is a simulated sweep from 1 – 500 MHz. Granted, this may not be a very accurate model but it does show that reactances do matter in the realm of RF electronics.

Anyway, hope you enjoyed reading my post!

73,
Joyce (9V1AN)

License Renewed – A year in review

So, it has been more than a year since I have become an amateur radio operator! Looking back, it certainly has been a year of learning, experimentation and fun, of course!

So far, I have:

  • Helped organize 3 QSO nights (articles coming soon!)
  • Played around with different antennas like a TV yagis
  • Helped with some aspects of setting up the VHF repeater (Ex: Antenna tuning)
  • Talked about amateur radio in a school and at the Singapore Maker Faire

There are some of the things I have done. It certainly has been interesting and fun doing all these. As you know, amateur radio is a hobby about experimentation and learning, so what do I plan to do in the next few months?

One thing I plan to do is to really, learn more about RF electronics! I’d like to improve my knowledge on RF electronics so that I can understand more on how radio communication and their electronics work, especially since I would be looking at building a SSB transceiver from scratch, but I would be looking at power amplifiers first.

This year, I would also be looking at antenna designs and how they work, and specifically, try to turn my TV Yagi into a dual-band antenna (Not gonna be that simple, haha =P).

Finally, I might also fool around with moon-bounce communications. Of course, I am not going to do it alone. A few months back, I met a person named Roland Turner at the SARTS meeting, and he expresses interest in moon-bounce communications, especially with lower power levels (<25 watts). If I could, I’d like to work with him on the subject. Oh! Check out his Facebook page on his moon-bounce experiments here!

That’s all from me for now,  here’s to a fun and fruitful year of learning and experimentation ahead!

73,
Joyce (9V1AN)

Amateur Radio at the Singapore Maker Faire 2015

Hi there! This year, a group of members from SARTS, including myself, took part in the Singapore Maker Faire and set up a booth there. We set up 2 booths, one being an EchoLink booth, and the other, being an outdoor HF station.

What made this event special was that this year’s Singapore Maker Faire is now a full scale Maker Faire event, and also, some of my classmates and I did this as part of a school project. I certainly do hope that they learned something of value from this event. I would like to say, many, many, many thanks to them for helping out with manning the booth.

Here are some photos taken from the event:

Our booth:

 

 

 

 

 

 

 

Engaging visitors:

 

 

 

 

 

 

 

 

My classmates and friend engaging visitors:

 

 

 

 

 

 

 

 

Visitors participating:

I met this visitor in the picture above 2 years ago, when we were participating in a 24 hour programming competition. It was nice to see him again, and it certainly was nice that he could still recognize me after 2 years.

 

 

 

 

 

 

This visitor, Mr Lim Khuan is a licensed operator, who came to visit our booth. Thanks for coming! Oh and don’t worry! I am still trying to fix your radio! =P

Setting up:


 

 

 

 

 

Testing the antenna with a radio:

 

 

 

 

 

 

 

 

Well, it has been fun, and we’ll certainly do it again next year, if we can.

Thanks for reading!

Joyce (9V1AN)

VHF repeater moved!

Hi everyone! Our VHF repeater has now been moved to its permanent location at Dover. It’s a better location as there are almost no obstructions in the areas surrounding the repeater.

The repeater was placed at Mr Jeff’s office, in the Bukit Batok Industrial area.

The repeater was not sensitive to weak signals, and it was hard to make contacts on the repeater, so Mr Jeff went back to the office on Christmas 2014 to tune the duplexer, and try to solve the issue.

The issue was due to site noise around the location, and the antenna was blocked by the building. There was a measured 14dB of antenna noise in the area. As a result, not much could have been done.

 

 

 

 

 

 

One day, Mr Jaya, 9V1AI decided that he would want to take the repeater back and install it at his place in Dover (We intended to install it there anyway).

Since the repeater was now in a new location, Mr Jeff sent out emails to the members of the SARTS, asking them to test the repeater from different locations. Quite a number of members, including myself, helped out with the testing of the repeater from different locations, and I have done a presentation of the VHF repeater testing in May this year.

Here are the slides that was used in the presentation: Here!

In any case, if you want to help test or use the repeater, here are the details:
You transmit on: 145.025 MHz
Repeater re-transmits on 145.625 MHz
CTCSS tone: 156.7 Hz

Please do leave comments about your testing experience, and help us test the repeater out!

Thanks for reading!

