Broadband HF Dipoles In Use By FLEX-6000 Owners ?

Steve N4LQ

Can you be more specific on that resistor? I looked at Ohmite's docs and don't see a TA800. Would that be 800 watts? TA100 is 100 watts. 

Paul, WB5AGF

(My lack of response (until now) does not mean that I'm not reading everyone's comments .... I'm mulling them over.)

I've been doing some thinking .... I found KB7GF'S Shared Apex Loop (http://www.arraysolutions.com/Products/sal_array.htm) intriguing, not only because of what it does but also because it caused me to have the sudden realization that perhaps maximum power transfer is not necessarily the holy grail of antenna design .... at least insofar as HF/MW receiving antennas are concerned.

(I'm beginning to think about a 3-wire terminated folded-dipole for broadband receive and a tuned loop for transmitting in the manner of W5QJR's design.)

Everyone please keep talking.

- Paul, WB5AGF

kr4k

Sorry - Ohmite TAP800.

K4SC

I have been using the B-Square Engineering 122' FTD for three years and have nothing but praise for its quality and performance.  Recently took it down because I've moved from South Carolina to Iowa; what was I thinking?  Am in the process of reinstalling it at my new QTH, and will be using it with the Flex 6500.  I did use it before with the Flex 3000 and an Ameritron ALS-600 solid state amplifier and no tuner.  It worked fantastic.

Currently I am working 300 miles away from home and staying in an upstairs apartment.  I have the 6500 connected to a Pixel Magnetic Loop antenna for receiving and use a 33' fiberglass kite pole with insulated wire threaded inside for transmitting utilizing the Flex's internal ATU.  Both are mounted on my fire escape railing.  The mag loop works just super with the broadband Flex.  I can get a very good signal on all bands except 10 meters and up.  You might consider one of those for a receive antenna instead.  It really cuts the noise level down but enhances the signal to noise ratio.

Chuck K4SC Red Wing Minnesota/Mount Pleasant Iowa

Steve N4LQ

I have the Pixel Loop. Don't know about the S/N ratio but signals are cut down to the point that the noise is too weak to hear (as with many signals). Personally i think that's why everyone thinks it's quieter. IMHO etc. 

Chuck - KJ6HT

I am very happy with the broadband performance of my Tennadyne TD-90, folded terminated dipole. It is at least 1.9 to 1 from 1.8-30 MHz. My experience has been that it performs about the same as a dipole and is not as susceptible to man made noise. Rog at Tennadyne is a great guy and will answer any questions you have.

Ron K2RAS

I also have the Pixel and find it works well.  Don't forget to try turning the ANT RF Gain up to +20db.  On most bands I generally leave it there and it helps significantly.  It would be interesting to hear a consensus (likely chance...) on a broadband transmit-only antenna for MagLoop receive-only users with space restricted locations.

Ron, K2RAS

Paul, WB5AGF

Just this afternoon I was working my way through the logic of 'long' (i.e. very-long) terminated dipoles (I've been looking at the response curves that Bushcomm Antennas so kindly provides in many of their antenna brochures and Jack Belrose's (VE2CV) technical comments back in the May 1994 issue of 'QST') and also looking at 'cage dipole' characteristics.

Then the idea occurred to me .... wondering what would happen if one were to build a long cage-dipole (to lower the 'knee' in its response, if it were a terminated antenna, below the lowest frequency one might wish to transmit on) and then run a wire through the middle of it .... with a terminating resistor in the middle.

I don't know how I was lucky enough to select the right search term but I found these articles by Martin Ehrenfried, G8JNJ, from the May & June 2014 issues of 'RadCom' .... his 'Terminated Coaxial Cage Monopole' (TC2M) Antenna ..... see : http://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf ... is essentially 'my' (in my head) cage dipole with a terminating resistor in the middle .... the word serendipitous immediately comes to mind.

