R75
- Thread starter TheGator
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N_Jay
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TheGator said:
What frequency range is the discone designed for?
What frequencies do you want to listen to on the R75?
What are you planning on using to connect the two radios to one antenna?
CAT
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- May 12, 2002
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Any antenna will work outside of it's designed frequency range, but with a good deal of attenuation, and if the discone in question is of the 25-1300MHz variety, then a dedicated HF antenna will easily surpass the discone’s performance when connected to the IC-R75. BTW you can connect several receivers to the same antenna, but you need a special splitter to avoid interference.
N
N_Jay
Guest
CAT said:
A discone has a natural bandwidth of about 3 to 1.
So a 25MHz to 1300MHz discone has a lot of "Snake-Oil" in it somewhere.
An antenna with a good deal of attenuation is called "Not much of an antenna".
IF you want HF, the an HF antenna is best.
If you want VHF low, then a big discone will do OK, and still give you some upper VHF.
The discone is rated for 25MHz to 1300MHZ.
I am New New To this hobby but I would like to listen to milair, and just about anything else interesting up north or over seas, I Live in florida but from NJ.
I am using RG8 wire for my discone antenna to my 796D I thought I could just use a PL T conector to split the signal within 3 or 4 feet behind both radios, is this posible or would each radio interfere with each other?
I am New New To this hobby but I would like to listen to milair, and just about anything else interesting up north or over seas, I Live in florida but from NJ.
I am using RG8 wire for my discone antenna to my 796D I thought I could just use a PL T conector to split the signal within 3 or 4 feet behind both radios, is this posible or would each radio interfere with each other?
N
N_Jay
Guest
TheGator said:
RG-8 is not that great at 450 and above, so watch the length.
"T"ing antannas will produce random results.
At best you will have 3 to 6 dB of loss and very well might have desense and noise generated by one radio affecting the other.
Depending on the frequency and cable lengths you could easily have up to 20 dB or more of loss on some frequencies.
Using a pssive splitter will give you 3.5 to 6 dB of loss, but it should be faily consistant across all bands.
It will also give you 6 dB (aproximatly) of isolation from any noise generated from the other receiver.
An amplified spliter will negate the loss (except for any difference in the noise figure of the amp in teh splitter) as long as it is not overloaded.
A well designed active spliter will have well over 6 dB of isolation.
Thank you your response guys, I guess I was Trying to avoid putting up anther Antenna, if I keep the discone antenna for the 796D what would a good antenna for the R-75 on the outside of the house, ( short Of using a 18ft glass antenna) would like something fairly small on the outside, also How close could I put the other antenna to the discone?
N
N_Jay
Guest
TheGator said:
The T can/will still cause some very odd losses.
The discone is going to suck at HF (I assume that is what you use the R75 for?)
I have to tell you guys, the knowledge you guys have in all phases of radio and electronics simply amaze me. and this goes for most all on this website.I hope one day to have just a fraction of knowledge that I have been reading in the last few weeks. with that all aside where would I get that splitter u are talking about, RS. would you suggest a different wire for the R75, or even the 796, I only said RG8 only because I am trying to do some research myself and this is what I can up with. but with my Knowledge on this matter I am sure open to suggestions.
Check out www.rffun.com This is Universal Radio's website. They have quite the selection of antennas that will work well with the R75. Personally, I use a fifty foot piece of randon wire connected to the High Z input, and it works quite well. I regularly catch Brisbane and Auckland in the mornings, which is not easy to do since I'm on the east coast. I also have caught Diego Garcia on 11.175.
Hi guys,
Take it from a "professional" Amateur Radio operator, you're way off base. A discone is an extremely wideband receiving antenna and resonant on Amateur 2M and 70cM bands so it can transmit using low power. No snake oil, we use antenna grease to make the electrons slide down the coax.
Speaking of coax, next to expensive special stuff and hardline Belden 9913 gives lowest loss for the price. Height is might so when it comes to VHF/UHF antennas do a Squint Eastwood on them, Hang 'Em High.
To use one or more rigs on one antenna and vice-versa use a coaxial switch designed for HF/UHF and nothing else or you'll run into loads of problems. For one thing those passive splitters use F connectors that won't fit on 9913 without adapters and each output port provides 3db loss of signal and that is exactly half of what went in. 2 output ports are bad enough but with 4 you end up with 1/4 the signal you started with at each port. Forget about isolation when you can't hear much to begin with. A T connector will split the signal alright but couple the receivers together as well so the LO in one will be heard in the other sounding like a popping noise as channels are scanned. Then there is a bad impedance mismatch all the way around like a resistor netork gone wild, huge signal loss is the result.
BTW, a neat trick is using RG-6U low loss 75 ohm CATV coax the cable companies use for drop lines and in house wiring. An installer likely has some spool ends he will toss your way rather than have them end up in the dumpster or you can rip down some unused lines like I did off the apartment building I used to live in. You have to use crimp on F connectors and adapters but if you get it for nothing the advantage is obvious. Neither the scanner nor the antenna mind the impedance mismatch, transmitting with it gives only a 1.5:1 SWR which amounts to practically nothing.
Take it from a "professional" Amateur Radio operator, you're way off base. A discone is an extremely wideband receiving antenna and resonant on Amateur 2M and 70cM bands so it can transmit using low power. No snake oil, we use antenna grease to make the electrons slide down the coax.
Speaking of coax, next to expensive special stuff and hardline Belden 9913 gives lowest loss for the price. Height is might so when it comes to VHF/UHF antennas do a Squint Eastwood on them, Hang 'Em High.
To use one or more rigs on one antenna and vice-versa use a coaxial switch designed for HF/UHF and nothing else or you'll run into loads of problems. For one thing those passive splitters use F connectors that won't fit on 9913 without adapters and each output port provides 3db loss of signal and that is exactly half of what went in. 2 output ports are bad enough but with 4 you end up with 1/4 the signal you started with at each port. Forget about isolation when you can't hear much to begin with. A T connector will split the signal alright but couple the receivers together as well so the LO in one will be heard in the other sounding like a popping noise as channels are scanned. Then there is a bad impedance mismatch all the way around like a resistor netork gone wild, huge signal loss is the result.
BTW, a neat trick is using RG-6U low loss 75 ohm CATV coax the cable companies use for drop lines and in house wiring. An installer likely has some spool ends he will toss your way rather than have them end up in the dumpster or you can rip down some unused lines like I did off the apartment building I used to live in. You have to use crimp on F connectors and adapters but if you get it for nothing the advantage is obvious. Neither the scanner nor the antenna mind the impedance mismatch, transmitting with it gives only a 1.5:1 SWR which amounts to practically nothing.
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