HOW TO GET RF OUT OF THE SHACK

[WA1GFZ]

I have a hunk of mil 214 going up my tower that was installed in '78 and still fresh.
There are some surface marks but very clean inside. I make it a point to run cable up the tower on a side that does not face the sun. 

[Steve - WB3HUZ]

If you doubled the size of it, then it was no longer a G5RV. Louis Varney, G5RV developed the antenna to produce a clover leaf pattern (4 lobes) on 20 meters. All other uses or dimensions change it to something other than a G5RV.

Steve said:

The G5RV was originally designed for use on 20 meters. Trying to make it a multiband antenna seems futile.

I think I would dispute that, Steve. Duane, KK4AM (sans KN0R), had one that we doubled the size of the flat top and the 450 ohm feeder, (from 102' to 204'; 32'feeder to 64' feeder). It worked quite well on 160, 75, & 40 that I know of. But I will agree with you on attempting to use the original G5RV on 160 was feeble at most. Running in Marconi style let you work all TV's, radios, stereos, etc.

[Ed Nesselroad]

Is it true that the Brits drink beer warm because of Lucas refrigeration?

[Vortex Joe - N3IBX]

What was that routine about.. "I have a G5RV and a Kenwood 520, can I be a strapping Am'er on 75?"

 

(something like that...)

I don't think the 520 does AM but I agree with the point.

G5RV's seem to be the 21st century Gotham antennas.

I have a TS-520 and (unfortunately) they don't do AM. Other than that it's a FBOM rig. The TS-520-S had 160M, where the regular TS-520 doesn't. Regarding the G5RV, I use one for the higher bands and don't have any real complaints about it. I've heard people both praise and curse them. I guess a lot depends on one's particular installation and expectations.

The G5RV was basically designed as a 20M antenna that can be used on other bands with a tuner. I've had a variety of them up and down throughout the years, and found that ten turns of RG8 in a 8" loop makes an effective RF choke to stop stray RF from getting in the shack. I used to run one with a Yaesu FT-301AD and would get RF in the audio. Once I wound the choke, no more RF in the audio!

Best Regards,
                  Joe N3IBX

[Vortex Joe - N3IBX]

Is it true that the Brits drink beer warm because of Lucas refrigeration?

Ah yes, Lucas - "Prince of Darkness"

[Steve - WB3HUZ]

The TS-520 can be modified for AM transmit.


======
3. Amplitude Modulation
This radio can talk AM in a pinch.  You will be limited to SSB reception though.
That's OK if you don't mind playing with the RIT to get rid of the beat tones.
I decided it was degrading the specs when I put in a regular AM detector so I pulled it out.
Here is how you make it talk.
Get a DPDT relay (12v) and connect it inline with the fixed channel selector switch, so
that when you select crystal 4 the relay energizes.
Now lets take the relay in two sections.  The first is connecting the ouptut of the
mic amp into a matching transformer via this relay.  You want it connected so that
the MA O is on the wiper and the relay NC1 is connected to the Balanced Modulator.
Connect the other relay terminal NO1 to the low impedance side of the transformer.
Connect the other lead of this winding to ground.  So when you select fix channel 4, the
relay energizes, and disconnects the mic from the balanced modulator and connectes it
through the transformer to ground.

Ok now the second part of the AM mod.
Take the HIGH impedance winding of the transformer and connect one leg to ground.
Take the other leg and connect it to a 47uF cap.(neg lead)
Connect the positive side of the cap to an 820 ohm resistor.
Connect the resistor to the 9v terminal (on the RF board or most any other board)
Connect the junction of the resistor/capacitor to the NO2 terminal of the relay.
Connect the wiper of the relay to S on Q3 on the RF board.  I found R17 to have its
exposed wire connected to S on Q3.  Simply scratch the paint away on R17 and solder
to the resistor. 
Since this design modulates after the IF, you will have full fidelity and bandwidth of
your audio.  If you use an EQ, don't be excessive with the highs or you will have
enemys from the splash you create.  Also, there is no limiter here.  If you have
access to one, install it in the EQ loop.
http://www.phreak.org/radio/mods/ts520.txt

[Vortex Joe - N3IBX]

The TS-520 can be modified for AM transmit.


