[600MRG] 630-Meter Antenna Z Measurements

Thu Mar 21 15:49:47 CDT 2013

The absolute best thing for measuring antenna impedance (R+ or - j).  Is 
still the big General Radio RF Bridge!  It uses a receiver for a null 
detector and can be relied on although the auxiliary stuff required is a 
receiver and a good stable signal generator.   Most of the bridges that are 
solid state and "all in one" all can be compromised by interference by 
strong fields the "antenna under test" happens to be "immersed" in!  I guess 
this is why they still are in use by a lot of the broadcast band engineers.

73,
Sandy W5TVW

-----Original Message----- 
From: Joe K I 5 F J
Sent: Thursday, March 21, 2013 3:35 PM
To: Warren K2ORS ; 600mrg at w7ekb.com
Subject: [600MRG] 630-Meter Antenna Z Measurements

Folks,
My 160-M Horizontal  LOOP (Up 35 Ft)
receives the two local AM Stations
570 & 1450 kHz at +60 and + 40 db over S9.

My approach to measuring my future
630-M TX antenna is to utilize a
Heath-Kit Noise Bridge to feed a High Q
(TUNED for 475 kHz) MW 12 Inch Frame loop.

The loop is placed horizontal to the Earth to minimize BCB pickup. The loop 
magnetically couples to a portable MW  AM receiver.

I think in a high BCB RF environment,
a TUNED measurement technique will
improve any 630-Meter measurements.

I will soon try measuring my loop configured
as a top loaded vertical.

I have constructed a 550 Ft elevated Counter-Poise (> 1/4 wl).

My plan is to TUNE the CP with a home-brew
sliding plate capacitor of about 2600 pF.

73
Joe O,   K I 5 F J
NNNN

________________________________
From: Warren K2ORS <k2ors at verizon.net>
To: 600mrg at w7ekb.com
Sent: Thursday, March 21, 2013 12:35 PM
Subject: Re: [600MRG] modified MFJ Antenna analyzer failure

Mike,

     The Hermes is the way to go, not only an excellent test instrument
but an unbeatable transceiver. The Hermes is still available from Apache
Labs. Apache is the original developer of the Hermes PCB.

https://apache-labs.com/al-products/1022/OpenHPSDR-Hermes-Transceiver-Card-Assembled--Tested.html

73 Warren K2ORS

On 3/21/2013 11:00 AM, Michael Mussler wrote:
> John,
> I have been using the Hermes software defined radio with a home-brew 
> coupler to do vector network analyzer measurements on my 600m system. The 
> Hermes covers 100 kHz to 54 MHz and includes a half watt output 
> transmitter.
>
> Here's a link to the TAPR website that has all of the information on it:
>
> http://openhpsdr.org/wiki/index.php?title=HERMES
>
> Public domain software runs the SDR in the network analyzer mode:
>
> http://openhpsdr.org/wiki/index.php?title=VNA
>
> There is a catch to the Hermes approach- Hermes production boards were a 
> limited run and I don't think the loaded board is available any longer. 
> The circuit board and a bill of materials is available and I believe a 
> number of people are ordering the parts and loading their own Hermes 
> boards. It is surface mount technology so that may be an issue as well. 
> The VNA technique should be possible with any assembled SDR that offers 
> both a transmit and receive function.
>
> I ran some measurements on my antenna matching network and I was able to 
> set up the L-Network so that the VSWR 2:1 points were at the upper and 
> lower band edge frequencies. This has been a good match for the tube 
> finals I use in my system. Weather related impedance changes don't de-tune 
> it enough to cause any problems when I am operating mid band where the 
> best match occurs. I monitor the RF current at both ends of the feed line. 
> There is a detector based ammeter at the transmitter output and a thermo 
> couple based ammeter at the antenna connection to the L-Network. I have 
> good history on the currents at both ends so I can tell if there is a 
> problem in real time. Another approach people are using is to place a Bird 
> Thru Line wattmeter in line. The HF slug has less sensitivity at MF but 
> the decrease is the same for forward and reverse measurements. Since power 
> level is not a factor as long as you can get a reasonable measurement 
> level, VSWR measurements
are valid.
>
> Yesterday I pressed the Hermes VNA into service to check impedance of the 
> short whip antennas I recently set up for receive use. Results help with 
> matching networks  needed to make them work over the frequency range I'm 
> interested in (LF through 30m). I've used the Hermes to track down noise 
> sources and to modify the PA and exciter stages for operation in the 
> proposed amateur allocation. Best of all it can be used as a receiver and 
> exciter on 600m the proposed LF allocation.
>
> Let me know if I can you provide more information on Hermes or 
> applications.
>
> 73
> Mike
> WD2XSH/12
> AI8Z
>
>
> _______________________________________________
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>

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