Thursday, November 23, 2017

Archive of early technical magazines

American Radio History is a fantastic archive of early electronics, technology, sound recording and broadcast magazines. Mostly UK and US. It includes some classics including Byte, Popular Electronics, Modern Electronics, Wireless World, and some educational titles.

I saw this on Roger G3XBM's excellent blog that is (mostly) about ham radio but I find the occasional diversions most entertaining. Roger wants an IC-7300 for Xmas I see.

Tuesday, November 21, 2017

Tuning 40m at a low noise location near Dorrigo

What a pleasure it is to tune the 40m band at a location where the only noise is the occasional "tick tick" of electric fences. Here's a bit of a tune around this week.


We need some remote receivers at places like this. Unfortunately there is no mobile reception at this property.

Monday, November 20, 2017

Low RF noise location - near Dorrigo

This week I'm spending a few days at a very low noise location in northern New South Wales near Dorrigo.


Yesterday I tuned around 40m and experienced S0 noise. There were some stations in Victoria and Tasmania coming through well. Tonight I will try to join the Home Brew Group's net. Here is my squid pole hanging off a stake. (I'm told there are much better stakes, normally used for electric fence supports, available for about $4 - will investigate).



The local paper, the Don Dorrigo Gazette, here is printed with the old letterpress system and looks amazing.


Internet here is pretty slow so I won't be posting much.

These posts, seen below with the orange loop at the top, are widely used to hold up electric fences. They have a convenient foot hook for pushing them in to the ground.


It's lovely here, audio and electrically quiet. The only sound on radio is the clicking of electric fences - how ironic.


Saturday, November 11, 2017

Blog hits a million page views

A milestone today, the page views on this little blog has just hit one million. This blog is really a personal notebook where I write little posts that I can find again later to remind me how to do various things.

The first post was on October 12, 2006 back in the days when email spam was still a problem. Before this blog I had another, rather too serious blog. I found that I'd set the bar too high. Posts were essays and I couldn't keep it up. I was foolishly thinking too much about the audience. Giving that up and just posting notes to myself has done the trick.

The blog is never a chore and many times I've searched for how to do something and found my own blog post from the past. I fear that social platforms like Facebook are becoming the owners of our writing and much like GeoCities will some day disappear with all of that content. Arguably a blog on Google's Blogger suffers the same drawback but I hope that Google is more likely to keep it up.

Thanks everyone for visiting, for comments and for getting in touch.

73

Peter
VK2TPM

Friday, November 10, 2017

Comparing antennas with WSPR

The new end fed antenna has obviously higher signals but also higher noise. The question is.. which antenna is better?



I now have three antennas that work on 40m (7MHz). The real test of an antenna, at least on receive, is the signal to noise ratio, and WSPR is a great way to measure this. I've set up three receivers, with three computers, all running wspr with the following call signs.
  • VK2TPM/1 is a half G5RV into an FT817
  • VK2TPM/2 is the new end fed into an IC7300
  • VK2TPM/3 is my old dipole fed with open wire feeder into a KX3
At the time of this first post, I'm surprised to report that my half G5RV is significantly better than the dipole or end fed for most reception.

Reception of VK2RG who is 48km away.



Reception of VK3AFE, who is 718km south of me.


Reception of ON7KO who is 16,732km away.




Comparing antennas is not simple. Each antenna is directional so performs better for stations in certain directions. Local stations are received quite differently to remote stations where signals come in from above. Some antennas pick up more local noise than others.

WSPR is a great tool for antenna comparison. Is there a better way to plot the data?

Update: I'm wrong

I think my analysis above is incorrect. Looking at all data over a 24 hour period it's clear that the big dipole receives more spots overall, which is a good measure of overall receive performance.


For what it's worth, here's the average received signal to noise ratio, spot counts and total distance of all spots received. (I don't actually think adding all S/N db figures makes any sense).


So in the end the dipole I think performs better even though signals (and noise) are higher on the end fed. John, VK2ASU, correctly points out that I haven't attempted to tune the end fed for 40m properly and that may well improve it.

Monday, November 06, 2017

Built an end fed match box

At QRP by the harbour I put up a dipole for 40m and John VK2ASU put up an end fed antenna which seemed to work better. My dipole was held up in the centre on a 6m squid pole and the ends drooping down to ground stakes at each end.

John's end fed went straight up to a squid pole and then over to a nearby tree. He cleverly used a bottle filled with water to throw the end up there (to save weight {although he also carried a lead mallet for the ground stake}). In the end John's antenna was more in the air than my inverted V.

Inspired by David, VK3IL's build of a matchbox for an end fed half wave which was inspired by PA3HHO's end fed half wave article I reproduced their work today.


Like David, I used 150pF on the input.

Connected to my end fed inverted L it shows decent SWR on 40 and 20m. My transceiver's built-in ATU easily matched on both those bands. Compared to the 40m dipole signals are stronger but so is noise so perhaps the best way to compare is to run WSPR on each for a while.

Like John, I used an FT240-43 toroid and wound 0.8mm wire on it. Cable ties hold the core in place. The plastic box has a snap on base.



Thanks to all who went before. This is a very easy project to build and could be very handy in the field.

Sunday, November 05, 2017

Active on 6m with new J-Pole antenna


My thanks to Peter, VK2EMU, who manufactured a few J-Pole antennas for 6m. A beautiful addition to the shed.

Thanks also to Stephen, VK2BLQ, who kindly gave me a length of water pipe to mount the antenna on.

The antenna is manufactured from square aluminium tube, welded and with a perspex spacer at the top of the J.

I found that mine was a bit short and have added a sliding section of right angle stock to the end to get it to tune up.

The 6m band is quite wide and it's hard to choose where to tune as I'm interested in both 52.525MHz for FM all the way down to 50.293MHz for WSPR and below for digital modes.

The taps for the stub are attached with U-bolts at the moment for easy adjustment. I'm not confident that the connection will be good after a while in the weather but so far seems fine. Peter also supplied some stainless steel long bolts and nuts that I'll switch to in time.

Here's the matching step connected to u-bolts:


I've wrapped the coax ends in self-annealing tape to keep the water out and used some hook and loop wrap to keep a loop of coax in place.


It's resonant at 52.28MHz although the impedance is a little low. My rig can tune it up without any problem.


As soon as I called CQ on 52.525, Ron, VK2GO immediately responded - it's great that there's people around responding to random CQ calls. Thanks Ron.