======
3. Amplitude Modulation
This radio can talk AM in a pinch.  You will be limited to SSB reception though.
That's OK if you don't mind playing with the RIT to get rid of the beat tones.
I decided it was degrading the specs when I put in a regular AM detector so I pulled it out.
Here is how you make it talk.
Get a DPDT relay (12v) and connect it inline with the fixed channel selector switch, so
that when you select crystal 4 the relay energizes.
Now lets take the relay in two sections.  The first is connecting the ouptut of the
mic amp into a matching transformer via this relay.  You want it connected so that
the MA O is on the wiper and the relay NC1 is connected to the Balanced Modulator.
Connect the other relay terminal NO1 to the low impedance side of the transformer.
Connect the other lead of this winding to ground.  So when you select fix channel 4, the
relay energizes, and disconnects the mic from the balanced modulator and connectes it
through the transformer to ground.

Ok now the second part of the AM mod.
Take the HIGH impedance winding of the transformer and connect one leg to ground.
Take the other leg and connect it to a 47uF cap.(neg lead)
Connect the positive side of the cap to an 820 ohm resistor.
Connect the resistor to the 9v terminal (on the RF board or most any other board)
Connect the junction of the resistor/capacitor to the NO2 terminal of the relay.
Connect the wiper of the relay to S on Q3 on the RF board.  I found R17 to have its
exposed wire connected to S on Q3.  Simply scratch the paint away on R17 and solder
to the resistor. 
Since this design modulates after the IF, you will have full fidelity and bandwidth of
your audio.  If you use an EQ, don't be excessive with the highs or you will have
enemys from the splash you create.  Also, there is no limiter here.  If you have
access to one, install it in the EQ loop.
http://www.phreak.org/radio/mods/ts520.txt

Steve - many thanks for the info!

[WD8BIL]

RF in the shack

I just open the window and pull back the famed blue curtains !!!

[Ed-VA3ES]

Sigh....

The G5RV must be the worst fraud perpetrated on Amateur Radio in  decades.  It was never designed for 75M operation and when used on that band, there are inherant problems.

The foremost problem is drastic loss of efficience caused by  coaxial losses.  The fact that the antennal  presents an odd if not low impedance to the coax is the first problem. Notwithstanding that "matching" section of 33 feet of twinlead, their is still a drastic mismatch at the coax wher it meets the twinlead.

Any coaxial cable  feeding such a low Z will exhibit exponential losses, as the Z  deviates from 50 ohm.  Assuming a  Z of say 10 ohms at the feed point, this  means the SWR will be 5:1.   Coax cable seeing a 5:1 mismatch will exhibit losses exceeding 6dB (maybe higher).

So, right off the bat we have losses inherant in the system, plus an additional loss of about say 1 dB from the short radiators, and  the net loss is 7dB or greater.

No wonder G5RV users are piss weak!

I used to work a guy with a G5RV. He was consistently S5 - S8, when propagation was good.  I kept at him to change out his G5RV, for a balanced fed doublet.  He had the room after all, but the G5RV was his first antenna  (natch!).  One Saturday night, we hooked up, and  lo and behold - he was 30 over 9!!!  Strapping.  So I asked him what he did, and guess what? He changed over to a  balanced feed doublet as I suggested.

Never fails.  That's why I call the G5RV the world's biggest fraud.

[K1JJ]

Hi Ed,

How did you arrive at a 6db coax loss for 5:1 swr, or maybe I am figgering something wrong myself?

According to the coax loss calculator url below, a G5RV antenna's 3.4:1 swr using 100' of RG-213 on 3.8 mhz is only about 0.66db coaxial loss.

Adding in a db for the smaller 108' flat top would mean about a 1.6db total loss for a G5RV on 3.8 mhz vs: a perfectly matched full size dipole. 

BTW, notice below the input impedance on each band at the end of the open wire (twinlead here) stub where the coax connects. It is truly a compromise antenna. These coax losses will increase on the higher bands and as is, is unusable on 10M.