- Paul, WB5AGF

Steve N4LQ

One point missing in this discussion is the antenna's pattern. 
We go to great lengths (pun) to make the resistor antenna long enough so as to avoid the large loss at low frequencies but forget about the narrow lobes that may make it difficult to communicate in certain directions on the higher frequencies.

Paul, WB5AGF

Steve;

All engineering design is compromise .... to one degree or another.

When I began-my-quest for a broadband antenna I did not forget the matter of the antenna's pattern but rather I pushed it off-to-the-side ..... to be looked at once (if?) a suitably broadband antenna (Zo-wise) reared-its-head above the background noise.

Now .... if I understand G8JNJ's terminated coaxial cage monopole (TC2M) antenna .... perhaps its omnidirectional azimuthal pattern is a positive thing ? (Alright ... I hear you .... But what about its elevation lobes being frequency sensitive ? .... Sigh .... What was the saying about Rome not having been made-in-a-day ?)

So .... do we throw-the-bathwater-out-with-the-baby ? Or do we agree that a variation in pattern with frequency is something which can be tolerated if it gets us the broad-banding we desire ?

I wonder how a TC2M design co-mingled with elevated radials would look ? (I got all interested in elevated radials awhile back when the thought of 120 radials in the grass seemed unappetizing.)

(Enter 'whimsy-mode' .... How about two FLEX-6000s time sync'd together in a spread-spectrum routine that searches for optimal frequencies ..... it would take into account both propagation and antenna patterns at the same time ! Every few mS they would chirp to determine if conditions had changed.)

- Paul, WB5AGF

AA0KM

How about this vertical?..

A monster Omni..lol

Great post's on this topic.

Paul, WB5AGF

Say ..... You are a trouble maker aren't you ?

My next door neighbor would throw-a-fit ....

(I especially like the DANGER RF RADIATION sign.)

Andrew VK5CV

Just what I have always wanted.

Steve N4LQ

So the basic concept is this: 
To apply RF power to a resistor but in doing so cause radiation?
--------------------------------------------------------------------------------------------------------------------------------------
The answer seems to be:
Use a long feedline (the antenna) to the resistor and hope it all radiates before power gets to the resistor.
--------------------------------------------------------------------------------------------------------------------------------------

A problem is:
If the "feedline/antenna" is of low impedance the wires must be close together and it won't radiate much.
-----------------------------------------------------------------------------------------------------------------------------------
Answer for this is:
Make the feedline high impedance so we can increase the distance between the wires. (pull them apart). 
--------------------------------------------------------------------------------------------------------------------------------------
This produces another problem:
The RF source, feedline and resistor need to be the same impedance:
--------------------------------------------------------------------------------------------------------------------------------------
The solution for this is:
Use a balanced transformer to increase the source impedance to that of the feedline then use a higher value resistor to match both. 
------------------------------------------------------------------------------------------------------------------------------------
Then we find:
The higher the frequency, the greater distance in wavelength is between the feeder wires thus the more radiation from them and the less consumed by the resistor.
---------------------------------------------------------------------------------------------------------------------------------
What we need is:
Some way to measure the power consumed by the resistor for any given frequency. 
-----------------------------------------------------------------------------------------------------------------------------------
It doesn't seem too difficult:
An RF voltmeter across the resistor would tell the story but so far nobody seems to have done so.
---------------------------------------------------------------------------------------------------------------------------------
One idea:
Wireless telemetry  of the RF voltage via a uhf link. 
--------------------------------------------------------------------------------------------------------------------------------
Danger: The results could be depressing. 

Steve N4LQ

Steve N4LQ

Paul
A rat is smelled.
How'd they come up with zero db gain in a resistor antenna? 
My smoke and mirror detector just went off.

kr4k

Recommend reading Cebik's articles for the theory and modeling of these antenna types.

Martin Ehrenfried

Hi All,

The problem with most comparisons of terminated dipole antennas is that they are usually not compared like for like with similar sized antennas, the term apples and oranges spring to mind.

