[Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston

Thu Feb 21 10:56:26 EST 2019

I understand the mismatch and its engineering implications.

My question is why would anybody design mismatch in the system.  Most transmitters used an antenna coupler anyway.

From: milsurplus-bounces at mailman.qth.net <milsurplus-bounces at mailman.qth.net> On Behalf Of Jim Whartenby
Sent: Wednesday, February 20, 2019 10:53 PM
To: Francesco Ledda <frledda at att.net>
Cc: MilSurplus QSLNet <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston

Frank asked: "Wonder why?"

Most likely since at HF, the impedance mismatch is pretty much insignificant, especially if one considers the length of the coax run from antenna to RX.  https://www.pasternack.com/images/ProductPDF/RG8A-U.pdf 

So about 1 dB loss at 30 mc per 100 feet or 0.2 db loss at 1 mc per 100 feet.

From: http://wc7i.com/Vertical%20Antenna%20Conclusions.htm

Z of a vertical antenna is about 36 ohms, Z of horizontal antenna is about 72 ohms, both give a 1.4:1 VSWR.  The VSWR from mating a 50 to 75 ohm coax is 1.5:1  In all of the above cases, the load mismatch attenuation is under 0.2 dB

Comparing UHF connectors to most modern connectors is also interesting.  I myself wonder why the the UHF connector is still used?

See: https://www.hamradio.me/connectors/uhf-connector-test-results.html for connector comparisons from SMA to UHF.

Regards,

Jim

I wonder why people argue over the 10% of their differences and ignore the 90% they agree on?

On Wednesday, February 20, 2019, 6:09:03 PM CST, Francesco Ledda <frledda at att.net <mailto:frledda at att.net> > wrote: 

Also, the CU-1099/FRR is 70 ohm. It was used with receivers with Z 50 ohm.  Wonder why....

Sent from my iPad

On Feb 20, 2019, at 17:50, W2HX <w2hx at w2hx.com <mailto:w2hx at w2hx.com> > wrote:

Probably the gain in the unit compensated for any losses due to impedance mismatch

Sent from  <http://www.9folders.com/> Nine

  _____  

From: Nick England <navy.radio at gmail.com <mailto:navy.radio at gmail.com> >
Sent: Wednesday, February 20, 2019 5:00 PM
To: W2HX
Cc: MilSurplus QSLNet; r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net> ; John Flood
Subject: Re: [Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston

The parts list says it has UG-58A/U connectors. Everything I can find says that is a 50 ohm connector.

I think all the military type N listings are 50 ohm.

Nick England K4NYW
www.navy-radio.com <http://www.navy-radio.com> 

On Wed, Feb 20, 2019 at 2:56 PM W2HX <w2hx at w2hxcom <mailto:w2hx at w2hx.com> > wrote:

John et al., 

This is an interesting multicoupler. One interesting thing I've wondered about...It has a 70 ohm antenna matching input impedance. And i always wondered if the antenna connector was a 75 ohm N connector or the standard 50 ohm (The difference is that the male center pin is thicker on the 50 ohm version, and will damage a 75 ohm female part)
Just something to look out for.

Wikipedia has a nice photo of both impedances and genders.

73 Eugene W2HX

________________________________________
From: boatanchors-bounces at mailman.qth.net <mailto:boatanchors-bounces at mailman.qth.net>  <boatanchors-bounces at mailman.qth.net <mailto:boatanchors-bounces at mailman.qth.net> > on behalf of John Flood via Boatanchors <boatanchors at mailman.qth.net <mailto:boatanchors at mailman.qth.net> >
Sent: Wednesday, February 20, 2019 1:24 PM
To: MilSurplus QSLNet; r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net> ; BOATANCHORS2 LIST
Subject: [Boatanchors] CU-872A/U antenna coupler FS near Boston

Greetings,
This is working, some "test" readings are a bit on the low side so perhaps some of the 6922 tubes are getting tired.  There is some glue residue below the normal data tag most likely from some other data tag that was mounted there.  Looking for a local sale in the Metrowest or North Shore Boston (This of course means that the first reply will come from Alaska!).  I'm not really interested in shipping this or dealing with Paypal any more in MA.  Any interest?  I could bring it to the Lewiston ME, Nashua, NH, or Framingham, MA fleas.  Nearfest as well but I hope it finds a home sooner than May!
John Flood N1JAF978-979-2807
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