Lee, I will experiment initially with 4 elements to increase the height, reduce the capacitance, improve the ground, and use multiple wires. I also will try 24 feet long aluminum pipes.
Ignacy On Wed, Sep 20, 2023, 12:58 Lee STRAHAN <[email protected]> wrote: > Ignacy, > > From your description I think I see another problem with your RX array. > If you have 4 foot ground posts buried 2 feet deep, you must have 2 feet of > pipe inside the fiberglass. If your antenna wire is secured to the outside > of that fiberglass that has the copper pipe inside you are actually > creating a capacitor that will shunt intended signals to ground. The > antenna wire is running parallel to the pipe inside the fiberglass causing > this capacitance. In addition the fiberglass insulator has a dielectric > constant of 5 or 6 which will cause this capacitance to be 5 or 6 times > what it was if the wires were just parallel. You need to space the element > away from the fiberglass where there is pipe inside or eliminate what you > can of the pipe inside the fiberglass to reduce this load on the elements. > Because your thin # 14 wire elements are around 40 pF of source capacitance > it takes very little shunt capacitance to drop the signal level. The Hi-Z > amps of plus-6 vintage are around 12 to 15 pF input capacitance by > themselves. Add to this a randomly chosen value of 25 pF of element/pipe > load capacitance and you have lost 6 dB of your signal. > > Thicker elements are a lot easier to work with in the long run as they > have increased source capacitance causing less error from other capacitive > loading from mounting arrangements and etc. .. > > This again suggests to me if you can that you should send me a couple > pictures of your antenna element setup. > > > > *Lee K7TJR OR* > > > > > > > > *From:* Ignacy Misztal <[email protected]> > *Sent:* Tuesday, September 19, 2023 7:16 PM > *To:* Lee STRAHAN <[email protected]> > *Subject:* Re: Topband: HiZ 4-8 and beverages > > > > Lee, > > For grounding I use 4 ft 1/2 inch diameter copper pipes. They are driven 2 > ft into a clay ground, and a fiberglass pole inserts over the rest of the > pipe. 18 ft of 14# copper wire. > > > > I will try to add extra grounding and will make the vertical element > thicker. > > > > Sorry for not following with you earlier - 3 months of overseas travel. > > > > Ignacy NO9E > > > > On Tue, Sep 19, 2023 at 8:12 PM Lee STRAHAN <[email protected]> wrote: > > Ignacy, > There are 2 things that come to mind with your array elements as you > describe them. > The very first thing is when this has happened before it has been the > result of not sufficient earth grounding from a ground rod mechanism at > each element. > This can result from insufficient ground rod size/length or the ground > condition itself. Dry and or rocky soil is insufficient to cause a low > impedance signal source to the Hi-Z amps and under extreme cases will cause > a low frequency loss of performance. If this is the condition it can be > remedied by installing 6 to 8 ground radials at each antenna element that > are roughly the same length as the radiator itself. Space radials the same > for all elements > The second thing is your element description sounds as if you have used > very small wire as the element itself at 18 feet length. These shortened > elements exhibit a very small capacitance as the output impedance of the > element itself. Larger diameters have a greater output capacitance which > increases signal and also decreases the chance for differences between the > elements. > Personally I would add 2 or 3 more wires the length of each element to > increase its apparent diameter. Then make sure there was a good earth > ground under each element with and/or without adding radials. > It also may be of help if you sent some element mounting and grounding > pictures direct to me for comment. > > Lee K7TJR OR > > > > -----Original Message----- > From: Topband <[email protected]> On Behalf Of > Ignacy Misztal > Sent: Tuesday, September 19, 2023 12:48 PM > To: [email protected] > Subject: Topband: HiZ 4-8 and beverages > > I have 600 ft reversible BevFlex beverages and recently I bought a used > HiZ 4-8. > Both are about 300ft away from a shunt-fed tower for 160m and 4 sq for 80m. > > On 80m, HiZ has a better F/B and hears slightly clearer than the beverages. > On 160m Hi-Z is deaf, with S/N at least 6 db below the beverages. A > marginal copy on the Hi-Z is a clear copy on the beverages, and a marginal > signal on the beverages is no copy on Hi-Z 4-8. Does not matter what > direction. No big buildings around although some large trees. > > My verticals are wires attached to 18ft telescopic fiberglass poles. > > The noise level from Hi-Z is decent so the preamps must be working. All > directions show the same background noise so probably the individual HiZ > Plus amps are OK. The whole array had lightning damage before and was > repaired by an associate of Lee. > > I have a triangular Hi array at another QTH, very close to TX antennas and > large trees. It has old ANT amps (not plus). Its sensitivity was never a > problem. > > Does anybody have an idea what could cause HiZ to be poor on 160 while > being good on 80m? > According to reviews, HiZ should be pretty good on 160m. > > Ignacy NO9E > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