Folks just see the resistive load and assume the worst without bothering to quantify the losses.

Every antenna system has some losses, the trick is to know how big these losses are, where they are occurring, and if this is likely to cause a problem in the intended application. In in some cases moderate loss may not be an issue, especially if the convenience of wide frequency coverage is the main concern. Examples of which include Frequency hopping, ALE, propagation monitoring etc.

Folks may actually be surprised to discover that the distributed losses in a tuned antenna system can sometimes be greater than the power dissipated in the resistive load of a terminated antenna, but because it's not so easy to 'see' or 'feel' these distributed losses they tend to be ignored.

Many of the questions raised in this thread WRT broadband dipole type antennas, and the TC2M in particular are covered in the TC2M article which can be found at this link.

http://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf

These include calculated gain at 20 degree elevation and measured field strength, power dissipated in the load, properties of cage antennas WRT impedance variation and and null filling etc.

The TC2M is a good omni-directional 'search' antenna (as RX S/N is generally not defined by the antenna) which can also be used for opportunistic DX chasing if required. 

However if you just want a broadband receive antenna then consider using a good (there are lots of bad ones out there) active antenna, which is what the military and professional agencies tend to use. Either a single omni for casual listening or a steerable array or phased loops for improved S/N ratios.

The bottom line is that directional gain antennas are not ideal for broadband monitoring unless you want to concentrate on just a specific region on all frequencies at the same time. In which case a log-periodic, Beverage, or terminated Vee beam my be worth considering.

Terminated antennas have their merits, but are often criticised for the wrong reasons.

Regards, 
Martin - G8JNJ 

tc2m.info@yahoo.com

www.g8jnj.net 
www.tc2m.info 
http://websdr.suws.org.uk/

k3Tim

Hey Martin,

Thanks for the insight and the link the your articles. Very nicely done and an interesting read. The vertical version of this class of antenna is very intriguing, It seems one could also make a version that is disguised as a small  "antique" Wind Mill or something similar.

Best 73's!

k3Tim / PE / MSEE / PPSEL-IIR / 2pts
  

k3Tim

To measure RF voltage is not enough, one must measure the in-phase current also to determine REAL power lost.  The easiest measurement would be the temperature rise above ambient.  That is showing real-power lost in the resistor.

The B2Eng site pointed out the resistor was a Zero voltage node on a certain band (160??) so there would be no loss.  

_..--
k3Tim

Steve N4LQ

With a zero voltage node, do we even need the resistor? 
If we don't need the resistor then we have invented a new multiband antenna. eh?

k3Tim

For the particular frequency the resistor is at zero voltage but when the VFO moves away from this, then the resistor is needed.  Check the B2E info as well as Martin's work (below). 
--...  ...--

Paul, WB5AGF

Steve;

I believe that your comment about making the feedline (antenna) as long as possible and then hoping that most of the RF power radiates before it gets to the terminating resistance is most probably the central idea to having a terminated antenna reasonably efficient when used for transmitting.

When I (earlier) remarked about my looking at the 'knee' in the radiation efficiency graphs in some of the Bushcomm brochures, and referencing VE2CV's 'Technical Correspondence' comments in the May 1994 'QST', that is what was in the back-of-my-mind ..... 'above' that 'knee' (i.e. at higher frequencies) the terminated antenna is getting long enough (wavelength-wise) such that more of the applied RF gets radiated (and is not used to heat up the terminating resistor).

(I noted that the Bushcomm terminated dipoles advertised as being good down to 160M appeared to have their 'loss-knee' up near 80M and so, if the real estate was available, it would seem prudent to use those antennas for 80M - 10M. If a person was determined to transmit on 160M then an even longer terminated dipole would seem called for.)

If we were to put up an extremely long dipole (and not worrying about the antenna pattern for now) then I believe that it would show little reflected power (regardless of frequency) because the reflected component getting back to the feedpoint would be very low compared to the applied signal. (An infinitely-long antenna should show no reflected power regardless of the applied RF frequency.)

