Can’t hear the weak stations, and all the interesting stuff on 160?
I’m often asked about the receiving antennas in use here at g7klj. Many, many stations are missing most of the fun on the low bands by persisting in using a transmit antenna as the rx antenna also. THIS IS NOT GOOD.
Some stations have been known to “adjust” their transmit antennas to simply improve reception. Here’s the deal:
A DECENT, LOW ANGLE TRANSMIT ANTENNA _SHOULD_ PICK UP LOTS OF NOISE!!!
If you adjust the tx antenna for “low noise receive”, you are likely seriously compromising the transmit signal, at least at the low angles required for long distance. Forget all about adjusting the transmit antenna for best noise, and use a completely separate receiving antenna. The aim of a decent transmit antenna is gain (you want to be loud) and efficiency (you don’t want to warm up the worms!) With a receive antenna, you have completely different requirements: you need good directivity (so as to avoid QRM), gain is NOT important, but signal to noise is. I’ll expound on this soon..
If you are new to the low bands, and are just plain put off when you hear s9+ noise on your tx antenna, please don’t be put off! I can tell you web searches for things like Waller Flags, K9AY loops and similar will help you out loads!
And this is true even if you have a small plot…the published design size for a K9AY loop requires a circle of around 30ft. Even if you cannot manage that, make a half-size one! I have a half-size k9ay here I use to null out troublesome local QRM sources, and it has a FANTASTIC front to back ratio for ground wave signals! As the loop gets smaller, signal pickup of course does get less, but you can compensate for this by carefully applying gain with something like a home-brew w7iuv preamp (which I can fully recommend, using a 2n3866 transistor, which are readily available here in the UK. Although I built the half-size K9AY precisely as the noise antenna for my TimeWave ANC-4 noise canceller, I can report it is also an excellent rx antenna in its own right — especially for 160m AM ground wave working in the daytime, with stations up to around 50 miles distant. (Which is daytime DX, considering we all have a power limit of abourt10 Watts carrier in the portion of the band where AM is mostly used).
So — no more excuses! If you have the tiniest of plots, I’m sure you can fit in a half-size K9AY loop for top-band reception. To test it, listen for the local Kent and Essex stations between 5 and 6pm Mon-Sat on, or near the following frequencies: 1908 kHz, 1950kHz, 1966 kHz. WARNING: Some of the stations locally use the appropriately-named (by G3ORP) “chair-leg” antenna for top band — also known as a “shit transmitting antenna”. Combined with low rf power, some of these stations are super-tough to hear, so be patient and wait for the right conditions. Most should be audible throughout Kent, parts of Essex, Sussex and possibly London under daylight conditions. Don’t you just love the chair-leg antenna?!
If you think this article is brief and lacking in detail (and I would agree!), then let me give you some phrases to Google for low-noise rx on the low bands: Beverage antenna, BOG, K9AY loops, Double Delta receive loop, W7IUV pre-amp (this is a GREAT pre-amp — and easy to make!) , EWE antenna.
UPDATE: The following antenna, and others like it, for low-band receive makes me start to think more and more that the best plan (for inter-G working as opposed to very low angle DX) is an aerial that receives the high angles very well, but somehow does not respond to mostly vertically-polarized local junk from crappy Chinese power supplies and their ilk. The latest info I have on this is from this excellent webpage:
My top-band AM ‘partner in crime’, Dave, GW4GTE has promised to test the high-angle rx antenna out, and I will report what he finds…
UPDATE: initial reports for inter-G sky-wave from Dave are not good. This may well be the end of the experimenting with this particular idea.
For moderate and low-angle top-band signals (“ground wave”) and 500+ miles at night, try the k9ay loop article I wrote. Amazing receive on the low-bands!
For high-angle (out to about 500 miles at night) 160m reception, a properly balanced horizontal doublet / dipole, even short and low will give, in my experience, the best signal to noise ratio on “sky wave” signals arriving at an angle of 50-60 degrees and greater. If short and low, its a crap tx aerial, but for receive only, something as small as 2 x 5m with a pre-amp (at the aerial end) will work wonders, provided you decouple the co-ax properly. The shorter the rx dipole, by the way, the more difficult this is to do.