Antenna Ideas for 1710 kHz thru 160 meters

Pirate radio transmitters, transmitting antenna systems, pirate radio equipment suitable for AM or shortwave broadcasting. Reviews, modifications, other info specific to shortwave pirate radio broadcasting.
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Antenna Ideas for 1710 kHz thru 160 meters

Post by JohnPoet » Tue May 24, 2011 11:02 pm

Installing an antenna for 1710 kHz has its own unique complications. A 1/4 wave at that frequency is about 140 feet, making a full vertical impossible for most people. Compromise on the length or polarization is therefore necessary.

Because of their proximity in frequency, almost any antenna designed for 160 meters will be usable on the top end of the AM band, with suitable adjustments to length and tuning for that frequency range.

I've actually done some experimentation on this, and research into antennas that could be adapted to 1710 AM-- particularly designs intended for 160 meters.

Quite a few of these could be adapted for 1710 AM, particularly the 160 meter types by simply lengthening the dimensions appropriately using quarter or half-wave formulas. The linear-loaded vertical is the effective equivalant to a 1/4 wave vertical, but requiring maybe only a third or less of the usual vertical space. Since there is a horizontal counterpoise, it operates sort of like a dipole or a top-fed inverted L; neither of those require a ground radial system.

Linear-loaded vertical
http://ke4uyp.tripod.com/80m_160m_Antenna.html

Half-helical with loading wire
http://www.iw5edi.com/ham-radio/?a-prac ... -metres,32

Links to many antennas
http://www.dxzone.com/catalog/Antennas/160M/index.shtml

The inverted U antenna
http://users.erols.com/k3mt/inv_u/u_160.htm

I actually got quite good results one night simply tying the two sides of an 80-meter horizontal V dipole together at the antenna tuner, operating it as a "T" against station ground (which was not extensive at all-- just one or two ground rods and a couple very, very short radials) and transmitting around 1710. Of course in that configuration, the coax also becomes part of the antenna. I was running a Johnson Valiant (150 watts) into an MFJ Versa V 3kw tuner. Reports were published from listeners about 400 miles away from me, which rather surprised me when I had been using such a jury-rigged antenna. (I was only interested in DX hobbyists, not local coverage. Local coverage was very poor considering the power level, I would start losing the signal about two miles from the QTH.)

Using that much power into an antenna tuner is troublesome at 160m, worse below it. (You can get arcing, which sounds like a clicking noise coming from inside the antenna tuner). The tuner would get awfully hot. Less power would be less of a problem. If you have an antenna analyzer and can use it to tune up the antenna and/or tuner before applying any big wattages, that would be good. It would be best to have adequately low SWR on the antenna so that you can run without any tuner, but that may be difficult to achieve with limited antenna height at that frequency range. Fifty watts or less probably wouldn't be that big of a problem, but don't use any of those tuners rated 300 watts or less unless you're running closer to QRP, maybe 20-30 watts carrier.
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syfr
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Re: Antenna Ideas for 1710 kHz thru 160 meters

Post by syfr » Sun May 29, 2011 6:36 pm

One tuner that is often overlooked is the "Low Power" Johnson Matchbox. You'll need to provide 110V , or jumper the relay (a 2 min job) but the caps in that WON'T arc over with 100 watts. It's 300 watt rating was back in the Valiant and Viking 2 days, and can easily handle that. It's a balanced line tuner but there's instructions on how to jumper it for unbalanced operation. They can be easily found for ~100 or less.

A good antenna to try would be a top loaded vertical formed using the guy wires as the top load. It's of no concern that they fold back down at an angle. There's plenty of references on the web for such, or I'll post some if there's any interest. For 1700 khz, a vertical is the way to go.

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Re: Antenna Ideas for 1710 kHz thru 160 meters

Post by CaptMarbles » Tue May 31, 2011 2:38 pm

Just to add to what syfr says, a 250w Johnson Matchbox can be found for $200 and is built like a brick sh*thouse. I use a Palstar BT1500A which is also very good but expensive. The Johnson is better value for money.

You could also try and an inverted-L antenna which is a variation on the top loaded vertical. It can be fed at the base but requires ground radials, or at the midpoint essentially like a dipole. I have a link somewhere if you're interested.

If you want to go the commercial route, Butternut makes the HF2v with a top loading kit and 160m adapter. Again mucho $$$s but you could easily make a homebrew version.

Capt. Marbles

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Re: Antenna Ideas for 1710 kHz thru 160 meters

Post by redhat » Sun Jun 05, 2011 1:21 am

The problem with most "amateur" tuners, outside of the general poor build quality, it they don't really have enough "reach" to get to the top end of the band. An expanded band AM facility I worked for once contemplated using a ham tuner to get one of the abandoned directional towers running as a spare tower while the main tower was painted. We gave up after burning up the tuner. The old tuning network from the stations' former home several miles away was liberated and retuned, using some of the old sample line as the feed cable. We were able to get about 250 watts into it before the TX got pissed at the SWR. It wasn't pretty, but it got us through the weekend.

Some people have had success with electrically short top loaded antennas for upper AM channels where zoning will not allow a full size antenna to be erected. there was a write-up in radio guide about two years ago showing such a project in the pacific northwest. The principle construction material was telephone poles, about 40' high. five of them are arranged in a circle, the fifth being in the center. Four inverted L shaped elements are tied together to form a cage antenna with a capacity "radial" system.

The ARRL antenna book has plans for a 6' high 40M vertical with a 6 foot capacity hat on it. Very narrowband, but very stealth.

+-RH

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