HAM radio

Slightly off thread ….. today is the day when the Manchester University “ Baby “ Programmable Computer went live ,,,

Manchester Baby and the birth of the computer

…. and the link with Ham Radio is that I bought as a teenager in the 50’s an Ex RAF Radar Display Unit complete with two spare 6" CRT’s ... cost < £10 … with the free included circuit diagrams I converted the unit into a simplistic Oscilloscope which I used when building / modifying radios , One of the spare CRT’s was long persistence and I am convinced the same type as used initially in “ Baby “ … made a nice profit when I sold my Oscilloscope on …. Anyhoo back on thread .
 
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A couple of months ago I posted about the Software Defined Radio (SDR) dongle I had purchased, and while it was an interesting little gadget I was not having a lot of luck with the cheap little antenna that came with it.
Since then I have been doing some research and hit on an article on "Flower Pot Antennas" and how to build one. As far as the creation on the antenna is concerned, it's as simple as stripping back the shielding on the coax "this" far, wrapping the cable around something cylindrical to make a chole "this" far down the cable from where I stripped off the shielding and there you go. Took me about 20 minutes, taped it to a thin piece of wood and hung it from a tree outside and voila, it worked!
It's not perfect but it's an improvement on what I had, the next step is to make it a bit more "formal" (the original plan used a 25mm water pipe to house the antenna) and have a crack at another plan for an ADSB antenna which uses a coke can....
If nothing else, I'm having fun just tinkering about and using stuff I have around the house....
PM me if you want me to put you in contact with one of the guys at my radio club out west of Sydney. He's a flower pot antenna guru.
 
PM me if you want me to put you in contact with one of the guys at my radio club out west of Sydney. He's a flower pot antenna guru.
Cheers, I may well do that.
 
Is that Bill or Ben ?
Or "Weeed!"

Funnily enough the story goes that the original antenna was stuck in a flower pot and flowers grown up it to hide it, the neighbour of the inventor didn't like antennas....
 
Here is another for you to try, I am making one tonight at the club. Its a bit more involved but worth the extra effort for mobile work. Just hang it from a nearby tree. I borrowed one from a club member to try out and it makes an excellent 2m/70cm antenna, SWR 1.1 when cut to length.



Edited to add the link.
Thanks for that I'll have a look. Althoughh I'll ask the dumb question now, how critical is SWR when I am just receiving? And if I don't have a transmitter how do I measure it?

But I have to say, when I read your post I did wonder why you borrowed a tree from a club member....
 

hoofie

Clanker
The club scene is slowly dieing off literally as the membership gets older. The explosion of social media means much more information is available than before and it's easier to connect with other Amateurs. There is certainly new blood coming in especially thanks to lockdowns but they aren't going near any clubs.

Clubs do bring shared facilities though. The closest one to me has a little govt built clubroom with a couple of towers etc but it's in a large area which is "zoned" for things like shooting clubs, model aircraft, equestrian etc.
 
Thanks for that I'll have a look. Althoughh I'll ask the dumb question now, how critical is SWR when I am just receiving? And if I don't have a transmitter how do I measure it?

But I have to say, when I read your post I did wonder why you borrowed a tree from a club member....
An antennas resonance is important in the receiving mode and lots of experiments have been done with wires in various shapes. A long wire going straight up, a sloper which slopes, a dipole which is two wires separated by an insulation piece and the downlead goes to the receiver as a co-ax or ladder type wire. The length of the wire(s) can be determined by experimentation. As for measuring you can use a Antenna Tuning Unit (ATU) which can be constructed quite easily or purchased for a reasonable price. Below, good site with lots of info :cool:
 
Thanks for that I'll have a look. Althoughh I'll ask the dumb question now, how critical is SWR when I am just receiving? And if I don't have a transmitter how do I measure it?

But I have to say, when I read your post I did wonder why you borrowed a tree from a club member....
Rambling Sid here. Because I didn't have one... SWR is not critical for receiving, but it will improve reception when completed. The antenna, as designed. will work well without adjusting for SWR. but better if it is adjusted.
I built one last night and put it on a network tester to trim it. Nice flat response on the 2m band and good on the 70cm but not totally flat. Just got to wind a choke on the coax and I will go live with it this afternoon.
 
Just some random thoughts ... are there many HAM Operators who still use CW ... when I was interested that was the preferred method for DX .... indeed you had to pass a 12 WPM Morse Test as part of the application for a Transmitting Licence ..." Paddles " ? were de rigueur across the pond ....I also remember parts of the Amateur Spectrum being reserved for RTTY .... probably long gone
 
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DK27

Old-Salt
Just some random thoughts ... are there many HAM Operators who still use CW ... when I was interested that was the preferred method for DX .... indeed you had to pass a 12 WPM Morse Test as part of the application for a Transmitting Licence ..." Paddles " ? were de rigueur across the pond ....I also remember parts of the Amateur Spectrum being reserved for RTTY .... probably long gone
CW is still quite active on HF. As for RTTY, there is still reserved parts of each band. This is generally lumped in as data modes, RTTY, PSK, etc. There is a part allocated for SSTV so as not lumped in with the data modes.