- Paul, WB5AGF

Rick Hadley - W0FG

Many years ago, Doc Braley, W0GET or Ted Hunter, W0NTI of the Eye Bank Network fame (I don't remember which)  used to have a conical monopole like that set up at their house north of Iowa City.  They both had huge signals on 3970 every evening.

Doug Hall

K3TIM, if the resistor is non-reactive then any voltage across it results in real power being dissipated, no? In this case isn't it enough to know the magnitude of the voltage?

SteveM

Here is a presentation covering various dipole antennas. It concludes with a recommendation for the ZS6BKW which is a tweaked G5RV design allowing operation without a tuner on most of the bands. As a bonus, it is also shorter and lower than the G5RV.

https://www.youtube.com/watch?v=9G_j0UekbzM

W9OY

I use 3 different antennas.  Given the antenna port construction in the Flex this is easy to implement.  I use a 23 ft magnetic loop antenna based on the wellbrook ala100M amplifier for receive from 100khz through 30 mhz.  The loop is constructed out of a couple of 8ft 3/8 fiberglass poles from Max Gain.  Result.  It works extremely well.  I did not bother with a rotor.  If you don't have a pole you can hang it from a tree or even on the wall but it works best away from the house and other antennas and radial fields.  Total cost for the loop aspect was $12 plus the cost of the preamp.  On my radio this antenna resides on the XVTR port.  This solves your receive dilemma.  The magnetic nature of the antenna dramatically reduces local noise. 

For transmit you can use something standard like a G5RV and the built in Flex tuner if you want to run 100W.  A G5RV can be made to tune any band from 160-6 with the Flex tuner.  80, 40, 20, 12 are down less than 0.5 dB from a full size dipole for the given band.  15 is down 1.5 dB. 17 is down 4 dB, 30 is down 6 dB and 10 is down 7 dB.  Your worst case is only down an S unit and for most bands it virtually identical to a dipole.  It's a piece of twin lead and 102 ft of wire AKA CHEAP and dead simple to build.  I use one of these in the W5GI variant.  You can add a third antenna like a vertical or inverted-L to the setup and have the G5RV on ANT-1 and the vertical on ANT-2.  I have a 160M inv-L fed against radials which works quite well on 160 but also works well on other bands with the tuner.  Also quite a cheap antenna if you have a tree or two.

DDUTIL allows you to choose many variations of TX/RX antenna combinations at the push of a button using macros, like XVTR/ANT1  XVTR/ANT/2  ANT/1/ANT/1  ANT2/ANT2 etc so you can rapidly cycle through combinations and choose the best.

73  W9OY

W9OY

I bought a mfj 929 off swap.qth for $100 and stuck it in a 50 cal ammo can 

k3Tim

Hi Doug,

It looks like you are correct and I am incorrect  I was thinking P = V * I and taking into account the possibility that the voltage and current are not in phase due to complex  impedance of the antenna itself, that is measuring back at the Coax end.  If one measures across the resistor only, that's different.

Checking the ARR Handbook 2014, section 2.10.7 "Reactive Power" they show a R L series network being driven by a 250V-AC 60 cycle power source.  The voltage across the L=200V and across R=150 with the current = 2 amps.  The voltage adds to 350V, more than the 250V applied due to the L.  But the power in the resistor is 300W.  V^2/R or I^2*R works either way. The Handbook says the V and I will be in phase at the resistor, at least that is the way I read it. 

Therefore measuring the V of the termination resistor and calculating V^2*R is enough to determine the real power lost in the device.  

I have to review the  Handbook and refresh my analog circuit skills!  The handbook is a great technical resource and a true bargain.

Thanks for questioning this and catching the blunder.  

My apologies to the group for causing this confusion.  

:-(   !

k3Tim

Steve N4LQ

Tim
Your punishment is to determine a means of measuring RF voltage while suspended 40 feet in the air and not upsetting the system with wires and equipment.
Telemetry?