73,
T

Coax loss calculator:
http://www.ocarc.ca/coax.htm


Taken from website: http://www.qsl.net/k2hq/g5rv.htm

"The following table shows how 27.7 ft. of 300 ohm twinlead (velocity factor = 0. transforms the EZNEC antenna impedance at the twinlead/coax junction in a typical G5RV. The figures were obtained from EZNEC using the transmission line feature."

MHz Twinlead/Coax Junction Impedance 50 ohm Coax SWR

3.8 14.6 + j2.9 (Imp) 3.44:1 (swr)
7.2 27.9 - j54.8 4.3
10.125 31.6 + j274 50
14.2 103 - j49 2.6
18.14 44.3 - j290 40
21.3 24.2 + j80.7 7.8
24.95 79.3 + j41.5 2.2
28.4 3049 + j655 64

[Steve - WB3HUZ]

What is not included in your calculations is the loss in the balun. Many G5RVs come with crappy baluns. I'm guess that's where a bunch of loss occurs. Then, on 75 meters, I think a tuner is needed as well. If the was using a crummy tuner, add in some more loss. Next thing you know, this signal is down 10-15 dB!

[Jim, W5JO]

Heh, heh.. Lucas Electric. Their switches have two positions: Off and Intermittent.

Lucas Electric, the reason the British drink warm beer.  Lucas Electric, the company that invented darkness.  And there are more.

[K1JJ]

What is not included in your calculations is the loss in the balun. Many G5RVs come with crappy baluns. I'm guess that's where a bunch of loss occurs. Then, on 75 meters, I think a tuner is needed as well. If the was using a crummy tuner, add in some more loss. Next thing you know, this signal is down 10-15 dB!

I see what you're saying...

Though, I'm talking about the general G5RV design. Maybe the store bought ones use a ferrite balun of some kind? Do you have some data on the losses incurred with these types of baluns on 3.8mhz at 3.4 :1 swr?  Normally, beads and ferrite transformers are not that bad. I use ferrite transformers up to 50 mhz with good results, though the swr is usually under 2:1. ie,  Do the losses increase tremendously with ferrite balun vs: a coax balun for a given swr?

Let's look at a reasonable mechanical design anyone could put together:

If you used a coaxial (choke) balun like 12 turns rolled on a 4" PVC form, this adds another 3.14 * 12T * 4" = 150"/12= 12' extra length. The loss in 12' of coax with an swr of 3.4:1 is another .07 db.  A tuner is not needed with a 3.4:1 swr loss-wise using a tube final, but if a good series link tuner had to be inserted for good measure with a solid state final, that can't be more than 0.25 db addtional insertion loss at most.

I dislike the G5RV design as much as anyone, but I don't see a well designed one, in the clear, straight and flat, being down more than 1-2db from a full size, matched dipole on 3.8 mhz.  I realize the ham anecdotal evidence suggests otherwise, but I need more proof.  caw mawn - 

T

[Steve - WB3HUZ]

I gotta break out NEC and take a look. You are right, a balun shouldn't have that much loss. Neither should tuners, but many do.

Another thing to consider is often those utilizing G5RVs do so because the don't have much space (lured by the promise of multiband capability), often resulting in a poor installation (i.e. low to the ground, bent, close to metal objects, phone lines, etc). They may be just about as PW with a plain jane coax fed dipole in similar circumstances.

Finally, the cheapie G5RV use garbage 300 Ohm twin lead. You know how lossy the brown crap 450 Ohm ladder line gets when wet. The 300 Ohm stuff is even worse. So, there has to be some loss going on there too.

[K1JJ]

Yeah, I know we discussed this somewhere before - about the idea of newbies doing poor installations of their first Gotham/G5RV antenna...    I talked about this back a few posts in this thread.

When I get caught up here, I vow to put up a G5RV - properly designed. Since 1-2db cannot usually be detected with local contacts, I'm willing to bet $1 that no one will know what antenna I'm on when doing an A/B against a standard dipole.

Using #12 wire for the flat top, good homebrew openwire for the stub and a RG-213/U coaxial choke balun should work FB. But what a Rube Goldberg way to go, huh?  The idea of going from openwire in mid-air to coax is a gagger. It's simply a coincidental event that 4-5 bands work out so that the swr is "reasonable" with that stub length.

