Long Wire RX Antenna - How Long is Too Long?

[ultravista]

Is there a point of diminishing return when it comes to the length of a long wire RX antenna?

In other words, does doubling the length provide measurable benefits?

I ran a 500 foot spool of 14 gauge wire through the woods this weekend. Run through screw-on insulators at a height of 14 foot. 500 foot is a long run, I underestimated just how long it would be.

So ... will this 500 foot long wire 'capture' more signal say a 250 or 100 footer?

 

[ka3jjz]

Yes there is. The longer the antenna at a given frequency and height above ground, the more directional it becomes off its ends. The classic Beveridge antenna uses this very same principle.

Such a long antenna is probably best used by desktops and ham transceivers (which have general coverage radios built in). Portables and SDRs would be heavily overloaded with such antennas unless you are WAY out in the boonies - and even then overloading might still be an issue. In such cases a passive preselector would almost certainly be needed.

Mike

 

[ultravista]

Hi Mike - I am using this with a Palomar 1:9 balun feeding a Yeasu FT-950.

 

[natedawg1604]

Is there a point of diminishing return when it comes to the length of a long wire RX antenna?

In other words, does doubling the length provide measurable benefits?

I ran a 500 foot spool of 14 gauge wire through the woods this weekend. Run through screw-on insulators at a height of 14 foot. 500 foot is a long run, I underestimated just how long it would be.

So ... will this 500 foot long wire 'capture' more signal say a 250 or 100 footer?

Are you trying to RX on 160 or 80? I'll be curious how this works out for you.

 

[RFI-EMI-GUY]

Put a couple of these out there to make and break some sections to see what works best.

You will definitely need a tune-able preselector for an SDR and even some modern radios.

 

[w2xq]

A Beveridge antenna is optimal at 1 wavelength. The aperture decreases as the number of wavelengths on the wire increase. My experience? A 1000' was not useful above 40/41m. Otherwise, the antenna is a blast! See some articles here:

W2XQ.com : Amateur Radio

amateur radio, ham radio

w2xq.com

HTH.

 

[RFI-EMI-GUY]

Don't forget some decent lightning protection along the way. Those near hits are going to be direct hits.

 

[ka3jjz]

+1 on the lightning protection....and yes it would be nice to know what you are trying to hear with that....

And as for an example of a preselector that is transmit-protected (in case you do so accidentally)...

MFJ-1048, PRE-SELECTOR, PASSIVE, W/T-R RELAY, 1.6-33MHz

MFJ Passive Preselector with T/R Relay 1.6-33 MHz IN STOCK! READY TO SHIP! MFJs new Passive Preselector has extremely high dynamic range! It improves the performance of nearly any HF or shortwave receiver/transceiver. It vastly improves the most expensive receivers. Especially helpful to those...

mfjenterprises.com

Mike

 

[ultravista]

Are you trying to RX on 160 or 80? I'll be curious how this works out for you.

I run through the entire spectrum of the Yaesu, from LW through HF. Other than an occasional NDB, I don't get anything below the AM band.

The Pixel look does a good job @160/80/40 meters.

What would be good for lightning protection?

 

[ka3jjz]

Well one issue is that your 500 foot wire is not going to have a great match using a 9:1 on every frequency. The impedance on that is going to be all over the place. That's why a true Beveridge is a tuned antenna....the Pixel will do better on LW for sure...

3 letters for lightning protection, assuming you're in the US

NEC

'nuff said

Mike

 

[ka3jjz]

We've had numerous discussions on grounding in this forum, the amateur radio antennas forum and elsewhere. I'd suggest using a good search tool and reading up on the subject. It is NOT ramming a rod into the ground and that's it. The NEC code has very specific guidelines for this. You can't redesign your home to be absolutely safe from lightning, but you can reduce the chances. That's about as far as the average citizen can do

Mike

 

[ultravista]

I ran tests last night and this morning and have to say, I am surprised that the 500 foot wire and Pixel 1B were nearly identical. The antennas are connected to a Palomar 4 port switch box.

Yaesu FT-950 > RSP2 (panadapter) > HDSDR with auto-gain disabled to keep settings constant between both antennas.

Tuning from LW through HF, both were comparable in signal strength (audibly/visually in HDSR). The Pixel at some frequencies was a slightly better or worse than the wire. This I attribute to the position of the loop being static and nulling some/improving some.

At LW, I can routinely pickup a NDB @ 415 khz. It was slightly better with the Pixel.

I thought the 500 foot wire would outperform the Pixel. It did not ... and I would like to know why.

How can a 4 foot loop, 4 feet off the ground, perform as well as 500 feet of copper 14 feet off the ground?

 

[ka3jjz]

Keep in mind loops are directional - I'd bet that if you turned it in the right direction, the signal would improve somewhat. That's something that can be only done with a Beveridge by having more of them in different directions (and using a phasing unit).

Why the two work differently takes a great deal to understand, and it's something that can't be covered in a forum like this. You are trying to compare apples to grapefruits - the 2 antennas work in very different ways. There are many books from the American Radio Relay League (ARRL) and the Radio Society of Great Britain (RSGB) that can teach you about antennas.

Mike