Receiving MF and Below

You'd like to start playing with MF or below; specifically you'd love to try the 'new' 2200m band in VK. A good place to start with this may be attempting to just receive a few of the active stations already up and running. Below I hope to give you some ideas on where you might start with this. After that, you can move onto TX – I'm still working on that.

First up, couple of things to keep in mind:
  • Your HF dipole probably has a balun in it that effectively acts as a bandpass filter with a passband between about 1.6MHz and 30MHz;
  • Your HAM transciever – even thought it claims to go down to the LF frequencies – is probably rather deaf down there;
  • You don't need a half wave dipole to start receiving – because obviously you're going to struggle with this if you're in suburbia; and
  • All these items though are easily addressed – in a number of ways.
To start with, I suggest considering your antenna. My first reception on the 600m band was actually with a typical HiFi AM loop antenna hooked up to my FT-817. The signal was weak, but I was very excited when I achieved this – considering prior to this I was attempting via my HF dipole and hearing nothing. With that success, I then quickly threw up a random wire antenna (now understanding the issues with balun's) and was amazed to see the increase in signal strength.

However, this was only receiving VK1 stations (either VK1SV or VK1DSH – can't remember which). This setup failed to receive any stations further afield. This was when I learn the need for some form of pre-amplification to overcome the rather deaf HF transciever.

Therefore, one option (that I didn't try – but am considering) is to simply use your random wire antenna connected to a dedicated pre-amp then straight into your transciever. This would be rather simple and fit in a small aluminium enclosure – maybe including an LPF for extra selectivity.

A slightly more involved option that I went down the path of was creating the rather common PA0RDT mini-whip. I recommend searching the web and read up on this, and take note of the various improvements one can make. But one issue with this, is that one of the key transistors (2n5109) is somewhat hard to find – or impossible. So normally it's substituted, and in my case I used a 2n2219.

Anyway, this provided me with an active antenna, thereby providing me both with a small antenna and also an amplifier to help overcome the deafness of my HF transciever.

However, a simpler antenna option (albeit slightly larger with a diameter of about 2.2m) may be this:

I really like the sound of it, and more so the minimal part count and simplicity of build. It may provide an easy alternative to the mini-whip. But, I've not built one so I can't say for sure.

In it's circuit though, I wonder about using it's amplifier hooked up to a random wire antenna as a nice simple option. Maybe something you may like to try, once you had the parts that build would probably be about one hour – including enclosure setup.

Finally, I've mentioned deaf transcievers above, and have mentioned the key to over coming this is through some form of pre-amplifier – well, other than getting yourself a more specific receiver. Keep in mind though, each transciever has different abilities here. The FT-817 is known to be rather deaf down low, and indeed I was amazed at the improvement I gained by using my IC-718 instead for LF (actually received my first ZL station on 600m as a result of that simple change). The FT-450 also get's mention on the web, with some reporting you have to make sure you turn off it's built-in pre-amp because otherwise it activates a filter that blocks LF – or I think that's the gist of what I read (use google to check).

So the key here is that if you'd like to start playing with LF, consider:
  • Building a dedicated antenna (maybe just a random end fed wire);
  • Building a basic pre-amp to help your transciever; or
  • Building an active antenna.
You don't need a lot of space for these, and you may be amazed what you start receiving – plus, good excuse to build some more gadgets hey. 😉
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s