Yes CW is alive and well and very popular with those that build their first transmitters or those using low power.

Hope this helps, check out the RSGB band plans.
 
Thanks for that I'll have a look. Althoughh I'll ask the dumb question now, how critical is SWR when I am just receiving? And if I don't have a transmitter how do I measure it?

But I have to say, when I read your post I did wonder why you borrowed a tree from a club member....
Standing Wave Ratio is only relevant to transmission lines and antennas which carry transmitted power.
Receivers do not* send radio waves out of an antenna, therefore there is no power to be reflected back to towards the receiver due to mismatch and so no standing wave ratio.

Adjusting the electrical length of the antenna and matching it's impedance to the receiver will help. For HF, band pass filters can help reduce unwanted signals and noise to the receiver, although there may be a small amount of attenuation (insertion loss). When using a preselector or antenna matcher, tuning / peaking for maximum noise will tend to indicate optimal resonance.

*Technically, yes, there can be a very tiny amount of RF energy leaked out through the receiving antenna but as far as the electronics in the radio are concerned it is of no consequence. In certain scenarios it is desirable to suppress such emissions.
 
Rambling Sid here. Because I didn't have one... SWR is not critical for receiving, but it will improve reception when completed. The antenna, as designed. will work well without adjusting for SWR. but better if it is adjusted.
I built one last night and put it on a network tester to trim it. Nice flat response on the 2m band and good on the 70cm but not totally flat. Just got to wind a choke on the coax and I will go live with it this afternoon.
Thanks for that, so what is this network tester that you speak of?

I did some research on antenna tuning units but most of the pages and videos are talking about using a transceiver to check, only one video I saw appeared to do some manual twiddling of inductance and capacitance based on the audible volume of static, then plugged in a transmitter to confirm.

No Tx, no ability to check performance!
 
Standing Wave Ratio is only relevant to transmission lines and antennas which carry transmitted power.
Receivers do not* send radio waves out of an antenna, therefore there is no power to be reflected back to towards the receiver due to mismatch and so no standing wave ratio.

Adjusting the electrical length of the antenna and matching it's impedance to the receiver will help. For HF, band pass filters can help reduce unwanted signals and noise to the receiver, although there may be a small amount of attenuation (insertion loss). When using a preselector or antenna matcher, tuning / peaking for maximum noise will tend to indicate optimal resonance.

*Technically, yes, there can be a very tiny amount of RF energy leaked out through the receiving antenna but as far as the electronics in the radio are concerned it is of no consequence. In certain scenarios it is desirable to suppress such emissions.
Thanks for the info, the one thing that has been stuck at the back of my mind is that having built this antenna I have no real way of getting rid of an impedence losses because I don;t know they are there. Short of hacking an inch off the cable at a time until I get a better signal I will probalby need to hack together some form of ATU and see what effect it has.

Something else to tinker with......
 
Muchos gracias, I reckon that was the website I found the original plan on.

Another one I want to try is this one:

An ADS-B Antenna Built From Actual Garbage
Check this out: Diary: Testing homebrew DIY ADS-B antennas - Feb 2017

Another DIY antenna builder said:

"The co-co antenna was better than the tuned original antenna. But after the very simple 4 radial spider performed just as well, I concluded that homebrew coaxial collinear antennas may just not be worth all the additional effort. That said, with greater accuracy in construction and perhaps different coax, I think they could give results. It’s just hard to achieve this accuracy with fairly basic tools and no network analyser to characterise the finished antenna." Making Antennas for 1090MHz ADS-B Aircraft Tracking - lucsmall.com

I'd think about using a biscuit tin, an old oil can or a small bicycle wheel as a ground plane, then put the antenna that comes with a USB-DVB stick on it. If that improves things, it's maybe a good starting point.
 
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Check this out: Diary: Testing homebrew DIY ADS-B antennas - Feb 2017

Another DIY antenna builder said:

"The co-co antenna was better than the tuned original antenna. But after the very simple 4 radial spider performed just as well, I concluded that homebrew coaxial collinear antennas may just not be worth all the additional effort. That said, with greater accuracy in construction and perhaps different coax, I think they could give results. It’s just hard to achieve this accuracy with fairly basic tools and no network analyser to characterise the finished antenna." Making Antennas for 1090MHz ADS-B Aircraft Tracking - lucsmall.com

I'd think about using a biscuit tin, an old oil can or a small bicycle wheel as a ground plane, then put the antenna that comes with a USB-DVB stick on it. If that improves things, it's maybe a good starting point.
Thanks for that, I'll give is a read.
 

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