Joyce (9V1AN)

School Visit at Christ Church Secondary School

Hi! Didn’t post for quite a while. Anyway, I gave a presentation at my previous school, Christ Church Secondary. We connected a handy-talkie to Echolink using a audio interface board which I presented during the March meeting at SARTS. Link to materials here. Here are some photos of the presentation.

Students watching my TV Yagi Experiment:

 

 

 

 

 

 

Me with the students! =D

 

 

 

 

 

 

A student making contact over the radio! =)

 

 

 

 

 

 

 

 

 

Teacher making contact over radio!

 

 

 

 

 

 

 

 

 

Anyway, thanks for reading!

73,
Joyce

2 antennas: Same model, different characteristics

Hi there! Some of you may remember that I used a RH-770 antenna for my handy-talkie. I found out that the one I had been using was a imitation. So, I obtained a Diamond brand RH-770 antenna from Blazer Electronics Center in Sim Lim Tower. That being said, if you are in Singapore or manage to get a chance to come, you should visit the shop one of these days!
It is located at the basement, for your information.

So, here are the 2 antennas side by side. Can you guess which one is the imitation? 😉

 

 

 

 

 

 

 

 

So, Mr Jeff used his Anritsu Site Master to test the performance of the antennas. Here are the results of the imitation antenna.

VSWR plot:

 

 

 

 

 

 

 

Smith Chart:

As you can see, the imitation antenna is good on the VHF band but it doesn’t perform as well on the UHF band. What about the Diamond RH-770? Here are the results.

VSWR plot:

 

 

 

 

 

 

 

Smith Chart:

 

 

 

 

 

 

 

So, the old saying is true, you get what you pay for! The Diamond RH-770 works well on both VHF and UHF bands! Definitely will recommend people to get this antenna for their handy-talkies if I can.

Anyway, thanks for taking your time to read my blog!

73,
Joyce Ng (9V1AN)

A new year, a new beginning

Hi there! I haven’t written anything since last year, so that being said, Happy New Year! =)

Its almost a year since I got involved in the hobby of amateur radio. So, what are my plans for this year?

Firstly, I’ll continue to do all sorts of experiments like what I have been doing, and of course, you’ll get to see them here! =)

Secondly, I’ll be giving presentations at SARTS, and hopefully, at schools like my secondary school so that I can introduce youth to the hobby of amateur radio. I’ll be doing a few technical presentations this year. Hope that I can impart some of my knowledge to everyone!

Thirdly, I’ll be organizing or helping out with events such as field day in Singapore and maybe set-up temporary radio stations at schools for students and the general public?

This year will definitely be packed with various events. Hope to be able to learn more things about radio this year!

Thanks for reading!

73,
Joyce Ng (9V1AN)

Repeater antenna tuning — A sad but interesting find

Hi everyone! A few days ago, I was told that the antenna meant for use with the new repeater had a few tuning issues. They just couldn’t get the antenna SWR for the 2 meter band to be lower than 2. Feeling ambitious enough, I decided to try tuning the antenna with my friend, Yong Quan.

This is a picture of the antenna.

 

 

 

 

 

 

 

 

 

So, we laid it down on the floor and started to move sections of the antenna up and down to  try to tune it. Here’s the original VSWR plot before we started.

 

 

 

 

 

 

 

Doesn’t look too good for the 2 meter band, ain’t it? We moved sections of the antenna up and down, and even removed some of the radials of the antenna to try to isolate the problem. We removed the feed point from the bottom half of the antenna, leaving only the top part of the antenna connected to the feed point, like this:

 

 

 

 

 

 

This is the VSWR curve now:

 

 

We got a SWR of 2.6! That still isn’t good, even though it decreased. We suspected something was wrong, and we removed the top section of the antenna from the feedpoint, leaving only the feedpoint.

 

This is the set-up:

 

 

 

 

 

 

 

 

 

 

And this is the SWR curve:

 

 

 

 

 

 

 

The SWR curve looks just about the same! And do you realize something? The
lowest dips in SWR are frequencies off our target frequencies! In fact,
we found that the antenna has a fixed resonant frequency around 133 –
135 MHz, which is around 10 MHz off the 2 meter amateur radio band
allocated to us! What in the world is going on here?!?

We decided to unscrew the cover of the feed point. This is what we got:

 

 

 

 

 

 

 

 

 

 

Yup, a tuned LC circuit. Apparently, they tried to make the antenna resonant only at a specific set of frequencies using this tuned LC circuit. However they are off by quite a lot.

Well… I feel for the person who bought this antenna. It cost more than SGD $400. This was a sad, but yet interesting and informative find.

Anyway, thanks for reading my article!

73,
Joyce (9V1AN)