Later Dude -

T

[Glenn NY4NC]

Oh I see now!!!!......  

The TS-520 can be modified for AM transmit.

[W2VW]

So was the guy who wrote that mod.

[Ed-VA3ES]

Hi Tom,
A little late getting  back to this thread...

You're right. My calculations (which were off the top of my head) were based on a feedpoint Z of about 12-15 Ohms.   Not sure where that 6dB loss figure came from - maybe an erroneous cable nomograph.  Loss should not be more than 1 dB tops when feeding a 15 ohml oad. I assumed a 5:1 SWR. Stll won't produce 6 db!!   I guess I'm just soured on those G5RV's and assumed they exhibited 6dB loss. At least that's what they always sounded like to me.

I should be finishing my dipole up soon.  Fed with 450 ohm line. Up at 50'.  Still  lot's of prep to do.

[Steve - WB3HUZ]

A fairly extensive analysis of the G5RV at the URL below. The lowest loss "version" is one using open-wire line to a tuner in the shack - surprise, surprise!

An interesting section in the conclusion section


===
Configuration: Balanced line matching section of 9.85m of wet Wireman 554,  extended by 15.15m of RG58C/U coaxial cable to a "local" tuner.

   Comments:  unacceptable losses on most bands.
===

Ed: 6 dB may not be that far off, depending on the quality of the G5RV involved. Looking at Figure 3 (Fig 3: 15.15m RG58C/U - tuner version of G5RV), the loss looks like around 4 dB at 4 MHz. In a paragraph preceding this section, the author admits his loss estimations are probably low since he uses an L-Tuner which is less lossy than the typical ham tuner, a T or Pi type. So tack on a db or two and you're at 6 dB of loss.


http://www.vk1od.net/G5RV/index.htm

[K1JJ]

As the author summarizes in the article, Steve -

The G5RV:

1) does not have acceptable feed performance on 1.8MHz;
2) does not have acceptable feed performance on most WARC bands;
3) does not have acceptable feed performance on 28MHz.

Yep, it is interesting that the final conclusion is to just feed the 108' flat-top with good quality open line and a good antenna matcher. Forget about the stub and coax. Use it at 1:1 vswr from 1.8-30mhz continuos. (Just like the sage advice that everyone gives out here for multi-band use)

T

[WA1GFZ]

So here is one for you. I have enough room to put up about 150-160 feet flat top at the beach qth. Would it be better to drop ends vertical to resonate on 160 or build a tuner to handle the low Z on 160. I have #8 for the antenna and #10 spaced 4 inches with Johnson spreaders for feeders. Ends will be up 60 to 80 feet. I also could do an M shape but feed point will be only 30 feet.  I end up with a 90 degree Vee if I use the neighbor's tree but that angle is pretty sharp for 160 and 75 m.
A flat top I could also feed it as a T.
No g5rv for me

[Steve - WB3HUZ]

You could always build a strapping tuner, but I think you would be better off making the antenna longer, even if you still use a tuner. Adding just 20 foot sections on each end gets the total length up to 200 feet. This length should tune quite easily on 160.

[WA1GFZ]

Yup a strapping tuner will be included either way. I wonder how close I can drop the ends to the ground without messing up performance. Feed line will be about 70 feet so 200 feet of antenna may be easy to match.

[Steve - WB3HUZ]

You'll put out an FB signal, I'm sure.

[K1JJ]

Yup a strapping tuner will be included either way. I wonder how close I can drop the ends to the ground without messing up performance. Feed line will be about 70 feet so 200 feet of antenna may be easy to match.

Yep, you have the right idea, there Franz.

The ends are much like vertical capacity hats you see on shortie beams and have little current there.  However, on 75M, you will see your current points come out more to the center of each leg.

I would make the end drops JUST enuff to give you a good input impedance on 160M and this way your 75M pattern will still stay reasonably broad and not get too narrow like two half waves in phase. There will be less cancellation on 75M this way. 15' per side will be fine giving you a total of 180' if the flattop is 150'. I would not go over that. . Plus you will keep the current points on 75M up as high as possible.

From that salt water environment, you will be very strapping on 75/160M with that setup. No compromises, really.

T